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Marta Isabel Vanegas-Arroyave, Annabelle Blangero, Simon Kelly; Direct neurophysiological measurement of surround suppression in humans. Journal of Vision 2014;14(10):50. doi: https://doi.org/10.1167/14.10.50.
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© ARVO (1962-2015); The Authors (2016-present)
Surround suppression is a well-known example of contextual interaction in visual cortical neurophysiology, whereby the neural response to a stimulus presented within a visual neuron's classical receptive field is suppressed by the presence of surrounding contrast. Human psychophysical reports present an apparent analog to these single-neuron effects: stimuli appear lower-contrast when embedded in a surround. Surprisingly, surround suppression effects have not been demonstrated in human electrophysiology to bridge between perceptual reports and neuronal responses. We recorded electroencephalography (EEG) in sixteen subjects while passively viewing a series of full-screen stimuli, in which a "foreground" stimulus of different contrasts flickered over various static "surround" patterns. The flickering foreground elicits a steady-state visual evoked potential (SSVEP) over posterior scalp, from where we derived corresponding contrast response functions. We tested both parallel and orthogonal surrounds, both peripheral and foveal foregrounds, and both low and high flicker frequencies (7.2Hz and 25Hz). Using the same flickering stimulus, participants also performed a psychophysical matching task in which an isolated foreground (match, varying contrast) was compared to a surround-embedded foreground (test, fixed at 50% contrast). We demonstrate marked suppression of the foreground response which scales with the contrast of the surround. In keeping with both human psychophysics and animal neurophysiology, we found that suppression was stronger for surrounds that matched the foreground in orientation, and for peripheral compared to foveal foregrounds. This pattern was reproduced in psychophysical reports of perceived contrast in the same individuals, and the degree of electrophysiological and psychophysical suppression was correlated across subjects. Analysis of amplitude changes over time revealed effects of short-term contrast adaptation, which variously caused the foreground signal to fall or grow over time depending on the relative contrast of the surround contrast, consistent with steeper adaptation of the suppressive drive.
Meeting abstract presented at VSS 2014
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