Face recognition and cortical responses show similar sensitivity to noise spatial frequency

To find cortical correlates of face recognition, we manipulatedthe recognizability of face images in a parametric manner bymasking them with narrow-band spatial noise. Face recognitionperformance was best at the lowest and highest noise spatialfrequencies (NSFs, 2 and 45 c/image, respectively), and degradedgradually towards central NSFs (11–16 c/image). The strengthof the 130–180 ms neuromagnetic response (M170) in thetemporo-occipital cortex paralleled the recognition performance,whereas the mid-occipital response at 70–120 ms actedin the opposite manner, being strongest for the central NSFs.To noise stimuli without faces, M170 was small and rather insensitiveto NSF, whereas the mid-occipital responses resembled closelythe responses to the combined face and noise stimuli. Theseresults suggest that the 100 ms mid-occipital response is sensitiveto the central spatial frequencies that are critical for facerecognition, whereas the M170 response is sensitive to the visibilityof a face and closely related to face recognition.