Affect and Attention
1
Affective Pictures Influence Holding but not Drawing
of Attention in a Modified Dot-Probe Paradigm
Ulrich Schimmack
University of Toronto, Mississauga
RUNNING HEAD: Affect and Attention
February 2002
about 4,000 words
Author’s Note.
Correspondence concerning this article should be addressed to Ulrich Schimmack,
Department of Psychology, UTM, 3359 Mississauga Road North, Mississauga,
Ontario, L5L 1C6, Canada, email: uli.schimmack@utoronto.ca
Affect and Attention
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Abstract
The influence of affective picture on drawing and holding of attention in a
modified dot-probe paradigm was examined. Pairs of pictures combining seven
levels of valence ranging form strong displeasure to strong pleasure were
presented for 200 ms in two out of four possible locations. The pictures were
replaced by two circles. Participants had to determine whether a target circle was
broken once or twice as fast as possible. Affective pictures in the location of the
target circle had no influence on response latencies. Strong unpleasant pictures in
the non-target location produced slower response latencies than neutral pictures in
the target location. The results suggest that strong unpleasant pictures hold
attention, but that affective pictures do not draw attention.
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Affective Pictures Influence Holding but not Drawing
of Attention in a Modified Dot-Probe Paradigm
The influence of affective stimuli on attention has been documented in
numerous studies (e.g., Fox, Russo, Bowles, & Dutton, 2001; MacLeod, Mathews,
& Tata, 1986; Mogg, McNamara, Powys, Rawlinson, Seiffer, & Bradley, 2000;
Rozin & Royzman, 2001). The existing evidence demonstrates that affective
stimuli attract more attention than neutral stimuli and that unpleasant stimuli tend
to attract more attention than pleasant stimuli. This article presents the results of a
modified dot-probe study with affective pictures as stimuli. The study contributes
to research on affective influences on attention in three ways. First, most studies
have used words as stimuli. In recent years, a few studies have examined the
influence of facial expressions on attention (Bradley, Mogg, Falla, & Hamilton,
1998). However, very few studies have examined the influence of affective
pictures on attention (Mogg et al., 2000). De Houwer and Hermans (1994)
demonstrated that affective pictures have a stronger influence on attention than
affective words. Research with pictures also has a higher ecological validity than
research with words. Hence, more research with affective pictures is needed to
understand how affective stimuli influence attention in everyday life.
The second contribution of this study is the systematic manipulation of
stimulus intensity. The only previous study found a negativity bias (i.e.,
unpleasant words attracted more attention than pleasant words). The negativity
bias was not moderated by the extremity of the unpleasant words (Pratto & John,
1991). The present study examined whether the negativity bias would generalize
to affective pictures as stimuli, and whether it would be consistent across different
levels of intensity.
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The third contribution of this study concerns the differentiation between two
types of attention (Fox et al., 2001). Over time, attention shifts between different
stimuli. Affect can influence drawing and holding of attention (Fox et al., 2001). If
affective stimuli draw attention, they facilitate responses to other stimuli in the
location of the affective stimulus. If affective stimuli hold attention, they impede
responses to other stimuli in other locations than the affective stimulus.
Most studies of affect and attention have used one of two tasks, namely the
Emotional Stroop task and the dot-probe paradigm. As noted by Fox et al. (2001),
the Emotional Stroop task cannot differentiate between drawing and holding of
attention because a single stimulus is presented in the focus of visual attention.
Hence, the location of attention is predetermined by the task and it is impossible to
determine whether affective stimuli draw attention to their location. The dot-probe
paradigm is better suited for the examination of drawing and holding of attention.
In this paradigm, an affective stimulus is presented with a neutral stimulus for a
relatively short time (500ms). Afterwards, one of the two stimuli is replaced by a
dot. Participants have to press a key as soon as they detect the dot. Participants are
able to detect the dot faster, if they are already attending to the location where the
dot appears (e.g., Mogg et al., 2000).
Unfortunately, most studies employing the dot-probe paradigm could not
separate drawing and holding of attention because they did not include a control
condition with neutral stimuli. Without this condition, faster responses to dots in
the location of the affective stimulus can be due to drawing or holding of attention,
or both. That is, the affective stimulus may draw attention to its location so that
participants already attend to the location of the dot. Alternatively, participants
may randomly attend to either one of the two stimuli. When attention is directed to
the affective stimulus, it holds attention in that location, which makes it harder to
detect the dot in the other location. With a control condition, it would be possible
Affect and Attention
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to distinguish these two processes. If affective stimuli draw attention, they should
facilitate responses to dots in the target location in comparison to the neutral
control condition. If affective stimuli hold attention, they should delay responses
to non-affective stimuli in the opposite location compared to response latencies in
the control condition.
Fox et al. (2001) used a slightly different approach for the same purpose. The
authors modified the exogenous cuing paradigm (Posner, Inhoff, Friedrich, &
Cohen, 1987). In this paradigm, participants also have to detect a target (a dot or a
square), which is displayed in one of two locations. Before the appearance of the
dot, a cue appears either in the target location or in the opposite location. On valid
trials the target appears in the location of the cue (80%); on invalid trials the target
appears in the opposite location (20%). Neutral cues (a flashing light) lead to
faster responses on valid trials and slower responses on invalid trials. Fox et al.
(2001) modified this paradigm by using three different types of cues (neutral,
positive, threatening). If affective stimuli influence drawing of attention, affective
cues should produce faster responses on valid trials than neutral cues. If affective
stimuli influence holding of attention, they should produce slower responses on
invalid trials than neutral cues. The authors conducted a series of studies with
words and angry facial expressions as stimuli. The general result was that none of
the affective stimuli influenced drawing of attention. Threatening stimuli
influenced holding of attention for high-anxious participants but not for low
anxious participants. Yiend and Mathews (2001) used the exogenous cuing
paradigm with gray-scaled affective pictures, which were either threatening
(mutilations, dangerous animals) or not threatening (landscapes). The authors
found the same pattern of results. That is, threatening pictures did not produce
faster responses on valid trails than non-threatening pictures. Threatening pictures
produced slower responses on invalid trails than non-threatening pictures, but this
Affect and Attention
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effect was only observed for high-anxious individuals. These studies suggest that
affective stimuli influence holding rather than drawing of attention.
The major difference between the affective exogenous cue paradigm (Fox et
al., 2001) and the dot-probe paradigm with a control condition is the presentation
of one or two pictures before the appearance of the target. I used the dot-probe
paradigm because the presentation of two stimuli has two advantages over
paradigms with a single stimulus. First, the presentation of two stimuli has higher
ecological validity for situations, in which people have to detect affective stimuli
in an array of multiple stimuli (e.g., see the snake between flowers, rocks, etc.).
Second, the presentation of a single stimulus may attenuate effects of affective
stimuli on drawing of attention (cf. Fox et al., 2001). The reason is that suddenly
occurring stimuli already draw attention (Yantis, 1996). Hence, the appearance of
a single stimulus may be sufficient to draw attention to that location independent
of the stimulus’s affective valence. However, if two stimuli appear suddenly on a
screen, sudden onset cannot determine which location draws attention first.
Affective stimuli may be more likely to draw attention to their location in this
situation.
To summarize, this study examined the influence of affective pictures that
varied systematically in valence and intensity on the drawing and holding of
attention in a modified dot-probe paradigm. I expected the following results.
(a) Affective pictures should influence the holding of attention and not the
drawing of attention. This prediction is based on the only study that differentiated
drawing and holding of attention (Fox et al., 2001). Although the authors did not
study affective pictures as stimuli and used a slightly different paradigm, it is most
parsimonious to assume that their findings generalize to other stimuli and a
slightly different task.
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(b) Unpleasant pictures have a stronger influence on attention than pleasant
pictures because negative stimuli have shown to attract more attention than
positive stimuli (Pratto & John, 1991; Rozin et al., 2001).
(c) Negativity dominance should be modified by affect intensity. This
prediction is based on the only study with affective pictures that manipulated the
intensity of unpleasant pictures, and found that strong unpleasant pictures attracted
more attention than mild unpleasant pictures (Mogg et al., 2000).
Method
Participants
Forty-three Introductory psychology students (29 female, 14 male) at the
University of Toronto, Mississauga, participated in this study for course credit.
Materials
The pictures for this study were taken from the International Affective
Picture System (IAPS; Lang, Bradley, & Cuthbert, 1995) and the Internet. The
pictures were selected from pilot studies with participants from the same
population to represent seven levels of valence (on a 7-point bipolar scale ranging
from –3 to +3): strong displeasure (M = -1.91), moderate displeasure (M = -1.25),
mild displeasure (M = -0.69), neutral (M = 0.10), mild pleasure (M = 0.60,
moderate pleasure (M = 1.20), and strong pleasure (M = 1.91). The stimulus set
did not include pictures with erotic content or mutilations. The picture set included
98 pictures; 14 pictures for each level of valence, which allowed the complete
pairing of all levels of intensity without repeated presentations of the same picture.
The size of the pictures was 180 x 270 pixels on a screen with a 1024 x 768 pixel
resolution.
Procedure
The design of the study was a complete 7 x 7 design, in which each level of
valence was paired with all levels of valence. All participants first completed a
Affect and Attention
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different task, in which they saw the same pictures and rated their affective
reactions to the pictures. The results of this task are not relevant for the present
study. However, it is important to note that participants were at least vaguely
familiar with the pictures. Before the dot-probe task, participants received
extensive instructions about the task. They clicked a button on the screen to start
the dot-probe task. The computer first presented four practice trials, which were
the same for all participants and used eight pictures that were not included in the
experimental picture set. Then the computer presented two repeated blocks of the
49 experimental trials. In each block, individual pictures from the seven sets were
randomly assigned to the 49 pairs. As a result, different participants saw different
combinations of pictures and each participant saw different combinations of the
pictures in the two blocks. Each trial started with a fixation cue (a red square) in
the center of the screen. The fixation cue was shown for 250ms. Afterwards, two
pictures appeared in two of four locations (upper left, upper right, lower left, lower
right). The pictures remained on the screen for 200ms. Afterwards, the pictures
were replaced by two circles. One of the two circles (the target circle) was broken
either once (on the top) or twice (on the top and the bottom). The circles remained
on the screen for 2000ms or until participants responded.
Participants had to indicate how often the target circle was broken. They
responded by pressing one of two mouse buttons (left button = once broken; right
button = twice broken). This modification of the dot-probe task was used for two
reasons (see Bradley et al., 1998). The presentation of two stimuli was used to
inhibit the influence of sudden-onset on attention. A single stimulus that suddenly
appears automatically attracts attention (Yantis, 1996). Hence, people can quickly
detect targets even if their attention was not in that location. By presenting the
target circle with a non-target circle, the target does not automatically attract
attention due to its sudden onset. The broken circle was used to ensure that
Affect and Attention
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participants had to attend to the target stimulus to provide a correct response. I
hoped that this task would produce larger effects than the typical dot-probe
paradigm, which often produces very small differences in response latencies due
to affect (MacLeod et al., 1986). The interval of 200ms was chosen to allow for
enough time for an eye-movement to the location of an affective stimulus,
although eye-movements in the dot-probe paradigm are rare (cf. Fox et al., 2001).
This interval also happened to be similar to the interval in Fox et al.’s (2001)
studies (150ms).
Results
I used HLM5 (Raudenbush, Bryk, Cheong, & Congdon, 2000) to analyze the
response latencies. HLM is useful for the investigation of unbalanced designs.
Although the present design was balanced, missing data in response latencies
render the design essentially unbalanced. HLM can estimate group averages from
data with missing data, whereas Analysis of Variance requires a balanced data
structure. This statistical approach was particularly necessary in the present study,
which relied on relatively few trials.
Participants responded correctly on 89% of the trials. Trials with incorrect
responses were excluded from the analysis of the response latencies. The relatively
low hit rates indicate that this task was more difficult than the mere detection of a
probe (Fox et al., 2001). Extreme response latencies were eliminated following the
guidelines by Fox et al. (2001). First, response latencies that were faster than
300ms (N = 4, 0.1%) and responses that were slower than 1500ms (N = 63, 1.7%)
were eliminated. Next, response latencies that were 2.5 standard deviations slower
or faster than individuals’ mean latencies were also excluded (N = 42, 1.1%). The
final analysis is based on the response latencies of 86% of the trials. The response
latencies were still slightly skewed (skewness = .47), which was eliminated by
Affect and Attention
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logarithmic transformation (skewness = .04). Hence, logarithmically transformed
response latencies were used as the dependent variable.
Type of picture in the target location and type of picture in the non-target
location was dummy coded with neutral pictures as the contrast for all other types
of pictures. In addition, block was included as a predictor. Table 1 shows the fixed
effects with robust standard errors. The results reveal trivial effects for the
Intercept (i.e., participants needed time to respond) and block (i.e., participants
became faster over time). Importantly, there were no significant effects for type of
picture in the target location. This finding supports the hypothesis that affective
stimuli do not draw attention. However, type of picture in the non-target location
produced a significant effect for strong unpleasant pictures. The positive sign of
this effect reveals that participants needed more time to respond to the target circle
when a strong unpleasant picture was presented in the non-target location than
when a neutral picture was presented in the non-target location. Two effects
showed a tendency towards significance, namely moderate unpleasant pictures in
the non-target location, and strong pleasant pictures in the target location. The
finding that strong negative pictures were the only pictures that produced a
significant effect supports the second hypothesis of a negativity bias.
The next model tested whether strong and moderate unpleasant pictures
differed significantly from each other. This model constrained the gammas for
these two picture types in the non-target location to be equal. The fit of the
constrained model was not significantly worse than the fit of the unconstrained
model, χ2 (df = 1) = 1.67, p = .19. However, a model that constrained the gammas
of all levels of unpleasant pictures in the non-target location did not fit the data as
well as the unconstrained model, χ2 (df = 2) = 6.30, p < .05. This finding supports
the hypothesis that the influence of negative pictures on attention is moderated by
the extremity of the negative pictures. Although the difference between strong and
Affect and Attention
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moderate pictures did not reach significance, the difference between strong and
mild negative pictures was significant (see Figure 1 for the retransformed response
latencies as a function of picture type in the non-target location). In a final model,
I included an interaction term between block and the dummy variable coding for
strong unpleasant pictures in the non-target location. The interaction was not
significant, beta = 0.00, p = .84, indicating that the effect of strong unpleasant
pictures did not diminish with repetition.
Discussion
I examined the ability of affective pictures to draw and to hold attention. The
results supported three predictions. First, the present study failed to find
significant effects of affect on the drawing of attention to the location of affective
stimuli. This finding replicates previous findings with the exogenous cuing
paradigm (Fox et al., 2001; Yiend & Mathews, 2001). As noted earlier, one
concern with the findings in these studies could be the presentation of a single
stimulus. It is possible that the sudden onset of a single stimulus is sufficient to
draw attention, precluding any additional effects of affect. This concern is
alleviated in the present study that presented two pictures at a time. Still, affective
stimuli did not facilitate responses when the appeared in the location of the target
stimulus. This finding provides additional evidence that affective stimuli do not
draw attention. The results also supported the predictions that negative pictures
have a stronger influence on the holding of attention than positive pictures, and
that this effect is moderated by the extremity of negative pictures. Indeed, only
strong negative pictures produced a significant effect on the holding of attention,
although moderate negative pictures showed a trend in the same direction, and the
difference between strong and moderate pictures was not statistically significant.
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Limitations
The greatest limitation of the study is the reliance on ready-made pictures for
the manipulation of affect. Although the use of these stimuli is common practice in
affect research, it prevents a causal interpretation of the results. It is possible that
the effects were due to other features of the pictures than their affective value. I
tried to address this problem as best as I could by sampling pictures from a large
set of affective pictures that have been used extensively in affect research (Lang et
al., 1995). It seems unlikely that the significant effect for the strong unpleasant
pictures is due to unique perceptual features of this heterogeneous set of pictures
(e.g., a dead cat, messy toilet, airplane crash). Salient perceptual features (e.g.,
high contrast to background) should also have influenced drawing of attention
(Yantis, 1996).
One plausible alternative explanation of the effect is in terms of novelty.
Unpleasant pictures are more unusual than pleasant pictures. However,
participants were already familiar with the pictures from a previous task, and there
the ability of strong negative pictures to hold attention did not decrease over
repeated blocks. Hence, it seems unlikely that the effect is due to novelty. Another
alternative explanation is arousal. Strong unpleasant pictures are more arousing
than strong pleasant pictures when erotic pictures are excluded (Bradley,
Codispoti, Cuthbert, & Lang, 2001; Schimmack, Colcombe, & Crites, 2001).
Future research needs to disentangle the influences of displeasure and arousal on
attention. The present study also does not address the possibility that specific
unpleasant stimuli (snakes, spider, threatening stimuli) influence attention
differently than other strong unpleasant pictures. However, Fox et al.’s (2001)
found that angry facial expressions, an evolutionarily significant threat stimulus,
did not draw attention.
Affect and Attention
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Another limitation of this study was the neglect of individual differences.
Many studies have demonstrated that high-anxious individuals show stronger
effects of negative stimuli on attention than low-anxious individuals (Fox et al.,
2001; Matthews et al., 1986; Mogg et al., 2000; Yiend & Mathews, 2001). The
present study could not examine this question because studies of individual
differences require many trials to eliminate random error. In future research it will
be important to examine whether the present findings are moderated by individual
differences.
Implications
Despite its limitations, the present study contributes to the literature on affect
and attention in several ways. First, it is one of the few studies that systematically
varied the intensity of stimuli along the valence dimension (Pratto & John, 1991).
Affect words showed a categorical effect on attention. However, the present study
demonstrated a significant effect of stimulus intensity. This finding replicates
Mogg et al.’s (2000) finding that strong unpleasant pictures influenced attention
more than milder unpleasant pictures. Hence, the findings suggest that affective
pictures do not produce a categorical negativity bias. This finding casts doubt on a
hard-wired detection mechanism that equally draws attention to all unpleasant
stimuli. As noted by Yiend and Mathews (2001), such a mechanism would not be
adaptive because it is often important to ignore negative stimuli (e.g., pain in a
battle; minor discomfort while pursuing an important task). However, strong
negative stimuli are more likely to pose a threat to survival and should demand
more attention than mild negative stimuli.
The present study also contributes to the distinction between affective
influences on drawing and holding of attention (Fox et al., 2001; Yiend &
Mathews, 2001). Consistent with previous studies, affect was only related to
holding of attention. The failure to demonstrate effects on drawing of attention has
Affect and Attention
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important theoretical implications for models of the interplay between cognitive
and affective processes. The Emotional Stroop task has often been interpreted in
terms of fast and automatic appraisal processes. However, this paradigm shows
stimuli in the focus of attention with instructions to evaluate these stimuli. This
situation is quite different from the everyday situation, in which people are
confronted with dozens of stimuli at the same time. In this situation affective
stimuli do not seem to automatically draw attention to their location.
One objection to this argument could be the short stimulus-onsetasynchronies. Maybe 200 ms are too short for the appraisal process to draw
attention. Future studies need to examine this question. However, 200 ms are
sufficient to draw attention by means of other hard-wired processes such as the
sudden onset of a novel stimulus (Yantis, 1996), or the matching of a stimulus to
representations in working memory (Downing, 2000). More research is needed to
examine the effects of different affective stimuli and different stimulus onset
asynchronies using a variety of paradigms to examine the ability of affective
stimuli to draw attention.
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References
Bradley, B. P., Mogg, K., Falla, S. J., & Hamilton, L. R. (1998). Attentional
bias for threatening facial expressions in anxiety: Manipulation of stimulus
duration. Cognition and Emotion, 12(6), 737-753.
Bradley, M. M., Codispoti, M., Cuthbert, B. N., & Lang, P. J. (2001).
Emotion and motivation I: Defensive and appetitive reactions in picture
processing. Emotion, 1(3), 300-319.
De Houwer, J., & Hermans, D. (1994). Differences in the affective processing
of words and pictures. Cognition and Emotion, 8(1), 1-20.
Fox, E., Russo, R., Bowles, R., & Dutton, K. (2001). Do threatening stimuli
draw or hold visual attention in subclinical anxiety? Journal of Experimental
Psychology: General, 130(4), 681-700.
Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1995). International affective
picture system: Technical manual and affective ratings. Gainesville, FL:
University of Florida.
MacLeod, C., Mathews, A., & Tata, P. (1986). Attentional bias in emotional
disorders. Journal of Abnormal Psychology, 95(1), 15-20.
Mogg, K., McNamara, J., Powys, M., Rawlinson, H., Seiffer, A., & Bradley,
B. P. (2000). Selective attention to threat: A test of two cognitive models of
anxiety. Cognition and Emotion, 14(3), 375-399.
Posner, M. I., Inhoff, A. W., Friedrich, F. J., & Cohen, A. (1987). Isolating
attentional systems: A cognitive-anatomical analysis. Psychobiology, 15(2), 107121.
Pratto, F., & John, O. P. (1991). Automatic vigilance: The attention-grabbing
power of negative social information. Journal of Personality and Social
Psychology, 61(3), 380-391.
Affect and Attention
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Raudenbush, S., Bryk, A., Cheong, Y. F., Congdon, R. (2000). HLM 5:
Hierarchical linear and nonlinear modeling. Lincolnwood, IL: SSI.
Rozin, P., & Royzman, E. B. (2001). Negativity bias, negativity dominance,
and contagion. Personality and Social Psychology Review, 5(4), 296-320.
Schimmack, U., Colcombe, S., & Crites, S. L. Jr. (2001). Affective reactions
to conflicting stimuli: Examining appealingness and appallingness appraisals.
Manuscript submitted for publication.
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45-76Washington, DC, US: American Psychological Association.
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Affect and Attention
Table 1
Coefficients of HLM model predicting log(RT).
Effect
Coefficient
Standard Error
T-ratio
Intercept
6.85
.03
245.64*
Block
-.06
.01
5.88*
Strong Negative
.00
.01
0.15
Moderate Negative
.00
.01
0.10
Mild Negative
-.01
.01
0.55
Mild Positive
-.01
.01
0.67
Moderate Positive
-.01
.01
0.64
Strong Positive
-.02
.01
1.77
Strong Negative
.03
.01
2.71*
Moderate Negative
.02
.01
1.73
Mild Negative
.00
.01
0.37
Mild Positive
.00
.01
0.31
Moderate Positive
.00
.01
0.17
Strong Positive
.01
.01
1.00
Target Location Dummy
Non-Target Location Dummy
* p < .05
17
Affect and Attention
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Figure Caption
Figure 1
Response Latencies as a Function of Picture Valence in the Non-Target Location
Note. –3 = strong displeasure, -2 = moderate displeasure, 1 = mild displeasure, 0 =
neutral, +1 = mild pleasure, +2 = moderate pleasure, +3 = strong pleasure
Affect and Attention
Response Latency (ms)
980
970
960
950
940
-3
-2
-1
0
+1
+2
+3
19