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Valerie Goffaux, Corentin Jacques, Andre Mouraux, Frederic Gosselin, Philippe G Schyns; Superstitious perceptions of a face revealed by non phase-locked gamma oscillations in the human brain. Journal of Vision 2003;3(9):94. doi: 10.1167/3.9.94.
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© ARVO (1962-2015); The Authors (2016-present)
In humans, non phase-locked (NPL) brain oscillations in the gamma band (30 – 80 Hz) have been related to the integration of widely distributed cortical representations and are thought to participate in the top-down modulations of visual processes, and more generally in the constructive aspects of perception (Engel et al., 2001). In the present study, we employed the technique of Superstitious Perceptions (Gosselin & Schyns, 2003) to better understand the neurophysiological determinants of the superstitious perception of a face.
Using high-density EEG recording, sixteen observers were asked to detect a face while stimulated with only white noise (400 different templates of 32× 43 pixels, to mirror the aspect ratio of a face). Superstitious perceptions occur whenever the observer believes that a face is present in the white noise. This paradigm is better suited to isolate top-down components of visual processing because white noise is only very weakly correlated with a face signal. The observers detected a face on 36% of the noise templates, on average. When observers reported seeing a face, EEG recordings at posterior-visual scalp regions revealed a NPL increase of gamma (∼40 Hz) oscillation amplitudes centred around 200 ms post-stimulus onset. A classification image rendered the face information that best predicts the superstitious perceptions, and the gamma activity. This image reveals two eyes, bilaterally organized around the X axis, at about 2/3 height on the Y axis. This study shows that NPL gamma oscillations in the human visual system subtend the type of top-down activity required for superstitious visual perceptions.
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