Implicit responses to face trustworthiness measured with fast periodic visual stimulation.

People rapidly and spontaneously form trustworthiness impressions based on facial appearance. Studies using functional magnetic resonance imaging find that activity in the amygdala and other brain regions tracks with face trustworthiness, even when participants are not explicitly asked to judge face trustworthiness. The current study investigated whether it would be possible to detect implicit responses using another method: fast periodic visual stimulation (FPVS). While scalp electroencephalogram (EEG) was recorded, participants viewed sequences of faces in which a single base face was presented at a rate of 6 Hz and oddball faces with different identities were presented every fifth face (6 Hz/5 = 1.2 Hz). Within a given sequence, the oddball faces were all either less trustworthy-looking or trustworthy-looking. The base face either matched the oddball faces on trustworthiness or did not match, so that the experiment had a 2 (trustworthiness of oddball) × 2 (match between base/oddball faces) design. Although participants' task was unrelated to the faces, the trustworthiness of the oddball faces had a strong influence on the response at 1.2 Hz and its harmonics. There was a stronger response for sequences with less trustworthy- versus trustworthy-looking oddball faces over bilateral occipitotemporal sites, medial occipital sites, and beyond. In contrast, the match in trustworthiness between the base face and the oddball faces had only a minimal effect. The effect of oddball type was observed after a short recording time, suggesting that FPVS offers an efficient means of capturing implicit neural responses to face trustworthiness.