Visual mental imagery and perception produce opposite adaptation effects on early brain potentials.

Event-related potentials (ERPs) were recorded during a rapid adaptation paradigm to determine whether visual perception and visual mental imagery of faces recruit the same early perceptual processes. The early effect of face and object adaptors, either perceived or visualized, on test stimuli, was assessed by measuring the amplitude of the N170/VPP complex, typically much larger for faces than for other object categories. Faces elicited a robust N170/VPP complex, localized to posterior ventrolateral occipitotemporal cortex. Both visualized and perceived adaptors affected the N170/VPP complex to test faces from 120 ms post-stimulus, reflecting effects on neural populations supporting early perceptual face categorization. Critically, while perceived adaptors suppressed the amplitude of the N170/VPP, visualized adaptors enhanced it. We suggest that perceived adaptors affect neural populations in the neocortex supporting early perceptual processing of faces via bottom-up mechanisms, whereas visualized adaptors affect them via top-down mechanisms. Similar enhancement effects were found on the N170/VPP complex to non-face objects, suggesting such effects are a general consequence of visual imagery on processing of faces and other object categories. These findings support image-percept equivalence theories and may explain, in part, why visual percepts and visual mental images are not routinely confused, even though both engage similar neural populations in the visual system.