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Research report

Examining the effects of inversion on lateralisation for processing facial emotion
Victoria J. Bourne*
School of Psychology, University of Dundee, UK

article info
Article history: Received 7 October 2009 Reviewed 20 January 2010 Revised 24 January 2010 Accepted 18 March 2010 Action editor Stefan Schweinberger Published online 1 May 2010 Keywords: Face processing Emotional expression Lateralisation Hemispheric specialisations Inversion

abstract
There is an increasing amount of evidence which suggests that each hemisphere is differently specialised for processing facial stimuli, with the right hemisphere specialised for the processing of configural information and the left hemisphere specialised for the processing of featural information. While there is evidence for this distinction from studies of face recognition, it has not been shown in studies of lateralisation for processing facial emotion. In this study the chimeric faces test was used with faces expressing anger, disgust, fear, happiness, sadness or surprise, presented in either an upright or an inverted orientation. When presented upright, a significant right hemisphere bias was found for all six emotions. However, when inverted, a significant left hemisphere bias was found for the processing of happiness and surprise, but not for the processing of negative emotions (although the analysis was approaching significance for anger). These findings support the hypothesis that each hemisphere is differently specialised for processing facial emotion, but contradicts previous work that examined the effects of inversion on chimeric face stimuli. ª 2010 Elsevier Srl. All rights reserved.

1.

Introduction

It is quite widely accepted that there are hemispheric differences in the ability to process faces with the right hemisphere being specialised to a greater extent than the left hemisphere. In terms of processing facial emotion, this right hemisphere dominance has been shown in a wide range of studies using chimeric face stimuli. This behavioural paradigm presents vertically split half faces in which one hemi face is neutral and the other hemi face is expressive. Participants tend to rate a face as more emotive when the emotional expression is shown in the left hemi face (their left visual field) than when the emotional expression is shown in the right hemi face (their right visual field). This left visual field bias is interpreted as reflecting the right hemisphere superiority for face processing and has been shown in a large number of studies (e.g.,

Levy et al., 1983; Bourne, 2005, 2008, in press; Burt and Perrett, 1997). Evidence for the left visual field bias found in the chimeric faces test reflecting right hemisphere superiority for the processing of faces has been shown in two studies of visual field biases in participants with unilateral brain lesions (Bava et al., 2005; Kucharska-Pietura and David, 2003). In both studies, participants with left hemisphere lesions showed the usual right hemisphere bias on the chimeric faces test, whereas those with right hemisphere lesions showed no clear visual field bias. Although there is considerable evidence for the right hemisphere being dominant for the processing of facial emotion, it is important to acknowledge that there are contrasting theories regarding the lateralisation of emotional face processing. The right hemisphere hypothesis suggests that the processing of all facial emotion is lateralised to the right

* School of Psychology University of Dundee, Park Place, Dundee, UK. E-mail address: v.bourne@dundee.ac.uk 0010-9452/$ e see front matter ª 2010 Elsevier Srl. All rights reserved. doi:10.1016/j.cortex.2010.04.003

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hemisphere (Borod, 1992) whereas the valence hypothesis proposes that the processing of