Abstract
The introduction of face masks during COVID-19 presents a potential challenge for human face perception and recognition. Face masks possibly hinder the holistic processing of faces leading to difficulty in facial recognition. Our present study aims to investigate this issue by probing the neuropsychological mechanisms of face recognition, while also exploring a possible learning effect observed in regularly seen (personally familiar) masked faces. Our stimuli consisted of personally familiar, famous, and unfamiliar Indian faces in masked and unmasked conditions. 31 subjects participated in a 2-back task wherein 450 trials were balanced within and across blocks to represent all conditions identically, while behavioral and EEG (12 subjects) responses were recorded. A post-experiment questionnaire was used to validate subjects’ prior familiarity with stimuli displayed. A two-way ANOVA showed significant effects of familiarity and mask-conditions on performance-accuracy (F(2,46)=9, p<0.001; F(1,23)=7.74, p<0.05, respectively) and reaction-time (RT) (F(2,46)=6.29; p<0.01; F(1,23)=7.55, p<0.05, respectively). The highest performance accuracy was observed for familiar and unmasked faces and the least for unfamiliar and masked ones, whereas RTs followed expected reverse trends. Notably, the difference in performance accuracy between unmasked and masked famous faces was more prominent (p<0.001) than that for familiar faces (p=0.02). Furthermore, the difference in mean RT between unmasked and masked famous faces was significantly larger (p<0.001) than that for familiar faces (p=0.18). This is suggestive of a learning effect found for regularly seen masked faces. Masked unfamiliar faces contributed to most false-positive responses (F(5,115)=19.88, p<0.00001), indicating the inherent difficulty in processing novel masked faces compared to known ones. ERP analysis revealed significant effects of familiarity and mask-conditions post 250 ms in occipito-parietal electrodes, with familiar faces showing comparatively more sustained negativity across conditions. Our study suggests that personal familiarity aids perceptual learning of masked faces, and this learning may not generalize across familiarity levels.