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Emotional arousal amplifies the selectivity of visual selective attention
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Emotional arousal amplifies the selectivity of visual selective attention
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Content
EMOTIONAL AROUSAL AMPLIFIES THE SELECTIVITY OF VISUAL SELECTIVE
ATTENTION
by
Matthew Ryan Sutherland
A Thesis Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF ARTS
(PSYCHOLOGY)
December 2010
Copyright 2010 Matthew Ryan Sutherland
ii
Table of Contents
List of Tables iii
List of Figures iv
Abstract v
Introduction 1
Experiment 1 6
Experiment 2 14
Experiment 3 21
General Discussion 28
References 33
iii
List of Tables
Table 1: Descriptive Statistics for Letter Identification Scores 10
and Covariates (Experiment 1)
Table 2: Results of Multi‐level Analysis with all Covariates 12
Included (Experiment 1)
Table 3: Descriptive Statistics for Experiment 2 Condition 1 15
Table 4: Descriptive Statistics for Experiment 2 Condition 2 16
Table 5: Experiment 2 (Condition 1) Results of Multi‐level 18
Analysis with all Covariates Included
Table 6: Experiment 2 (Condition 2) Results of Multi‐level 19
Analysis with all Covariates Included
Table 7: Descriptive Statistics for Letter identification Scores 22
(percent correct) and Covariates (Experiment 3)
Table 8: Significance Test for Main Factors and Interaction 23
Table 9: Results of Multi‐level Analysis with all Covariates 23
Included
iv
List of Figures
Figure 1: Timeline diagram of experimental procedure. Each letter 6
array consisted of 3 high contrast letters and 5 low contrast
letters.
Figure 2: Letter Identification rates (percent correct) for low and 11
high contrast letters on neutral and arousing trials
(Experiment 1).
Figure 3: Letter Identification rates (percent correct) for low and 17
high contrast letters on neutral and arousing trials
(Experiment 2, Condition 1).
Figure 4: Letter identification rates (percent correct) for low and 26
high contrast letters on neutral and arousing trials collapsed
across Experiment 1, Experiment 2 Condition 1 and
Experiment 3.
v
Abstract
In 3 experiments 111 young adults (ages 18‐30) performed a letter identification
task to test the hypothesis that emotional arousal increases attention to high
priority stimuli and inhibits attention to low priority stimuli. A circular array of
letters was briefly presented to each subject following exposure to negative
arousing or neutral sounds. Contrast level of the letters was manipulated to make
some letters higher in priority. The results support the arousal‐biased competition
hypothesis, as exposure to emotionally arousing sounds increased identification
rates for high priority letters and decreased identification rates for low priority
letters. Yet this effect was limited to inter‐stimulus intervals (ISI) from 750 to 3000
milliseconds (ms).
1
Introduction
Attention controls what information enters awareness. It also shapes what
we remember and how we behave. Similarly exposure to emotionally arousing
stimuli also influences what enters awareness, what we remember, and guides
subsequent behavior. Studies examining interactions between emotion and selective
attention indicate that emotionally arousing stimuli occupy a privileged position in
the competition for attentional resources, often at the expense of competing non‐
emotional stimuli (Alpers & Pauli, 2006; Alpers, Ruhleder, Walz, Muhlberger, &
Pauli, 2005; Anderson & Phelps, 2001; Vuilleumier, Armony, Driver, & Dolan, 2001).
But more recently it has been shown that these perceptual enhancements may
persist after an emotional stimulus disappears, resulting in enhanced perception of
subsequent neutral stimuli (Bocanegra & Zeelenberg, 2009; Phelps, Ling, &
Carrasco, 2006; Zeelenberg & Bocanegra, 2010). Yet little is known about how
exposure to an emotionally arousing stimulus influences perceptual processing of
multiple non‐emotional stimuli competing for the same attentional resources. In
three experiments we investigate the effects of emotional arousal on biases in
selective attention for competing non‐emotional visual stimuli. We provide
preliminary evidence that emotional arousal influences selective attention by
amplifying biased‐competition processes.
From a behavioral perspective, objects rather than locations is the level at
which selective attention operates (for a review see Scholl, 2001). When two objects
2
occupy the same location, and attention is directed to that location, perceptual
enhancements for both objects are not observed (O`Craven, Downing, & Kanwisher,
1999; Vecera & Farah, 1994). Instead they compete with one another for the same
attentional resources. Moreover, single cell studies of primates (Chelazzi, Duncan,
Miller, & Desimone, 1998; Chelazzi, Miller, Duncan, & Desimone, 2001) and fMRI
studies with humans (Kastner, De Weerd, Desimone, & Ungerleider, 1998) suggest a
similar object‐based view of attention. These models posit that neural
representations of objects come at the cost of weaker representations of other
objects, as neural responses to single objects are inhibited when additional objects
are placed into one’s field of view (Desimone, 1998; Desimone & Duncan, 1995;
Duncan, 2006; Kastner & Ungerleider, 2001). Yet this inhibition is lifted when
attention is directed to a single object, allowing it to dominate the competition for
neural resources. For this reason selective attention is conceived of as a biasing
mechanism that manipulates contests among perceived objects vying for neural and
mental representation.
Yet understanding the forces that influence selective attention is as
important as understanding how it operates. A wide range of findings suggest that
interactions between the perceptual saliency of a stimulus, its affective properties,
and the current goals of the perceiver determine what objects are given high
priority with respect to perceptual processing. For example, increasing the contrast
level of a visual stimulus enhances neural responses to that stimulus (Proulx &
Egeth, 2008). Similarly, when directed to covertly attend to a visual stimulus,
3
increases in neural responses to the attended stimulus are also observed (Chelazzi,
et al., 1998). Thus, the perceptual saliency of a stimulus and the task‐demands
placed on the perceiver together control what objects are given priority (Fecteau &
Munoz, 2006). However, the affective properties of a visual stimulus can also bias
the distribution of neural and mental resources to sensory input. Stimuli capable of
eliciting an emotional response dominate competitions for neural resources (Lang,
et al., 1998; Vuilleumier, Richardson, Armony, Driver, & Dolan, 2004) and more
easily enter awareness (Alpers & Pauli, 2006; Alpers, et al., 2005; Anderson &
Phelps, 2001; De Martino, Kalisch, Rees, & Dolan, 2009). Because emotions mobilize
our bodies and thoughts to deal with environmental challenges—such as an
approaching rattlesnake in the grass or a near collision on the highway—it seems
quite plausible that perception becomes more selective under states of emotional
arousal. Many studies corroborate this assumption, yet the observed increases in
selectivity are usually confined to the emotion‐eliciting stimulus, for in these studies
the emotional cue both serves as an emotion elicitor and as a target for attention
(Alpers & Pauli, 2006; Alpers, et al., 2005; Anderson, 2005; Anderson & Phelps,
2001; Keil & Ihssen, 2004; Knight, et al., 2007; LaBar, Mesulam, Gitelman, &
Weintraub, 2000; for a review see Mather & Sutherland, under review;
Nummenmaa, Hyona, & Calvo, 2006).
However, more recent investigations indicate that brief exposure to an
emotionally arousing stimulus can increase perceptual sensitivity to non‐emotional
targets. For example, brief exposure to faces expressing fear can enhance one’s
4
ability to identify tilt directions of Gabor patches presented at low contrast levels
(Phelps, et al., 2006). Moreover, briefly viewing an emotionally arousing word can
enhance perception of non‐emotional words presented next (Bocanegra &
Zeelenberg, 2009). And similar enhancements can occur across different sensory
modalities. When participants hear rather than view emotionally arousing words,
this can enhance their ability to visually identify briefly presented non‐emotional
words (Zeelenberg & Bocanegra, 2010). These findings suggest that once emotional
arousal is elicited, and the arousal‐eliciting stimulus is removed, perception of non‐
emotional task‐relevant stimuli is enhanced. However, no studies have examined
how emotional arousal influences visual perception for multiple non‐emotional
targets that are in direct competition for attention.
In regard to visual processing, priority is controlled by interactions between
the perceptual saliency of a stimulus and the goals/task‐demands of the perceiver. If
a stimulus is perceptually salient or goal‐relevant, it will receive a higher degree of
priority, and will thus dominate the competition for attention. Therefore, an
investigation into the effects emotional arousal has on attention should begin by
examining how emotions impact perceptual processing of high and low priority
stimuli. Thus far studies demonstrating perceptual enhancements for non‐
emotional stimuli have used paradigms where only a single target stimulus is
presented (Bocanegra & Zeelenberg, 2009; Zeelenberg & Bocanegra, 2010), or
multiple targets that are equally salient (Phelps, et al., 2006). These results suggest
that visual processing of high priority stimuli is enhanced by emotional arousal.
5
Moreover, biased competition models of attention suggest that focusing on one
object inhibits the processing of other objects (Desimone, 1998; Desimone &
Duncan, 1995; Duncan, 2006; Kastner & Ungerleider, 2001). Therefore, if emotional
arousal enhances perceptual processing of high priority stimuli, it should also
increase inhibition of low priority stimuli.
6
Experiment 1
To test the hypothesis that exposure to emotionally arousing stimuli
enhances perception of high priority stimuli, at the cost of processing low priority
stimuli, we briefly presented participants with an array of letters that differed in
contrast level, and preceded each presentation with a negative arousing or neutral
auditory stimulus (see Figure 1). Each letter‐stimulus in the array was equal with
respect to goal‐relevance. However, we assumed high contrast letters would receive
higher priority than the low contrast letters due to greater perceptual saliency. For
this reason we predicted that exposing participants to emotionally arousing sounds
would increase identification rates for high contrast letters and decrease
identification rates for low contrast letters.
Figure 1: Timeline diagram of experimental procedure. Each letter array consisted
of 3 high contrast letters and 5 low contrast letters.
7
Stimuli
Emotional arousal was manipulated using auditory stimuli from the
International Affective Digital Sound system (Bradley & Lang, 2007). Each audio clip
lasted 6 seconds, and consisted of naturally occurring sounds such as screams,
vomiting, car accidents and bomb explosions. The audio was presented via
headphones. Each participant was exposed to 40 sound clips, 20 of which were high
in arousal and of negative valence, while the remaining were low in arousal and of
neutral valence.
The visual stimuli used in the letter detection task consisted of letters that
appeared in uppercase Arial font, with each subtending 1.12°. All letters in the
alphabet were used with the exception of ‘I’, as it too closely resembled lowercase
‘L’. The high contrast letters had RGB values of #666666, while the low contrast
letters had RGB values of #CCCCCC. Stimuli were presented on an iMac monitor with
media white point values of X: 0.9505 Y: 1.0 Z: 1.0891.
Prior to the experiment, participants completed the Positive Affect Negative
Affect Schedule (PANAS) as a measure of their current positive and negative
affective state (Watson, Clark, & Tellegen, 1988). Participants also completed the
Center for Epidemiological Studies Depression scale (CES‐D) as a measure of
depressive symptoms experienced during the past week (Radloff, 1977).
Participants
Thirty‐two young adults (22 female) participated in Experiment 1. Subjects
consisted of USC students and individuals from the surrounding community. All
8
subjects either received course credit or a monetary compensation for their time.
Ages ranged from 18 to 28 (M = 19.9). Fifteen participants identified themselves as
Caucasian, 13 as Asian, 1 as African American, and 1 as bi‐racial. The remaining two
participants did not identify with any of the racial categories listed.
Method
Informed consent was obtained upon arrival. Participants then completed a
demographic questionnaire followed by the CES‐D and the PANAS measures. Each
trial began with a fixation cross that appeared at the center of the screen and
remained on the screen for most of the trial. After 4 seconds, participants were
exposed to an audio clip that lasted 6 seconds. Once the audio clip ended a circular
array of eight letters were presented around the fixation cross. Each array consisted
of three high contrast letters and five low contrast letters. A short inter‐stimulus
interval (ISI) between the end of the audio clip and the presentation of the letter
array was used, ranging from 750 to 3000 ms. The letters remained on the screen
for 200 milliseconds (ms). After the letters were removed, the fixation cross was
replaced by the words “recall now” (Figure 1). Participants were directed to focus
on the fixation cross at all times. Each letter was an equal distance from the fixation
cross. Moreover, participants were directed to ignore differences in contrast level
among the letters. They were specifically informed not to purposely attempt to
detect only the low or high contrast letters on any given trial. They were instead
directed to simply try to identify as many of the letters in the array as possible.
Participants reported what letters they saw via key press. It was also emphasized
9
that they should be less concerned with making errors and more concerned with
identifying letters.
When all 40 trials were complete, each sound was rated. After each sound
clip participants provided valence and arousal ratings on a scale from 1 to 9 via key
press. The ratings were followed by a post test questionnaire that included inquiries
about how challenging they found certain parts of the task, and what strategies they
may have developed in identifying the letters. Participants were then debriefed and
excused from the study.
Data Analysis
Letter identification rates were analyzed in a 2 × 2 factorial with both factors
representing within‐subject variables. Each subject had four separate scores, which
included identification rates for low and high contrast letters on either arousing or
neutral trials. Moreover, we had three covariates: PANAS scores for both positive
and negative affect, and CES‐D depression scores. Letter identification rates were
calculated as percent correct. All three covariates represented continuous variables
and were calculated as total raw scores. The data were first subjected to a 2 ×2
repeated measures ANOVA. We then subjected the data to a multi‐level model
analysis using each subject as the classification variable (see Singer, 1998).
Results and Discussion
The descriptive statistics can be observed in Table 1. The repeated measures
ANOVA yielded a significant main effect of contrast level, indicating that as expected
high contrast letters were more often detected than low contrast letters, F(1,31) =
10
41.48 p < 0.001. No main effect of arousal was observed F(1,31) = 0.39, p = 0.54,
suggesting that overall letter detection rates did not differ across arousing and
neutral trials. However, a disordinal interaction was observed between contrast and
arousal, F(1,31) = 6.25, p = 0.018, indicating that high contrast letters were more
often identified on arousing trials (M = 0.67) compared to neutral trials (M = 0.64),
while low contrast letters were more often identified on neutral trials (M = 0.39)
compared to arousing trials (M = 0.37) (Figure 2).
Table 1
Descriptive Statistics for Letter Identification Scores and Covariates (Experiment 1)
Variable N Min Max Mean SD
Neutral 32 0.325 0.731 0.481 0.091
Arousing 32 0.350 0.713 0.480 0.091
Low Contrast 32 0.005 0.630 0.379 0.145
High Contrast 32 0.383 0.983 0.650 0.144
PANAS
Positive
32 13 45 27.2 7.397
PANAS
Negative
32 10 20 12.7 2.635
CES‐D 32 3 21 10.8 5.331
Next we performed a mixed model analysis. We first entered both factors
(arousal and contrast level) into the model without covariates. The contrast term
was significant, t(93) = 5.66, p < 0.001 indicating that high contrast letters were
more often identified compared to low contrast letters. The arousal term was not
11
significant, t(93) = ‐1.43, p = 0.1559, however the interaction term did reach
significance, t(93) = 2.62, p = 0.0103, again suggesting the existence of a disordinal
interaction in the predicted direction. Finally, a paired t‐test revealed that there was
no difference in errors made across emotional (M = 16.81) and neutral (M = 16.56)
trials, t(31) = ‐0.37, p = 0.714. These data support our hypothesis, as performance
increased for high contrast letters and decreased for low contrast letters on
arousing trials, compared with neutral trials.
Figure 2. Letter Identification rates (percent correct) for low and high contrast
letters on neutral and arousing trials (Experiment 1).
In addition, when all three covariates were entered into the mixed model, the
arousal, contrast and interaction terms remained virtually unchanged (see Table 2).
However, the PANAS positive affect term appeared as a marginally significant
predictor, t(28) = 1.96, p = 0.06 indicating that those experiencing higher levels of
12
positive affect performed better on the letter detection task after controlling for all
other variables in the model.
Table 2
Results of Multi‐level Analysis with all Covariates Included (Experiment 1)
Effect b SE df t Sig
Intercept 0.410 0.080 28 5.10 p < 0.0001
Arousal ‐0.020 0.014 93 ‐1.43 p = 0.1559
Contrast 0.245 0.043 93 5.66 p < 0.0001
PANAS pos 0.004 0.002 28 1.92 p = 0.0647
PANAS neg ‐0.010 0.006 28 ‐1.62 p = 0.1165
CES‐D ‐0.001 0.003 28 ‐0.22 p = 0.8288
Arousal ×
Contrast
0.052 0.020 93 2.62 p < 0.05
These results suggest that exposure to emotionally arousing sounds
amplifies biases in attention towards high priority stimuli, which comes at the cost
of attending to low priority stimuli. The main effect of contrast level confirmed that
high contrast letters were given high priority, as they were more often identified
compared to low contrast letters. However, no main effect of arousal was observed,
suggesting that overall identification rates did not differ across emotionally
arousing and neutral trials. Moreover, these results were corroborated by a mixed
model analysis, which also suggests that these observed effects were present after
controlling for differences in depressive symptoms experienced over the past week,
13
and differences in positive and negative affective state. In addition, positive affect
appeared as a marginally significant predictor suggesting that those experiencing
more positive affect identified more letters. Taken together, these findings indicate
that emotional arousal interacts with biased competition processes in attention, and
does so by amplifying differences in selection, allowing high priority stimuli to
dominate attention to an even greater extent, while low priority stimuli are
inhibited to an even greater degree.
14
Experiment 2
To corroborate the results of Experiment 1 and to further explore the length
of time that arousal impacts selective attention, we added a second condition that
included longer intervals between the audio stimulus and the presentation of the
letter array.
Participants
Thirty‐two young adults (24 females) ranging from 18 to 22 (M = 19.9)
participated in condition 1. The same number of young adults (29 females) ranging
in age from 18 to 26 (M = 20.9) participated in condition 2. Subjects were randomly
assigned to one of the two conditions. Participants were USC students and
individuals from the surrounding community. They received either 1‐hour of course
credit or monetary compensation for their participation. Of those who completed
Condition 1, 8 identified themselves as Caucasian, 11 as Asian, 3 as Hispanic, 3 as
African American, 5 as biracial, and the remaining either selected ‘other’ or declined
to state their race/ethnicity. Of those who completed Condition 2, 12 identified as
Caucasian, 11 as Asian, 3 as African American, 3 as Hispanic, 4 as biracial, and the
remaining identified with no racial categories listed.
Method
The procedure for Condition 1 was identical to that of Experiment 1. The
procedure for Condition 2 was similar to Experiment 1, except the duration of time
between the audio stimulus and the letter array presentations varied from 4000 to
6000 ms, rather than 750 to 3000 ms.
15
Results and Discussion
The descriptive results for Conditions 1 and 2 can be observed in Tables 3
and 4, respectively. For Condition 1, a repeated measures ANOVA performed on
letter identification rates revealed a significant main effect of contrast level, F(1,31)
= 29.21, p < 0.001, again indicating that high contrast letters were more often
identified compared to low contrast letters. The main effect of arousal was not
significant, F(1,31) = 0.73, p = 0.40. A disordinal interaction in the expected
direction was only marginally significant, F(1,31) = 2.914, p = 0.098 (Figure 3).
Paired t‐tests revealed no difference in incorrect responses between emotional (M =
16.3) and neutral trials (M = 15.19), t(31) = ‐1.454, p = 0.156.
Table 3
Descriptive Statistics for Experiment 2 Condition 1
Variable N Min Max Mean SD
Neutral 32 0.338 0.675 0.502 0.080
Arousing 32 0.344 0.656 0.493 0.070
Low Contrast 32 0.245 0.665 0.434 0.100
High Contrast 32 0.317 0.883 0.605 0.133
PANAS
Positive
32 12 42 25.9 7.938
PANAS
Negative
32 10 41 13.58 5.97
CES‐D 32 2 48 8.84 8.837
16
Table 4
Descriptive Statistics for Experiment 2 Condition 2
Variable N Min Max Mean SD
Neutral 32 0.363 0.619 0.492 0.080
Arousing 32 0.325 0.669 0.489 0.088
Low Contrast 32 0.13 0.605 0.434 0.105
High Contrast 32 0.358 0.792 0.584 0.106
PANAS
Positive
32 14 45 27.7 7.44
PANAS
Negative
32 10 19 13 3.27
CES‐D 32 1 32 10.19 7.4
As in Experiment 1, the results of Condition 1 were subjected to a mixed
model analysis using subject as the grouping variable. The contrast term was
significant, t(93) = 4.67, p < 0.001, indicating that high contrast letters were more
often detected compared to low contrast letters. In contrast to the results of
Experiment 1, the arousal term was marginally significant, t(93) = ‐1.91, p = 0.0597,
indicating better performance on neutral versus arousing trials when controlling for
all other variables in the model. Moreover, as in Experiment 1 the interaction term
was significant, t(93) = 2.11, p = 0.0378 indicating that on arousing trials
performance increased for high contrast letters and decreased for low contrast
letters. The results of the mixed model analysis remained virtually unchanged when
all three covariates were entered into the model (Table 5). However, contrary to
17
Experiment 1 PANAS positive affect scores failed to reach significance, t(28) = ‐0.67,
p = 0.51.
Figure 3. Letter Identification rates (percent correct) for low and high contrast
letters on neutral and arousing trials (Experiment 2, Condition 1).
18
Table 5
Experiment 2 (Condition 1) Results of Multi‐level Analysis with all Covariates
Included
Effect b SE df t Sig
Intercept 0.4237 0.05246 28 8.08 p < 0.0001
Arousal ‐0.02219 0.01164 93 ‐1.91 p = 0.0597
Contrast 0.1543 0.03306 93 4.67 p < 0.0001
PANAS pos ‐0.00105 0.001563 28 ‐0.67 p = 0.5079
PANAS neg 0.004408 0.003833 28 1.15 p = 0.2599
CES‐D ‐0.00101 0.002595 28 ‐0.39 p = 0.6988
Arousal ×
Contrast
0.03469 0.01646 93 2.11 p = 0.0378
All analyses performed on Condition 1 were performed on data from
Condition 2. The repeated measures ANOVA revealed a significant main effect of
contrast level, F(1,31) = 34.15, p < 0.001, indicating that high contrast letters were
more often identified compared to low contrast letters (see Table 4). But neither the
arousal main effect, F(1,31) = 0.457, p = 0.504 nor the interaction term reached
significance, F(1,31) = 0.918, p = 0.345. Moreover, apart from the contrast term,
t(93) = 5.86, p < 0.001 demonstrating that high contrast letters compared to low
contrast letters were more often identified, the mixed model analysis revealed no
significant results. And these findings remained unchanged when all 3 covariates
were entered into the model (see Table 6). Finally, no differences in errors were
observed across emotionally arousing and neutral trials, t(31) = ‐0.536, p = 0.596.
19
Table 6
Experiment 2 (Condition 2) Results of Multi‐level Analysis with all Covariates
Included
Effect b SE df t Sig
Intercept 0.3908 0.08153 28 4.79 p < 0.0001
Arousal 0.005625 0.01377 93 0.41 p = 0.6839
Contrast 0.1601 0.02734 93 5.86 p < 0.0001
PANAS pos 0.003473 0.002046 28 1.70 p = 0.1006
PANAS neg ‐0.00471 0.004117 28 ‐1.14 p = 0.2622
CES‐D 0.000508 0.002100 28 0.24 p = 0.8105
Arousal ×
Contrast
‐0.02177 0.01947 93 ‐1.12 p = 0.2665
We then analyzed data from both conditions simultaneously using a 2 × 2 × 2
repeated measures ANOVA with contrast and arousal as within‐subject variables,
and condition type as a between‐subject variable. A main effect of contrast was
observed, F(1, 62) = 62, p < 0.001, indicating that high contrast letters (M = 0.60)
were more often identified compared to low contrast letters (M = 0.43). In addition,
the interaction between arousal, contrast and condition type was marginally
significant, F(1, 62) = 3.463, p = 0.067, consistent with the finding that the observed
interaction between arousal and contrast occurs only at shorter ISI. No other effects
reached significance.
These results both corroborate and extend the findings of Experiment 1,
suggesting that emotionally arousing stimuli amplify biased competition processes,
20
but only at shorter ISI. In Experiment 1 and Condition 1 of Experiment 2, the letter
array appeared between 750 and 3000 ms after the auditory stimulus was removed.
This duration of time was extended in Condition 2, with the letter array appearing
between 3000 and 5000 ms after removal of the auditory stimulus. Thus it appears
that exposure to emotionally arousing auditory stimuli enhances perception for high
priority stimuli and decreases perception for low priority stimuli, but only for a
short period of time after the exposure.
21
Experiment 3
To further corroborate the results of Experiments 1 and 2, we performed a
third experiment and included skin conductance measures as a marker of
sympathetic arousal responses to the auditory stimuli. We predicted that SCR
magnitude would positively and negatively correlate with letter identification rates
for high and low contrast letters, respectively.
Participants
Fifteen young adults (10 female) consisting of USC students and individuals
recruited from the surrounding community participated for a monetary
compensation. Ages ranged from 19 to 29 (M = 23.2). Five participants identified
themselves as Caucasian, 5 Asian, 3 African American, 1 Hispanic and 1 as bi‐racial.
Method
Electrodermal activity (EDA) was recorded using a Biopac Systems MP 150
and a GSR 100c amplifier. Disposable electrodes were placed on the index and
middle fingers of the non‐dominant hand. Skin conductance responses (SCR) were
sampled at a rate of 62.5 samples per second with a threshold of 0.001 μmho. Event‐
related electrodermal activity in response to the sounds was defined as any
response occurring 1000 ms to 7000 ms after auditory stimulus onset. Apart from
the physiological recording devices, Experiment 3 was identical to Experiment 1 and
Condition 1 of Experiment 2.
22
Results and Discussion
The descriptive results for Experiment 3 can be observed in Table 7. The
repeated measures ANOVA revealed a significant main effect of contrast as in the
previous 2 experiments, F(1,14) = 21.69, p < 0.001, while the main effect of arousal
did not reach significance, F(1,14) = 1.13, p = 0.305. However, in contrast with the
previous 2 experiments the interaction did not reach significance, F(1,14) = 1.68, p =
0.216. Yet this test most likely failed to reach significance due to low statistical
power (n = 15), as mean scores were in the expected direction.
Table 7
Descriptive Statistics for Letter identification Scores (percent correct) and
Covariates (Experiment 3)
Variable N Min Max Mean SD
Neutral 15 0.431 0.825 0.520 0.097
Arousing 15 0.450 0.806 0.564 0.092
Low Contrast 15 0.210 0.565 0.386 0.010
High Contrast 15 0.358 0.950 0.648 0.168
PANAS
Positive
15 16 38 29.73 7.38
PANAS
Negative
15 10 18 12.4 2.13
CES‐D 15 3 23 12.47 5.71
The mixed model analysis revealed similar results, as only the contrast term
reached significance (see Table 8). Moreover, these results remained virtually
unchanged when all 3 covariates were entered into the model (see Table 9).
23
However, the PANAS positive affect term did reach significance, t(10) = 2.71, p <
0.05, indicating that those experiencing greater affect prior to the experiment
performed better on the letter detection task when controlling for all other
variables in the model.
Table 8
Significance Test for Main Factors and Interaction
Effect b SE df t Sig
Intercept 0.3857 0.02889 13 13.35 p < 0.0001
Arousal ‐0.01000 0.01701 39 ‐0.59 p = 0.5601
Contrast 0.2738 0.05528 39 4.95 p < 0.0001
Arousal ×
Contrast
‐0.02786 0.02406 39 1.16 p =0.2600
Table 9
Results of Multi‐level Analysis with all Covariates Included
Effect b SE df t Sig
Intercept 0.1813 0.1465 10 1.24 p = 0.2441
Arousal ‐0.01000 0.01701 39 ‐0.59 p = 0.5601
Contrast 0.2738 0.05527 39 4.95 p < 0.0001
PANAS pos 0.007034 0.002600 10 2.71 p < 0.05
PANAS neg ‐0.00068 0.008748 10 ‐0.08 p = 0.9399
CES‐D 0.000342 0.003391 10 0.10 p = 0.9217
Arousal ×
Contrast
‐0.02786 0.02406 39 1.16 p = 0.2540
24
One subject was excluded from SCR correlation analyses, as zero responses
to the audio stimuli were detected. The mean number of SCR’s detected across the
40 trials was 12, and the number of responses detected for arousing (M = 6.47) and
neutral trials (M = 5.47) did not significantly differ, t(14) = ‐1.45, p = 0.169.
Correlations between mean SCR (magnitude) collapsed across all trials did not
correlate with overall letter identification rates for high, r(12) = 0.221, p = 0.448,
and low contrast letters, r(12) = 0.09, p = 0.769. Next we calculated Pearson r
correlation coefficients between mean SCR and low contrast letters, and between
mean SCR and high contrast letters for each individual subject, resulting in two
correlation coefficients for each subject. The means of these correlation coefficients
for high and low contrast letters and SCR were compared via paired t‐test. However,
no differences in mean correlation coefficients between SCR magnitude and
accuracy for low contrast letters and SCR magnitude and accuracy for high contrast
letters were observed, t(13) = 0.428, p = 0.676.
Cross Experiment Analyses
Given that Experiment 1, Experiment 3, and Condition 1 of Experiment 2
were identical, we combined these data to increase statistical power and performed
repeated measures ANOVA on letter identification rates. In addition we also
performed item analyses by testing correlations between mean subjective valence
and arousal ratings for each auditory stimulus and letter identification rates for high
and low contrast letters. The results of the repeated measures ANOVA support our
initial hypothesis, as a main effect of contrast was observed, F(1,78) = 89.86, p <
25
0.001, η
p
2
= 0.535, no main effect of arousal was observed, F(1,78) = 0.18, p = 0.675,
η
p
2
= 0.002, while a disordinal interaction in the predicted direction was observed,
F(1,78) = 10.74, p = 0.002, η
p
2
= 0.121 (Figure 4). We then directly compared
identification rates for high and low contrast letters on arousing and neutral trials
using paired t‐tests. These analyses revealed that low contrast identification rates
were significantly higher, t(78) = 2.86, p = 0.005, on neutral trials (M = 0.41)
compared to arousing trials (M = 0.39); and that identification rates for high
contrast letters were significantly higher, t(78) = ‐2.58, p = 0.012, on arousing trials
(M = 0.64) compared to neutral trials (M = 0.62). These results concur with the
results observed individually in each experiment, indicating that letter identification
rates for low and high contrast letters are influenced differently by exposure to
emotionally arousing auditory stimuli. Moreover, no differences in errors were
observed across emotionally arousing (M = 15.91) and neutral (M = 15.58) trials,
t(78) = ‐0.662, p = 0.536.
26
Figure 4. Letter identification rates (percent correct) for low and high contrast
letters on neutral and arousing trials collapsed across Experiment 1, Experiment 2
Condition 1 and Experiment 3.
For the item analyses, we expected mean valence ratings for each auditory
stimulus to negatively and positively correlate with mean letter identification rates
for high and low contrast letters, respectively. In addition, we also expected mean
arousal ratings to negatively correlate with low contrast identification rates, and to
positively correlate with high contrast identification rates. The correlation test
between arousal ratings and high contrast identification rates for the 40 auditory
stimuli did reach marginal significance, r(38) = 0.265, p = 0.099, however the
correlation between arousal ratings and low contrast identification rates failed to
reach significance, r(38) = ‐0.139, p = 0.394. With respect to valence ratings, the
correlation test with high contrast identification rates did not reach significance,
r(38) = ‐0.206, p = 0.202, yet the correlation with low contrast identification rates
27
did, r(38) = 0.340, p = 0.032, suggesting that auditory sounds that were rated more
positively were associated with better performance for low contrast letters across
all trials.
28
General Discussion
The goal of this study was to test the hypothesis that, following exposure to
emotionally arousing sounds, high priority visual stimuli would dominate attention
to an even greater extent, while the inhibition of low priority stimuli would further
increase. Previous studies have demonstrated that exposure to emotional stimuli
enhances visual perception for non‐emotional stimuli that are the focus of attention.
However, no previous studies have examined whether this enhancement is
observed in the presence of other stimuli vying for the same limited pool of
resources. Furthermore, enhancements in perception for non‐emotional stimuli
have only been observed at low ISI—no more than 1000 ms. Finally, no studies have
used physiological markers of arousal to predict perceptual enhancements for non‐
emotional stimuli. Our study addressed each of these issues, and our results indicate
that arousal enhances perception for non‐emotional visual stimuli that are high
priority due to stronger perceptual contrast. But such enhancements come at the
cost of processing competing stimuli that are low priority due to their low
perceptual contrast.
According to arousal‐biased competition theory, emotional arousal enhances
perception for high priority stimuli and minimizes perception for low priority
stimuli (Mather & Sutherland, under review). When multiple stimuli are perceived,
each stimulus is given a degree of priority based on its perceptual saliency and its
relevance to current goals or task demands. The higher the priority, the more
29
attention the object receives. We manipulated the contrast level of multiple non‐
emotional stimuli to make some higher in priority, and thus more likely to be
selected by attention. We reasoned that high priority stimuli would more easily
capture attention and thus enjoy the perceptual benefits afforded by exposure to
emotionally arousing stimuli. However, we assumed this would come at the cost of
attending to competing stimuli that were lower in priority, and thus less likely to
capture attention.
At the neural level, selective attention mechanisms are biased towards high
contrast (Proulx & Egeth, 2008) and goal‐relevant stimuli (Chelazzi, et al., 1998).
Given that every letter in the stimulus array was equated in terms of goal‐relevance,
we argue that our findings show that exposure to emotionally arousing sounds
amplifies existing selection biases in attention that are driven by perceptual
contrast. Previous findings indicate that exposure to an emotionally arousing
stimulus can enhance perception for single task‐relevant targets (Bocanegra &
Zeelenberg, 2009; Phelps, et al., 2006; Zeelenberg & Bocanegra, 2010), hinting at the
possibility that emotional arousal enhances visual perception for stimuli that are the
focus of attention. Our results confirm this possibility, as high contrast letters
dominated the competition for attention in the presence of competing low contrast
letters—an effect that was enhanced following exposure to emotionally arousing
sounds.
Enhancements in perception for visual stimuli following exposure to
emotionally arousing stimuli has only been observed at relatively short inter‐
30
stimulus intervals (ISI), ranging from 0 to 1000 ms (Bocanegra & Zeelenberg, 2009;
Phelps, et al., 2006; Zeelenberg & Bocanegra, 2010). Results from experiments one
and two add to these findings, and suggest that arousal‐induced perceptual
enhancements for high priority stimuli can occur at 750 to 3000 ms ISI. To further
examine the duration of this effect, experiment two included a second condition
where ISI ranged from 4000 to 6000 ms. Arousal did not enhance identification
rates for the high contrast letters in this condition, nor did it reduce identification
rates for low contrast letters. Thus it appears that exposure to emotionally arousing
sounds does not enhance visual perception beyond 3000 ms.
Contrary to expectation, EDA responses to the audio stimuli were limited,
and were not significantly greater for arousing than for neutral sounds. The
expected correlations between mean EDA responses and performance on
identification rates for low and high contrast letters were not observed. Yet one
must consider that the letter identification task involved central fixation, which may
have elicited orienting responses throughout the experiment. This may have
masked EDA responses that are known to occur in response to the emotional stimuli
used in our experiment (Bradley & Lang, 2000).
Depression scores were included in our analyses as a covariate based on
evidence that depression is associated with reduced electrophysiological responses
to visual perceptual contrast (Bubl, Kern, Ebert, Bach, & van Elst, 2010) and slower
rates of information processing (Tsourtos, Thompson, & Stough, 2002). However,
controlling for depression scores had no effect on other variables included in the
31
mixed model analyses, and did not appear as a significant predictor. Measures of
affective state were included in the mixed model, as there is evidence that positive
mood increases one’s scope of visual attention (Fredrickson & Branigan, 2005;
Rowe, Hirsh, & Anderson, 2007). In Experiment 3, PANAS positive affect cores
appeared as a significant predictor when entered into the mixed model analysis as a
covariate, and in Experiment 1 these scores also appeared as a marginally
significant predictor. This suggests that higher levels of positive affect predicted
better overall performance on the letter identification task—a finding that is
consistent with the Broaden and Build Theory of Positive Emotions (Fredrickson,
1998). According to this theory, positive affect increases an individual’s scope of
attention, enhancing one’s ability to focus on global rather than local features of
visual stimuli (Fredrickson & Branigan, 2005; Gasper & Clore, 2002). And other
studies have shown that individuals experiencing more positive affect have greater
difficulty ignoring distracting information, as in the Eriksen flanker tasks, where
flankers divert attention away from task‐relevant stimuli (Rowe, et al., 2007). In
other words positive affect allows one to focus on a broader array of information,
which in the Eriksen flanker paradigm includes distracter stimuli that interfere with
rapid responses to task‐relevant stimuli.
Taken together, our findings indicate that when in direct competition for
attentional resources, exposure to emotionally arousing stimuli increases the
margin by which high priority stimuli dominate competitions for perceptual
processing. These results provide evidence for the arousal‐biased competition
32
hypothesis (Mather & Sutherland, under review), which predicts that experiencing
emotional arousal amplifies biased competition processes by strengthening
representations of high priority stimuli, and weakening representations of low
priority stimuli. These results also lend support to the idea that experiencing
positive affect increases one’s scope of attention, a prediction made by the Broaden
and Build Theory of Positive Emotions (Fredrickson, 1998).
33
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Abstract (if available)
Abstract
In 3 experiments 111 young adults (ages 18-30) performed a letter identification task to test the hypothesis that emotional arousal increases attention to high priority stimuli and inhibits attention to low priority stimuli. A circular array of letters was briefly presented to each subject following exposure to negative arousing or neutral sounds. Contrast level of the letters was manipulated to make some letters higher in priority. The results support the arousal-biased competition hypothesis, as exposure to emotionally arousing sounds increased identification rates for high priority letters and decreased identification rates for low priority letters. Yet this effect was limited to inter-stimulus intervals (ISI) from 750 to 3000 milliseconds (ms).
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Sutherland, Matthew Ryan
(author)
Core Title
Emotional arousal amplifies the selectivity of visual selective attention
School
College of Letters, Arts and Sciences
Degree
Master of Arts
Degree Program
Psychology
Publication Date
12/17/2010
Defense Date
10/20/2010
Publisher
University of Southern California
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Tag
emotional arousal,OAI-PMH Harvest,selective attention,stimulus priority
Language
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Mather, Mara (
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), Dawson, Michael E. (
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