Suppression of 12-Hz SSVEPs when viewing familiar faces: An electrophysiological index to detect recognition.

Criminal investigation often involves finding out what a suspect knows about people, such as victims and confederates, who are involved in the crime. This study explored the possibility of determining a person's recognition of other individuals by analyzing the steady-state visually evoked potentials (SSVEP) triggered by visual oscillations of familiar and unfamiliar faces. In our study, 23 adult (10 men) participants gave subjective familiarity ratings (in a 7-point Likert scale) of >300 celebrities' and strangers' faces. For each participant, ten familiar and ten unfamiliar faces were selected based on his/her ratings. The selected faces were presented at 6 Hz while the participants performed a color change detection task orthogonal to the attributes of faces. The task was designed to maintain participants' visual attention towards the faces throughout the stimulus oscillations. Any difference between conditions would indicate modulation of visual attention by face familiarity. Results showed that the 12-Hz event-related spectral perturbations (ERSPs in decibel) at parietal-occipital electrodes were significantly lower when viewing familiar faces compared to unfamiliar faces. In individual level analysis, 18 out of 23 (78%) participants had significantly lower 12-Hz ERSPs at left parietal-occipital ROI in familiar face than unfamiliar face trials. This is the first study to demonstrate that SSVEPs triggered by stimulus oscillations can reveal people's recognition of faces with only 20 trials per condition and 10-s for each trial.