Involuntary Eye-Movement Signatures Differ for Recognition of Oneself, Familiar and Unfamiliar Faces

Miniature, involuntary eye movements occur continuously during fixations. Two important examples of these involuntary movements are pupil dilation, which responds primarily to luminance changes, and fixational eye movements, specifically microsaccades, which perturb the gaze during fixations at a rate of about 1/s. Both movements are primarily functionally-driven but are also subject to modulation by cognitive and emotional influences. Face recognition is a process which is tightly coupled to visual, cognitive, and affective processing. Here, we show that the signatures of both microsaccades and pupil size are different when a face is recognized compared to unknown. We conducted a highly-powered (n=116) visual fixation experiment, comprising two distinct groups. Participants knew the faces of the people in their own group, but not of the other group. We then compared self-recognition (i.e., seeing one's own face), other-recognition (i.e., seeing a familiar face), no recognition (i.e., a stranger's face). The pupil typically constricts in response to new stimuli, followed by a dilation. We show that constriction is attenuated and the dilation increased during recognition compared to unknown faces. This effect is strongest for self-recognition. The microsaccade rate is typically inhibited by stimulus onsets. We find that inhibition is strongest during self-recognition, followed by recognition of familiar faces, and weakest in response to unknown faces. Our results are consistent with findings from the Oddball Paradigm that show stronger pupil dilation and stronger microsaccade inhibition effects in response to the infrequent target stimuli, related to increased attention. The difference in our task was that familiar and unfamiliar faces occurred with the same frequency. Thus, effects can be clearly attributed to recognition processes. Our results shed light on the process of face recognition and indicate a potential use of oculomotor measures in revealing hidden knowledge or in biometric identification procedures.