Functional Specificity In Eye Gaze Processing: Evidence From Developmental Prosopagnosia
The eyes of other people subserve two core functions in human social cognition: gaze perception and face identity recognition. This thesis reports two psychophysical studies that examine the degree of functional specificity between eye gaze processing and face identity processing by testing if various aspects of gaze processing are intact in people with developmental prosopagnosia (DP) – the lifelong inability to recognise face identity. Study 1 investigates spatial integration in eye gaze perception using two tasks. DP and control participants completed one task that measured perception of gaze direction from the two eyes and another that measured the Wollaston illusion (whereby perceived eye gaze is pulled by head rotation; requiring the integration of eye and head direction). Study 2 investigates temporal integration in eye gaze perception using two tasks. The first task measured adaptation effects in eye gaze perception, which reflects sensitivity to gaze direction and its sensory representations. The second task measured serial dependence in gaze perception, which reflects temporal integration of gaze direction and its perceptual stability. Despite their deficits in recognising face identity, DP participants showed normal gaze processing across all studies. These results demonstrate the functional specificity of gaze processing and imply that gaze perception is carried out by dedicated mechanisms not used for processing identity. Our findings align with models of face processing that posit distinct pathways for gaze and identity analysis, and further clarify the selectivity of face processing dysfunctions in developmental prosopagnosia.