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Sven P. Heinrich, Ad Aertsen, Michael Bach; Striking Gestalt modulates EEG gamma activity — but not in accordance with the temporal binding hypothesis. Journal of Vision 2002;2(7):230. doi: 10.1167/2.7.230.
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© 2017 Association for Research in Vision and Ophthalmology.
The binding of stimulus features into the percept of a coherent object is a fundamental task of the visual system. According to the temporal binding hypothesis, this might be coded by neural synchronization. Animal studies suggest gamma-range (30–100 Hz) neural oscillations to be involved in this process. Reports about binding-related oscillations in the human EEG are contradictory, though. Most previous experiments were based on a stimulus-onset paradigm. Thus, the EEG always contained responses to trivial local stimulus changes in addition to binding-related components. We used a new approach with a Gestalt emerging from a continuous movement of stimulus elements without any temporal discontinuances. EEG was recorded from 18 subjects. 3 different stimuli were presented repeatedly in randomized order within each experimental block: a Gestalt consisting of a line grid, the same Grid rotated by 45°, and a stimulus without Gestalt (random line arrangement). Before each block, subjects were instructed to attend to one of the 3 stimuli and indicate its occurrence by pressing a button. For each of the 3 possible tasks a total of about 140 trials per stimulus were recorded. The stimuli produced a striking Gestalt percept and elicited strong event-related potentials with a weak task dependence. Grand-mean 30–100 Hz gamma activity was assessed. An ANOVA applied to 3 perceptually relevant time intervals indicates a significant effect of task (p<0.05), stimulus (p<0.05), and time interval (p=0.001). The effects were small, though, and the characteristics were not as predicted by the binding hypothesis. E.g., differences between both Gestalt stimuli, though perceptually similar, were larger than between Gestalt and non-Gestalt stimuli and occurred mainly before the stimulus had reached a configuration that allowed for perception or identification of a Gestalt. Thus, the striking change of Gestalt is not accompanied by any marked modulations of gamma activity.
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