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Joan Liu-Shuang, Anthony M. Norcia, Bruno Rossion; Objective measurement of face discrimination with a fast periodic oddball paradigm. Journal of Vision 2013;13(9):172. doi: 10.1167/13.9.172.
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© ARVO (1962-2015); The Authors (2016-present)
The mechanisms underlying visual objects perception remain poorly understood, especially for visually homogenous categories such as human faces. We propose a novel paradigm using fast periodic oddball stimulation to objectively and rapidly quantify individual face discrimination, separately from a general response to faces. We recorded 128-channel EEG in 20 observers presented with 60-second sequences of face stimuli shown at a constant frequency of 5.88 Hz. One face (A) was repeated throughout each sequence. Different "oddball" faces (B, C…) were introduced at fixed intervals (every 5 faces: 5.88 Hz/5 = 1.18 Hz), resulting in the following sequence structure: AAAABAAAAC... The responses at 1.18Hz and its harmonics (2F = 2.35 Hz, 3F = 3.53 Hz…) were taken as an index of face discrimination. To isolate high-level face perception, we manipulated size (face size randomly varied every cycle), orientation (upright vs. inverted, Experiment 1) and contrast (normal contrast vs. contrast-reversed, Experiment 2). In both experiments, normal faces evoked highly significant responses at 1.18 Hz and its harmonics, particularly on right occipito-temporal channels. Inversion and contrast reversal significantly reduced the oddball responses, while the basic 5.88 Hz response did not differ between conditions. In Experiment 3, we tested the fast oddball paradigm with upright faces in a well-known case of acquired prosopagnosia, PS (Rossion et al., 2003, Brain), who is specifically impaired at individual face perception (e.g., Busigny et al., 2010, Neuropsychologia). Although PS’ general periodic response to faces (5.88 Hz) did not differ from young controls (N=11), her right occipito-temporal oddball response (1.18 Hz and its harmonics) was significantly reduced compared to controls. These observations underline the interest and high diagnosticity of the fast oddball paradigm to assess face discrimination on a neural level.
Meeting abstract presented at VSS 2013
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