Abstract
Right hemisphere lateralization for face processing is well documented in typical populations. At the behavioral level, this right hemisphere bias is often related to a left visual field (LVF) bias. A conventional mean to study this phenomenon consists of using chimeric faces that are composed of the left and right parts of two faces. In this paradigm, participants generally use the left part of the chimeric face, mostly processed through the right optic tract, to determine its identity, gender or age. To assess the impact of early auditory deprivation on face processing abilities, we tested the LVF bias in a group of early deaf participants and hearing controls. In two experiments, deaf and hearing participants performed a gender categorization task with chimeric and normal average faces. Over the two experiments the results confirmed the presence of a LVF bias in participants, which was less frequent in deaf participants. This result suggested modifications of hemispheric lateralization for face processing in deaf participants. In Experiment 2 we also recorded eye movements to examine whether the LVF bias could be related to face scanning behavior. In this second study, participants performed a similar task while we recorded eye movements using an eye tracking system. Using areas of interest analysis we observed that the proportion of fixations on the mouth relatively to the other areas was increased in deaf participants in comparison with the hearing group. This was associated with a decrease of the proportion of fixations on the eyes. In addition these measures were correlated to the LVF bias suggesting a relationship between the LVF bias and the patterns of facial exploration. Taken together, these results suggest that early auditory deprivation results in plasticity phenomenon affecting the perception of static faces through modifications of hemispheric lateralization and of gaze behavior.
Highlights
Hemispheric specialization of cognitive function in typical adult brain is well documented
We found a significant interaction between Group and the Type of Face (Entire, Chimeric) [F(1,42) = 7.70, p = 0.01], indicating that the increased response times for the Deaf group was important for chimeric faces and not for entire faces
To sum-up on the result of this simulation under the null hypothesis of no left visual field (LVF) bias in the population average, finding 3 individuals with a significant LVF bias is likely (p = 0.23), in contrast, finding 6 individuals is very unlikely (p = 0.017). It is an indirect way of testing the presence of a larger bias in the hearing group, these results point in the same direction than the linear model analysis of the LVF bias: that it is stronger on average and more frequent at the individual level in the hearing population. This experiment was designed to determine if modifications of the hemispheric lateralization for face processing happened in early deaf participants during a gender categorization task with chimeric faces
Summary
Hemispheric specialization of cognitive function in typical adult brain is well documented. Visual Field Asymmetries in Deaf Adults processing abilities would be lateralized toward the right hemisphere. This right hemisphere dominance for face processing has been originally demonstrated, thanks to prosopagnosic patients – patients showing specific inability to recognize faces following brain damage. Prosopagnosics generally suffer from bilateral lesions, a right hemisphere lesion seems sufficient to produce significant impairments in face recognition (De Renzi, 1986; De Renzi et al, 1991). The hypothesis of a right hemisphere advantage for face processing is supported by fMRI results, showing a functional asymmetry in favor of the right hemisphere during face processing, in the Fusiform Face Area (FFA; Badzakova-Trajkov et al, 2010; Rossion et al, 2012; Bukowski et al, 2013)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call