RUNNING HEAD: CEREBRAL ASYMMETRY AND THE PERCEPTION OF EMOTIONS
Cerebral Asymmetry:
Affective
Styles and the Perception of Approach-Withdrawal Emotions
Karyn A. Vacanti
St. Bonaventure University
Abstract
This study was designed to examine the influence of how approach-withdrawal emotions and affective styles influence cerebral asymmetry. Cerebral asymmetry is the separation in functioning of the right and left hemispheres. Two hypotheses explain how emotions are processed; the valence and the approach-withdrawal hypothesis. The valence hypothesis states positive emotions are processed by the left and negative emotions by the right hemisphere. The approach-withdrawal hypothesis states approach emotions are processed by the left and withdrawal emotions by the right hemisphere. This study looked at individual differences in the form of affective styles. It was predicted that people with a negative affective style would process withdrawal emotions faster than approach, and positive affective people would demonstrate the opposite. The results supported the prediction, and a 3-way interaction between visual field, emotion type, and affective style was found.
Cerebral Asymmetry:
Affective
Styles and the Perception of Approach-Withdrawal Emotions
The perception and processing of emotions is a complex procedure in the brain. Currently there are two hypotheses regarding which hemisphere, the right or the left-brain processes which emotions. The most common is the valence hypothesis. This states that the right hemisphere is dominant in the processing of negative emotions, and the left hemisphere is dominant for positive emotions (Rains, 2002).
The valence hypothesis has been challenged. Several studies have yielded contradictory results. A study by Asthana and Mandal (2001) did not find a lateralization pattern of the processing of emotions according to the hypothesis. This study tested normal men with no brain damage. To test for cerebral asymmetry faces with happy or sad emotions are shown to the right and left visual fields. Visual fields are contra lateral to each hemisphere of the brain. Therefore objects presented to the right visual field go towards the left hemisphere of the brain, and objects shown to the left visual field are routed to the right hemisphere (Rains 2002). It was not clear that the left hemisphere processes all positive emotions and the right hemisphere processes all the negative emotions through this experiment. This particular study found a lateralization of negative emotions only. Sad facial emotions were seen as more expressive in the left visual field than in the right visual field (Asthana & Mandal, 2001). There was no asymmetry of happy faces found. This is one study that shows results not conducive to the valence hypothesis.
A second study by Crews, Jr. and Harrison (1994) looked at cerebral asymmetry and facial affect perception in women who were depressed and non-depressed. It was hypothesized that women with a depressed mood would show significantly slower overall reaction times to emotional facial stimuli than non-depressed women, and sad faces would be identified quicker within the left visual field than the right visual field. This study found that depressed women have significantly quicker reactions times for sad images presented in the right visual field, left hemisphere, than non-depressed women. When presented to the left visual field, depressed women identified happy faces reliably more quickly than non-depressed women, and happy faces were also identified quicker in the left than the right visual field. Overall, for sad faces non-depressed women had significantly faster reaction times to sad faces shown in the left visual field. There was a lack of asymmetry in reaction times for sad faces in the left and right visual fields for depressed women. Depressed women processed sad faces relatively the same in both visual fields. The results yielded from the study do not support the researchers’ hypothesis. There is no concrete evidence to show that emotions are processed by their hedonic value. Again this study provides contradictory support for the valence hypothesis.
A
possible theoretical vehicle to unravel the emotion lateralization controversy
is by the addition of the approach-withdrawal hypothesis. The approach system facilitates appetitative
behavior and generates certain types of positive affect that are
approach-related; for example an emotion that occurs as an individual moves
closer to a desired goal. The withdrawal
system facilitates the withdrawal of an individual from sources of aversive
stimulation or organizes an appropriate response to a threat (Davidson,
A study by Harmon-Jones and Allen (1998) looked specifically at anger. The approach-withdrawal dimension rather than valence is thought to underlie the asymmetry because positive affective states are inferred to reflect approach tendencies and negative affective states are inferred to reflect withdrawal tendencies. Harmon-Jones and Allen (1998) decided to look at anger because individuals with high levels of approach motivation had high levels of positive affect as well. To test whether valence or direction underlies the asymmetry an approach motivational tendency with a negative valence needed to be tested.
Many researchers have studied the approach-withdrawal dimension of emotions. One study by Davidson, Ekman, Saron, Senulis, and Friesen (1990) found that activation asymmetry in the anterior cortical regions discriminates between positive and negative emotions that are associated with approach and withdrawal. For this study the participants were hooked to an EEG machine, and watched film clips. Two clips were positive and two were negative. Disgust is considered a withdrawal emotion, and happiness is an approach emotion. All of the participants showed more right sided frontal activation during disgust versus happiness. The left side showed more activation for happiness versus disgust (Davidson et al., 1990). There is evidence from this study to support the approach-withdrawal hypothesis.
Lesion
studies support the approach- withdrawal hypothesis as well. It has been found that individuals with
damage to the right hemisphere are more impaired in the perception of facial
emotions. Right hemisphere damaged
patients in one study were significantly less accurate compared to left hemisphere
damage patients in the perception of negative and withdrawal emotions than for
positive and approach emotions (Mandal, Borod, Asthana, Mohanty, Mohanty, &
Koff, 1999). Other studies have found
that damage to the left hemisphere will lead to an increase in the incidence of
depressive symptoms. This could be due
to the fact that these people can process negative and withdrawal emotions more
efficiently than positive and approach emotions (Davidson,
Individual differences play an important role in the asymmetry of the prefrontal cortex. Emotion facilitates decision making, influences learning and memory, provides the motivation for critical action in the face of environmental incentives, and it is the basis for individual differences. Emotion is one of the key components of personality and the vulnerable factors that leave people at risk for psychopathology (Davidson et al., 2000). Specifically affective states differ among people, and this can influence the hemispheric lateralization and the perception of emotions. Affective states are consistent individual differences in emotional regulation and reactivity. Specifically this is how one responds to emotional challenges, cognitive processes, and dispositional moods (Davidson, 2000). For example the failure to recover rapidly after a negative event can lead to vulnerability to mood and anxiety disorders, especially when a negative affective style is mixed with frequent exposure to negative events over a sustained period of time. There would be sustained elevations in multiple systems that are activated in the response to negative events when an individual fails to adequately recover from them. The contrary is true for those who can recover rapidly from after negative events. This person is resilient. Resiliency is the maintenance of high levels of positive affect and well being when faced with adversity. An individual with a positive affect can still experience negative affect, but it does not persist, for they have the ability to overcome aversive events quickly (Davidson, 2000). Affective styles can influence how resilient one will be in difficult situations.
Generally people with increased right-sided activation will show an increase in vulnerability to moods, emotions, and psychopathology linked with withdrawal. These people are therefore more susceptible to the emotions of disgust and fear, more dispositional negative affect, and more weakness to anxiety disorders that have a strong withdrawal dimension, like phobias (Davidson, 1993). Individuals with elevated right-side frontal activation state more intense levels of disgust and fear in response to short film clips intended to draw out these emotions than did subjects with left-sided activation (Davidson, 1993). A study by Davidson et al. (2000) investigated this pattern of activation in individuals and their responses to the emotions of fear and disgust.
Davidson et al. (2000) studied how inducing approach-related positive and withdrawal-related negative affective states would affect the asymmetry in the prefrontal cortex. It was found that emotions like fear and disgust, withdrawal and negative emotions, increase relative right-sided prefrontal activation. The opposite pattern of activation occurred when an approach and positive affective state was induced. Individuals with more left-sided prefrontal activation reported more positive affect to the positive film clips, and those with more right-sided prefrontal activation reported more negative affect to the negative film clips (Davidson et al., 2000). It would be important to study negative emotions that have an approach tendency. This would solidify the idea that emotions are processed based on their motivational nature rather than their valence.
From the previous research it can be hypothesized that individuals with a negative affective style will process withdrawal emotions quicker in the right hemisphere than individuals with a positive affective style. Also people will process approach emotions faster with a positive affective style opposed to a negative affective style in the left hemisphere. Finally the valence of the emotions, positive or negative, will not determine how they are processed; rather the approach-withdrawal dimension of the emotions will influence how quickly they are processed. Therefore approach emotions will overall be processed more rapidly in the right visual field, and withdrawal emotions will be processed the quickest in the left visual field.
Method
Participants
Fifteen
male and 15 female college students from
To assess the affective style of the participants the Positive and Negative Affect Schedule (PANAS) will be used. This is a self-report emotion measure. The PANAS is a trait measure of negative and positive affect. It contains a total of 20 emotion descriptors. Ten of them assess the high activation pole of negative affect, and the other 10 assess high activation pole of positive affect. The GEN version of the PANAS was used because it allows respondents to indicate how they feel in general. The internal consistency reliability of the Positive and Negative Affect scales of the PANAS-GEN is .88 and .87 (Jacobs & Snyder, 1996).
For this study stimulus slides representing different emotions were chosen from the standardized series of Ekman slides. These slides showed facial emotions of disgust, surprise, anger, and happiness (Fourie, 1995). Disgust, for example, is considered a withdrawal emotion because the withdrawal entails terminating the sensory input, which could be olfactory, oral, or visual (Davidson et al., 1990). Along with the expressive faces, there were also neutral faces of the same person to match the other slides. The pictures were displayed to the participants through an electronic tachistoscope that is capable of exposing the photographs from 1 ms to 1000 ms. One hundred fifty milliseconds was the exposure duration of each photograph (Asthana & Mandal, 2001).
Design
& Procedure
A 2 (visual field) x 2 (emotion type) x 2 (affective style) factorial design was performed. Participants received the images in both visual fields. They were shown both types of pictures, the approach and withdrawal pictures. This experiment consisted of eight conditions, with fifteen participants in each condition. Each participant was shown two pictures in each condition, for a total of thirty reaction times in each category.
The participants were given the PANAS-GEN first. They were then divided into two groups of 30, one group with a positive affective style and the other with a negative affective style. Once this was completed they viewed the four emotions depicted on the faces on the slides. The participants were told to look through the central eyepiece of the tachistoscope and fixate their eyes at the central point after a ready signal. Next the slides, in a counterbalanced sequence, were shown in either the right or left visual field. The slides were counterbalanced through a Latin square. The slide with the emotional face was shown to one visual field and the neutral face was shown to the opposite visual field. Visual field was counterbalanced as well through ABBA counterbalancing. All together the participants saw 8 slides, two of each type of emotion. Each emotion was viewed once in the left and right visual field. The participants were to push the button of the visual field that contained the most emotional face. The reaction time was then recorded for each photograph the participants viewed.
Results
It was found that in the right visual field a person with a positive affective style processed approach emotions on the average of 0.73 seconds, and a standard deviation of 6.945E-02. On the other hand someone with negative affective style processed approach emotions on average 0.79 seconds, SD=7.391E-02. (See Table A1). In the left visual field approach emotions were processed at 0.89 seconds (SD= .1100) by positive affect people and 0.97 seconds (SD= .2222) by negative affect people. (See Table A2) There was a significant interaction between affective style, visual field, and type of emotion. The F(1,232) = 4.5, p = 0.035. (See Figures B1 & B2) There were also main effects of the type of emotion, approach or withdrawal F(1,232) = 4, p = 0.0467, and of affective style F(1,232) = 6, p = 0.015. In conjunction with this there were also significant interactions between visual field and emotion type F(1,232) = 75, p<.0001, visual field and affective style F(1,232) = 4.5, p = 0.035, and affective style and emotion type F(1,232) = 39, p<.0001. (See Table A3)
Discussion
These results support the hypothesis that individuals with a negative affective style processed withdrawal emotions quicker than the approach, and positive affective style people processed the approach emotions quicker than the withdrawal. The significant three-way interaction shows that the proficiency of processing emotions not only depends on the visual field in which the emotional information is presented to, but the affective style of the individual and the type of emotion being shown. Overall people with a negative affective style tend to process withdrawal emotions quicker in both visuals fields, opposed to someone with a positive affective style. On the contrary, an individual with a positive affective style processes approach emotions the quickest in both visual fields.
The results support the approach-withdrawal hypothesis as well. People tend to process emotions based on the motoric component rather than the valence dimension. The valence of the emotions had no bearing on how quickly they were processed. This study therefore contradicts the valence hypothesis. Approach emotions were perceived more rapidly in the right visual field, left cerebral hemisphere, and withdrawal emotions were processed faster in the left visual field, right cerebral hemisphere. These results are conducive with a study by Davidson (1993) that found greater left-sided activation associated with approach emotions, and greater right-sided activation linked with withdrawal emotions. The evidence from this study suggests that approach and withdrawal related systems are localized in different cerebral hemispheres. The left frontal hemisphere is implicated in approach related emotional behavior, and withdrawal related emotions are implicated in the right frontal hemisphere (Davidson, 1993).
This study supports the idea that emotions are processed based on whether the emotion is approach or withdrawal. There are implications for future studies. The study lacked empirical evidence to show which hemisphere of the brain was actually activated during the presentation of the photographs. An EEG or PET scan should be used so the experimenter can visually see what hemisphere is being activated during the task. Also participants with a negative affective style, increased right frontal activation should demonstrate an increase in vulnerability to moods, emotions, and psychopathology associated with withdrawal. These individuals should be more susceptible to emotions of disgust and fear, should show more dispositional negative affect, and should be more prone to anxiety disorders, especially phobias, which include a strong withdrawal component (Davidson, 1993). This could be studied more in depth by eliciting specific mood states in the participants and to see how they react based on affective style. This study provides increased support for the approach-withdrawal hypothesis, but there are still many aspects of emotional processing and affective style that needs to be studied.
References
Asthana, H.S., & Mandal, M.K. (2001). Visual-Field Bias in the Judgment of Facial
Expression of Emotion. Journal of General Psychology, 128, 21-29.
Crews, W.D., Jr., & Harrison, D.W. (1994). Cerebral Asymmetry in Facial Affect
Perception
by Women: Neuropsychological Effects of Depressed Mood.
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Davidson, R.J., Ekman, P., Saron, C.D., Senulis, J.A., & Friesen, W.V. (1990).
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Appendix
A
Table A1
|
Right Visual Field (Left Hemisphere) Mean
Reaction Times (Seconds) |
|
Positive Affect 0.73 6.945E-02 1.07 .2856 Negative Affect 0.79 7.391E-02 0.84 7.908E-02 |
|
|
Table A2
|
Left Visual Field (Right Hemisphere) Mean
Reaction Times (Seconds) |
|
Positive Affect 0.89 .1100 0.85 8.006E-02 Negative Affect 0.97 .2222 0.76 .1127 |
|
|
Table A3
ANOVA Summary Table
|
Source |
df |
MS |
F |
P |
|
Visual Field (A) Emotion Type (B) Affective Style (C) A x B A x C B x C
A x B x C Error Total |
1 1 1 1 1 1 1 232 239 |
0.01 0.08 0.12 1.5 0.09 0.78 0.09 0.02 |
0.5 4 6 75 4.5 39 4.5 |
0.48 0.047 0.015 <0.0001 0.035 <0.0001 0.035 |
Appendix B
Figure B1. Average reaction times in the right visual field as a function of affective styles and approach or withdrawal emotions.
Right Visual Field
Figure B2. Average reaction times in the left visual field as a function of affective style and approach or withdrawal emotions.
Left Visual Field
