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

Steady-state visually evoked potential is modulated by the difference of recognition condition

Recent researches revealed that the EEG component caused by the flickering visual stimulus, which is called steady-state visually evoked potential (SSVEP), might be a potential index for object recognition. This study examined whether SSVEP reflects different states during object recognition. In one trial, a binary image (BI), which is difficult to recognize, was followed by a grayscale image (GI) of the same object as the answer. Both BI and GI were presented in a flickering manner at a frequency of 7.5 Hz. Participants were first asked to answer whether they could recognize BI. Then, after GI was shown, participants were requested to answer whether they recognized it. We analyzed the evoked and induced component of SSVEPs from the two recognition conditions. As a result, the SSVEPs to BI were significantly larger than that to GI. In addition, induced component to GI after the BI was unrecognized was smaller than after the BI was recognized. The present data provide evidence that SSVEPs reflect a transition of cognitive state to ambiguous figures is reflected.

An objective, sensitive and ecologically valid neural measure of rapid human individual face recognition

Humans may be the only species able to rapidly and automatically recognize a familiar face identity in a crowd of unfamiliar faces, an important social skill. Here, by combining electroencephalography (EEG) and fast periodic visual stimulation (FPVS), we introduce an ecologically valid, objective and sensitive neural measure of this human individual face recognition function. Natural images of various unfamiliar faces are presented at a fast rate of 6 Hz, allowing one fixation per face, with variable natural images of a highly familiar face identity, a celebrity, appearing every seven images (0.86 Hz). Following a few minutes of stimulation, a high signal-to-noise ratio neural response reflecting the generalized discrimination of the familiar face identity from unfamiliar faces is observed over the occipito-temporal cortex at 0.86 Hz and harmonics. When face images are presented upside-down, the individual familiar face recognition response is negligible, being reduced by a factor of 5 over occipito-temporal regions. Differences in the magnitude of the individual face recognition response across different familiar face identities suggest that factors such as exposure, within-person variability and distinctiveness mediate this response. Our findings of a biological marker for fast and automatic recognition of individual familiar faces with ecological stimuli open an avenue for understanding this function, its development and neural basis in neurotypical individual brains along with its pathology. This should also have implications for the use of facial recognition measures in forensic science.