Abstract
The face inversion effect (FIE) is considered a key marker of holistic face processing; participants are slower and less accurate when judging the identity of inverted compared to upright faces. While this effect is robust in neurotypical adults, the FIE in developmental prosopagnosia (DP) – a neuro-developmental condition associated with difficulties recognising familiar and distinguishing unfamiliar faces – has not been consistently replicated. In DP, the absence of a disproportionate impairment when perceiving inverted faces has been attributed to an impairment of holistic processing. However, this effect could likewise be attributed to the difficulty of matching tasks previously used; if the accuracy of upright identity judgements are close to chance in DP, inversion will cause a smaller drop in performance relative to controls. Here, we compared the FIE in 12 DPs and 12 age- and gender-matched controls using sensitive time-accuracy function analysis. On each trial, participants viewed a single face presented for one of ten durations (1, 2, 3, 4, 6, 8, 10, 14, 18, 24 frames), and participants were asked to make a binary gender (‘male’/’female’) judgement. The point at which each observers’ performance reached asymptote (i.e. where performance stopped improving as a function of increased stimulus presentation time) was modelled. As expected, we found a significant effect of orientation on asymptote level, with performance for upright faces reaching a higher asymptote level than inverted faces. Importantly, this FIE was found in both the control and the DP group, despite the DP group achieving significantly lower asymptotes than the controls overall. These results suggest that, when a sensitive task is used, it is possible to observe the FIE in DP. The results also challenge the view that face processing impairments seen in DP can be explained by deficits in holistic processing.