Abstract
Several studies have found that developmental prosopagnosics (DPs) have face perception deficits when using face matching tests and also that these deficits can be quite varied across DPs. However, it is currently debated what underlies these deficits and whether there is a single vs. multiple mechanisms. One important potential mechanism, holistic face processing, has often been shown to be deficient in DPs. Additionally, DPs have also exhibited poorer facial feature discrimination, particularly with the eye region. Some researchers have posited that prosopagnosics' eye processing deficits may result from reduced holistic processing abilities, e.g., numerous eye region elements overwhelming limited holistic processing abilities, but this has not been empirically tested. In the current study, we recruited a large group of DPs (N=69) and controls (N=45) and administered face matching tasks (Computerized Benton, Cambridge Face Perception Test) to assess face perception deficits, along with a holistic face processing task (Part-whole), and internal/external feature discrimination task (Georges task). Compared to controls, DPs were significantly worse at face matching (DP mean z-score=-1.05/SD=1.2), had reduced holistic processing (DPs: M=-.62/SD=.41, controls: M=-.03/SD=.52, p<.01), and had less accurate inner feature discrimination performance, particularly of the eyes (DPs: M=.63/SD=.08, controls: M=.74/SD=.06, p<.001). In contrast, DPs performed numerically better than controls at discriminating outer features (forehead/chin). Notably, when including holistic processing and eye processing into a regression predicting DPs' face-matching abilities, we found that each predicted unique variance (total model R2=.27). Further, mediation analyses indicated that both eye discrimination ability and holistic processing partially mediated each other’s relationship with face matching ability. Finally, we found dissociations in DP cases where individuals had significantly impaired holistic processing but normal eye processing abilities and vice versa. Together, this suggests that holistic processing and eye processing may represent partially overlapping but distinct mechanisms and uniquely contribute to DPs' face perception deficits.