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Nihan Alp, Naoki Kogo, Goedele Vanbelle, Johan Wagemans, Bruno Rossion; EEG frequency-tagging yields a neural signature of integration of parts into perceptually organized wholes. Journal of Vision 2014;14(10):44. doi: https://doi.org/10.1167/14.10.44.
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© ARVO (1962-2015); The Authors (2016-present)
How does a holistic representation arise in the visual system? Although this question has been under investigation for more than hundred years since Wertheimers seminal work, it is still unclear how the visual system integrates the parts of an object into a whole representation. The general intuition from Gestalt psychology has been that the whole-based activation requires non-linear interactions between the parts but current methods have not been able to pinpoint exactly what they are. Here we applied high-density electroencephalography (EEG) in combination with the technique of frequency tagging (Regan & Heron, 1969) to define an objective trace of a Gestalt in the visual system. Specifically, by using the Kanizsa square figure, we tracked the emergence of an illusory surface. In the "experimental condition", four pacmen were placed to form an illusory square. In the "control condition", the four pacmen were rotated away so that the illusory surface disappeared. The two diagonal pacman pairs were 100% contrast-modulated at different frequency rates (f1= 3.57 and f2= 2.94 Hz) for 13 seconds. Fourier transform of the EEG recordings (12 participants) showed robust low-level responses specifically at these fundamental frequency rates, which did not differ between conditions. Most importantly, strong nonlinear intermodulation (IM) components (e.g., 3.57-2.94=0.63 Hz) appeared in response to the illusory figure. These IMs can only be produced by neuronal populations that integrate the two stimulations nonlinearly (e.g., Boremanse et al., 2013), and they were only present in the experimental condition where all the parts (pacmen) are integrated coherently to form an illusory surface. Moreover, changing the support ratio influenced the amplitude and the distributions of IMs, but not the fundamental frequencies. These results indicate that IM components in EEG provide a neural signature of Gestalt configurations.
Meeting abstract presented at VSS 2014
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