Brain responses for the subconscious recognition of faces

We investigated the event-related responses following subthreshold and suprathreshold stimulation with facial and non-facial figures using magnetoencephalography (MEG) and EEG recordings to clarify the physiological nature of subconscious perception. Event-related magnetic fields and potentials were recorded from the right hemisphere in eight healthy subjects. Three types of stimulus, i.e., facial image (Face), letters of the alphabet (Letters) and random patterns of dots (Dots), with different presentation periods, subthreshold (16 ms), intermediate (32 ms) and suprathreshold (48 ms) were visually presented in a random order. A psychological discrimination task using the same stimuli was also employed. Clear MEG and EEG responses were recorded for all the stimuli, but the amplitude of the responses was largest for Face and smallest for Dots even in the subthreshold stimulation. The equivalent current dipoles (ECDs) for Face were located around the fusiform gyrus, although the correlation coefficients for ECDs were low under subthreshold and intermediate conditions. The ECDs for Letters and Dots were not estimated with reliable correlation coefficients. The results from the psychological task correlated with the dominancy of face recognition. Face perception was processed differently in the subthreshold condition as well as suprathreshold condition. The subconscious recognition of face might be processed around the fusiform gyrus.