Face Recognition and Cortical Responses Show Similar Sensitivity to Noise Spatial Frequency

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Abstract
To find cortical correlates of face recognition, we manipulated the recognizability of face images in a parametric manner by masking them with narrow-band spatial noise. Face recognition performance was best at the lowest and highest noise spatial frequencies (NSFs, 2 and 45 c/image, respectively), and degraded gradually towards central NSFs (11–16 c/image). The strength of the 130–180 ms neuromagnetic response (M170) in the temporo-occipital cortex paralleled the recognition performance, whereas the mid-occipital response at 70–120 ms acted in the opposite manner, being strongest for the central NSFs. To noise stimuli without faces, M170 was small and rather insensitive to NSF, whereas the mid-occipital responses resembled closely the responses to the combined face and noise stimuli. These results suggest that the 100 ms mid-occipital response is sensitive to the central spatial frequencies that are critical for face recognition, whereas the M170 response is sensitive to the visibility of a face and closely related to face recognition.