Abstract
Developmental prosopagnosia (DP) is a neurodevelopmental condition associated with difficulties recognising familiar faces and distinguishing unfamiliar faces. However, the extent to which DP is associated with deficits in processing other facial attributes, such as emotion and gender, is still debated. Recent evidence suggests that when sensitive tasks are used (e.g. where participants are not at ceiling performance), DPs have difficulties recognising emotional expressions relative to controls. The extent to which DPs also have difficulty extracting facial gender is unclear, as findings to date have been mixed. We tested 12 DPs on two sensitive gender categorisation tasks and compared results to that of age- and gender-matched controls. In the first task, trials presented faces drawn from a morph continua that blended an average male face with an average female face. Observers were required to make a binary ‘male’/’female’ judgement on each trial; psychometric functions were modelled using cumulative Gaussians. Results showed that judgement precision, inferred from the slope of each function, was significantly lower in the DP than the control group. In the second task, trials presented stimuli that blended female or male facial identities with a gender-neutral average face. Observers categorised each stimulus as either ‘female’ or ‘male’, and we measured their sensitivity (d′). Task difficulty was manipulated by varying the strength of each facial identity, relative to the weighting of the gender-neutral average face (20–80%, 30–70%, 40–60%, or 50–50%). As expected, categorisation accuracy varied as a function of the strength of the gender signal. However, DPs were significantly less sensitive at all morph-levels than controls. The results from these two studies confirm that, in many cases, visual processing difficulties seen in DP extend beyond the extraction of facial identity. Evidence of gender processing deficits accords with an apperceptive characterisation of DP.