Using steady-state visual evoked potentials (SSVEP) to measure brain responses to faces and objects

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The proposed research investigates the neural correlates of human face and object perception using steady-state visual-evoked potentials (SSVEP). It has been shown that repetitive stimulation of the human visual system produces oscillations in the electroencephalogram (EEG) that mimics the frequency of the repeating stimulus – the SSVEP (Regan 2009). The proposed experiments will employ an adaptation paradigm in which an adapting face of the same identity (e.g., “Joe”) is repeatedly flashed on the screen at a periodic rate of presentation (4 Hz). Based on a previous study (Rossion & Boremanse, 2011), the continuous presentation of the same face identity produces a reduction in the neural signal (i.e., repetition suppression effect). In the test phase, faces of different identities (e.g., “Fred”, “Bob”, “Bill”, etc.) are shown at the rate of stimulation used for adaptation. The presentation of different faces cause an abrupt increase in the EEG signal indicating that the SSVEP is sensitive to the changing identities of individual faces. The advantages of the SSVEP technique over traditional event-related potentials (ERPs) are that the method yields a high signal-to-noise ratio, requires substantially fewer experimental trials and is a robust measure of perceptual discrimination in high-level vision. However, it is not known if the SSVEP is responsive to the effects of perceptual experience and learning. These questions are addressed in the current proposal by testing real world and laboratory-trained experts. In the first series of experiments, real world bird experts who have extensive experience to birds and mono-racial people who have extensive experience to own-, but not other-race faces will be studied. We hypothesize that bird experts and own-race face experts will exhibit a greater SSVEP to stimuli in the domain of expertise (i.e., birds for bird experts, own-race faces for own-race experts) than novices. Moreover, SSVEP differences will be correlated with differences in recognition of objects and faces from the domain of expertise. Second, we will investigate the acquisition of perceptual expertise in a laboratory training studies. We predict that it is the kind, not the amount of perceptual experience that determines perceptual expertise and modulates the strength of the SSVEP signal. In the final set of experiments, we will examine whether the magnitude of the SSVEP distinguishes individual differences in face recognition and inter-group differences between neurotypical people and a population with known face recognition deficits (i.e., people on the autism spectrum). In summary, the proposed program of research fills a critical gap in our understanding of mechanisms that guide the processes of high-level vision, linking the observer’s perceptual experience and abilities with differences in brain activity.