Transient interference of right hemispheric function due to automatic emotional processing
Introduction
Asymmetries in hemispheric involvement for several cognitive functions, most notably for language, have been demonstrated. However, rather than each hemisphere specializing in distinct cognitive processes, the cerebral hemispheres have been characterized as complementary and integrative processing systems [1]. While basic bilateral and complementary organization appears to be true also for emotional processing, neuropsychological [9], electrophysiological [5], [11], neuroimaging [3] and behavioral [23] evidence supports cerebral asymmetries relating to perceiving, expressing, experiencing and responding to emotions. An overall right hemispheric bias for mediating the perception and expression of emotion has been suggested, while the lateralization of functions subservient to emotional experience seems to depend upon the valence of the emotions, with the left hemisphere being more engaged in pleasant and the right hemisphere in unpleasant emotions (for reviews see Refs. [10], [21]). While the evidence for emotion-related asymmetries is robust, there is limited evidence on how this asymmetric hemispheric activation affects other lateralized brain processes.
The cerebral hemispheres may be asymmetrically activated by processes that favor one hemisphere over the other [12]. Furthermore, depending on task-specific factors, this activation may lead to facilitation [12] or interference [8], [13] with other processes performed by the activated hemisphere. Facilitation of perceptual processes may occur due to attentional bias to the contralateral hemifield of the activated hemisphere [12]. This type of facilitation for left visual field (LVF) performance has been shown using threatening words [22]. On the other hand, interference may occur due to limited resources [8], [13]. For example, emotional Stroop studies show interference of task-irrelevant emotional stimuli on cognitive performance [18].
It is clear that emotional processing interacts with cognitive processes in a variety of ways. However, little is known how emotion-related asymmetries in hemispheric activation contribute to this interaction. We examined whether brief, lateralized, task-irrelevant emotional pictures affect subsequent hemispheric visual discrimination performance and whether the valence of the pictures (pleasant, unpleasant or neutral) has an effect. In accordance with the hypothesis of the right hemispheric bias for emotional processing, we predicted greater right hemispheric activation with both pleasant and unpleasant emotional stimuli affecting performance in the contralateral left hemifield. In contrast, according to the valence hypothesis, pleasant emotional stimuli would be predicted to affect the RVF performance and unpleasant stimuli the LVF performance.
Another contributing factor in interactions between lateralized emotional and cognitive processes is spatial attention. According to Stormark et al. [20], emotional stimuli may attract attention leading to improved performance in the location of the emotional stimuli. Bradley et al. [2], on the other hand, has shown attentional bias away from threatening stimuli in nondysphoric subjects leading to improved performance in the opposite location to the emotional stimuli. These reports led us to further investigate how visual performance in a bi-field discrimination task is influenced by the spatial relation between the emotional stimuli and a subsequent target.
Section snippets
Subjects
Eighteen college students (11 females, seven males) with no neurological or psychiatric disorders were recruited and paid for their participation. All subjects were right-handed. The age of the subjects ranged from 18 to 29 years (mean: 22). Each of the subjects gave their consent according to university guidelines.
Stimulus selection
Three sets (pleasant, unpleasant and neutral) of 48 colored pictures were chosen from the International Affective Picture System [4]. The mean pleasure ratings for pleasant,
Results
Repeated analysis of variance (ANOVA) was performed on reaction times (RT) of correct responses with ‘emotional valence’ (pleasant, unpleasant, neutral), ‘picture location’ (pLVF, pRVF) and ‘target location’ (tLVF, tRVF) as factors within subjects and sex as a factor between the subjects. In addition, separate ANOVA's were performed for unpleasant, pleasant and neutral stimuli as well as for comparing unpleasant to pleasant, unpleasant to neutral and pleasant to neutral. The mean RTs to LVF and
Discussion
The current study shows that independent of field of presentation, brief emotional stimuli selectively interfere with right hemispheric visual discrimination performance. Both pleasant and unpleasant stimuli lengthened RTs to targets presented in the LVF, with unpleasant stimuli showing a greater effect. These findings provide additional new evidence for right hemispheric bias in processing emotional information. The data further suggest that regardless of valence, the right hemisphere is
Acknowledgements
We thank Clay Clayworth and Monica Chu for their help. Supported by the Finnish Academy and Grants NS 32893 and NS21135
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