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Charles C.-F. Or, Bruno Rossion; Category-selective response to periodic face stimulations in natural-image sequence degrades nonlinearly with face omissions. Journal of Vision 2019;19(10):258a. doi: https://doi.org/10.1167/19.10.258a.
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© ARVO (1962-2015); The Authors (2016-present)
Periodic presentations of variable natural face images in a rapid sequence of variable images of nonface objects elicit sensitive category-selective neural response captured in the human electroencephalogram (EEG) objectively at the periodic face frequency (Rossion et al., 2015, J Vis). Here, we test the resistance to degradation of the face-selective response by systematically varying the proportion of periodic face occurrence in the nonface object stream. High-density EEG was recorded from 16 observers during presentations of 54-s sequences of random object images sinusoidally contrast-modulated at F = 12 Hz (i.e., 12 images/s; 83-ms stimulus-onset asynchrony). Observers performed an orthogonal task by responding to random colour changes of a central fixation cross. There were 9 conditions. In the 100% condition, natural face images were embedded in the sequence always at a fixed interval of F/9 (1.33 Hz; every 9th image). In other conditions, a proportion of periodic face events was omitted, replaced by nonface object images. The percentages of periodic face events tested in the 9 separate conditions were 0% (i.e., no face presented), 12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, and 100%. Selective responses to faces recorded at 1.33 Hz and harmonics (2.67 Hz, etc.) mainly over occipito-temporal areas emerged significantly only at 25% of face images and followed a nonlinear power-function relationship (coefficient: 1.54, sum of scalp-averaged responses over significant harmonics) with the percentage of periodic face events. Removing half of the periodic face events reduced the response by 66%. The results reveal that a face-selective neural response results from complex, nonlinear comparisons between face exemplars and nonface objects.
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