Modifications of Visual Field Asymmetries for Face Categorization in Early Deaf Adults: A Study With Chimeric Faces

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.

Keywords: categorization task; chimeric face; early deafness; eye movements; gender; hemispheric laterality.

FIGURE 1

Example of the stimuli used in this experiment. (Top) Blended male and female faces. (Bottom) Chimeric female/male (Bottom left) and male/female (Bottom right) faces.

FIGURE 2

Visual field bias for deaf and hearing participants. Box center and limit give the median, 1st and 3rd quartile. Each data point represents a participant. Filled data points indicate significant bias according to a χ² statistics. Two participants showed a RVF bias (filled dots < 50%).

FIGURE 3

Visual field bias for deaf and hearing participants in Experiment 2. Box center and limit give the median, 1st and 3rd quartile. Each data point represents a participant. Filled data point indicates significant bias according to a χ² statistics. Three participants showed a RVF bias (filled dots < 50%).

FIGURE 4

Proportion of looking time in AOI for the hearing (Top) and deaf (Bottom) group. Black bars give the 95% confidence interval for the mean proportion of looking time.