PURPOSE: The neural mechanism underlying face processing involves both bottom-up sensory processing of a face stimulus and top-down modulation. Face stimuli can elicit specific event-related potentials (ERPs), including N170, vertex positive potential (VPP), and P2, which are based on different bottom-up and top-down interactions at different processing levels. The specific top-down face processing without bottom-up contamination remains largely unknown. Particularly, it is unclear what neural responses manifest the top-down face-specific modulation while bottom-up inputs of physical features of faces are eliminated.
METHODS: This study was to examine the ERP components that are specifically modulated by the face imagery when random ambiguous visual stimuli are presented. Sixteen participants received two blocks of ambiguous stimuli, in which they were instructed to imagine either faces or houses upon looking at the ambiguous stimuli. The waveforms of VPP at the fronto-central sites, and N170 and P2 at the occipito-temporal sites were measured and analyzed.
RESULTS: Both VPP and P2 responses were enhanced by the face imagery compared to the non-face (house) imagery, and N170 disappeared when eliminating the physical face features.
CONCLUSIONS: Ambiguous-stimulus-induced VPP and P2, but not N170, can be modulated by the top-down face-imagery processing when bottom-up face-signal inputs are eliminated.