Objective Neural Markers of Identity Familiarization via Passive Exposure and Fast Periodic Visual Stimulation EEG

Despite a wealth of information provided by face perception research, the neural processes by which unfamiliar faces become familiar-particularly via passive exposure-remain poorly understood. Here, we introduce a novel fast periodic visual stimulation electroencephalography (FPVS-EEG) paradigm designed to objectively track neural familiarization. Specifically, our paradigm measures the emergence of implicit face-identity familiarity during brief, passive repetition learning, without requiring explicit recognition or task engagement. The paradigm uses ecologically valid stimuli incorporating image variations characteristic of forensic material. We tested 28 (18 females) healthy human volunteers including neurotypical civilians and law enforcement professionals, all with typical face-processing abilities. Neural responses were measured to a 1 Hz tagged oddball identity embedded within a 6 Hz stream of changing base images, using high-quality mugshot and CCTV-like stimuli. Results showed that neural signatures of implicit familiarity can emerge rapidly within minutes of passive exposure but only when high-quality mugshot images are used. These familiarity-related responses were characterized by concurrent neural suppression and enhancement, likely to reflect the co-occurrence of repetition detection and identity learning processes. The FPVS-EEG approach reported here provides an objective and quantifiable measure of implicit, early face learning that could complement behavioral assessments and inform future research on individual differences and applied contexts.