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Visual Evoked Potentials, Laterality Of Eye Movements, And The Asymmetry Of Brain Functions

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Visual Evoked Potentials, Laterality Of Eye Movements, And The Asymmetry Of Brain Functions

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Content VISUAL EVOKED POTENTIALS, LATERALITY OF
EYE MOVEMENTS, AND THE ASYMMETRY OF
BRAIN FUNCTIONS
by
W arren Shelburne Brown, Jr.
A D issertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In P artial Fulfillm ent of the
Requirem ents for the Degree
DOCTOR OF PHILOSOPHY
(Psychology)
August 1971
BROWN, Jr., Warren. Shelburne, 19 441-.
| VISUAL EVOKED POTENTIALS, LATERALITY OF
I EYE MOVEMENTS, AND THE ASYMMETRY OF BRAIN
FUNCTIONS.
I University of Southern California, Ph.D., 19 71
fe Psychology, experimental
j..-
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| University Microfilms, A X E R O X Com pany, Ann Arbor, Michigan
i ', '
l i : . . . . . . . . . . . . . . . . . . . . . . . .
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED
UNIVERSITY O F SO U TH ERN CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS A NGELES, CALIFORNIA 9 0 0 0 7
T his dissertation, w ritten by
................................
under the direction of h.is... D issertation C om
m ittee, an d a p p ro v e d by a ll its m em bers, has
been presented to and accepted by T he G radu
ate School, in p artial fulfillm ent of require
ments of the degree of
D O C T O R O F P H I L O S O P H Y
o
Dean
Date...e mb e r_.
DISSERTATION COMMITTEE
PLEASE NOTE:
Some Pages have i n d i s t i n c t
p r i n t . Filmed as re ceiv ed .
UNIVERSITY MICROFILMS
ACKNOWLEDGMENTS
| The author wishes to express his appreciation to those who
I
have contributed to the completion of this dissertation. A debt of
gratitude is owed Dr. Gary G albraith, com m ittee Chairm an, for his
help, and instruction and p articu larly for the high standard of
achievem ent he has encouraged. Thanks a re also due Dr. E rnest
G reene and Dr. Henry Slucki for their participation on the d is s e r
tation com m ittee, and D r. James B irren and Dr. E ric Holmes, who,
because of conflicting responsibilities, were not able to participate
in the final evaluation of the d issertatio n --y et still contributed
significantly as com m ittee m em bers.
The author is indebted to the U niversity of Southern
i
C alifornia System s Simulation Laboratory and its staff for the use of
th eir computing facilities and help in trouble-shooting program s.
The friends of the author who volunteered to be subjects are also to
be thanked for their contribution.
Finally, the author would like to thank his parents, D r. and
M rs. W. Shelburne Brown, for their support and encouragem ent;
and, m ost of all, his wife, Janet, who participated in this project
from its inception "in sp irit and in flesh" and to whom this paper
is dedicated.
TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS..................................................................... ii
LIST OF T A B L E S.............................................................................. vi
LIST OF ILLUSTRATIONS............................................................. viii
Chapter
I. INTRODUCTION............................................................. 1
Functional Brain A sym m etry
Electrophysiological C orrelates of
Functional A sym m etry
L ateral Eye-M ovements and Subject
D ifferences in A sym m etry
C hapter Summary
II. RESEARCH HYPOTHESES............................................. 20
III. M ETHOD.............................................................................. ’ 24
Subjects
Procedure
Apparatus
Analysis
IV. EXPERIMENT 1................................................................ 32
Method
Results
iv
Chapter Page
V. EXPERIMENT I I .............................................................. 46
Method
Results
VI. DISCUSSION....................................................................... 68
Subject Effects
Stimulus Effects
VII. SUMMARY.......................................................................... 81
APPENDIXES.......................................................................................... 84
Appendix A ...................................................................... 85
Appendix B ...................................................................... 88
Appendix C ...................................................................... 92
BIBLIOGRAPHY.................................................................................... 94
v
LIST OF TABLES
Table Page j
j
1. Eye Movements and SAT Scores ................................. 35
2. C entral Evoked Response and Eye Movement .... 36 |
3. Parietal Evoked Response and Eye Movement. . . . 37
4. C entral Evoked Response and SAT-Score Ratio. . . 38
5. Parietal Evoked Response and SAT-Score Ratio . . 39
6. Frequency D istribution of Eye-Movement Scores . 49
7. Intercorrelation M atrix of Subject F acto rs ............. 51
8. Analysis of V ariance Table: Eye-m ovem ent,
E lectrode, and Stimulus Effects on VER
Area R a tio s ................................................................... 55
9. Analysis of V ariance Table: Eye-m ovem ent, |
E lectrode, and E lectrode Effects on j
VER A re a s..................................................................... 56 j
i
10. Analysis of V ariance Table: Eye-m ovem ent,
H em isphere, and E lectrode Effects on the
Sum of the Intercorrelations between
Stimulus V E R s ............................................................. 59
11. Analysis of V ariance Table: Eye-m ovem ent,
E lectrode, and Stimulus Effects on VER
Inform ation C ontent.................................................... 61
12. Analysis of V ariance Table: Eye-m ovem ent,
Stim ulus, and H em isphere Effects on C entral-
Parietal VER C o r r e la tio n s ...................................... 64
v i
Table
13. Analysis of V ariance Table: Eye-m ovem ent,
Stim ulus, and Electrode Effects on C ross-
H em isphere VER C o rre la tio n s....................
LIST OF ILLUSTRATIONS
Figure Page
1. Recording and Stim ulating A p p a ra tu s ........................ 28
2. Data Processing A p p a ra tu s ............................................ 30
3. Computation of VER A rea-U nder-T he-C urve . ... 34
4. C entral VER A re a -R a tio s................................................ 40
5. Parietal VER A re a-R a tio s................................................ 41
6. C entral VER A re a -R a tio s................................................ 52
7. Parietal VER A rea-R atio s................................................ 53
CHAPTER I
INTRODUCTION
Functional Brain A sym m etry
i
In recent years there has been a renew al of in te rest and
resea rch in hem ispheric asym m etry in co rtical functioning. The
resu lt of these studies has been a new concept of the localization of
language between the hem ispheres, as well as indication that there
m ay also be an im balance in the representation of other abilities
in the right and left sides of the brain.
Concepts of functional co rtical asym m etry developed around j
the middle of the last century, with the recognition that aphasia j
!
alm ost always followed lesions of the left hem isphere. Left hem is
phere dominance in language was linked to right-handedness with the
work of Bouillaud (1864), Broca (1865), and Dax (1865). With the
appearance in the lite ra tu re of som e cases of aphasia in left-handers
with right hem isphere lesions (Jackson, 1868, 1880), it became
1
generally accepted that speech processes w ere localized in the
hem isphere contralateral to the p refe rred hand- -a phenomenon which
is usually term ed cereb ral dominance.
In the past few decades a g reat deal of resea rch has been
reported to dispute the localization of language in the hem isphere
opposite the p referred hand. While it is still felt that nearly all
right-handers have language represented in the left hem isphere, it
has now been shown that m ost left-handers also have language
abilities localized in the left hem isphere (Humphrey & Zangwill,
1952; Goodglass & Quadfasel, 1954; Penfield & Roberts, 1959;
Zangwill, 1960; M ilner, Branch & Rasm ussen, 1964; E spir &
R ussell, 1961). F o r example, Penfield and Roberts (1959) report
that while 115 of 157 right-handed patients (73. 2%) developed aphasic
symptoms afte r surgery of the left hem isphere, 13 of 18 left-handed
; patients (72.7%) also developed aphasia a fter surgery to the sam e
; hem isphere. Only one of 196 right-handed and one of 15 left- !
i handed patients developed aphasic symptoms afte r right hem isphere j
surgery. In another se rie s of studies using electrical stim ulation
of the exposed human cortex, Penfield and Roberts (1959) found
much the sam e resu lts and w ere led to conclude:
From the standpoint of c ereb ral dominance, the data from
| ele ctrica l interference support the conclusion . . . that the
left hem isphere is usually dominant for speech regardless
3
of the handedness of the individual, with the exclusion of
those who have c ereb ral injuries early in life. [p. 137]
Brenda M ilner and her associates (1964) injected sodium
am ytal into the carotid a rte rie s of their patients to in terfere tem por
a rily with the functioning of one of the hem ispheres and observe
whether o r not language skills w ere affected. These authors found
that 64% of left-handers or am bidextrous patients had speech
localized in the left hem isphere, 20% in the right half of the brain,
and 16% in both halves. These authors rem ark that th eir results
"em phasize the im portance of the left hem isphere for language,
this im portance being attenuated in the case of left-handers, but
still dem onstrable" (M ilner, et al. , 1964, p. 205).
Although it can be stated with authority that in the
m ajority of people (both right- and left-handed) the left hem isphere
is dominant in language, the failure to localize indisputably language '
p rocesses of all left-handers in eith er hem isphere has led som e
i investigators to the idea that cereb ral dominance might indeed be a
i m atter of varying degrees of dominance in different individuals.
Zangwill, in commenting on the work of M ilner and h er colleagues
(in de Reuch & O’Conner, 1964, p. 216) stated that "one m ust regard
| dominance as a m atter of degree. The main difference between
! right-handed and so-called left-handed people is that the gradient is
j
j rath e r flatter in the non-fully right-handed person. " Support for
this notion of degrees of dominance com es from the fact that there
: is a g re a te r likelihood that left-handers will recover from aphasia
i
when caused by damage to the left hem isphere. This indicates that,
I though the m ajority of the language functions of the left-hander lie in !
| }
the left hem isphere, the localization of language is probably less |
complete in sin istra l adults, and the right hem isphere has p reserved ;
some of its capability of subserving language. Another hypothesis
that has been put forward to explain the evidence on dominance and
handedness is that the two a re independent tendencies toward right-
handedness and left hem isphere dominance in language (Osgood &
; Miron, 1963). However, the fact that left-handers a re m ore likely
than right-handers to be right dominant for language indicates som e
j relationship between handedness and the patterning of cortical
| asym m etry of function regarding language. j
i
Probably the m ost revealing work on the hem ispheric
distribution of verbal abilities was done by Sperry and his
colleagues (sum m arized in Sperry, 1968). These investigators used
patients in which the corpus collosum had been severed to control
the spread of epileptic seizures. By controlling what information
was received by each hem isphere, it was possible to determ ine the
intellectual abilities of the "m ajor" (left) and "m inor" (right)
hem ispheres. It was found, as might be expected, that the right
hem isphere could not speak--in the sense that the patients were
: unable to verbalize inform ation reaching the m inor hem isphere.
However, the m inor hem isphere was not agnostic and could respond j
i j
! I
| to stim uli if the c o rre c t response opportunity was provided,
: pointing with the left hand, for exam ple. In fact, the m inor
hem isphere was shown to be able to com prehend sim ple spoken or
w ritten m aterial, as well as do sim ple single-digit calculations,
but could not respond to these in any verbal form . T herefore, these :
studies by Sperry and his asso ciates tem per somewhat ideas of
functional asym m etry by distinguishing between abilities to express
and comprehend.
An even m ore interesting development in recent years has
| been the evidence that other functions m ay be asym m etrically re p re - ;
I i
! sented in the human cortex and that for som e of these functions the I
I
right hem isphere m ay be dominant. A num ber of investigators have
I
found deficits in visuo-spatial and associative-m anipulative abilities,
as well as other higher visual-perceptive abilities, to be m ost
common with lesions of the right hem isphere (reviewed by Zangwill,
1961). T euber (1962), for exam ple, studied the effect of brain
wounds on soldiers and found that left lesions produce what looked
like an overall decline in I. Q. (as m easured by the Army G eneral
I. Q. T est) even in the absence of aphasia. However, right lesions
produced th eir own complex sym ptom s, such as deficits in visuo-
spatial orientation, visual construction, and auditory localization.
T euber concludes that "subtle losses in complex perceptual achieve- {
i ■
I m ent turn out to be m ore frequent, o r m ore pronounced afte r lesions
| of the so-called 'non-dom inant' hem isphere" [p. 155].
Piercy, Hecaen, and A juriaguerra (1960) dem onstrated a
statistically reliable tendency for right hem isphere lesions to
produce constructional apraxia. Among patients with unilateral
post-R olandic lesions, 17% with left lesions and 38% with right
lesions showed such deficits. Also, in those with right lesions, the
; provision of a model in the task did not help improve perform ance as
it did in those with left lesions. T herefore, there was a difference
both in the frequency and in the nature of the disability between left ;
i j
I and right lesions. It has also been noted that such deficits as
anosognosia and unilateral neglect, both problem s involving bodily
perception, a re m ore frequent with right lesions (Zangwill, 1961).
The perception of nonverbal auditory stim uli, such as
m elodies, appears also to be asym m etrically distributed in favor of
the right hem isphere. M ilner (1962) found that some of the scales
on the Seashore M easures of M usical T alent a re affected by lesions
of the right hem isphere, but not the left. K im ura (1961a, 1961b,
1963, 1964) has done a se rie s of studies using techniques of accuracy
in dichotic listening which not only supports the im portance of the
left hem isphere in the perception of verbal stim uli (1961a, 1961b),
! but gives further evidence for the localization of nonverbal auditory
| perception in the right hem isphere (1964). Kim ura found that in
norm al subjects a g re a te r num ber of accurate identifications of
; m elodies was m ade for the left e a r than for the right. Since audi
tory pathways have m ore num erous co n tralateral connections, left
e a r superiority in melody identification is interpreted by Kim ura
to indicate at least p artial localization of this ability in the right
hem isphere. Shankweiler (1966) has supported this interpretation
by showing that right tem poral lobectomy im pairs total perform ance
i on the m elodies' test used by Kim ura.
| The distribution of function between the hem ispheres was
l
dem onstrated also in a study by Cohen and his colleagues (1968).
These investigators used a population of right-handed Ss who w ere
to be given electroshock therapy (EST) to the right, left, or both
hem ispheres. The Ss w ere given a visuographic learning task and a
paired asso ciates' task on the day before the beginning of a se rie s of
five EST sessions (two to three days apart). When tested afte r the
la st EST session, it was found that the right hem isphere EST group
showed a g re a te r decrem ent in the visuographic test than in the
paired asso ciates' task, and the left group a la rg e r paired asso ciates'
8
decrem ent than visuographic, while the b ilateral EST group had
the g rea test combined decrem ent.
In sum m ary, the resea rch regarding asym m etry of cortical
function appears to support the following conclusions:
1. In the m ajority of people, whether right-handed
o r left-handed, processing of verbal inform ation
from auditory o r visual senses takes place p re
dom inately in the left hem isphere.
2. Processing of nonverbal inform ation, at least
visuo-spatial inform ation and tonal patterns,
appears to be localized in the right hem isphere.
Electrophysiological C orrelates of Functional A sym m etry
F u rth e r evidence regarding functional asym m etry is
offered by inform ation from electroencephalographic studies of
I hem ispheric differences. Alpha rhythm s have been found by Raney |
(1939) and Liske, et a l. (1967), to be of la rg e r amplitude and m ore
frequent in the right hem isphere of the brain. Repetitive photic
stim ulation elicits higher amplitude EEG from the left hem isphere
in humans (Lansing & Thomaa, 1964), but elicits g rea ter following
responses from the right hem isphere (Freedm an, 1963).
G iannitrapani (1965, 1966, 1967, 1969; Giannitrapani,
et al. , 1964, 1966) has done a se rie s of studies dealing with
asym m etry of EEG frequencies from the left and right hem ispheres
in humans. He has dem onstrated a strong relationship between
"average frequency asym m etries in left and right homologous a re as"
and I. Q. (Giannitrapani, 1969). The correlations w ere higher in
p o sterio r are as and with Perform ance I. Q ., rath e r than Verbal I. Q.
(WAIS 1. Q. scores). A composite of the asym m etries from all four
areas investigated (frontal, tem poral, p arietal, and occipital)
correlated .72 with full I. Q. sco res. The frequency analysis used
in this study consisted of a crude hand-counting method and the data
m ust be replicated using com puter techniques. N evertheless, the
data show not only that asym m etries can be detected by electro-
physiological techniques, but that they can be related to subject
differences in intellectual ability.
Averaged visual evoked responses (VER) and auditory
evoked responses (AER) have also been shown to reflect hem ispheric
asym m etry. The im portance of hem ispheric asym m etry of VERs in
intelligence has been em phasized by Rhodes, et al. , (1969). These
investigators show that bright children have larg e r amplitude VERs
than dull children. They also point out that dull children have equal
b ilateral VER amplitude, while bright children have la rg e r VERs in
| the rig h t-cen tral (C^) than in the left (Cg). If amplitude is to be
10
regarded as indicating g re a te r reactivity, bright children have re la
tively m ore reactive right h em isp h eres--at lea st to flash stim uli.
Diminished asym m etry in VER amplitude has also been replicated in
retard ates by Galbraith, et a l., (1970).
G reenberg and Graham (1970) have dem onstrated that AER
asym m etries exist during the learning of speech and non-speech
discrim ination tasks and that the amount of asym m etry was related
to the degree of learning and type of task. During the learning of
the speech discrim ination task (nonsense syllables) the larg est am
plitude sp ectral component of the AER from the left hem isphere
decreased as learning approached the 100% level, while the larg est
component from the right hem isphere held constant at a lower
amplitude. However, during the discrim ination of the non-speech
stim uli (piano notes) the larg est component in the right hem isphere
increased as learning progressed until it exceeded in amplitude the
: larg est component of the left hem isphere. T herefore, while the left
| hem isphere was m ore responsive at the beginning of both tasks,
and decreased as learning progressed, the right hem isphere became
m ore responsive only in the processing of the non-speech stim uli.
This study seem s to support the data of Kim ura (1967) regarding
; the accuracy of dichotic listening for verbal and non-verbal stim uli
]
j for the right and left e ars. The waveform differences between
11
stim uli were g reatest for late VER components ( > 300 m s e c .) when
waveforms from the sam e electrode w ere com pared. However, the
verbal versus non-verbal response differences, which w ere m ost
prom inent in the left hem isphere, occurred predom inantly in early
components ( < 190 m se c.). Thus, differences in VERs evoked by
a verbal and non-verbal stim ulus w ere g reatest in late components
in both hem ispheres, but in the early components there was a g re a te r
stim ulus difference in the left hem isphere than in the right.
Buchsbaum and Fedio (1969, 1970) have also shown that
evoked responses from verbal stim uli show different asym m etries
than nonverbal stim uli. Using stim uli consisting of dots arranged in
th re e -le tte r words, random patterns, o r geom etric designs, all
generated by a com puter, these investigators showed (1) that the
latency of the peak positive component was sh o rter for words than
designs o r random patterns, and (2) that VERs to verbal and non-
! verbal stim uli w ere m ore different in waveform in the left hem is-
i
j
phere than in the right hem isphere.
It appears, then, that electrophysiological m easures,
p articu larly the evoked potential, have been useful in replicating what
is known of the asym m etries in the distribution of cereb ra l functions
in man. However, the dem onstration of such hem ispheric differences
in the AERs and VERs of humans does m ore than support what is
12
already known of functional asym m etry. Such dem onstrations also
m ake available an im portant technique for further study of the
ch arac teristic functions of the hem ispheres. F o r example, such
problem s as the distribution of cereb ra l processing of stim uli that
a re not clearly verbal, or possible individual differences in cereb ral
dominance can be studied using these electrophysiological techniques.
L ateral Eye-M ovements and Subject D ifferences in A sym m etry
Another line of resea rch has recently developed which m ay
shed light on the problem of hem ispheric functions, p articularly in
reg ard to individual differences in functional dominance. Several
investigators (Day, 1964, 1967; Duke, 1968; Bakan, 1969) have
dem onstrated a phenomenon of la te ra l eye-m ovem ent during
reflective thinking that Bakan feels may be related to individual
differences in both the lateralization of reactivity of the cereb ral
hem ispheres and the distribution of m ental ability between m athe-
m atic and verbal capacities.
The la te ra l eye-m ovem ents occur in dyadic verbal communi
cation when the E asks a question of the S. If the answ er is not
im m ediately available and req u ires som e amount of reflection, the
S will disengage eye contact with the E m om entarily while shifting
his attention inwardly to a rriv e at an answ er. Under these circum -
13
stances, Ss can be classified as left-m overs (LM) or right-m overs
(RM). Day (1964, 1967) em phasizes that the necessary elem ent for
: the elicitation of the movement is the shift on the p a rt of the S from
| an external, passive, listening mode of attention to an internal,
! active, expressive mode.
The direction of these movements has been shown to c o rre
late with certain personality c h aracteristics. Day (1964) reports
that RMs experience anxiety as a "panicky feeling with externalized
perception of cause, " while LMs experience anxiety as "tension, as
in internally perceived im pulse feeling. " It has also been demon
strated that there is a lack of such eye movements when an S is
highly anxious, and a high frequency of occurrence of the m ove
m ents under conditions of m axim al interpersonal tru st and security,
i Also, schizophrenics, when they a re highly sym ptom atic, do not
i
!
j show these la te ra l eye-m ovem ents (Day, 1964).
j
Duke studied the eye-m ovem ent phenomenon in term s of its
relationship to such b ilaterally asym m etric behavioral functions as
handedness and eye-dom inance, as well as the relationship of the
eye m ovements to the sex of the S. While replicating the basic
finding of Day related to the elicitation of the phenomenon, Duke
found that m ales m ore consistently than fem ales turn their eyes
m ore often in one direction, but the direction of movement was not
14
related to sex. Also, handedness and eye-dom inance w ere found not
to be related to the direction of eye shift.
movement phenomenon in term s of the distribution of c ereb ral func
tion and co rtical reactivity. Bakan was basically interested in
hypnotic susceptibility and found that LMs tended to be m ore suscep
tible to hypnosis than RMs (based on the Stanford Hypnotic Suscep
tibility Scale). A relationship was also found between latera l eye-
movement and college m ajor, relative verbal (V) versus m athe-
m atic (M) sco res on the Scholastic Aptitude T est (SAT), and the
clarity of visual im agery. LMs w ere found to be "m ore hypnotizable,
m ore likely to be taking a 'so ft' o r hum anistic m ajor, likely to score
relatively higher on the V score than on the M score of the SAT, and
m ore likely to rep o rt c le ar visual im agery" (Bakan, 1969).
i tion of the distribution of psychological function between the hem is-
i
: pheres. RM would indicate activity in the contralateral frontal eye-
fields (Brodman's a re a 8 in the left hem isphere). This hem isphere
is known to serv e language and m athem atical abilities and to be
im portant in perform ance on I. Q. tests (Sperry, 1967, 1968; Cohen,
j
| et a l., 1968; W einstein, 1962; Teuber, 1962). LM would indicate
Bakan (1969) presents the firs t discussion of this eye-
To explain the relationships between the direction of eye
movement and these psychological variables, Bakan invokes the no-
activity in the right hem isphere which, as these investigators point
out, is dominant for such functions as spatial relations and other
complex perceptual p rocesses. The point Bakan (1969) makes is that
the eye movements a re m erely a by-product of other activity in the
hem ispheres and that the ch aracteristics of the hem isphere controll
ing the eye movement is very much like the relative dominance of
certain personality tra its of the LM o r RM. The ch aracteristics of
the LM, such as hypnotizable, taking a hum anistic m ajor, lower M
than V score on the SAT, and c le a re r visual im agery, appear to
Bakan as consistent with a relatively m ore active right hem isphere,
which is described by Bakan as "pre-verbal, pre-logical, subjective,
intuitive, global, synthetic, and diffuse. " The ch aracteristics of the
RM a re much like those of the left, dominant hem isphere, being
: logical, objective, and highly m athem atical and verbal.
An obvious factor which might have been confounded in
Bakan's data is handedness. Although Duke (1968) showed no
relationship between handedness and the direction of eye-shift, if S
was left-handed the relationship described by Bakan may not hold, for
the hem ispheric distribution of functions is somewhat different in
left-handers. As Teuber (1962) points out, language functions are
m ore diffusely represented in the brain of the left-hander. However,
as Bakan s tre sse s, since only 10% of the population is left-handed,
16
the effect of left-handers on the above relationship will be sm all,
: p articu larly since the sta tistica l relationship between personality and
i
| eye-shift found by Bakan was highly significant.
]
| The direction of latera l eye-m ovem ent during reflective
| thinking has been found to be related to EEG m easures. Bakan and
; Svorad (1969) have dem onstrated that LMs have a g re a te r amount of ;
EEG activity than RMs. In their experim ent alpha waves could be
detected in the EEG of LMs 52% of the tim e, com pared to 20% for
' RMs. These data have been replicated by S trayer (as reported in
Bakan, 1971), who found that left eye-m ovem ents w ere m ore frequent
I in persons with high basal levels of alpha activity. No mention was
| m ade in eith er study of any asym m etry of the alpha activity. How-
i I
| ever, since it is known that alpha rhythms a re m ore frequent over |
the right hem isphere (Raney, 1939; Liske, et al. , 1967), the fact
that LMs have a g rea ter amount of alpha indicates that LMs and RMs
do differ in th eir hem ispheric distributions of electrical activity, a
dem onstration n ecessary to acceptance of Bakan1 s interpretation of
the origin of the eye movements.
Evidence supporting a relationship between hem ispheric
im balances in cortical activity and lateral eye-m ovem ents can be
found in observations of neurological patients with unilateral lesions
o r epileptic foci. Im balances in activity caused by lesions resu lt in
17
a tendency for the patient to look toward the hem isphere with the
lesion. An epileptic discharge that is initiated in one hem isphere
often causes the patient to deviate his eyes laterally away from the
hem isphere involved in the abnorm al activity (De Jong, 1969). In
both situations the eyes a re deviating away from the m ost active
hem isphere, which, in the case of eye movements accompanying a
lesion, is the norm al hem isphere and, in the case of seizure
activity, is the abnorm al hem isphere. Thus, these neurological
symptoms a re consistent with Bakan's interpretation of the origin
of eye movements during reflective thinking as stem m ing from
differential activity in the two hem ispheres.
Bakan's interpretation of the eye-m ovem ent phenomenon is
given further support in a recent study by Robinson and Fuchs (1969)
in which the authors electrically stim ulated the frontal eye-fields of
the Macaca monkey. In stim ulating about 1, 000 different points in
this area they found that 96% of the movements elicited w ere con-
i I
i i
tra la te ra l saccadic eye movements and only 0.2% produced single !
i
ip silateral saccades. Of p articu lar im portance to this discussion is j
the finding that b ilateral stim ulation, instead of producing an a ll-o r-
none response as in hom olateral stim ulation, produced a graded
response. These graded eye movements could be regulated by the
| current with which each side was stim ulated in o rd er to produce any
18
response between those elicited by hom olateral stim ulation. The
im portance of this study lies in the dem onstration that saccadic eye
movements can be elicited by an im balance of electrical activity in
Brodman's area 8 and the resulting movement will be contralateral
to the m ost active hem isphere.
C hapter Summary
The lite ra tu re reviewed above provides inform ation support
ing sev eral im portant concepts of functional brain asym m etry. F irst,
evidence for a dual-dom inance interpretation of hem ispheric
functioning has been cited. Such an interpretation em phasizes the
fact that, while the left hem isphere is dominant for verbal, arithmetic^
and analytic functions, the right hem isphere is dominant for other
I functions which have been described as visuo-spatial perception,
: melody recognition, and im agery. Secondly, evidence has been r e
ported indicating that asym m etries a re detectable both in ongoing j
; EEG and in averaged evoked potentials which in som e cases co rrelate
I
with what is known of functional asym m etry. Finally, a recent
theory of Bakan's has been reviewed which proposes that Ss differ
in relative hem ispheric dominance in a way related to certain p er-
j sonality and intellectual tra its and predictable by the direction of
|
| la te ra l eye movement. It was therefore the object of the present
19
re se a rc h to use evoked potential methodology in the study of the r e
lationship between functional hem ispheric asym m etry and stim ulus
inform ation and subject tra its.
CHAPTER II
RESEARCH HYPOTHESES
Based on the recent work described in the preceding chapter
! dem onstrating VER co rrelates of functional asym m etry, it was the
purpose of this re se a rc h to explore asym m etries in evoked
: potentials and th eir relationship to (1 ) stim ulus inform ation,
(2 ) individual differences in direction of la te ra l eye-m ovem ent,
; and (3) verbal versus non-verbal abilities.
The dependent m easure p rim arily employed in this study
i
was the VER area-u n d er-th e-cu rv e. E ssentially, a re a-u n d e r-th e -
curve m easures the energy content o r total excursion in the
waveform and is generally related to VER amplitude. Studies using
this m easure have been reported in the recent literatu re (Dustman
& Beck, 1969; Bigum, et a l. , 1970). In the p resent study area-
under-the-curve was used as an index of hem isphere reactivity.
Also employed as dependent m easures w ere Pearson product-
moment coefficients of correlation between VER waveform s.
20
21
T hree hypothesized relationships were tested in this study,
i F irst, the relative distribution of activity between the hem ispheres
I of different stim uli (random, verbal, quantitative, and geom etric)
| was studied in an attem pt to replicate the work of Buchsbaum and
i
| Fedio (1969, 1970), showing VER co rrelates of the functional
■ dominance of verbal processing in the left hem isphere. These j
investigators did not use a stim ulus with quantitative o r m athe- |
m atical inform ation. According to the work of Sperry, a ll but the
sim plest of m athem atical ability is localized in the left hem isphere.
T herefore, a quantitative stim ulus should be distributed between the
i hem ispheres in much the sam e way as a verbal stim ulus. Buchsbaum;
i :
and Fedio (1969, 1970) used a complex sta tistic representing com- !
| parisons of coefficients of correlations between replicated and non- :
i |
replicated VERs as a m easure of the inform ation processing of
each hem isphere. The present resea rch sought to look at stim ulus
differences in term s of the relative hem ispheric reactivity as
reflected in ratios of the VER area-u n d er-th e-cu rv e (R/L), and
in term s of the degree of uniform ity of inform ation processing
as reflected in correlations between VER waveform s.
Secondly, Bakan's hypothesis that RMs have m ore reactive
left than right hem ispheres and LMs m ore reactive right
22
than left hem ispheres was tested. In term s of a statistic rep re se n t
ing right divided by left hem isphere activity, it was hypothesized
that LMs should have higher ratios of area-u n d er-th e-cu rv e, re p re
senting g re a te r right hem isphere activity. RMs, then, should have
lower ratios. Assuming eye movement to be continuously d istrib u
ted, a third group in which a predom inate direction of eye movement
could not be detected (NM) was tested, and it was hypothesized that
the VER ratios for this group should fall between those of LMs and
RMs.
Finally, the im plications of Bakan’s theories, that subject
differences in relative verbal versus non-verbal ability might be
related to, o r at least reflected in, the im balances of activity in the
two hem ispheres, w ere tested. Based on Bakan's data showing that
LMs tended to score relatively higher on the verbal section of the
SAT test, and RMs tended to score higher on the quantitative
section, it was hypothesized that Ss who a re relatively m ore verbal,
like LMs, should have relatively higher VER ratios (indicating
g re a te r right hem isphere reactivity), and Ss who a re m ore quanti
tative, like RMs, should have lower VER ratios. The present
re se a rc h directly tested the relationships hypothesized by Bakan
based on correlational data.
Two different tests of these relationships a re reported.
The first rep resen ts a pilot study undertaken to refine procedures
and to determ ine if any evidence could be detected in support of the
hypotheses. T herefore, a sm all num ber of Ss was tested, liberal
significance levels accepted, and the Ss preselected in such a way
as to m axim ize the probability of observing any relationships. The
second experim ent represents a la rg e r study using m ore common
procedures and m ore extensive analyses.
CHAPTER III
METHOD
This section includes a description of the general methods
| and procedure common to Experim ents I and II. Procedural
|
; differences between these experim ents will be described in the
I
I sections on each experim ent.
Subjects
Ss w ere sam pled from somewhat different populations in
each of the two experim ents reported herein. T herefore, a fuller
description of the Ss follows. However, the Ss in both studies
w ere intellectually norm al high school o r college students both
m ale and fem ale, predom inantly upper or middle socioeconomic
levels, fifteen to twenty years of age, and with no known CNS
abnorm ality which m ight have affected hem ispheric dominance or
evoked potentials.
24
25
Procedure
Ss w ere brought into the laboratory and seated in a shielded
: i
: room sep arate from the recording equipment. Upon entering the !
; j
experim ent the Ss knew nothing of the nature of the experim ent e x c e p t:
that it involved the relationship between "brain-w aves and thinking
p ro c e sse s." E lectrodes w ere attached to the head at bilateral
p arietal and cen tral scalp locations (P^, P^, Cg, and according
to the International Ten-Twenty System; Jasper, 1958). E ar-clip
electrodes w ere used as referen ces for m onopolar recording (right
ear) and as subject grounds (left ear). The electrodes w ere checked
for resistan ce in o rd er to keep electrode resistan ce below 20K, and
records w ere periodically m onitored throughout the experim ent to
i check for artifact.
Ss' c h arac teristic direction of eye movement was then deter-1
! I
| mined by the following method. E sa t d irectly in front of the S and
! read the first p a rt of the experim ental instructions contained in
[
I Appendix A. If the S had no questions about the experim ent, E p ro
ceeded to ask the 14 questions also found in Appendix A. The E
was careful to m aintain eye-contact with the S during the asking
of the questions so that the S's eyes sta rte d in a forw ard-gazing
| direction and the first eye-m ovem ent following the question could
j be observed and recorded. The eye movements w ere scored for each
26
question with a + 1 for a right m ovement, a - 1 for a left movement,
and a 0 for no movement at all. At the end of the 14 questions the
num bers w ere sum m ed to obtain a score between +14 and -14,
representing the num ber of right and left eye-m ovem ents.
Ss w ere then instructed concerning the second p art of the
experim ent and shown eighty 35mm slides which w ere divided among
four types of stim ulus inform ation: (1 ) random stim uli with no
apparent design; (2 ) verbal stim uli consisting of sim ple th re e -le tte r
words; (3) quantitative stim uli composed of easy m athem atical p ro
blem s; and (4) sim ple geom etric designs. Each stim ulus was form ed
from equal-sized white dots on a black background, with the num ber
of dots on each slide m atched with one slide from each of the other
three types in o rd er to control luminance (see Appendix B). These
slides w ere random ly in tersp ersed and shown three tim es, consecu- ;
| tively, totaling 60 presentations of each type in an experim ental j
| session. j
i
I
j
| The Ss sa t in a dim ly lit recording room approxim ately
i
10 feet from the screen on which the slides appeared. In o rd er to
m aintain som e level of attention the Ss w ere asked to respond
verbally to each stim ulus by saying "random " for random stim uli,
reading the th re e -le tte r words, giving the answ er to the sim ple
| m athem atical problem s, and describing in a word o r phrase the
27
geom etric stim uli. In o rd e r to avoid movement artifact obscuring
the evoked potential, the Ss w ere asked not to respond im m ediately
a fte r the stim ulus.
Apparatus
The slides w ere projected through a Kodak C arousel 500
projector. Stimulus duration was controlled by a W ollensak Alphax
shutter. The p rojector was se t to advance autom atically every five
seconds. Since 450 m sec, of data w ere included in each average,
the sh u tter was se t for a 500 m sec, stim ulus exposure to avoid
inclusion of off-responses in the data. A b eam -sp litter and photocell
w ere used to detect stim ulus onset for recording purposes.
The four channels of EEG w ere am plified by a G rass IV
electroencephalograph se t to pass between 1 and 35 Hz at -3db. and
| recorded on m agnetic tape by a Honeywell 7600 FM tape reco rd er,
i The output of a Schm itt trig g er was also recorded on a fifth channel j
i j
of the m agnetic tape in o rd e r to have a perm anent record of
stim ulus occurrence for averaging. EEG records w ere periodically
checked on the G rass electroencephalograph to insure that the data
w ere free of artifact. One channel of tape playback was also
m onitored on an oscilloscope. (F or apparatus, see Figure 1.)
Screen
Monitor
Photo-
Cell
Input Output
Projector Tape Recorder
Tape Amps
Pen Recorder
Stin.
Fig. 1. - -Recording and stim ulating apparatus.
29
Analysis
]
The tape-recorded EEG records w ere analyzed at the
| U niversity of Southern C alifornia System s Simulation Laboratory on
an IBM 360-44 Com puter interfaced with a Beckman 2132 EASE
Analog Computer (see Figure 2). An analog-to-digital converter,
controlled by the F o rtran program , transform ed the EEG inform ation
into digital form which could be read and processed by the IBM
360-44.
The com puter was program m ed to continually test the
stim ulus channel until the pulse was encountered. Upon encountering
a pulse, the com puter sam pled the four data channels at a rate of
800 sam ples/sec. /channel. (Since the tapes w ere played back at
four tim es the recording speed, this represented an actual rate of
j
: one sam ple every 5 m s e c .) Data lengths of 90 sam ples were taken
\ I
I for each of the four channels of data on each tria l. A control card
was read into the com puter to indicate which of the 240 tria ls re p re
sented data from which type of stim ulus. T herefore, depending on
the value read from this card and the channel from which the data
w ere received, the sam ples were added to the appropriate p arts of a
4x4x90 arra y , representing 90-sam ple averages of evoked potentials
recorded from four electrode placem ents and caused by four different
Tape Recorder
Fortran
Program
Output Input
Converter
Disc
Storage
IBM
360-44
Computer
Output
* Printer
Fig. 2. --D ata processing apparatus.
types of stim uli. In this way the resu lts of the 60 presentations, of
each stim ulus type were averaged. The resulting VERs were
i stored on com puter disc for further analysis. A digital record of
| the VERs, as well as an X-Y plot of the potentials, was also
i obtained in the form of com puter print-out.
CHAPTER IV
\ ;
i I
EXPERIMENT I !
i
Method
■ i
Sixteen sophom ore psychology students w ere chosen for this
experim ent in such a way as to form two groups of 8 Ss, representing
the high and low extrem es of a statistic indicating the percentage
by which the M score of the Scholastic Aptitude T est was higher or
low er than the V score ( (M-V)/V; range of ratios: high quantitative
group, +. 468 t o +. 396; low quantitative group, 080 t o 102).
This is the sam e sta tistic used by Bakan in dem onstrating a
correlation between eye movements and m ental abilities. Choosing
i Ss in this way therefore gave maximum probability of detecting any j
j
| group differences in hem ispheric VER ratio s. Ss w ere also tested
in the laboratory to determ ine if they w ere right or left eye-m overs
according to the procedure outlined in the previous chapter. VERs
3 3
w ere obtained using the methods described above and analyses of
j variance w ere run com paring the effects of the four stim ulus cate-
| |
j gories and the subject groups (either LM vs. RM o r high quantitativej
vs. low quantitative on SAT scores) on the sta tistic which expressed
| the relative VER area-u n d er-th e-cu rv e of the right to the left
I hem isphere, sep arate analyses being done for each electrode p air j
(P4 /P 3 ; C4 /C 3). Thus, large ratios represented la rg e r right
hem isphere evoked potentials as would be expected for the LM
o r high quantitative group. Low ratios represented g re a te r left j
| hem isphere VER area-u n d er-th e-cu rv e and were expected in
: the RM o r low quantitative groups. (See Figure 3 for method of
I i
; calculating a re a -u n d e r-th e -c u rv e .) !
' !
; 1
! Results
I ------------------------------------------------------------------------------------- ---------------------
Of the 1 6 Ss chosen, only 14 agreed to participate in the
experim ent. Of these Ss, it was possible to determ ine the
ch arac teristic direction of eye movement in a ll but two (Table 1).
As one can see from Table 1, in the rem aining 12 Ss the relationship
between direction of eye movement and SAT scores was not perfect,
but tended significantly in the direction described by Bakan (1969)
2
(x = 1. 33, p < .05). Due to equipment problem s, the data on five
Ss w ere not a rtifa c t-fre e , leaving four LMs, four RMs, and one
34
f \
Left
Right
Fig. 3. - -The above is an exam ple of the right central and
left central evoked responses to a random stim ulus. A rea-under-
the-curve was calculated from each of the above responses by
sum m ing the absolute differences between the 90 consecutive points
making up the average according to the following form ula:
89
Area = |Xj -Xi , where Xi rep resen ts
i = 1
the amplitude of point i on the VER. The a re a -ra tio for the above
VERs would then be:
area right _ 4917 _ , nftl-n
area left 4532 i - 0850-
35
TABLE 1
EYE MOVEMENT AND SAT SCORES*
High Quantitative Low Quantitative j
Left-m over 2 4 |
Right-m over 4
2 !
Undetermined 1 1
*x2 = 1.334, p < .05
undeterm ined S for the analysis of evoked response ratio s. Because
four of the 12 Ss did not fit the expected relationship between eye
movements and SAT sco res, both variables were used separately
as factors in the analyses-of-variance (the undeterm ined S being
left out of the analyses using eye movement).
Tables 2 through 5 give the data m eans for the evoked
potential ratios and the resu lts of the analysis of variance for the
four possible combinations of independent variables (eye movement
and SAT scores) and dependent variables (central and p arietal
evoked potentials), and the effect of the stim ulus variable on each
of the four. In F igures 4 and 5 one can see the resu lts represented
in graphic form . Since, in Experim ent I the EEG machine was not
well calibrated between channels, the absolute values of the means
TABLE 2
CENTRAL EVOKED RESPONSE AND EYE MOVEMENT
Random Verbal Quantitative Geom etric S Mean
Data Means
Left-m over .937 .860 1.017 1.041 .964
Right-m over .882 .827 .841 1 . 0 1 1 .890
Stimulus Mean .909 .844 .929 1.026
Analysis of Variance
F actor df SS MS F
Total 31 .864
Between Ss 7 .395
A (LM vs. RM) 1 .044 .044 .748
S/A 6 .351 .059
Within Ss 24 .469
B (Stimulus) 3 .137 . 046 2.706*
AB 3 .027 .009 .529
SB/A 18 .305 .017
*p< .10
TABLE 3
PARIETAL EVOKED RESPONSE AND EYE MOVEMENT
Random V erbal Quantitative Geom etric S Mean
Data Means
Left-m over .705 .678 .696 .811 .723
Right-m over . 660 .681 .637 . 676 .664
Stimulus Mean .684 .680 . 6 6 6 .744
Analysis of Variance
Factor df SS MS F
Total 31 . 2 0 0
Between Ss 7 .060
A (LM vs. RM) 1 .029 .029 5. 800*
S/A 6 .031 .005
Within Ss 24 .140
B (Stimulus 3 .029 . 0 1 0 2 . 0 0 0
AB 3 .018 .006 1 . 2 0 0
SB/A 18 .093 .005
*p < .10 (5.99 = . 05)
0 3
TABLE 4
CENTRAL EVOKED RESPONSE AND SAT-SCORE RATIO
Random V erbal Quantitative Geom etric S Mean
Data Means
Low Quantitative .980 .900 .967 1.062 . 977
High Quantitative .850 .934 .891 .990 . 891
Stimulus Mean .908 .863 .925 1 . 0 2 2
Analysis of Variance
F actor df SS MS F
jl W O O O I
i
a i D D IO B I '
i
Total 35 .779
Between Ss 8 .398
A (Low vs. High
Quantitative) 1 .065 .065 1.383
S/A 7 .322 .047
Within Ss 27 .382
B (Stimulus) 3 . 1 2 1 .040 3. 333*
AB 3 .007 . 0 0 2 .167
SB/A 2 1 .254 . 0 1 2
* p < .05
TABLE 5
PARIETAL EVOKED RESPONSE AND SAT-SCORE RATIO
Random V erbal Quantitative G eom etric S Mean
Data Means
Low Quantitative .722 .696 . 665 .714 .690
High Quantitative .657 .659 .675 .746 .693
Stimulus Mean . 6 8 6 .679 .670 .732
I
Analysis of Variance
F actor df SS MS F
Total 35 .204
Between Ss 8 .061
A (Low vs. High
Quantitative) 1 . 0 0 1 . 0 0 1 .116
S/A 7 .060 .0086
Within Ss 27 .143
B (Stimulus) 3 . 0 2 1 .007 1.373
AB 3 .014 .0047 .922
SB/A 2 1 .108 .0051
1.0
Mean
VEB ^ ^
Ratios
(B/L)
.8
Lit
Random Verbal Quant. Geom.
Stimuli
Fig. 4 . --C en tral VER a re a -ra tio s. Com parisons of the
m ean area-u n d er-th e-cu rv e ratios (R/L) for central VERs elicited by
four types of stim uli (Random, V erbal, Quantitative, and Geom etric)
in two groups of Ss (right eye-m overs and left eye-m overs).
41
Mean
Random Verbal Quant. Geom.
Stimuli
Fig. 5. - -P arietal VER a re a -ra tio s. Com parisons of the
m ean area-u n d er-th e-cu rv e ratio s (R /L) for parietal VERs elicited
by four types of stim uli (Random, V erbal, Quantitative, and
Geom etric) in two groups of Ss (right eye-m overs and left eye-
m overs).
42
a re not meaningful regarding hem ispheric VER asym m etry. How
ever, the calibration was consistent throughout the experim ent so
that the differences between group and stim ulus-condition m eans a re ;
both reliable and meaningful (i. e. the effect on ratios of channels
with differences in calibration would, nevertheless, be consistent
over a ll Ss and stim uli). From the analyses, the following sta te
m ents can be made:
Stimulus effects
C entral. - -In both of the analyses using central AER ratios,
the effect of the four different stim ulus categories was significant
using levels chosen for this analysis (p < . 10; see Tables 2 and 4;
these a re not independent analyses regarding the stim ulus variable
since they rep resen t repeated tests on the sam e data). The stim ulus ;
m eans found on Tables 2 and 4 indicate that the geom etric stim uli
w ere processed m ore in the right hem isphere than the left (mean j
|
ratio for geom etric, 1.026), while the verbal stim uli w ere processed
relatively m ore in the left (mean ratio for verbal, . 844). This
relationship is in accord with previous studies indicating verbal
processing in the left hem isphere and spatial-tem poral processing
in the right (see C hapter I).
Parietal. - -P arietal data indicated a significant (p < . 10)
43
difference between LMs and RMs in the direction of relatively larg er
VER ratios and, thus, g re a te r right ("non-dominant") hem isphere
reactivity for LMs (Table 3). This effect was in the sam e direction
; as that shown by the central data and was replicated in all stim ulus ;
categories except the verbal. The effect was also in the direction
which one would predict from the hypothesis regarding eye movements
stated by Bakan (1969). As in the central data, the sm allest subject
difference was shown in the responses to verbal stim uli; however,
the larg est S difference, instead of being in responses to quantita
tive stim uli, as in the central data, appeared in the responses to
geom etric stim uli.
Subject effects, SAT scores
The effect of grouping Ss according to their SAT scores
(M-V)/V) did not produce significant differences in the m ean AER j
; ratios from eith er cortical location. However, five of the eight
I differences between the group m eans over the two electrodes and
| four stim ulus categories w ere in the predicted direction (Tables 4
i
and 5).
I
Interactions
None of the interactions between subject and stim ulus
variables tested w ere statistically significant. N evertheless, there
w ere differences between LMs and RMs in th eir rank o rd er of right
; vs. left hem isphere activity over the four stim uli. F o r example, in
| the central data (Table 2), though the mean AER ratios were lowest
| for the verbal stim uli (stim ulus mean, . 844) and highest for the
| geom etric (stim ulus mean, 1.026) in both groups, the quantitative
ratio in the LMs tended to be m ore like that for the geom etric stim
uli than the verbal (1.017), while the RMs the quantitative ratio
was closer to that of the verbal stim uli than the geom etric (. 841).
The resu lts of E xperim ent I, then, give som e support to the
hypothesized relations between hem ispheric ratios of VER area
i and direction of eye movement or stim ulus inform ation. Differences
i
: between the VER ratios of LMs and RMs w ere in the direction
I predicted and appeared p articu larly strong for the geom etric VERs
|
in the p arietal a re a s and for the quantitative VERs in the central
a re as. The mean ratios for the verbal and geom etric stim uli for
both electrode placem ents w ere in agreem ent with the literatu re.
However, the sm all N and low levels of sta tistical significance
reduced confidence in the reliability of the resu lts. Also, in order
to m axim ize the probability of observing these effects, Ss were
preselected based on the extrem es of the distribution of SA T-score
ratio s. T herefore, this study did not provide inform ation relative
to the generality of the relationships. It was felt, then, that
further research employing a la rg e r N, traditional significance
levels, and a m ore random selection of Ss, was m erited.
CHAPTER V
EXPERIMENT II
Experim ent II was initiated in o rd er to te st the apparent
relationship observed in Experim ent I. However, the present
I experim ent differed in sev eral im portant aspects. Selection of Ss
was changed such that they were sam pled from a w ider age-range,
; with the only criterio n being an equal N in each group. Also, the
i am plifiers w ere accurately calibrated to allow determ ination of
| actual a re a -ra tio s. An attem pt was made to include a third group
j
I which did not show predom inant tendencies toward eye movement
in e ith er direction. Finally, due to the unavailability of SAT
scores for m ost Ss, a different m easure of verbal and non-verbal
ability was employed.
Method
F o rty Ss ranging in age from 15 to 20 years (X = 17 years,
5 months; S. D. = 16.7 months) w ere tested to obtain three groups
46
47
of 10 Ss representing right eye-m overs (scores between +14 and
+6), left eye-m overs (scores between -14 and -6), and non-m overs
j (NM; sco res b etw een+5 a n d -5). Inclusion of the NM group was
| done assum ing that there might be some continuous distribution in
| the population of eye-m ovem ent tendencies such that if there is a
i tru e relationship between eye movement and VER ratio s, the mean
: ratios of the middle group should fall between the m eans of the LMs
and RMs. All Ss w ere also adm inistered a se rie s of four tests
which resulted in sco res for two of the factors in G uilford's
Structure of Intelligence Model (Guilford, 1967): Cognition of
i F igural Units (FIG), and Cognition of Sem antic Units (SEM).
I These factors appeared to rep resen t the sem antic abilities of the
i left hem isphere (m easured by SEM) and the figural abilities of
| the right hem isphere (m easured by FIG). In that few of the Ss
i
in this p a rt of the experim ent had taken the SAT test, it was
thought that these te st sco res might provide m easures of relative
verbal and non-verbal ability.
Results
Of the 30 subjects originally selected, the data on two were
deem ed unacceptable because of artifac t in the EEG and one was
elim inated from the analysis because of a problem with extraocular
48
m uscles preventing a right eye-m ovem ent. T herefore nine Ss in
each of the groups w ere used in the following analysis.
From the m easurem ent of the eye movements and the two j
! paper-and-pencil te sts, four different modes of subject classifica- ;
tion, a ll thought to be related to hem ispheric asym m etry of function,
w ere studied in term s of their effects on the evoked potential ratios.
The first of these was the direction of la te ra l eye-m ovem ent during
reflective thinking. The distribution of lateral eye-m ovem ents on
the 14 questions for the 40 original Ss can be seen in Table 6. It
appears from this figure that the distribution is essentially bimodal,
as one would expect from the data of Bakan (1969) and others who
have investigated this phenomenon. The sp lit-h alf reliability in the
m easurem ent of eye movements was highly significant (r = +. 84).
Scores on the two factors (FIG and SEM) of Guilford’s Structure of
| i
Intelligence (Guilford, 1967) w ere also employed in the data analysis ;
i i
i as m easures on which to classify Ss. F or the fourth factor, a ratio !
i i
was computed between the FIG and SEM scores (FIG/SEM) for each j
j of the Ss, such that a high ratio represented relatively g rea ter
FIG scores and a low ratio, g re a te r SEM. Since VER ratios a re
expressed as right hem isphere divided by left, the hypothesis re la
ting individual differences in intellectual abilities and hem ispheric
| asym m etry would be supported by the high FIG/SEM -ratio Ss having
49
TABLE 6
FREQUENCY DISTRIBUTION OF EYE MOVEMENT SCORES
Score Frequency Group
-1 4 ,-1 3 XX
-12,-11 XXXXX
-10, -9 XX L eft-m overs (LM)
-8, -7 XXX (-14 to -6)
-6, -5 XXXXX
-4, -3 XX
-2, -1 XX
0 XX Non-m overs (NM)
1, 2
X (-5 to 5)
3, 4 XX
5, 6 X
7, 8 XXXXX
9, 10 XX R ight-m overs (RM)
11, 12 x x x x (6 to 14)
13, 14 XX
the highest VER ratios and vice versa.
C orrelational analysis of subject variables
Intercorrelations between these subject variables were
calculated to determ ine if the variables w ere truly independent in
these data (Table 7).
The SEM factor was found to be significantly correlated with
eye movement (r = +. 41, p < . 05), indicating that RMs tended to
score higher on this test. Although RMs w ere found by Bakan to be
relatively m ore quantitative than verbal on SAT tests, since RMs
a re thought to have m ore dominant left (verbal) hem ispheres, this
resu lt is not surprising. The only other significant correlations
between the m easures of S ability w ere found between the FIG/SEM
ratio and the FIG and SEM factors. This correlation is expected, as
the ratio is calculated from the SEM and FIG factors and is therefore
not independent of these.
i Since the Ss for Experim ent II encom passed a wider range
| of ages (15 to 20) than Experim ent I, it was also im portant to know
j
if any of the S variables w ere correlated with age. As can be
seen in the intercorrelation m atrix of Table 7, none of the linear
correlations with age w ere significant. T here was, however,
som e tendency for the younger Ss to be in the NM group. (Age
i
| m eans in months: RM, 212.9; NM, 206.7; LM, 208.4), a resu lt
which would not show up in a lin ear correlation test. A sim ple
51
TABLE 7
INTERCORRELATION MATRIX
OF SUBJECT FACTORS
j
!
FIG/SEM FIG SEM EM AGE
i
! FIG/SEM 1.00
FIG . 46* 1.00
SEM -.73* .24 1.00
EM -.3 3 .09 .41* 1.00
AGE -.1 8 .23 .35 .17 1.00
*p < .05
analysis of variance on the ages of Ss grouped by eye movements
; showed this tendency to be statistically insignificant.
i j
j A rea-under-the-curve
As in Experim ent I, ratios of the area-u n d er-th e-cu rv e for
each electrode p air w ere calculated as an index of VER asym m etry.
The mean VER ratios for the different eye-m ovem ent groups and
stim uli can be seen graphically for the central data in Figure 6 and
for the p arietal data in Figure 7. The VER ratios were subm itted
to four separate th ree-facto r analyses of variance, each com paring
the effects of one of the subject variables (i. e. eye movement, SEM,
FIG, FIG/SEM). The resu lts of the analysis using eye movements as
5 2
1.12
1.10
1.08
1.06
VER
1.04
Ratios
1.02
1.00
(R/L) .98
.96
.94
;92
Random Verbal Quant.
Stimuli
Geora.
Fig. 6 .--C en tra l VER a re a -ra tio s . A rea-under-the-
curve ratios (R/L) for bilaterally sym m etric central electrodes for
each of the four stim ulus types: Random, V erbal, Quantitative, and
G eom etric. A reas a re com pared for the three subject groups: RMs,
NMs, and LMs.
5 3
I
1.04
1.02
Ratios
1.00
Random Verbal Quant..
Stimuli
Geom<
Fig. 7 . --P a rie ta l VER a re a -ra tio s. A rea-under-the-
curve ratios (R/L) for bilaterally sym m etric p arietal electrodes for
each of the four stim ulus types: Random, V erbal, Quantitative, and
G eom etric. A reas com pared for the three subject groups: RMs,
NMs, and LMs.
the S variable can be seen in Table 8. It is evident that neither
the subject, nor the electrode, nor the stim ulus, nor any of the
interaction effects w ere statistically significant in term s of their
effects on VER ratio s. Sim ilar insignificant resu lts w ere obtained
using the other S variables and, therefore, a re not reported. In
the event that the computation of a ratio of VER area-u n d er-th e-
curve may have obscured some interesting effects, the absolute
a re as from the four electrodes w ere used as a factor, as well as
the stim ulus and eye-m ovem ent factors. This analysis of variance
is reported in Table 9. H ere again it can be seen that the subject
and stim ulus effects w ere insignificant, although there was a very
significant electrode effect. Examination of the m eans indicates
that this effect was due to la rg e r areas from the central electrode
■ p a ir (Cg and C^) than from the p arietal pair (P^ and P^). Sim ilar
! resu lts w ere again obtained from analyses using the other S factors,
| and therefore a re not reported.
Intercorrelations: waveform analysis
The preceding analyses are all based on an attem pt to
evaluate hem ispheric differences in inform ation processing in term s
of the amplitude (area-under-the-curve) of the evoked responses of
bilaterally sym m etric co rtical a re as. However, differences in size
| of the VER did not exhaust all the ways in which potentials might
TABLE 8
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT, ELECTRODE,
AND STIMULUS EFFECTS ON VER AREA RATIOS
F actor SS DF MS F
Total 7.51 215
Between Ss 3.48 26
S (RM-NM-LM) 0.04 2 0.02 0.15
Subjects within groups (S) 3.44 24 0.14
Within Ss 4.03 189
A (Stimuli) 0.01 3 0.00 0.44
AS 0.06 6 0.01 0.94
A X Subjects within groups (A) 0.73 72 0.01
E (Electrode) 0.11 1 0.11 1.03
ES 0.08 2 0.04 0. 37
E X Subjects within groups (E) 2.47 24 0.10
EA 0.01 3 0.00 0. 33
EAS 0.00 6 0 . 0 0 0.07
EA X Subjects within groups (EA)
e
0.57 72 0.01
j
c /1
c /1
TABLE 9
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT, STIMULUS
AND ELECTRODE EFFECTS ON VER AREAS
Factor SS DF MS F
Total 40,658, 533 431
1 Between Ss 20,716,032 26
S (LM-NM-RM) 214,272 2 107,136 0.13
Subjects within groups (S) 20, 501,760 24 854,240
Within Ss 19,942, 501 405
A (Stimuli) 330,752 3 110,250 1.94
AS 603,392 6 100,565 1.77
A X Subjects within groups (A) 4,084,480 72 56,729
E (Electrode) 3,244, 659 3 1,081,553 7. 65**
ES 18,944 6 3,157 0.02
1 E X Subjects within groups (E) 10,179, 314 72 141,379
! EA 45, 312 9 5,034 0.79
1 EAS 59,648 18 3,313 0. 52
j EA X Subjects within groups (EA) 1,375,999 216 6,370
**p < . 01
cn
ON
57
differ acro ss hem ispheres. Particularly, potentials may differ in
waveform without significant differences in amplitude. Components
of the VER can appear and disappear, increase or decrease, and j
I change in latency without necessarily affecting the total area-under-
the-curve.
It was thought, therefore, that inter-hem i^iheric differences
in brain activity in the present study might be detectable using a
Pearson product-m om ent coefficient of correlation between
individual VER waveform s, each of the points in the waveforms
being the m easures correlated. The calculation of such coefficients
gives one an index of VER waveform sim ilarity o r dissim ilarity,
with relatively high correlations representing m ore sim ilar wave
form s and low correlations, m ore d issim ilar waveforms. Use of
correlations in such a way is prevalent in recent literatu re !
| i
(Callaway, Jones, & Donchin, 1970; Donchin, Callaway, & Jones, j
1970; Roth, Kopel, & Bertozzi, 1970; Bejum, Dustman, & Beck,
1970; Rhodes, Dustman, & Beck, 1969; Dustman & Beck, 1969;
Buchsbaum & Fedio, 1969, 1970). It is generally assum ed that m ore
d issim ilar waveforms from the sam e electrode under different
stim ulus conditions rep resen t g re a te r amounts of information
processing, in that there has been a differentiation of the stim uli
! in the responses of that area of the brain. H em ispheric differences
58
in correlations would then be interpreted as showing g rea ter
inform ation (stim ulus) processing in the hem isphere with the
lowest correlation. This interpretation of correlations between
VERs to different stim uli in the sam e a re a is consistent with the
work of Buchsbaum and Fedio (1969, 1970).
Under these assum ptions the data from the present experi
m ent w ere reanalyzed in term s of coefficients of correlation rath e r
than area-u n d er-th e-cu rv e. The 16 VERs for each S w ere
in terco rrelated to a rriv e at a 16X 16 correlation m atrix. These
m atrices w ere calculated and transform ed into Z -sco re s by
com puter and stored on disc for analysis. A m atrix of mean
intercorrelation acro ss all Ss was also calculated (see Appendix C).
F irst, to a sse ss the total amount of information processing
a t each brain area, all of the Z -transform ed intercorrelations be
tween the responses to the four stim uli w ere summed for each
: electrode within each S. These sum s were then subm itted to a
! repeated m easures analysis of variance com paring the effects of
hem isphere (right vs. left), electrode (parietal vs. central), and
direction of eye movement (RM-NM-LM). This analysis resulted
in insignificant subject, hem isphere, and electrode effects (see
Table 10). However, there was a significant hem isphere X
| electrode interaction (p < .01) such that the lowest total inter-
TABLE 10
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT,
HEMISPHERE, AND ELECTRODE EFFECTS ON THE
SUM OF THE INTERCORRELATIONS
BETWEEN STIMULUS VERS
F actor SS DF MS F
Total 415.14 107
Between Ss 321.17 26
S (LM-NM-RM) 8.27 2 4.13 0. 32
Subjects within groups (S) 312.90 24 13.04
Within Ss 93.98 81
E (Electrode) 0.13 1 0.13 0. 22
ES 2. 55 2 1.28 2.15
E X Subjects within groups (E) 14.25 24 0. 59
H (Hem isphere) 2.30 1 2. 30 2.86
HS 1.20 2 0. 60 0.75
H X Subjects within groups (H) 19.29 24 0. 80
HE 14.47 1 14.47 9.77**
HES 4.23 2 2.12 1.43
HE X Subjects within groups (HE) 35. 55 24 1.48
**p < . 01
Data Means: Z -T ransform ed C orrelations
Parietal
C entral
Right
1. 5675
1.6845
Left
1.6386
1.5145
60
correlation, and thus by definition the g rea test amount of inform a
tion processing, occurred in the right p arietal and left central are as.
O ther interactions w ere not significant. Sim ilar analyses w ere done i
using the test sco res and ratio s (SEM, FIG, and FIG/SEM ratio)
as bases for dividing subjects, with exactly the sam e resu lts as
cited above (the hem isphere-by-electrode interaction, of course,
would not change by altering the between-Ss dimension). Since
the resu lts a re sim ilar, these analyses a re not reported.
Com parisons w ere also made between VER correlations in
such a way as to p reserv e inform ation about the effects of the type
of stim ulus inform ation on evoked response waveform s. To do this,
the random stim ulus was considered as a control, o r "non-inform a-
tional" stim ulus, and the effect of stim ulus inform ation on VER
waveform was m easured by the correlation between the VERs to
random stim uli and eith er verbal, quantitative, o r geom etric stim u li.;
Thus, the three Z -transform ed correlations, representing verbal, i
i
quantitative, and geom etric inform ation, for each of the four
electrode placem ents and the three eye-m ovem ent groups, were
subm itted to an analysis of v arian ce--th e resu lts of which can be
found in Table 11. Analyses of this type w ere not done using the
other S variables.
A strong stim ulus effect was found (p < .001), such that
61
TABLE 11
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT,
ELECTRODE, AND STIMULUS EFFECTS ON
VER INFORMATION CONTENT
F acto r SS DF MS F !
i
; Total 85.07 323
i
Between Ss 29.76 26
S (RM-NM-LM) 1.01 2 0. 50 0.42
Subjects within groups (S) 28.76 24 1.20
Within Ss 55. 30 297
E (Electrode) 1.31 3 0.44 5.15**
ES 0. 80 6 0.13 1.57
E X Subjects within groups (E) 6.10 72 0.08
A (Stimuli) 32.90 2 16.45 91.56***
AS 1.19 4 0. 30 1. 65
A X Subjects within groups (A) 8. 62 48 0.18
AE 0.07 6 0.01 0.43
AES 0. 64 12 0.05 2.07*
AE X Subjects within groups (AE)
i
3.69 144 0.03
*p < . 05
**p< .01
***p< .001
Data Means: Z~ T rans form ed C orrelations
V erbal Quantitative Geomet]
Right parietal 2.0872 1.4607 1.4363
Left p arietal 2.1809 1.5146 1, 5145
Right central 2.2219 1.5992 1. 5054
Left central 2.0991 1.4079 1.3467
6 2
the m ean random -verbal correlation was significantly higher than
eith er the random -quantitative or random -geom etric means
(p < . 001; Sheffe's m ultiple com parison method, 1959), while the ;
random -quantitative and random -geom etric m ean correlations did not!
differ significantly. A significant electrode effect was also found
( p < .01) which replicated the hem isphere-by-electrode effect
found when a ll the stim ulus VERs w ere in terco rrelated and th eir Z -
transform s sum m ed. Again the right p arietal and left central
electrodes produced relatively low mean Z -sc o re s, and the left
p arietal and right central relatively high m ean Z -sc o re s.
The stim ulus-by-electrode-by-subject interaction effect
was also found to be significant (p < . 01). Although the reason for
this interaction effect was difficult to discern, from the cell means
it appeared that the source of the effect was a re v e rsa l in the o rder
I of magnitude of Z -sc o re s for the quantitative and geom etric
! inform ation in the left and right p arietal and left cen tral areas for
j
! the NM group as com pared to the RM and LM groups. The subject-
| by-electrode effect, a m easure of differences between the groups
i
in hem ispheric inform ation processing, and the stim ulus-by-
electrode effect, a m easure of the stim ulus differences in hem is-
i pheric distributions of inform ation processing, w ere insignificant
I
| in this analysis.
6 3
| H em ispheric asym m etries in inform ation processing were
also evaluated using correlations between VERs occurring at
different electrodes. Here interpretations of the magnitude of
correlations is somewhat different, since the waveforms being
considered w ere not recorded from the sam e brain area. Much
the sam e problem is faced by those seeking to in terp ret the resu lts
of c ro ss-sp e c tra l analysis (Galbraith, 1967), and many of the sam e ;
ideas have been used for interpreting VER correlations and EEG
c ro ss-sp e c tra . The origin of the difficulty is the lack of conclusive
knowledge of the neural generation of EEGs and evoked potentials.
; However, interpretations of VER correlations have ranged from j
! i
i conservative interpretations assum ing nothing m ore than sim ilarity !
| or, somewhat less conservatively, "uniform processing" (Buchs-
i
| baum & Fedio, 1969, p. 27), to m ore liberal ideas of shared
i
activity o r shared inform ation (John, et a l. , 1964).
A com parison of in terest was the degree of interaction
occurring in this experim ental situation between the parietal and
central a reas. This inform ation was obtained from the correlations
between the p arietal and central VERs from the sam e hem isphere.
The resu lts of an analysis of variance using these correlations as
dependent m easures and the hem isphere, stim ulus, and subject
groups as independent factors can be found in Table 12. This
64
TABLE 12
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT, STIMULUS,
AND HEMISPHERE EFFECTS ON CENTRAL-PARIETAL
VER CORRELATIONS
F actor SS DF MS F
Total 30. 50 215
Between Ss 18.97 26
S (LM-NM-RM) 0. 68 2 0. 34 0.44
Subjects within groups (S) 18. 29 24 0.76
Within Ss 11.53 189
H (Hem isphere) 0.12 1 0.12 0. 86
HS 0.10 2 0.05 0. 36
H X Subjects within groups (H) 3.46 24 0.14
A (Stimuli) 1.01 3 0. 34 5.21**
AS 0.71 6 0.12 1.85
A X Subjects within groups (A) 4. 64 72 0.06
AH 0.19 3 0.06 3.74*
AHS 0.11 6 0.02 1.12
AH X Subjects within groups (AH) 1.20 72 0.02
* p < .025
**p< .01
Data Means: Z -T ransform ed C orrelations
Right Left Different
Random 1. 3563 1.4415 .0852
V erbal 1.3614 1.4819 .1205
Quantitative 1.2599 1.2665 .0066
Geom etric 1. 3069 1.2748 -.0321
6 5
analysis produced significant stim ulus and stim ulus-by-hem isphere
j
j effects (p < . 01 and p < . 025, respectively). The subject effect
was again insignificant. Sim ilar analyses w ere made using the
other S variables with sim ilar resu lts.
Table 12 also includes the m ean Z -sc o re s for the stim ulus-
| by-hem isphere interaction, as well as left minus right differences, j
A positive difference indicates g re a te r VER sim ilarity in the left ;
hem isphere; that is, intrahem ispheric correlations a re g reatest j
on the left side; and a negative difference indicates g re a te r sim il
a rity in the right hem isphere. T herefore, it can be seen from
these difference sco res that the verbal stim ulus produced m ore
sim ilar p a rietal-cen tral waveforms in the left hem isphere than the j
j 1
right, while the geom etric stim ulus produced the m ost sim ila r j
i
I
i
waveforms in the right hem isphere. The quantitative stim ulus j
i
showed nearly the sam e amount of sim ilarity in both hem ispheres.
It was also of in terest to know the degree to which the sam e
are as in different hem ispheres produced sim ila r o r d issim ilar VERs,
T herefore the correlations between the right and left hem isphere
VERs for the p arietal and cen tral a re as w ere subm itted to an
analysis of variance, again com paring the effects of the four stim uli
and three eye-m ovem ent groups. This analysis also produced
significant stim ulus effects (p < .01, see Table 13). The subject
effect, as well as the interaction effects, w ere again insignificant,
66
TABLE 13
ANALYSIS OF VARIANCE TABLE: EYE-MOVEMENT, STIMULUS,
AND ELECTRODE EFFECTS ON CROSS-HEMISPHERE
VER CORRELATIONS
F actor SS DF MS F
Total 36. 23 215
Between Ss 22. 22 26
S (LM-NM-RM) 0.38 2 0.19 0. 21
Subjects within groups (S) 21.84 24 0.91
Within Ss 14.02 189
E (Electrode) 0.54 1 0. 54 2.09
ES 0. 92 2 0.46 1.76
E X Subjects within groups (E) 6.23 24 0.26
A (Stimuli) 1.02 3 0. 34 7.07**
AS 0.19 6 0.03 0. 65
A X Subjects within groups (A) 3.46 72 0.05
AE 0.09 3 0.03 1.50
AES 0.07 6 0.01 0.56
AE X Subjects within groups (AE) 1.49 72 0.02
* * p < .01
Data Means: Z -T ransform ed C orrelations
P arietal C entral
Random 1.4363 1.2662
V erbal 1.4406
1.2877
Quantitative 1.2344
1.1708
Geom etric 1.2292 1.2133
6 7
and sim ila r analyses using the other S variables produced sim ilar
resu lts. It can be seen from the stim ulus-by-hem isphere means
reported in Table 13 that the verbal stim uli produced the m ost
sim ila r waveforms acro ss hem ispheres, while the quantitative and
geom etric, the least sim ilar waveform s.
CHAPTER VI
DISCUSSION
The p resent study sought to investigate asym m etries in
j the functional organization of the human cereb ra l cortex. The
resea rch was directed at two p articu lar problem s of functional
asym m etry. The firs t of these problem s was related to the
hypothesis of Bakan that Ss differ in term s of relative reactivity
of the cereb ral hem ispheres eith er in the predom inant direction
i
| of la te ra l eye-m ovem ent during reflective thinking, o r in
i
! relative verbal versus m athem atic intelligence. The second
problem for study involved the hem ispheric processing of
random, verbal, quantitative, and geom etric information.
H em ispheric asym m etries w ere evaluated by com paring the
amplitude and waveform of the visual evoked response from
b ilateral p arietal and central scalp electrodes.
The resu lts of the study a re discussed below in term s of
the m ain factors of the analyses of variance: subject effects, re la t
ing to the problem of individual differences, and stim ulus effects, to
69
asym m etries in the processing of inform ation.
Subject Effects
Using the methods employed in these experim ents it has
! not been possible to dem onstrate visual evoked response (VER)
co rrelates of the S differences in hem ispheric dominance proposed
by Bakan (1969). The hem ispheric ratio s of VER area-u n d er-th e-
curve w ere found not to be related to subject differences in (1)
direction of la te ra l eye-m ovem ent during reflective thinking,
(2) sco res on a test of verbal ability (SEM), (3) scores on a test of
figural ability (FIG), (4) ratios of figural versus verbal ability
(FIG/SEM), o r (5) relative verbal versus quantitative SAT o r ACT
sco res. Although the p arietal data in E xperim ent 1 tended to
support hypothesized differences in left eye-m overs (LMs) and
; right eye-m overs (RMs), the sam e data from Experim ent II were
; not only insignificant regarding this com parison, but the means
j w ere in the opposite direction from the hypothesis. It was also
dem onstrated in Experim ent II that co rre lates of these S variables
a re not to be found in the sim ilarity o r d issim ilarity of evoked
potential waveform s. N either the intercorrelations between
different VERs for the sam e electrode, nor the correlations between
VERs for different electrodes statistically differentiated between
70
the Ss.
The lack of a significant eye-m ovem ent effect cannot be
said to be due to a failure to replicate the eye-m ovem ent phenomenon:
In Experim ent I and II, direction of eye movement was found to
co rrelate well with SAT or ACT sco res (Tables 1 and 10). In
Experim ent II the distribution of eye-m ovem ent sco res was found
to be bimodal (Table 6), suggesting a binary classification between
LMs and RMs. The fact that direction of eye movement was
correlated with SEM scores also indicates that the eye-m ovem ent
variable was related to m ental abilities. It appears, therefore,
that the eye-m ovem ent phenomenon discussed by Bakan (1969) has
been replicated.
The amplitude m easure (hem ispheric ratios of VER a re a -
under-the-curve) used in these experim ents to detect differences I
|
j i
I in co rtical reactivity is consistent with Bakan's concepts. He
states,
j
I It may be that left- or right-m ovem ent associated with the
| reflective process is sym ptom atic of e a sie r triggering of
activities in the hem isphere contralateral to the direction
of eye movement. D ifferences in ease of triggering
dominant and non-dominant hem ispheres may in turn be
related to a wide variety of individual differences in
cognitive, personality, and physiological variables.
[p. 930]
A rea-under-the-curve is a m easure of energy content arriv ed at by
summing the total excursion, o r amplitude, acro ss die whole VER
71
waveform. The relationship between VER am plitude and reactivity
is supported in the literatu re by studies relating this VER m easure
: to reaction tim e and vigilance (F ruhstrofer & Bergstrom , 1969;
j H aider, Spong, & Lindsley, 1964; Donchin & Lindsley, 1966).
Robinson and Fuchs (1969), have shown that in b ilateral
stim ulation of the frontal eye-fields only a sm all difference in
stim ulating current is necessary to elicit an eye movement contra
la te ra l to the area of g reatest stim ulation. It would take only a
sm all difference in activity effecting these are as during reflective
thinking to cause the eyes to deviate, and, therefore, the
differences between hem ispheres electrically could be quite subtle
and still cause such eye m ovem ents. It may be that, though such
evoked potential ratio s a re consistent with the concepts involved in
Bakan's hypothesis, the subject effects, if they exist at all, a re too
j subtle to be detected by evoked potential techniques.
In the present experim ents, then, the test of Bakan's
hypothesis depended for verification on evoked potential differences.
However, the eye movements which a re used to differentiate Ss
occur when an S is not attending to external stim uli but has an
internal focus of attention involved in problem solving and reflecting.
It m ay be that Ss do not really differ in term s of "triggering of
i
i
| activities" in the hem ispheres by external stim uli, but differ som e-
72
how in term s of their preference for using predom inantly one
hem isphere o r the other during active problem solving. A better
m easure of subject differences in hem ispheric activity related to
: eye movement m ay be one of ongoing EEG, for exam ple spectral
analysis, taken during the type of reflective thinking used to elicit i
the eye movements originally.
The possibility that differences in hem ispheric reactivity,
if they exist, may indeed be subtle could also explain the difference
between the outcomes of Experim ent I and Experim ent II. A
re a l effect that is sm all can easily be obscured by an increase in
variance. Two factors served to increase variance in Experim ent
II. F irs t of all, in Experim ent I Ss w ere chosen according to th eir
SAT sco res in such a way as to m axim ize the probability of observ
ing correlated eye-m ovem ent differences and any concomitant evoked '
potential differences. In Experim ent II, because of (1) the j
| j
I desireability of obtaining a larg e r num ber of Ss, (2) the d esire to
test an interm ediate group (between RMs and LMs) to see if the
i
| phenomenon could be considered continuously distributed, and
(3) the unavailability of SAT scores on the m ajority of these Ss,
all Ss who m et the age criterion w ere accepted for the experim ent
as they w ere available. These Ss therefore represented a quite
different distribution of eye-m ovem ent sco res and m ental abilities.
7 3
A second factor increasing the variance involved the Ss' ages. The
Ss in Experim ent I, though having nearly the sam e mean age as
those in Experim ent II, w ere a ll approxim ately the sam e age, while j
the Ss in Experim ent II ranged in age over a five-year span.
| The age-range of the Ss in Experim ent II might have had
| another im portant effect. The NM group had a m ean age nearly
| j
; one year lower than that of the other two groups. It was also true
that the NM group had mean VER ratios below 1.00, while those
of both of the other groups w ere above 1.00. This finding indicates |
that the younger Ss m ay not have developed the kind of dominance :
! i
which would resu lt in evoked potential asym m etries and in la te ra l |
eye-m ovem ents during reflective thinking. Dustman and Beck
I (1969) have dem onstrated that the evoked potential in humans does
not stabilize in overall am plitude o r in hem ispheric asym m etry
until age 15, the lower age lim it for Experim ent II.
Stimulus Effects
Although hem ispheric asym m etries in VER amplitude and
waveform were not found to be related to S variables, definite
indication of hem ispheric differences in stim ulus processing were
found. However, the m easure of preference for assessing these
hem ispheric asym m etries appeared to be waveform correlations
74
and not amplitude. With the exception of a weak effect in the central
data of Experim ent I, all the analyses using VER area-u n d er-th e -
curve, whether are as them selves or right-left ratio s, failed to de-
i tect hem ispheric differences in stim ulus processing. Analysis of
VER waveform s, however, yielded a num ber of significant resu lts,
indicating that such m easures may be m ore sensitive to asym m etries
in stim ulus processing than am plitude m easures.
Several significant and interesting relationships between
the processing of verbal, quantitative, and geom etric stim uli
and VER waveform s w ere detected when considering the random
stim ulus as a "non-inform ational control, " and com paring it to the
other three stim uli. It was found that a geom etric o r quantitative
stim ulus produced VERs much less like the random -stim ulus VERs
than the verbal stim ulus (Table 11). Although such an effect is
; not representative of asym m etric functioning, it does indicate
| that relatively m ore differentiation of activity occurred for
geom etric and quantitative stim uli than for verbal stim u li. This
finding may reflect the fact that the task for the S in analyzing and
responding was somewhat m ore difficult for these stim uli than for
verbal. In the case of verbal stim uli the c o rre ct response did not
have to be determ ined, but was contained m ore directly in the
stim ulus itself.
Of p articu lar in terest in the present study a re data on
waveform sim ilarity between the p arietal and central VERs, and
the com parison of these correlations a cro ss hem ispheres (Table 12).
j A VER co rrelate of the relatively strong functional localization of
verbal abilities can be seen in the differences between Z -sco re s.
T here was a g re a te r amount of waveform sim ilarity for the verbal
stim ulus in the left hem isphere than for any other stim ulus in
eith er hem isphere. The cross-hem isphere differences in
intrahem ispheric correlations were also g reatest for the verbal
stim ulus, indicating g rea ter hem ispheric asym m etry in p arietal-
central waveform sim ilarity. In addition, the only stim ulus
producing a difference between means in favor of a g reater right
hem isphere interaction was the geom etric stim ulus. Although
| this distribution of processing of verbal stim uli has been demon-
| strated in other studies using evoked potential techniques (Buchsbaum
& Fedio, 1969, 1970), few, if any, studies exist which dem onstrate
asym m etries in the processing of geom etric (visuo-spatial)
inform ation using these techniques.
The processing of a quantitative stim ulus was an em p iri
cal question to be investigated. This type of stim ulus produced
nearly equal p arietal-cen tral correlations for the right and left
hem ispheres. However, in both hem ispheres the mean Z -sco re
7 6
was relatively low and therefore sim ila r to that of the geom etric
stim ulus. The fact that geom etric and quantitative stim uli produced
i lower correlations than random and verbal again may have been
i
| due to the g rea ter difficulty encountered in analyzing and responding
; to the quantitative and geom etric stim uli.
A ssessm ent of VER sim ilarity between responses from
hem ispherically sym m etric pairs of electrodes also produced
significant stim ulus differences. The distribution of the m eans
found on Table 13, in term s of the random, verbal, and geom etric
stim uli, replicates m ean correlations reported by Buchsbaum and
Fedio (1969), in that the verbal stim ulus in both studies produced
the g reatest cross-hem isphere correlation; the random stim ulus,
the next g reatest; and the geom etric stim ulus in the parietal data
j of this study, the least. The m ean cross-hem isphere Z -transform ed
! I
| correlations in Buchsbaum and Fedio's study were taken from I
j j
occipital are as and w ere higher in magnitude than the mean Z -sco re s
found in this study. Together, the two studies indicate that the
inform ation, in term s of VERs, begin with a high degree of
hem ispheric sim ilarity at the prim ary receiving areas (occipital),
and become m ore divergent as the inform ation is passed forward
to p arietal and central areas.
As mentioned above, the interpretation of correlations
77
between VERs recorded from different brain areas ra ise s a
theoretical problem . Some investigators choose to avoid in terp re-
| tation and m erely state that the evoked potentials were sim ilar
(Dustman & Beck, 1969). Buchsbaum and Fedio (1969, 1970) assum e
that "uniform processing" occurred in a re as with highly sim ila r
VERs. G albraith (1967) chooses to in terp ret sim ilarities in ongoing
EEG activity, theoretically a sim ila r problem , as indicating
ele ctrica l interaction ("coupling") of brain a re as. John, Ruchkin,
and V illegas (1964) in studying VER correlations in a num ber of
different brain are as during the learning of an avoidance response,
also in terp rets changes in VER sim ilarity as indicating functional
interaction. These w riters go so fa r as to state that "one can
conceive of the inform ation processing activity of the brain at
any m oment as a set of coherent events in its constituent neural
populations [p. 417]." They em phasize that, in their research,
as a stim ulus acquired "meaning" through the conditioning
procedures, the sim ilarity in waveform from different areas
increased and any failure to respond was accompanied by a d e te rio r
ation in the complex of waveform sim ila rities. Appropriate
response to the "meaning" of the stim ulus "appeared to require
correspondence of patterns of ele ctrica l activity [p. 417]. "
Should sim ilar waveforms thus rep resen t shared information,
78
the data from the p resent study indicate that there is g rea ter
: p a rie ta l-c e n tra l sharing of verbal inform ation in the left hem isphere,
i
and g re a te r sharing of geom etric inform ation in the right hem is-
| phere. The quantitative stim uli appeared to have caused nearly j
: equal intrahem ispheric correlation. Borrowing again from the j
interpretation of John, et a l. , (1964), it can be said that in the
present data the verbal stim ulus had g re a te r "meaning" for the
left hem isphere than the right. This interpretation is consistent
with S p erry 's dem onstration (1968) that verbal m aterial has
little meaning to the right hem isphere.
One further significant effect based on VER correlations :
that has yet to be discussed is the hem isphere X electrode
interaction effect which occurred when the stim ulus in te rc o rre - |
i i
| lations w ere summed for each electrode. It is interesting to
i
| note the a re a s producing the lowest intercorrelations and, th e re
fore, the g reatest differences in VERs for the four types of
stim uli. The right p arietal and left central a re as were both
significantly lower in mean Z -sco re than th eir cross-hem isphere
match. This effect also appears in the electrode effect of the
analysis of VER intercorrelations, using a random stim ulus as a
control.
T here a re two somewhat sim ila r interpretations of this
7 9
effect. F irst, the nature of the task required visual processing
of the relationship between the dots and then generation of an
| appropriate response. T herefore, it m ay have potentitated or
I facilitated concentration of analysis in both the right p arietal lobe,
! an a re a involved in visuo-spatial construction (Teuber, 1962), and
the left central are a, which is near B roca's speech a re a in the
hem isphere dominant for verbal function.
Another interpretation is that the g re a te r amount of
inform ation processing in these a re a s is not as directly related
to the nature of the task as it is to a basic ch aracteristic of the
brain. It seem s quite possible that dominance m ay vary in
laterality and degree from brain a re a to brain a re a. In the past,
hem ispheric asym m etry has been investigated only in term s of
i tasks o r subjects (right- and left-handed), in which each hem isphere
has been considered as a whole. Little has been done, however, to
determ ine if dominance is really a c h aracteristic of a hem isphere
as a whole, o r is a c h aracteristic which m ust be determ ined for
each brain area. The fact that verbal functions a re known to be
located predom inantly in the left hem isphere and in tem poral and
prefrontal a re a s indicates that for these p arts of the brain the
left hem isphere is dominant. By the sam e logic, the p arietal and
parietal-occipital are as and the right hem isphere being predom in
80
antly involved in visuo-spatial and tem poral processing indicates
that the right hem isphere is dominant for the p arietal a reas.
CHAPTER VII
SUMMARY
Two cu rren t concepts of the functioning of the cereb ral
hem ispheres of the human brain w ere explored in the present
| research . F irs t, it is known that the distribution of information
* processing between the hem ispheres differs depending on the
nature of the inform ation, and the present re se a rc h attem pted
to explore electrophysiological co rre lates of such asym m etries.
I Also, it has been speculated that subject differences in the
I distribution of intellectual ability between verbal, figural, and
■ m athem atic skills as reflected in the direction of latera l eye-
movement during reflective thinking is related to the relative
reactivity of the hem ispheres. These ideas w ere studied using
the average response recorded from b ilateral p arietal and central
scalp electrodes, evoked by four stim ulus types: random, verbal,
quantatitive, and geom etric. Responses from the two hem ispheres
w ere com pared both in term s of am plitude and of waveform in o rder
81
82
to detect hem ispheric asym m etries.
I Although som e basis was indicated in E xperim ent I for
relating asym m etries in VERs to the direction of la te ra l eye-
movement during reflective thinking, it m ust be concluded that the
| p resen t re se a rc h does not support the hypothesis that these eye
; movem ents a re related to differential responsiveness of the
hem ispheres as m easured by the evoked potential. N either
1 amplitude nor waveform c o rre lates of eye-m ovem ent, verbal or
figural intelligence, o r ratios of verbal and figural intelligence
could be found.
However, the data of Buchsbaum and Fedio (1969, 1970),
; dem onstrating that co rrelates of the asym m etric distribution of
i
I verbal inform ation processing could be detected in response
i
!
| waveform s, was replicated. In addition, a co rrelate of the
i
localization of visuo-spatial inform ation processing in the right
hem isphere was dem onstrated. The processing of quantitative
inform ation appeared to be nearly bilateral in the p resen t study.
The fact that the m ost significant co rrelate of the
asym m etric processing of verbal and non-verbal inform ation
occurred when com paring p a rie ta l-c e n tra l waveform sim ilarities
between hem ispheres, led to speculation that functional asym m etry
m anifests itself in a g re a te r sharing of inform ation between cortical
i are as in the dominant hem isphere. Also, in that the g reatest am o u n t;
j of inform ation processing occurred in the rig h t-p arietal and left-
i
central a re a s, it was concluded that functional dominance m ay be
different for different cortical a re a s , ra th e r than specifically
related to stim ulus inform ation o r subject ch aracteristics.
I
I
APPENDIXES
84
APPENDIX A
INSTRUCTIONS AND THOUGHT QUESTIONS FOR
EVOKING LATERAL EYE-MOVEMENTS
85
INSTRUCTIONS AND THOUGHT QUESTIONS FOR
EVOKING LATERAL EYE-MOVEMENTS
This is a study of brain waves during thinking. I will ask
you som e questions that will require that you reflect a moment
before you answ er. A fter thinking a moment, answ er each question, i
I
as best you can, in one o r two sentences. Please s it as still as you
com fortably can to allow for good brain-w ave recording. i
1 . Define the word "love. "
2 . How many letters in the word "psychology"?
3. What num ber when cubed gives 64?
4. What does the word "learning" mean?
5. If the w ar in Viet Nam would end tom orrow , what effect would
it have on our economy?
6 . Use the word "apathy" in a sentence.
7. How many edges does a cube have?
8 . Which is farth er south, Washington, D. C ., or San Francisco?
9. Spell the word "pneumonia. "
1 0 . What is the im portance of m an's landing on the moon?
87
11. Multiply 89 by 9.
1 12. What is the form ula for the circum ference of a circle?
13. Name a South A m erican country that does not border on
Brazil?
14. How many surfaces does a pyram id have?
In the second p a rt of this experim ent you will be watching
j
; pictures. You are to sim ply watch the slides and say out loud
what you see in each slide. T here will be four kinds of slides.
When you see dots with no apparent arrangem ent, respond by
saying "random . " When the dots form a th re e -le tte r word, read
the word (like for R-E-D , say "red"). If the dots form a
!
; m athem atical problem , say the answ er to the problem (like for
I 2 + 3, say "5"). A dot is used as a m ultiplication sign. Finally,
j
if the dots form a geom etric design, describe the design out loud
in one phrase (like "three squares").
Please allow at least one second to pass a fter each slide
before responding. Always keep your eyes focused on the middle
of the screen and sit as still as you can.
A re there any questions?
APPENDIX B
VISUAL STIMULI FOR EVOKING
EEG RESPONSES
8 8
8 9
o
90
91
•: •
• • •
• •
• • * © •
• • •
•• ••
t . :
•Mil
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•••:©
? * •
• v .:
• • •
; •
• • •
• • •
• .•>
f % :
• • •
*
• • • •
u <
< v .
V
.• V
i
• • • • • • •
• •
t *
• •
• • • !
• * •••
: • •%
• • • •
• • •
• • • • • • •
• • • •
• • • • • • •
*°k« ?
o
APPENDIX C
i MEAN VER INTERCORRELATION MATRIX
j
!
i
92
f l * * v *
MEAN VER INTERCORRELATION MATRIX
(Z-TRANSFORMED CORRELATIONS)
Right Parietal (P^
) Left Parietal (P
R V
Q
G R V
Q
J ?
3.00 2.02 1. 43 1.41 1.37 1 .25 1 .05
V 2. 02 3 .03 1.22 1.49 1.29 1.36 1.00
n
I. 43 1.22 3.00 1 .55 3.95 3.87 1 .19
G 1.41 1.49 I. 56 3.00 0. 97 0.95 I.10
1.37 1.29 0.95 0.97 3.00 2.14 1.49
V 1.26 1.36 0. 37 0.95 2.14 3.03 1.31
Q 1.36 1 .00 1.19 I. 13 1. 49 1. 31 3. 00
G 1.34 1.09 1.02 1.13 1.48 1.60 1.64
n 1. 31 1.25 0. 9 3 3. 93 1.41 1 .34 1 .04
V 1.20 1 .23 0.95 0.93 1.32 1.38 0.97
n
V 1. 12 1.35 1. 21 1.10 1. 14 1 .03 I .23
c 1.11 I .15 1.38 1.22 1.15 1.17 1.17
n . 1.33 1.27 1. 04 1.05 1.41 1.33 1 .15
V : 1.2 8 1.33 0.98 1.13 1.33 1 .43 1.13
Q
0.94 0.33 1.22 1. 03 0. 94 0.83 I .24
G 0.96 • '0.99 I. 11 I .26 C.97 0.95 1.20
Right Cencral (Cj) Left Central (C^)
G R V
Q G R V
Q G
1.34 ' 1.31 1.20 1.12 1.11 1.33 1.28 0. 94 0. 96
1. 09 1.25 1.28 1 .05 1 .15 1.27 1 .38 3. 83 0.39
1 .02 0.93 0. 85 1.21 1.38 1. 04 0.98 1.2? 1. 1!
1.13 0.93 0.93 1 .13 1.22 1.05 i.n 1.08 1.2‘
1.48 1.41 1. 32 1.14 1.16 1 .41 1.38 0. 94 0.9?
1.53 1.34 1.38 1.08 1.17 1.3" 1.43 o. 99 0. 91
1.64 1 • 04 0.97 1.23 1.17 1.15 1.13 1. 24
1.2:
3 .0 0 1.03 1. 06 1. 14 I. 31 1.13 1.23 1. 08 1 .26
1.03 3.03 2. 17 1.56 1 .4 a 1.24 1.19 0. 85 86
1.06 2. 17 3.00 1.39 1.63 1.16 l.?4 0. 81 0.8?
1.14 1.55 1. 39 3.00 1 .63 1 .12 1.07 1. 15 ..1.08
1.31 1.46 1. 63 1.63 3.03 1.11 1.19 I . n3 1 .18
1.13 1.24 1. 16 1.12 I .11 3.00 2.06 1. 41 1.34
1.23.' 1. 19 1.24 1.07 I. 19 2.06 3.00 1.24 1 .47
1 .33 0.85 0.81 1.15 1 .03 1.41 1.24 3.00;- 1.54
1. 26 0.35 0; 88 1.08 1. I* 1. 34 1.47 1.54 3.30
\ 0
CO
o
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94
I
i
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Asset Metadata

Creator Brown, Warren Shelburne, Jr. (author)

Core Title Visual Evoked Potentials, Laterality Of Eye Movements, And The Asymmetry Of Brain Functions

Degree Doctor of Philosophy

Degree Program Psychology

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,psychology, experimental

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Galbraith, Gary C. (committee chair), Greene, Ernest G. (committee member), Slucki, Henry (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-547809

Unique identifier UC11363343

Identifier 7206041.pdf (filename),usctheses-c18-547809 (legacy record id)

Legacy Identifier 7206041.pdf

Dmrecord 547809

Document Type Dissertation

Rights Brown, Warren Shelburne, Jr.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA