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Effects Of Task Performance Upon The Acoustic Reflex

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Effects Of Task Performance Upon The Acoustic Reflex

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Content This dissertation h u been
microfilmed exactly as received 66— 10,526
B E L L , D onald W illiam , 1936-
E F F E C T S O F TASK PERFORM ANCE UPON THE
ACOUSTIC R EFLEX .
U n iv ersity of Southern C a lifo rn ia, P h .D ., 1966
P sychology, e x p e rim en ta l
University Microfilms, Inc., Ann Arbor, Michigan
EPFECTS OP TASK PERFORMANCE UPON
THE ACOUSTIC REFLEX
by
Donald William Bell
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(Psychology)
June 1966
UNIVERSITY OF SOUTHERN CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANOELES. CALIFORNIA tOOOT
This dissertation, written by
mittee, and approved by all its members, has
been presented to and accepted by the Graduate
School, in partial fulfillment of requirements
for the degree of
D O C T O R O F P H I L O S O P H Y
Donald Villia* Ball
under the direction of h}:*...Dissertation Com -
Date..
ACKNOWLEDGMENTS
I wish to acknowledge with appreciation the guidance
provided by Dr. Milton Metfessel, Dr. William Grlngs, and
Dr. Victor Garwood throughout the various stages of this
study. I am grateful to Dr. Aram Glorig for his encourage
ment of the study. I further acknowledge my Indebtedness
to the staff of the Subcommittee on Noise Research Center,
especially Mr. Hervey Stern, who aided in nearly all phases
of this study. I also wish to acknowledge the help given
by my wife, Gloria, who was invaluable in the preparation
of the manuscript. The experiment reported herein was
supported in part by NIH grants Nos. OH 00053 end OH 00172.
11
TABLE OP CONTENTS
PAGE
I. PROBLEM....................................... 1
II. METHOD...................................... 11
Independent Variables ...................... 11
Dependent Variable........................ 12
Experimental Design ........................ 13
Subjects............ 14
Equipment............... 17
Visual-motor task........................ 17
Audltory-detectlon task.................. 18
Reflex arousal stimulus .................. 21
Acoustic reflex measurement .............. 22
Procedure................................... 30
III. RESULTS AND DISCUSSION....................... 33
Reliability................................. 42
Effect of RAS Level......................... 43
Effect of Task Performance................. 47
IV. SUMMARY AND CONCLUSIONS....................... 54
REFERENCES............ 57
APPENDIX A ......................................... 61
APPENDIX B ......................................... 63
APPENDIX C ......................................... 69
APPENDIX D ......................................... 71
ill
LIST OF TABLES
TABLE PAGE
1. Assignment of Subjects to Schemes for
Ordering of Experimental Presentations .... 15
2. Schemes for Counterbalancing Task and
RAS Level Order Through Trials .............. 16
3* Median Light Matrix Response Times ............. 34
4. Summary of McNemal Test of the Signifi
cance of Changes Applied to Preliminary
and Experimental Light Matrix Response
Times.................................. 36
5• Mean and Median Impedance Changes In
Relative Units Averaged Over Subjects .... 38
6. Means and Medians In Acoustic Ohms........ 40
7. Indices of Repeat Reliability Over Trials ... 44
8. Summary of the Friedman Analysis of
Variance for the Effect of RAS Level
for Each Task Condition................ 46
9. Summary of the Friedman Analysis of
Variance for the Effect of Task for
Each RAS Level.......................... 48
10. Summary of Wllcoxon Test of the Signifi
cance of Differences in Effect Between
Individual Task Conditions at Each RAS
Level.................................. 49
iv
TABLE PAGE
11. Impedance Change for Each Subject at
Each Taak-by-RAS Level Combination.......... 60
12. Phaee Change for Each Subject at Each
Taek-by-RAS Level Combination .............. 69
v
LIST OP PIQURES
FIGURE PAGE
1. Block Diagram of Equipment Used for
Presentation of RAS and the Tone Burst
of the Auditory Detection Task.............. 20
2. Power Spectrum of the R A S ........... 23
3. Block Diagram of Equipment Used to
Measure Impedance Change Associated
with Acoustic Reflex........................ 24
4. Diagram of the Probe Device.................. 26
5. Diagram Showing Components of Impedance .... 29
6. Mean Impedance Changes as a Function of
RAS Level. Task Is the Parameter ...... 41
7. Impedance Change as a Function of RAS
Level for Subjects 1-3* Task is the
Parameter.................................. 63
8. Impedance Change as a Function of RAS
Level for Subjects 4-6. Task Is the
Parameter.................................. 64
9. Impedance Change as a Function of RAS
Level for Subjects 7-9. Task Is the
Parameter................................ 65
10. Impedance Change as a Function of RAS
Level for Subjects 10-12. Task is the
Parameter.................................. 66
vi
FIGURE PAGE
11. Impedance Change as a Function of RAS
Level for Subjects 13-15. Task Is
the Parameter................................... 67
12. Impedance Change as a Function of RAS
Level for Subjects 16-18. Task Is
the Parameter................................... 68
13* Phase Shift as a Function of RAS Level
for Subjects 1-3* Task Is the
Parameter....................................... 71
14. Phase Shift as a Function of RAS Level
for Subjects 4-6. Task Is the
Parameter.............. . ...................... 72
15* Phase Shift as a Function of RAS Level
for Subjects 7-9* Task Is the
Parameter....................................... 73
16. Phase Shift as a Function of RAS Level
for Subjects 10-12. Task Is the
Parameter....................................... 74
17. Phase Shift as a Function of RAS Level
for Subjects 13-15• Task is the
Parameter . ....................................75
18. Phase Shift as a Function of RAS Level
for Subjects 16-18. Task Is the
Parameter....................................... 76
vil
I. PROBLEM
The purpose of this study was to Investigate the
effect of attention to auditory stimuli on the acoustic
reflex.
The middle ear is a mechanical system which serves
to transform airborne acoustic energy into mechanical
energy at the entrance to the inner ear. Extending from
the tympanic membrane to the oval window of the cochlea,
this mechanical system consists mainly of three articulated
bony structures, the malleus, Incus, and stapes, referred
to as the ossicular chain. The tensor tympanl muscle Is
attached to the manubrium of the malleus; the stapedius
muscle Is attached to the neck of the stapes. The tensor
tympanl stems from the first branchial arch and the motor
nerve supply is by the trigeminal nerve; the stapedius
stems from the second branchial arch and its motor nerve
supply is by the facial nerve (Jepson, 1955). Reflex
contraction of these two muscles elicited by Intense
auditory stimulation has been called the acoustic reflex.
Bilateral destruction of the cochleae abolishes the
acoustic reflex (Jepson, 1955)• The most widely-held
anatomical location for the center of the reflex Is the
superior olivary nucleus, which lies in the anterior part
of the reticular formation (Jepson, 1955). Contraction of
the two muscles has been shown to stiffen the ossicular
chain (Miller, 1965). Contraction of the stapedius also
changes the manner of articulation between the foot plate
of the stapes and the oval window (Bdkdsy, I960).
Previous work has demonstrated that contraction of
the stapedius muscle Is directly elicited by acoustic
stimulation, but there Is disagreement about whether con
traction of the tensor tympanl muscle Is also elicited
directly by acoustic stimulation or by prior contraction
of the stapedius (Klockhoff, 1961; Jepson, 1955)* The
latency of stapedl-us contraction is less than that of the
tensor tympanl (Jepson, 1955; Oalambos 1 Rupert, 1959)»
and the two muscles appear to be In. synergic relationship,
acting In combination (Mrfller, 1964).
There are currently two main types of hypotheses con
cerning the function of the acoustic reflex: protection
hypotheses and accommodation hypotheses. In the recent
past, the protection hypotheses have been favored. The
general Idea common to the various protection hypotheses
Is that the reflex serves to reduce the Input level of
high Intensity sounds which have a potential for damaging
the cochlea. Indeed, evidence clearly indicates that the
acoustic reflex does serve to reduce the cochlear micro-
phonic produced by a given sound (Simmons, I960; Mrfller,
1964; Oalambos f t Rupert, 1959; Hlldlng, 1961). But a
criticism that Is being raised against this Interpretation
of the function of the acoustic reflex Is that loud,
potentially damaging sounds are a rarity In nature, perhaps
produced only by extremely close lightning, a large tree
falling, or a landslide. Most loud, potentially damaging
sounds that an organism Is likely to encounter are produced
by man's activity, and it Is unlikely that such a compli
cated reflex would develop so widely in mammals In the
short period since man has had the means to create high
Intensity sounds. Among those favoring the protection
hypotheses, there is disagreement about whether the reflex
serves as an overall attenuator or as a peak-clipper
(Loeb A Rlopelie, I960; Ward, Selters, A Qlorlg, 1961;
Shapeley, 195*0. This difference In the effect of reflex
activity will undoubtedly be resolved by empirical study,
but the data at present are ambiguous.
Accommodation hypotheses have gone In and out of
favor, but recent evidence and reasoning lead to the
conclusion that the reflex probably does, at least In part,
serve an accommodative function. Originally, the accommo
dation hypotheses of Ostmann In 1898 proposed that the two
muscles act together to provide for the best possible
sound absorption characteristics, serving to enhance
sensitivity (Jepson, 1955s Kobrak, 1959)* The great number
of studies previously cited showing that the cochlear
mlcrophonlc is reduced by reflex activity seems to be
Insurmountable evidence against this view. More recent
views suggest that the reflex acts as a tuning mechanism,
favoring the passing of certain frequencies above others
(Weber & Bray, 19*2; Wlggers, 1937)* or that the acoustic
reflex serves to extend the dynamic range of the system by
acting as an automatic gain control (AGC), I.e., by
Increasing attenuation as sound level rises (Kobrak, 1959;
Nleder, 1953). Both of these Ideas appear to be feasible.
The reflex has been shown to shift the fundamental
resonance frequency of the middle ear system and so changes
the frequency region of maximum transfer (Mrfller, 1963)*
Reger (I960) hypothesised that this differential attenu-
atlve effect of the acoustic reflex may well account for
the shift In loudness functions as sound level Is raised.
As the level of stimulation Is Increased, both low and high
frequencies grow In loudness much faster than the mid
frequencies (Pletcher A Munson, 1933)* It hasbeen shown
that the reflex attenuation Is greatest In the lower
mid-frequencies (Mrfller, 1963; Wever A Vernon, 1956; Reger,
I960). Also, the reflex appears to provide Increasing
attenuation as the Incoming signal grows In Intensity.
This allows for finer discrimination at high levels on a
sensitivity scale which Is semilogarithmic, since, In
general, the Weber-Peehner ratio depicts changes In
loudness as a logarithmic function of changes In level.
This Implies that loudness resolution becomes poorer as
sound level Is raised. An automatic gain control would
tend to displace a sound toward the lower end of a loga
rithmic scale. Additionally, the acoustic reflex, by
reducing the level of Input sound may well serve to reduce
non-linear distortion of the overloading type. Difference
tones, which represent the harmonic type non-linear
distortion, may also be reduced since their origin Is
thought to stem from the loosely articulated malleolncudal
and Incudostapedlal Joints (Wever A Lawrence, 1954).
Stiffening up the middle ear system, presumably, lessens
the effects of the loose articulation.
The protection hypotheses Imply that the organism
Is passive In regard to the reflex; Indeed, since loud
sounds are often accompanied by events which are likely to
be distracting, reflex protection would be best If no
central system were Involved. On the other hand, the
accommodation hypotheses imply that the organism reacts
actively In response to loud .sounds* The acoustic reflex,
may be one of the mechanisms for processing Intense sounds.
That Is, the organism processes Input sound and responds
appropriately. Efferent Inhibitors have been found to
extend all the way down to the hair cells In the cochlea
(Oalambos, 1965)* Also, a central mechanism would be
necessary In taking account of reflex activity for loudness
judgments (Kobrak, 1959)*
In support of this latter hypothesis, it has been
shown that "attention" plays a large role In control of
acoustic reflex in cats. Carmel and Starr (1963), In
electromyographic and cochlear potential recordings from
cats, have found that middle ear muscle reflexes are modi
fied by (1) previous experience with loud sounds, (2) the
significance of the sounds, (3) bodily movements, and
(ft) vocalisation. Simmons, Oalambos, and Rupert (1959)
have reported conditioned response of the middle ear
muscles In cats. In addition, working on the reflex with
human beings, Klockhoff (1961) noted what appeared to be
an effect produced by voluntary shifts of attention. He
further reported that performing long division produced a
decrement In reflex, whereas attempting to overhear speech
by someone of "psychological significance" to the subject
produced an Increment In the reflex (Klockhoff, 1961).
The reflex was measured by an Impedance change technique.
Hernandes-Peon has reported that an Interesting visual
stimulus such as a mouse In a bottle produced a decrement
In electrophyslologlcal measures of cochlear nucleus
potential (Hernandes-Peon, Scherrer,ft Jouvet, 1956).
Changes In attention produced by Interest In the sound or
by distraction from extraneous sources would be an
Important consideration In evaluating an AQC hypothesis.
Observations by Simmons (196ft) have led him to propose
a perceptual theory of middle ear muscle function. He
notes three types of middle ear muscle activity: (1)
random reflexing, (2) reflexing to acoustic stimulation,
and (3) reflexing associated with somatic motor activity*
Reflex activity was found to be greatest In cats during
"alertness•■ Simmons proposes that random reflexing may
serve to continuously alter the resonance character of the
ear to avoid nulls and to provide continuously changing
stimuli* Resonances are more prominent In demuscled ears
and resonant peaks are sharper In stapedectomlsed ears*
By continuously changing the Input to the receptor, audi
tory attention may be heightened* The reflex may also
serve a protective function In the sense of being part of
an orienting response* If a sound can be attenuated with
acoustic reflex, It Is external and probably warrants
attention; If It cannot be attenuated, it Is probably
internal, e*g*, chewing and physiological noise*
If one follows the accommodation hypotheses, whether
tuning, AOC, orienting, or a combination, It seems reason
able to expect central control over reflex activity.
Information about reflex activity Is required If the
organism is to take account of reflex attenuation In
loudness Judgments, and If the reflex Is governed to some
extent by the signal being processed* This line of reason
ing leads to the general question: Is there central
control of the acoustic reflex in man and Is attention to
auditory signals Important for this control? More specific
questions can be stated as: Does reduction in attention
to auditory signals Impair the acoustic reflex? Does close
attention to auditory signals enhance the reflex?
From these specific questions, two hypotheses have
been derived for testing In this study:
Hypothesis I: Reducing attention to acoustic signals
by perforaance of a non-audltory task will produce a decre
ment In the acoustic reflex when reflex with task Is
compared to reflex with no task.
Hypothesis II: Increasing attention to acoustic
signals by performance of an auditory task will produce an
Increment In acoustic reflex when reflex with task Is
compared to reflex with no task.
Two alternative hypotheses can be stated for Hypothe
sis I. The first Is that perforaance of a non-audltory
task will produce no difference In the acoustic reflex
when reflex with task Is compared with reflex with no task.
Such a hypothesis would Imply either no central control
over reflex activity or Independence of central activity
with regard to the non-audltory task. The second alternate
Is that perforaance of a non-audltory task will produce an
Increment In the acoustic reflex when reflex with task Is
compared to reflex with no task. This hypothesis Implies
Inter-modallty facilitation which could enhance the
effective level of the reflex arousal stimulus. Either
interpretation associated with the first alternate would
be consistent with a protective function theory of acoustic
9
reflex.
Two alternative hypotheses can also be stated for
Hypothesis II. The first alternate Is that performance of
an auditory task will produce no difference In acoustic
reflex when reflex with task Is compared to reflex with no
task. This hypothesis Implies either no central control
over acoustic reflex or that the auditory signal used In
the task requires no processing by the reflex. The second
alternate hypothesis is that performance of an auditory
task will produce a decrement In acoustic reflex when
reflex with task Is compared to reflex with no task. This
final hypothesis Implies that task performance Itself,
regardless of content, either serves to reduce attention
to auditory signals or reduces reflex In some other way.
It Is very unlikely that this study could be a crucial
study In that it would permit complete and definitive
distinction between the experimental hypotheses and the
alternative hypotheses. Not enough Is known about central
control at any level In the auditory chain to Insure that
the Interpretations associated with the various hypotheses
are mutually exclusive, although the hypotheses themselves
are certainly mutually exclusive. This study can narrow
the possible Interpretations to those associated with the
hypotheses supported by the results.
Before becoming concerned with the details of the
experiment, two Important presuppositions need to be made -
clear. First, It is presumed that prolonged experience
with an acoustic stimulus, especially when the stimulus
has no special relevance to the subject, results in a
neutral level of attention to tfiat stimulus and to the
auditory modality. Second, it is presumed that performance
of a non-audltory task, I.e., a task not involving the
auditory modality, will be distracting from the non-
relevant neutral acoustic stimulus and generally reduce
attention to the auditory mode. Third, it is presumed that
performance of an auditory task. I.e., a task Involving
auditory signals, will tend to center attention on the
task signal and the auditory modality.
II. METHOD
Level of attention to auditory signals was one of the
two Independent variables used In this study. This vari
able had three levels, operationally defined as follows: .
1. Reduced attention: Performance of a visual-motor
(non-audltory) task during reflex arousal stimulus (RAS)
presentation.
2. Neutral (control) attention: No task performance
during RAS presentation.
3* Increased attention: Performance of an auditory-
detectlon task during RAS presentation.
Both tasks used to vary level of attention to auditory
signals were of the vigilance type. Task I. the visual-
motor task, presumed to reduce attention to auditory
signals, required subjects to continually scan a light
matrix In order to detect when one of 121 lamps went off.
The subject's task was to determine which light was off
and turn It back on by responding appropriately. Task II.
the audltory-detectlon task, presumed to Increase attention
to auditory signals, required that the subject detect a
tone burst occurring while noise was presented and respond
by pressing a button. Both tasks are described more fully
In the section on equipment. Responses on both tasks were
examined as evidence of active subject participation. A
control condition, presumed to give rise to a neutral level
11
12
of attention to auditory signals, was Included in which no
task was required during acoustic reflex measurement.
The other Independent variable In the study was level
of the reflex arousal stimulus (RAS). The levels used
ranged from a stimulus slightly above average reflex
threshold to a stimulus well above threshold. The levels
used were 95» 105, and 115 dB re. 0.0002 dynes/cm2, sound
pressure level (SPL).
In previous work with acoustic reflex recording, It
was noted that a band of white noise with a high pass cut
off at 1800 and a low pass cutoff at 2400 c/s Is a very
effective ellclter of acoustic reflex. There would appear
to be no reason for a differential effect of tasks on the
acoustic reflex when it Is elicited by various RAS
frequencies. Therefore, only the one noise band was used
as a RAS.
The dependent variable in this study was acoustic
reflex activity as -indicated by Impedance change. It has
been demonstrated repeatedly that acoustic reflex activity
causes an Impedance change of the middle ear system. I.e.,
the transfer function Is altered (Nets, 1954; Klockhoff,
1961; Jepson, 1955; Miller, 1958). Impedance change was
measured by observing changes In the transmission of a
carrier signal through the tympanic membrane. A change In
the measured amplitude of a constantly generated carrier
signal Is seen as a voltage change In the output of a
13
probe microphone. These voltage changes are proportional
to Impedance changes at the eardrum (Roller, 1958). A
further discussion of measuring theory and technique Is
presented under equipment.
Experimental Design. The study was designed so that
the effects of the two Independent variables would be
evaluated over three trials. Because between-subject vari
ability was expected to be large and wlthin-subject
variability was expected to be small, a complete factorial
design with mixed factors of the A x B x S type (Lindquist,
1953; McNemar, 1962) was planned. Although subject vari
ability was not of primary Interest In this study, It was
felt that a plotting of the data might reveal Interesting
subject differences, e.g., distinct types of responses to
the tasks which could be seen statistically only as a
treatment-wlth-subject Interaction. With this design
Involving three trials for each task-level combination, If
subject differences turned out to be of Interest, a four
way analysis of variance would be possible, using RAS
level, task, subjects, and trials as factors. However, If
subject differences turned out to be not of Interest, the
Identification arid control of subject variance could be
*
used to Increase the precision of the analysis. In this
case, the three trials for each combination would be used
to derive mean scores for the cell entries for greater
stability. The three RAS levels, three tasks (two tasks
14
and a control of no task), and three trials would yield
27 combinations for each of the 18 subjects. With this
design, there would be a total of 486 measures.
ttie order of presentation of each task-by-RAS level*
by-trial combination was controlled by the following:
1. Subjects were assigned to a scheme according to
the rotation in Table 1.
2. Each scheme had a counterbalanced order of
presentation for both RAS level and task condition. The
counterbalancing was through trials. Scheme details are
shown in Table 2.
3. Each task-by-trlal combination had a single order
of RAS level presentation associated with it as shown in
Table 2. These RAS level orders were counterbalanced
through trials. Each subject received all levels of RAS
at a given task-with-trlal combination before moving on to
his next scheduled task-by-trlal combination.
Subjects. Eighteen subjects were used with a mean
age of 24.4 years and a range from 20-29 years. There were
16 male and two female subjects. All subjects were paid.
This number was large enough to sample subject variation
and representation and yet small enough to allow the many
measures necessary for experimental precision. The
subjects were examined for both hearing loss and lack of
acoustic reflex. Auditory thresholds were determined for
each subject at .5, 1, 2, 3, 4, and 6 kc/s. Also, on the
15
Table 1
Assignment of Subjects to Schemes for Ordering
of Experimental Presentations. Schemes
are Pound in Table 2
Scheme Subjects
1 1 7 13
2 2 8 14
3 3 9 15
4 4 10 16
5 5
11
17
6 6 12 18
16
Table 2
Schemes for Counterbalancing Task and
RAS Level Order Through Trials
Scheme Order Trial 1 Trial 2 Trial 3
(1)
C c A a B - b
1 (2) A
—
b B
—
c C - a
(3)
B - a C - b B - c
(1)
A b B c C - a
2 (2) B
—
a C
-
b A - c
(3)
C - c A - a B - b
(1)
B a C b A - c
3 (2) C
•
c A
-
a B"- b
(3)
A - b B - c C - a
(1)
C c B b A - a
H (2) A
-
b C
—
a B - e
(3)
B - a A - e C - b
(1)
A b C a B - c
5 (2) B
—
a A
-
c C - b
(3)
C - c B - b A - a
(1)
B a A
_
e C - b
6 (2) C
•
c B
-
b A - a
(3) A b C a B - c
Note: A ■ Task 1, B ■ Task 2, C ■ Control
a - 95, 105, 115 dB SPL RAS
b 115, 95, 105 dB SPL RAS
c - 105, 115, 95 dB SPL RAS
17
first visit, the subject's acoustic reflex sensitivity was
determined as well as his ease of adjustment to the test
situation. In previous work, It has been found that the
techniques used In measuring the acoustic reflex are
objectionable to some subjects. Often subjects are sensi
tive to any object placed In the ear canal; female subjects
seem much more sensitive. No subject was Included In the
study with greater than 0 dB hearing loss (re. ASA
standards) through the range 500 to 6 kc/s. All subjects
showed acoustic reflex consistently elicited In the control
situation by a RAS of 90 dB SPL.
Equipment. To assist In describing the equipment, the
various sections of the equipment will be presented
separately.
Visual-motor Task. This task required detecting and
Identifying an off-going lamp In a matrix of lamps and
turning it on again. A light matrix had been devised that
employs relays, rotary switches, 22 push buttons, and 121
neon lamps. When the matrix Is set Into operation, all
lamps are lighted. Motors drove the rotary switches
through continuous rotations. As a heat sensitive relay
opened, the motors driving the switches turned off.
Depending upon the position of the two switches when the
motors turned off, one of the 121 lamps turned off. By
pressing the pair of buttons which corresponded to the row
and column In which the unllghted lamp occurred, the lamp
18
could be turned on again. When the lamp was turned on,
the cycle was resumed. The tine required for each cycle
was very Irregular, varying between about two seconds to
five seconds. Selection of the off-going lamp was. In
principle, random. However, because not all contacts of
the switches are equally smooth, certain positions were
somewhat more likely as stopping points. Great effort had.
been made to eliminate this effect and lamp selection
appeared to be random.
In a pilot study, median response time for four
subjects on the task was about six seconds with a range
from about two to about 20 seconds. Because the matrix Is
In the form of a square, some of the lamp-button combi
nations are obviously easier to identify. If one of the
four corner lamps went out, response was usually very
rapid, but response to any unllghted lamp was generally
somewhat less than 10 seconds. For this reason, the
response times represent fluctuations In attentiveness,
reaction time, and ease of identification. The first of
these three contributors to response times was the variable
that the task attempted to control. Fortunately, the range
of response times accounted for by the other two factors
was small.
Audltorv-detectlon Task. The auditory detection task
required correct detection of a tone burst occurring along
with the RAS. The frequency of the tone burst was 1 kc/s.
19
The level of the tone was such that the ratio of the false-
alarm rate to the correct-detectlon rate was approximately
0.75.
Figure 1 Is a block diagram of the equipment used for
presentation of the RAS and the tone burst of the auditory
detection task. The 1 kc/s tone was generated by a model
201 CR Hewlett-Packard audio oscillator. From the oscil
lator , the signal was passed through a model *71 Orason-
Stadler Interval timer to a model 829 D Orason-Stadler
electronic switch that controlled the rlse-decay time of
the tone burst. The signal was then passed through a
mixer, a Hunter timer, and then to the RAS earphone. The
Interval timer provided for turning the signal on and off
at the same relative phase positions each time. Setting
the on-golng and off-going points was done with the aid of
a type 502 Tektronix oscilloscope.
To provide for semi-random occurrence of the tone
burst along with the RAS, a type 161 Tektronix pulse
generator provided the pulse necessary to trigger the
Interval timer, which, In turn, controlled the electronic
switch which put out one tone burst for each pulse. A
randomising unit was In continuous operation and with the
associated equipment, the oscillator, Interval timer, and
electronic switch, a random tone burst occurred more or
less continuously through time. Occurrence of the tone
burst at the earphone was controlled by a Hunter timer.
\
NOISE FILTER AMPUFER FILTER PRE- AMPUFER TIMER
GEN.
AMPUFIER
EX AROUSAL SIGNAL
OSOLLATOR
INTERVAL
TIMER
RANDOMIZER
ELECTRONIC MIXER
*
TIMER
SWITCH
r
ATTENUATOR
TO EVENT
RECORDER
Fig. 1. Block diagram of equipment used for presentation
of RAS and the tone burst of the auditory detection task/
ro
o
This timer was In turn controlled by another Hunter timer,
the timer which controlled RAS duration. The RAS timer
turned on the burst timer, but the burst Interval termi
nated two seconds before the RAS Interval so that no
clipped sine wave would be presented. The randomlser
consists of two clock motors driving caais with widely
different duty cycles which open and close a set of relays;
when both relays are closed simultaneously, the randomlser
circuit Is closed and a pulse will be passed. Each time
a pulse was passed, In addition to triggering the Interval
timer, an Esterllne-Angus event marker also received a
pulse from a transistorised flip-flop fed by a Heathklt
power supply (not shown In Fig. 1 for simplification) and
recorded an event. Each time the subject's response
button was closed, an event was recorded on another channel
of the event marker. During this part of the response, the
strip from the event recorder was watched carefully. If
the subject's detection rate fell or his false-alarm rate
rose, he would have been reinstructed before proceeding
further. Actually, pretraining (see Procedure section)
made this unnecessary during experimental trials.
Reflex Arousal Stimulus. The equipment for generating
the reflex arousal stimulus Is also diagramed In Fig. 1.
White noise from a model 455 C Qrason-Stadler noise gener
ator was filtered by a model 2 Allison filter, amplified
by a McIntosh 30-watt audio amplifier, again filtered by
another Allison filter, amplified by a Qeneral Electric
preamplifier, and amplified by another McIntosh 30-watt
audio amplifier* The high-pass and low-pass sections of
both filters were Isolated by 10 dB attenuators to yield
sharper rejection rates giving narrow skirts to the RAS
band* The audio amplifier between the filters served as
an Isolator In addition to amplifying* RAS duration was
controlled by two Hunter timers after the final stage of
amplification* A model 350 B Hewlett-Packard attenuator
set following the timers controlled the RAS level to a
PDR-8 earphone which was mounted In a Clark muff.
The nominal rate of rejection of the filters when
cascaded as described Is 72 dB/octave. Figure 2 shows a
power spectrum of the RAS, using a General Radio beat
frequency oscillator coupled to a General Radio graphic
level recorder for analysis* The several stages of ampli
fication were necessary to achieve 110 dB SPL 1800-2400
c/s RAS*
Acoustic Reflex Measurement. Figure 3 Is a diagram
of the equipment used to measure the Impedance change
associated with acoustic reflex* A 450 c/s signal was
generated by a model 201 CR Hewlett-Packard audio oscil
lator and fed to a model E 3520 B Grason-Stadler phase
shifter* In the phase shifter, the signal was divided into
two 450 c/s signals, one of which was variable In phase
and amplitude relative to the other* From the phase
If
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VARIABLE 6
REFERENCE ©
-H MECHANISM H-
AMPEXTAPE
RECORDER
CMC
PROBE
TONE
GENERATOR
RLTER
OSCLLOSCOPE PHASE
SHIFTER
PROBE
MICROPHONE
GRAPHIC
LEVEL
RECORDER
OSCILLATOR
OPERATIONAL
AMPUFER
FULL WAVE
RECTF1ER
4
shifter, the variable signal was fed to the model 300 Anpex
recording amplifier and to a Tektronix dual-beam oscillo
scope to be displayed by one beam as the reference signal.
The fixed signal from the phase shifter was fed to a PDR-8
earphone which generated the probe tone presented to the
subject through the probe device. Figure 4 is a diagram
of the probe device. The probe tone was delivered Into the
cavity of the ear canal through one tube of the probe
device. The level of the probe tone at the end of the
probe device was measured by a Western Electric 640 AA
condenser microphone which picked up the tone through the
other tube of the probe device. The signal from the micro-
k
phone was passed by special cable to the microphone's
preamplifier. From the preamplifier, the signal was fed to
a Western Electro Acoustics Laboratory condenser microphone
complement where It was further amplified, then filtered
by a model 2 Allison filter and fed to another Ampex
recording amplifier. Two outputs of this signal were taken
from the recording amplifier. One output was fed to the
oscilloscope for comparison with the reference signal; the
other output was full-wave rectified, amplified with a
Tektronix type 0 operational amplifier acting as a differ
ence amplifier and displayed as the wrlte-out on a General
Radio graphic level recorder mounted with a linear dc
potentiometer.
The special cable between the microphone In the probe
MICROPHONE
640A A
PROBE TONE
INPUT
EARPLUG ^-ZWISLOCKI TYPE
SPECULUM
Fig. 4* Diagram of the probe device
27
device And the condenser microphone complement was flexible
and allowed limited subject movement*
The method of impedance measurement used In this study
and previously described In general by Beranek (19*9) and
in connection with this application by Zwlslockl (1957),
relies on the equation Z ■ V/I, where Z is impedance, V is
voltage, and I is current. The acoustic analog of thlu
equation is Z& ■ p/U, where Z& is acoustic impedance, p is
sound pressure averaged over a plane, and U is particle
velocity through the plane (Beranek, 19*9). If the two
tubes of the probe device, the tube through which the probe
signal is picked up and the tube through which the probe
signal is delivered, are small relative to the wave length
of the probe tone, their Impedance will be high. The '
assumption of a constant current source will be met, I.e.,
changes of impedance in the system to be measured will not
affect the current generated by the source. When this
assumption is satisfied, Z^ ■ V^/I^ and Z2 ■ V^/I^ so that
if 1^ ■ Ig, i.e., I is constant, then Z^-Z^ * Vi"V2*
Similarly, in the acoustic system, particle velocity is
constant but sound pressure varies with impedance. Changes
in sound pressure are transduced by the condenser micro
phone into changes in voltage. These changes in voltage
were the dependent variable in this study.
A change in phase is usually associated with impedance
change. At all frequencies but the resonant frequency of
28
an acoustic system, Impedance Is made up of two components,
a real and an Imaginary component* At resonant frequency,
the imaginary components cancel, leaving only the real
component. The real component is resistive and the
imaginary component is reactive, either capacitive
reactance, inductive reactance, or both. The reactive
components are opposite in sign and so are subtractive.
As frequency decreases below the resonant frequency, stiff
ness plays an increasingly greater role in impedance; as
frequency Increases above the resonant frequency, mass
plays an increasingly greater role in Impedance. Therefore,
in a simple mechanical system, the real component is
resistance, inductive reactance corresponds to mass, and
capacitive reactance corresponds to stiffness (Vever f t
Lawrence, 1954; Holler, 1964). Figure 5 is a diagram
showing the components of impedance. As can be seen, the
resistive component is at 90° to both imaginary components.
Inductive reactance is at 180° to capacitive reactance.
The difference between inductive and capacitive reactance
is the imaginary component. The vector resolving the
resistive and imaginary components is impedance. The angle
between the resistive component and Impedance is the phase
angle.
It was noted earlier that the phase shifter provided
two sine waves, variable in relative phase and amplitude.
Further, it was noted that the sine waves could be
MASS REACTANCE ( IMAGINARY COMPONENTS ) STIFFNESS REACTANCE
29
2
RESISTIVE
COMPONENT
REAL)
X
i i
IN )
2*
2
#
5. Diagram showing components of
« *
Impedance.
displayed simultaneously on the dual-beam oscilloscope.
By switching the selection of plates In the cathode ray
tube of the oscilloscope so that the two signals were used
to provide vertical and horlsontal deflection of electrons,
a llssajou figure could be formed having a one-to-one
ratio. By varying the phase of the variable sine wave
until the llssajou figure was a single sloping line, the
two sine waves could be brought Into phase. If the
impedance change had an Imaginary component, the single
line became an oval during acoustic reflex. If the
voltages of the two sine waves were equal, a circle was
formed when the signals were 180° out of phase and a single
line with a slope of unity was formed when the signals were
In phase.
Although phase changes were only of Incidental
Interest In this study, they are expected to be of great
interest In planned studies and so were measured In this
study for future reference.
Procedure. Subjects who showed no hearing loss and
adjusted well to acoustic reflex measurement were given
practice In the two task conditions. During practice,
median response times with the light task were noted for
later use as a control measure for determining that the
subject was performing In the test situation at a level
previously obtained when his attention was clearly focused
on the task. Various tone burst levels were presented to
the subject and an estimated detection rate and false-
alarm rate computed for each level* This allowed selection
of a tone burst level for use In the test condition which
Insured that the tone bursts were sufficiently difficult
to detect to require close attention to signal content
but detectable enough to yield usable detection rates when
the subject was performing the task as required.
The subjects were then assigned a number In order of
qualifying which corresponded to the block of Table 1. On
succeeding trials, his schedule of experimental conditions
followed the plan previously outlined under Experimental
Design.
Although conditioning of the acoustic reflex has not
been demonstrated in man, there Is a report of the reflex
having been conditioned In cats (Simmons, Galambos, A
Rupert, 1959)* To avoid the possibility of temporal con
ditioning, inter-RAS Intervals were semi-random and RAS
onset was controlled by the experimenter. At least 15
seconds of recovery was allowed between RAS presentation.
Plfteen seconds should have been ample time for the reflex
system to have returned to Its resting state following
termination of the previous RAS (Mtfller, 1962). RAS
duration was controlled by a Hunter decade Interval timer
and was five seconds.
Subjects were given a 10-mlnute rest after each task-
by-trlal series, I.e., after each presentation of the three
32
RAS levels. Each subject required about three two-hour
sessions to complete the preliminary and experimental
series•
A standardised procedure was used for fitting the
probe to the ear after each rest. This procedure has
worked well In the past. The probe was placed In the ear
and the subject told to adjust It so that the k50 c/s probe
signal sounded loudest; this Insured that the probe tip was
not blocked by the walls of the canal. The return probe
signal was observed on the oscilloscope; this Insured that
the probe tubes had not become blocked by dirt or cerumen
and that the probe tip was fitting tightly Into the
speculum. Once the probe tube was In place, the design of
the probe assembly was such that the subject was allowed
limited movement and the relationship of probe to head
remained fixed.
All measurements were made with the subject sitting
In a type 1202 Industrial Acoustics Company audlometrlc
testing booth. This double-walled booth provides an
extremely quiet environment for testing. Subjects could
be observed through a window In the wall of the booth. The
Interior of the booth was lighted and ventilated.
III. RESULTS AND DISCUSSION
The results and the discussion of the results will be
presented together for simplification and clarity. The
logical divisions of the results will be treated separately
in the following order: task response, statistical
description of the results, reliability of impedance change
measures, effect of RAS level on acoustic reflex, and
effect of task performance on acoustic reflex.
In the preliminary trials with the tasks, the level
of the signal to be detected in Task 2, the 1 kc tone, was
adjusted so that the detection rate was approximately .50.
Therefore, in order for the subject to respond appropri
ately during the task, i.e., respond only to a tone burst,
it was automatically necessary that he be performing up to
his preliminary" trial level. However, a similar situation
did not exist with the visual-motor task, Task 1. In that
task, the subject could perform the task appropriately,
i.e., turn on the lamp each time it went outj but do so at
a slower rate, a rate which could allow inattention to the
task at hand. To test for this possibility, the times
required to turn on unllghted lamps during the preliminary
trials were compared to the times required during the
experiment. Median times were computed for preliminary and
experimental trials for each subject. These can be found
in Table 3. To evaluate the significance of the changes inj
Table 3
Median Light Matrix Response Times
In 1/100 of a Minute
Subject Preliminary Experimental
1 5 3
2 8
7
3
6
5
4
10.5 7
5 5 6.5
6 6 5
7
6 6
8 6 6
9 6.5
6
10 4
4.5
11 9.5
10
12
5 5
13 5 6.5
14 6
5
15 5 5.5
16 6 6
17
8 7
18
13 10.5
performance times, the McNem&r (Siegel, 1956) test for the
significance of changes was used. A summary of this analy
sis is given In Table A. There was no significant change
In response times and the slight change that was found was
in the direction of Improvement, I.e., lower times, during
the experimental trials. Therefore, the change, If any,
would be most likely due to practice, not Inattention.
From the evaluations of task performance, the continu
ous observation possible during Task 2 and the statistical
evaluation used In assessing Task 1 performance, It can be
concluded that all subjects were attending to the
performance of the tasks at hand.
In the description of the equipment, It was pointed
out that voltages proportionate to Impedance changes were
produced by the probe microphone In response to changes In
the signal level In the closed external auditory canal due
to decreased transmittance through the basilar membrane as
Impedance Increased. At the same time, the phase shift
that occurred with acoustic reflex was also measured. The
Impedance change data for each subject at each task and
level combination averaged over the three trials can be
found in Appendix A. Impedance change for each subject as
a function of RAS level Is plotted In figures appearing In
Appendix B. Task Is the parameter. Individual phase
change data for each subject averaged over the three trials
can be found In Appendix C. Plots of phase change are
Table H
Summary of McNemar Teat of the Significance
of Changes Applied to Preliminary and
Experimental Light Matrix
Response Times
Experimental
+
Preliminary
A ■ 8 B -
C - 0 D -
5
x2 - ([A - D] - l)2
A + D
x2 - .378, df ■ 1, p < *01
given In Appendix 0.
Mean impedance change averaged over the 18 subjects
was computed for each task-by-level combination. These
means appear in Table 5* Standard deviations around these
means are given in the same table.
Study of Appendix A reveals that the distributions of
Impedance change through subjects are more or less skewed.
Por this reason, medians were computed for the task and
level combinations and are also given In Table 5• A com
parison of the means and medians verifies that the
distributions are Indeed not symmetrical, since the mean
and median do not coincide.
In order to obtain an idea of the magnitude of the
Impedance changes, the mean values for the 18 subjects were
converted from relative units to acoustic ohms. Por this
conversion, it was first necessary to scale the output of
the graphic level recorder to determine what each division
on the chart was equal to in terms of acoustic ohms. This
was done by measuring the change in output at the graphic
level recorder associated with the change in the Impedance
of a cavity as the volume was changed from 1.4 to 1.0 cc.
The impedance of these two hard-wall, nonabsorbative
cavities consisted of only an Imaginary component, i.e.,
with no resistive element. By comparing the voltages seen
at the graphic level recorder from the output of the probe
microphone with the two cavities and by calculating the
38
Table 5
Mean (H) and Median (Mdn) Impedance Changes In •
Relative Units Averaged Over Subjects.
Standard Deviations (o) In Relative
Units Estimate Variability Around
the Means
RAS Level Task 1 Control Task 2
95 dB M
3-63
5.58 4.21
95
a 2.12 2.88
2.59
95
Mdn 3.16
4.92 3.33
105 dB M 9.16 11.11 10.24
105 0 5.88
6.51
6.78
105 Mdn 7.*2 9.09 8.34
115 dB M
12.63 14.37
13.42
0
6.93
6.78 7.18
Mdn
11.17
12.09 10.91
39
acoustic Impedance of the two volumes of air,It was possi
ble to determine how large a voltage change would be
associated with a known change In acoustic Impedance In
terms of acoustic ohms*
It was calculated that each relative unit had a value
of 4*54 acoustic ohms. Therefore, to convert the relative
means given In Table 5 Into acoustic ohms, It was necessary
to multiply each relative unit by 4*54* This conversion,
has been made for both means and medians and the values are
given In Table 6. Mean Impedance change In acoustic ohms
Is plotted as a function of RAS level In Fig. 6. Task Is
the parameter. The means are averaged over the 18
subjects.
Although the design of the experiment permitted a
parametric analysis of variance using means from the three
trials for each subject at each task-by-level combination,
It was decided that the use of nonparametrlc statistics
might be more appropriate because of the previously
mentioned skewed Impedance change distributions. Another
complication which helped form this decision can be seen
with reference to the standard deviations given In Table 3.
The slses of the standard deviations are obviously related
to the level of the reflex arousal stimulus which would
tend to confound partitioning the between-RAS-level vari
ance Into treatment and error variance. With the data in
this study, neither one of these complications would have
40
Table 6
Means (M) and Medians (Mdn) Converted
into Acoustic Ohms
RAS Level Task 1 Control Task 2
95 dB
MQ 16.48
25.33 19.11
95 Mdnfi 14.34 22.28 15.12
105 dB MQ 41.59
50.44
46.49
105
MdnQ 33.68 41.26 37.86
115 dB MO 57.34 65.24
60.93
115
MdnQ 50.78 54.86 49.64
60
60
2 40
30
20
10
95 105 115
HI
R A S L E V E L IN 4B SPL
Pig. 6. Mean Impedance changes as a function
of RAS level. Task Is the parameter.
• *
been likely to lead to drawing erroneous conclusions had
the parametric analysis of variance been used. A study of
the data In Appendix A and the plot of the means In Fig. 6
Indicates that both effects of RAS level and task are very
large, ' so that borderline decisions relying heavily on
parametric assumptions of normal distributions (or even
symmetrical distributions) and Independent variances would
not have been encountered. On the other hand, with such
large effects, the greater power of the parametric sta
tistics Is not necessary, therefore, the decision In favor
of nonparametrlc statistics.
Reliability. The three measures of Impedance change
for each subject at each task and RAS level combination
permitted an estimation of the reliability of measurement.
Kendall's coefficient of concordance (Siegel, 1956) was
selected for the Index of reliability because It is a non
parametrlc correlation technique which can be used with
more than two sets of measures and It relates linearly to
Spearman's rho. It Is a rank correlation technique which
uses the variance of ranks summed through replications for
each subject. If there were little or no relation between
the ranking of subjects from trial to trial, the sums of
ranks would be about equal and the deviations would be
small. Since the coefficient of concordance, W, is a
function of the variance, V Increases linearly with
variance. As with other rank coefficients of correlation,
ties in ranking suppress the coefficient. The Spearman
correction for ties is also appropriate for the coefficient
of concordance. The Kendall coefficients of concordance
are given in Table 7 for each task and level combination.
As has been stated, the coefficient of concordance is
related linearly to average Spearman rho for the same set
of measures. These equivalent Spearman rho's (r„ ) are
°av
also given in Table 7 to aid in interpretation.
Additionally, a x 2 test of the significance of the
coefficient of concordance was computed for each task and
level combination and is given in Table 7*
It should be noted before discussing the results
further that the measures at each task and level combi
nation are quite reliable and the coefficients of
correlation are significant.
For clarity, the inferential analyses will be divided
into a section concerned with RAS level and a section
concerned with task.
Effect of RAS Level. To examine the overall effect
of RAS level on impedance change, the Friedman two-way
analysis of variance by ranks (Siegel, 1936) was employed
for each task, i.e., subjects and RAS level were used as
factors in three analyses, an analysis for each task
condition. This was the appropriate analysis to use
because of the scores in each case being related due to a
design which called for observation of each subject at all
44
Table 7
Indices of Repeat Reliability Over Trials:
Kendall Coefficient of Concordance (W)
and Spearman Rho (r. ). x2 Tests
av
Significance of the Reliabilities
RAS Level Task 1 Control Task 2
95 dB
95
95
95
W
‘ av
p<
• 652
• 63
33.2
.02
.612
.59
31.4
.02
.815
.80
41.6
.001
105 dB
105
105
105
X
p<
av
2
.870
.86
44.4
.001
.898
.89
45.8
.001
.913
.91
46.6
.001
115 dB
115
115
115
av
2
P<
.955
.95
48.6
.001
.938
.93
47.8
.001
.926
.92
47.2
• 001
treatments and levels of treatments. This analysis
compares the rankings of the treatment over subjects. If
the sum of the rankings are approximately equal for the
levels of the treatment. It Is likely that there Is no
effect due to treatment level. As the sums of ranks.depart
from equality, the likelihood that there Is an effect due
to treatment level Increases. The probability of sums
departing from equality by chance Is distributed as x2 and
the analysis ultimately employs x2 as a test of the null
hypothesis•
The x2 for the effect of RAS level for each task con
dition Is given In Table 8. The probability of rejecting
the null hypothesis when It Is true Is given for each x2
In Table 8. In the case of each task, the effect of RAS
level Is significant beyond the .001 level, I.e., the
probability of falsely rejecting the null hypothesis is
less than one In a thousand.
The sampling of several RAS levels was used as an
Indicator of measurement validity. The finding of a large
effect of RAS level on acoustic reflex activation Is very
well documented (Galambos f t Rupert, 1959; Jepson, 1955;
Klockhoff, 1961; Miller, 1958; Simmons, I960; Weiss,
Kundle, Cashln, f t Shlnabarger, 1962; Plsch f t Schulthess,
1963). The agreement between the data of this study and
the cited studies, studies employing both Impedance change
1
and electrophyslologlcal measures of acoustic reflex
46
Table 8
Summary of the Friedman Analysis of
Variance for the Effect of RAS
Level for Each Task Condition
Task 1 Control Task 2
X2
36 34.1 34.1
df 2 2 2
P<
.001 .001 .001
47
activity, leads to the conclusion that the technique was
valid and did measure an Indicator of reflex activity.
Another reason for sampling RAS level was to allow
examination of a possible RAS level with task interaction.
This will be discussed In the next section.
i
Effect of Task Performance. Again the Friedman analy-;
j
sis of variance by ranks was used. Task condition and
subject were the two factors In an analysis of the effect
of task performance at each RAS level. The x2 for task
effect at each RAS level Is given In Table 9» along with
the probability associated with each x2* Again, as with
RAS level, the task effect Is significant beyond the .001
level at each RAS level.
The Wllcoxon matched-palrs slgned-ranks test was used
to examine the significance of the difference in effect
between the individual task conditions at each RAS level.
The Wllcoxon test uses both the number of differences In a
given direction, e.g., one set of measures consistently
greater than another, and also the magnitude of the
i
differences. The null hypothesis prevails when about as
many differences go one way as another, Indicating that
neither set of measures' Is consistently larger, and the
total differences are approximately equal in magnitude.
i
Wllcoxon's T Is an Indicator of the Imbalance of differ
ences and Is given In Table 10 for each of the task
differences at each RAS level, along with the probability
48
Table 9
Summary of the Friedman Analysis
of Variance for the Effect of
Task for Each RAS Level
95 dB 105 dB 115 dB
X2 31.7 21.3
19.8
df 2 2 2
P<
.001 • 001 .001
Table 10
Summary of Wllcoxon Natched-Palrs Signed-Rank Test of
the Significance of Differences In Effect Between
Individual Task Conditions at Each RAS Level
RAS Level Control > Task 1 Control > Task 2 Task 2 > Task 1
95 dB T
3.5
1
35.5
95 P<
.005 .005
in
C M
o
.
95
N 18 16 18
105 dB
T
5.5 33
21
105 P< .005
H
O
.
.005
105
N 18 18 18
115 dB T 4
22.5 36.5
115
P<
.005 .005 .025
115
N 18 18 18
Note: T * Sum of ranks
N ■ Number of ranks
50
associated with each value of T. From the plot of mean
Impedance change as a function of RAS level given In Fig.
6, it was decided to use the tests as one-tailed tests,
stipulating that Control > Task 2 > Task 1, even though
the experimental hypotheses developed in the introduction
call for Task 2 > Control > Task 1, a situation which
clearly does not exist. Hypothesis II, that an auditory
detection task will produce an increment in acoustic
reflex, is clearly untenable. From Table 10 it can be seen
that the task effect is significant in each case beyond
the .025 level.
Using the results of the Friedman analysis of variance
and the Wllcoxon tests, it is possible to compare the mean
and median impedance changes as a function of RAS level and
task. From the results of the analyses, it is clear that
the means provide a much better descriptive statistic than
the medians in this case. Actually, the medians are quite
misleading, indicating almost no difference between Task 1
and Task 2 at 95 dB RAS level and that the value for Task 1
exceeds that for Task 2 at 115 dB RAS.
The results, then, clearly show a significant effect
on acoustic reflex activity produced by either the visual
or the auditory task. Further, from Fig. 6 it appears that
there is little or no interaction between effect of task
and RAS level. In terms of the experimental hypotheses
set forth previously, Hypothesis I, that performance of a
visual-motor task will produce a decrement In the acoustic
reflex* was supported. Both alternative hypotheses could
be rejected. But Hypothesis II* that performance of an
auditory detection task will produce an increment in
acoustic reflex* was not supported. Indeed* performance
of the auditory task not only failed to produce an incre
ment In acoustic reflex* but the task performance produced
a significant decrement supporting one of the alternative
hypotheses. It appeared that task performance In general
produced a decrement in reflex. Although the range of
tasks sampled was rather limited* It Is difficult to
Imagine a task setting more likely to enhance, acoustic
reflex activity than an audltory-detectlon task. Perhaps
using a different frequency for the to-be-detected signal*
a signal above the normal resonant frequency of the ear*
would have shown the hypothesised increment. Then the
reflex would tend to shift the resonant frequency of the
ear toward the signal. Such an argument would Imply that
the auditory system would be set to detect only the one
frequency* rather than set to process Important auditory
signals In general. A set for one frequency seems unlikely
because of Its limited utility In any but a laboratory
setting* and It Is difficult to believe that such a fine
control for detection of an expected tone would be
developed. Such an argument would also be In disagreement j
j
with Simmons* (1962 A 1964) theory of the auditory reflex
serving as part of an orienting response.
A difference In the to-be-detected signal far more
likely to be Important In producing an Increment in
acoustic reflex Is the natural significance of the signal.
Speech, as used by Klockhoff (1961), probably Is a more
meaningful and relevant signal for human subjects than a
pure tone, even when the subject Is Instructed to detect
the tone.
The Inability of confirming Klockhoff*s (1961)
results could stem from two differences In technique.
First, Klockhoff*s observation of acoustic reflex Increment
when his subjects were attempting to overhear someone of
"psychological significance" occurred In a contrived
setting. The subjects were not consciously performing a
task; the psychologically significant speaker happened to
enter the laboratory unexpectedly. Second, Klockhoff
employed a more relevant signal, speech In place of tone.
In regard to the two types of theories proposed for
accounting for the function of the acoustic reflex, pro
tective theories and accommodative theories, the results
of this study do not seem to support a protective theory.
The most reasonable prediction from-such a theory would be
that there would be no effect due to task performance. If
protection against high-level sounds were the primary
function of the acoustic reflex, an effect of task would be
defeating. On the other hand, the results do not clearly
53
support an accommodative theory either. . Both auditory and
non-auditory tasks decreased the magnitude of acoustic
reflex, although, as previously mentioned, this result may
have been due to the limited relevance and familiarity of
the to-be-detected signal. The hypothesis most consistent
with the results Is the alternative hypothesis, the
hypothesis that task performance as such interferes with
acoustic reflex. A criticism of this Interpretation Is
that It does not take Into account the consistently greater
magnitude of reduction due to non-audltory task performance
than that due to auditory task performance.
Qiacomelll and Moszo (1965) have Bhown that general
Impairment of synaptic activity In the reticular formation
also produces a decrement In acoustic reflex activity. The
reticular formation secures the connection between the
efferent and afferent parts of the stapedial reflex. With
various types of lesions In the reticular formation, the
reflex arousal threshold was raised permanently; with
administration of 100 mgr. of Chloropromasine, the reflex
arousal threshold was raised temporarily. They used human
subjects.
Whatever Interpretation is given, the Important con
clusion which can be drawn Is that task performance does
affect magnitude of acoustic reflex, so that a model of the
functioning of the middle ear system might appropriately
Include a central feedback mechanism.
IV. SUMMARY AND CONCLUSIONS
The purpose of this study was to Investigate the
effect of attention to auditory stimuli on the acoustic
reflex. Level of attention to auditory stimuli was oper
ationally defined by task performance: (1) reduced
attention was defined as performance of a non-audltory
task; (2) neutral attention was defined as no task
performance; (3) increased attention was defined as per
formance of an auditory task.
Impedance change was measured as an Indication of
acoustic reflex activity during the three task conditions,
visual-motor task, no task (control), and audltory-
detectlon task. The acoustic reflex was elicited by an
1800-2400 c/s band of noise at levels of 95$ 105» and 115
dB SPL. Eighteen subjects were used In a complete
factorial design with three trials at each task-by-level
combination. The major results were:
1. Task performance did not change from preliminary
to experimental trials In any significant way. The slight
change that was found was In the direction of Improvement.
Therefore, the operational definitions of levels of
attention were maintained.
2. Reflex arousal stimulus level was the largest
determiner of the magnitude of acoustic reflex, reflex
activity Increasing monotonlcally with RAS level.
55
3. Performance of either task caused a decrement In
acoustic reflex, with performance of the visual-motor task
causing a larger decrement than performance of the
audltory-detectlon task*
4* The effect of task performance on the acoustic
reflex was not dependent upon the level of the reflex
arousal stimulus within the range of RAS levels employed.
5* The measurement technique used gave reliable
results, and the phenomenon measured was reproducible, the
reliability being somewhat higher with the 105 and 115 dB
SPL RAS levels than with the 95 dB SPL RAS level.
Prom the results, It was concluded that attention to
auditory stimuli Is Important in evaluating acoustic reflex
activity and that central control of the acoustic reflex
appears likely. Attention to task performance itself,
however, seems more Important In altering acoustic reflex
than the particular type of stimulus used In the task. The
results tend to support theories that the acoustic reflex
serves a primarily accommodative rather than protective
function, although the type of accommodation is not clear.
REFERENCES
REPERENCES
Bdkdsv. 0. Experiments In Hearing. New York: McQraw-
Hill, I960. ------------------
Beranek. L. L. Acoustic Measurements• New York: John
Wiley, 19^9.
Carmel, P. W. & Starr, A. Acoustic and nonaooustio factors
modifying middle-ear muscle activity in waking cats. J.
Neurophvsiol.. 1963, 26, 598-616.
Flsch, V. A Schulthess, 0. V. Electromyographic studies on
the human stapedial muscle. Acta Oto-Larvngol.. 1963*
56, 287-297.
Fletcher, H. A Munson, W. A. Loudness, its definition,
measurement and calculation. J. Acoust. Soe. Amer..
1933, 5, 82-108.
Oalambos, R. Suppression of auditory nerve action by
stimulation of efferent fibers to the cochlea. J.
Neurophvsiol.. 1956, 19, 424-437.
Oalambos, R. A Rupert, A. Action of the middle ear muscles
in normal cats. J. Acoust. Soc. Amer.. 1959, 31, 349-
355.
Qiacomelli, F. A Mosso, W. An experimental and clinical
study on the Influence of the brainstem reticular for
mation on the stapedial reflex. Int. Audlol*. 1965. 4.
42-44.
Hernandes-Peon, R., Scherrer, H., A Jouvet, M.
Modification of electrical activity in the cochlear
nucleus during "attention" in unanesthetlsed cats.
Science. 1956, 123, 331-332.
Hlldlng, D. A. The protective value of the stapedius
reflex: An experimental study. Trans. Amer. Acad.
Ophthalmol. Otolaryngol.. 1961, 69, 07.
Jepson, 0. Studies on the acoustic stapedius reflex in
man. Unpublished doctoral dissertation, University of
Aarhus, 1955.
Klockhoff, I. Middle ear muscle reflexes in man. Acta
Oto-Larvngol.. Stockholm. 1961, Suppl. No. 164.
Kobrak, H. 0. The Middle Ear. Chicago: Unlver. Chicago
57
58
Press, 1959.
Lindquist, E. P. Design and Analysis of Experiments In
. Psychology and Education. Boston: Houghton Mifflin
company,
Loeb, M. A Rlopelle, A. J. Influence of loud contralateral
stimulation on the threshold and the perceived loudness
of low-freauency tones. J. Acoust. Soc. Amer.. I960. 32.
602- 610. ,
HeNemar, Q. Psychological Statistics. New York: John i
Wiley A Sons, xnc•, 1902•
Met*, 0. Studies on the contraction of the tympanic
muscles as indicated by changes in the impedance of the
ear. Acta Oto-Laryngol.. 1951, 39, 397-405.
Miller, A. R. Intra-aural muscle contraction in man
examined by measuring acoustic Impedance of the ear.
Laryngoscope. 1958, 68, 48-62.
Miller. A. R. Acoustic reflex in man. J. Acoust. Soc.
Amer.. 1962, 34, 1524-1531 *.
Miller, A. R. Transfer function of the middle ear. J.
Acoust. Soc. Amer.. 1963, 35, 1526-1534.
Miller, A. R. Effect of tympanic muscle activity on
movement of the eardrum, acoustic impedance and cochlear
mlcrophonlcs. Acta Oto-Laryngol.. 1964, 58, 1-10.
Miller, A. R. The acoustic impedance in experimental
studies on the middle ear. Int. Audlol.. 1964, 3, 1-13.
Miller, A. R. An experimental study of the acoustic
Impedance of the middle ear and its transmission
properties. Acta Oto-Laryngol.. 1965, 59, 1-19.
Nleder, P. C. Personal communication, 1965.
Reger, S. N. Effects of middle ear muscle action on
certain psychophysical measurements. Ann. Otol. Rhlnol.
Laryngol.. I960, 69, 1-20.
Shapley, J. L. Reduction in the loudness of a 250-cycle
tone in one ear following the introduction of a thermal
noise in the opposite ear. Proc. Ia. Acad. Sci.. 1954,
61, 417-422.
59
Siegel, S. Nonparametrlc Statistics. New York: McGraw-
Hill, 1956.
Simmons, P. B. Middle ear muscle protection from the
acoustic trauma of loud continuous sound. Ann. Otol.
Rhlnol. and Laryngol.. I960, 69, 1063-1071
Simmons, P. B. Perceptual theories of middle ear muscle
function. Ann. Otol. Rhlnol. and Laryngol.. 1964, 73,
724-739.-----------------------------
Simmons, P. B., Oalambos, R., A Rupert, A. Conditioned 1
response of middle ear muscles. Amer. J. Physiol.. 1959,
197, 537-538.
Ward, W. D., Salters, W., A Glorig, A. Exploratory studies
on temporary threshold shift from Impulses. J. Acoust.
.Soc. Amer.. 1961, 33, 781-793.
Weiss, H. S., Mundle, J. R., Cashln, J. L., A Shlnabarger,
E. W. The normal human lntra-aural muscle reflex In
response to sound. Acta Oto-Laryngol.. 1962, 55, 505-
515.
Wever, E. 0. A Bray, 0. W. The stapedius muscle in
relation to sound conduction. J. Exp. Psychol.. 1942,
31, 35-43.
Wever, E. G. A Lawrence, M. Physiological Acoustics.
Princeton: Princeton University Press, I9b*.
Wever, E. 0. A Vernon, J. A. The control of sound trans
mission by the middle ear muscles. Ann. Otol. Rhlnol.
Laryngol.. 1956, 65, 5-14.
Wiggers, H. C. The function of the lntra-aural muscles.
Amer. J. Physiol.. 1937, 120, 771-780.
Zwislockl, J. Some measurements of impedance at the
eardrum. J. Acoust. Soc. Amer.. 1957, 29, 349-356.
Zwislockl, J. Analysis of the mlddle-ear function. Part
I: Input Impedance. J. Acoust. Soc. Amer.. 1962, 34,
1514-1523.
Zwislockl, J. Analysis of the mlddle-ear function. Part
II: Guinea-pig ear. J. Acoust. Soc. Amer.. 1963, 35,
1034-1040.
APPENDICES
APPENDIX A
Table 11
Impedance Change for Each Subject at Each Task-by-RAS
Level Combination, Means of Three Trials
iject
95
Task 1
105 115 95
Task 2
105 115 95
Control
105 115
1 3.67 25.67 31.67 6.50 29.00 33.00
8.67 28.33
32.00
2 4.83 6.33 7.33
6.00 6.50 7.50 6.00 7.00 8.00
3
3.50 8.17 11.67 3.33
8.00
10.33 5.33 9.67
12.50
4
2.67 6.67 10.67
2.00 6.00
10.33 3.83
9.00
12.17
5 1.67 7.33 11.83 2.83
9.00
12.17 3.00
9.17 12.83
6 3.00 7.50
8.33 4.67 8.67
8.50 5.16 9.00 8.83
7
3.50 6.00
8.67 3.33
6.50 9.00 4.00 7.50
9.33
8
0.83 1.17 3.50 0.50
2.33 3.67 2.17 4.17 6.67
9 1.17 3.83 6.33
1.50 4.17 11.33
4.00 5.50 11.67
I
Continuation of Table 11
V
Task 1 Task 2 Control
Subject
95 105 115 95 105 115 95 105 115
10
8.17
13.00 16.00 10.00 14.50 17.67 12.33
15.00
18.33
11 5.83 8.33 10.17 5.33 8.67 10.83 5.33
9.50
11.83
12
2.83 5.33
7.50 2.17 3.83 7.33
5.50 9.00 10.83
13 5.83 9.50 12.83 6.33 11.83 14.83 6.17 10.83 13.83
14 2.00
5.83 9.83 2.83
7.00 11.00
4.67 6.67 12.00
15 3.33
14.00
20.67 3.50 18.00
20.17
4.00
17.17
20.00
16
8.33 21.33 24.17 9.83 23.33
25.50 13.00
25.67
27.50
17 2.33 9.33 18.67 2.67
11.00
20.67 4.67 12.67 22.17
18
1.83 5.50 7.50 2.50 6.00
7.67 2.67 4.17 8.17
ov
ro
32
i
30
i
I
28
< / > «
5 26
SO
« 24
>
5 22
-I
Ul -
e e
63
CONTROL
-TASK I
TASK 2
(9
O
Ul
2
115 95 105 115
95 105 115 95 105
RAS LEVEL dB SPL
APPENDIX B
Pig. 7. Impedance change as.a function of RAS
level for subjecte 1-3. Task is the parameter.
I
I
r
64
CONTROL
TASK I
TASK 2
90 105 115 95 (05 115
RAS LEVEL IN
95 105 115
SPL
• •
Pig* 8. Impedance change as a function of
RAS level for'subjects 4-6* Task is the parameter
CHANGE R E L UNITS
28
26
24
22
20
95 105 115 95 105 115
65
CONTROL
TASK I
TASK 2
RAS LEVEL IN 43 SPL
Fig. 9« Impedance change as a function of
RAS level for subjects 7-9* Task Is the parameter,
IM P CHANGE I N PEL UNITS
28
24
22
20
95 105 115 95 105 115
66
CONTROL
-TASK I
TASK 2
12
95 105 115
RAS LEVEL IN dB SPL
Pig. 10. • Impedance change as a function of
RAS level for subjects 10-12. Task Is the parameter
IMP CHANGE I N REL UNITS
28
CONTROL
TASK I
TASK 2
26
24
22
20
/
✓ /
t /
/
• 14
(
It
It
V
98 106 115 95 105 115
RAS LEVEL IN JB SPL
*
Fig* 11* Impedance change ae a function of
RAS level for subjects 13-15* Task Is the parameter.
28
24
22
C O N T R O L
TA SK I
TASK 2
It
t
I
! l
20
318
//
S 1 6
95 105 1 1 5 95 106 1 1 5 ^ 5 105 1 1 6
17
68
RAS LEVEL IN «IB SPL
Pig. 12. Impedance change as a function of
. c
RAS level for aubje'cta 16-18. Taalc.la .the parameter
APPENDIX C
Table 12
Phase Change for Each Subject at Each Task-by-RAS
Level Combination. Means of Three Trials
Subject
95
Task 1
105 115 95
Task 2
105 115 95
Control
105 115
1
3.3
20.6 22.1 3.8 21.5 23.1
6.8
19.5
20.1
2
3.5 7.1 7.1 3.8
7.3
7.8 5.8 7.0 7.8
3 2.5
4.8 6.1 2.1 3.0 8.1
3.3
3.0 6.8
*
5.1
10.6
13.3 5.1 8.5
12.0 6.1 11.1 13.5
5
3.6 7.0
9.3
1.6 7.1
7.8 v 1.1 7.8 7.6
6 4.6
7.3
7.6 5.0 5.6 8.0 4.1
6.3
6.8
7
1.6 5.0
5.3 3.1
4.8 6.8 2.2 6.0
6.3
8 1.6
1.5 3.5
1.0
3.1
6.0
2.3 4.3 7.1
9 1.3
4.1 5.0 1.1
. *.5
7.8 2.6 6.0 9.0
O N
V O
Continuation of Table 12
Task 1 Task 2 Control
Subject 95 105 115 95 105 115 95 105 115
10
9.5 12.5
14.1 9.6
13.5
14.1
11.3
13.6 15.0
11 2.6
5.5 5.1
3.8 5.5 6.5 3.1 5.5
6.6
12 2.0 4.8
4.5 2.3
4.6
7.1 3.5 "4.3 5.5
13 3.3 6.5
7.6
4.3
6.6 7.8 4.8 6.6 8.0
14 5.6
6.3 8.5 3.1
7.6 9.8
5.3
7.6
10.3
15
1.8 5.8 7.8 2.1
6.5 7.3
1.6
6.3
7.8
16 12.8 22.6
23.3 13.5 22.5 23.1
16.1
24.3
25.0
17
2.0 7.8 14.6
3.5
9.0 14.6 4.8 7.0
14.5
18 5.0
7.5
7.6 4.8 7.6 8.6
5.1 7.3
8.8
71
2
22
20
95 105
i
95 105 I T S
RAS LEVEL IN SPL
APPENDIX D
• •
Pig. 13. Phase shift as a function of RAS level
for subjects 1-3. Task is the parameter.
PHASE SHIFT I N DEGREES
24
22
20
95 105 115 95 105 115 95 105 115
RAS LEVEL IN JB SPL
Fig. 14. Phase, shift as a function of RAS
level for subjects 4-6. Task Is the parameter.
95 105 115
C
95 105 115 95 105 115
RAS LEVEL IN «IB SPL
Pig. 15. Phase shift as a function of RAS
level for subjects 7-9* Task is the parameter.
PHASE SHIFT I N DEGREES
24
22
20
18
16
14
12
10
8
6
4
2
•
•
c
7
. . -
\
i
C
/
o
< / >
Sll
/
//
* 1 2
95 105 115 95 105 115 95 105 |I5
RAS LEVEL IN .18 SpL
Fig* 16.r Phase shift as a function of RAS
level for subjects 10-12. Task is the parameter.
PHASE SHIFT I N DEGREES
75
24
22
20
C
&
Tt
95 105 115 95 105 115 95 105 115
RAS LEVEL IN & SPL
Flg« 17. r Phase shift as a function of RAS
level for subjects 13-15* Task is the parameter'
PHASE SHIFT I N DEGREES
76
24
22
20
17
95 105 115 95 115 95 105 U5
RAS LEVEL «IB SPL
i
Fig. l8.,£hase shift as a function of RAS
level fop subjects 16-18. Task Is the parameter.
-----------------:-----------------------------------.---------------------- i -........... ..........

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Asset Metadata

Creator Bell, Donald William (author)

Core Title Effects Of Task Performance Upon The Acoustic Reflex

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 Metfessel, Newton S. (committee chair), Garwood, Victor P. (committee member), Grings, William W. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-211350

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