Neural Correlates of Conscious Face Perception: A Single-Trial Study on the N170 Responses

JOAQUIN NAVAJAS; MARYAM AHMADI; RODRIGO QUIAN QUIROGA

Congreso; 8th Forum of the Federation of European Neuroscience Societies (FENS); 2013

Federation of European Neuroscience Societies (FENS)

When a face is flashed to an observer, a large negative component is elicited in the occipito-temporal cortex at around 170 ms from the stimulus onset (N170). While the selectivity of the N170 to different stimuli has been extensively studied, it remains unclear whether this activity depends on conscious processing of the stimulus. To address this question, we presented brief flashes of faces, coupled with backward masking, and varying degrees of Gaussian noise. Using a double staircase procedure, for each subject we determined the threshold of detection, where they failed to recognize the flash as a face in approximately half of the trials. We compared the activity elicited by subliminal and supraliminal faces and observed that stimuli that reached conscious access elicited a larger N170 component than those that did not trigger conscious perception. Furthermore, we implemented a denoising algorithm based in the Wavelet transform and extracted the single-trial N170 in order to decode participants? report. With this feature as classifier and linear discriminant analysis, decoding performance was above-chance and consistent across subjects. Altogether, these results suggest that activity in the occipito-temporal cortex play a decisive role in the dynamical processing of the stimulus that leads to conscious perception.