Tracking the emergence of hyperfamiliarity for faces: Late covert discrimination followed by hyperfamiliarity due to disrupted post-perceptual processes

Nell is a 49-year-old woman who had a severe migraine in August 2020. Since then, every face she has looked at has felt familiar. In an old-new test, she performed perfectly with old faces but miscategorized 63% of the new faces. She scored at chance when selecting the celebrity from face pairs consisting of a celebrity and the celebrity’s doppelganger. When presented with 318 famous and 314 non-famous faces during an EEG experiment, Nell categorized every face as “probably familiar” or “definitively familiar”. However, like typical participants, her N250 and P600 were stronger for famous than non-famous faces. While judging whether two sequentially-presented faces showed the same person, Nell inaccurately reported that similar-looking different pairs matched on 91% of trials, yet the N250r over the left hemisphere distinguished between same-identity and different-identity pairs. Nell’s ERP results indicate her visual identity face matching is intact and that her hyperfamiliarity arises at post-perceptual stages. To identify neural correlates underlying Nell’s hyperfamiliarity, she participated in an fMRI experiment in which she viewed a compilation of scenes from Game of Thrones (GoT). Nell had not watched GoT before but every face felt familiar to her. Nell’s results were compared with control groups who had (N=23) or had not (N=22) previously watched GoT. Bilateral regions of anterior temporal cortex and hippocampus showed significantly greater inter-subject correlations between Nell and the familiar group than between Nell and the unfamiliar group. Functional connectivity between face-selective areas in Nell was more strongly correlated with the connectivity of the familiar than the unfamiliar group. Together, Nell’s results indicate that 1) covert discrimination between familiar and unfamiliar faces occurs in hyperfamiliarity, 2) early (N250) and even late discrimination (P600) between familiar and unfamiliar faces can fail to reach awareness, and 3) post-perceptual processes modulate information about familiarity in face-selective areas.