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David Melcher
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience 1–18.
Published: 08 May 2023
Abstract
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Although visual input arrives continuously, sensory information is segmented into (quasi-)discrete events. Here, we investigated the neural correlates of spatiotemporal binding in humans with magnetoencephalography using 2 tasks where separate flashes were presented on each trial but were perceived, in a bistable way, as either a single or two separate events. The first task (two-flash fusion) involved judging one versus 2 flashes, whereas the second task (apparent motion: AM) involved judging coherent motion versus two stationary flashes. Results indicate two different functional networks underlying 2 unique aspects of temporal binding. In two-flash fusion trials, involving an integration window of ∼50 msec, evoked responses differed as a function of perceptual interpretation by ∼25 msec after stimuli offset. Multivariate decoding of subjective perception based on prestimulus oscillatory phase was significant for alpha-band activity in the right medial temporal (V5/MT) area, with the strength of prestimulus connectivity between early visual areas and V5/MT being predictive of performance. In contrast, the longer integration window (∼130 msec) for AM showed evoked field differences only ∼250 msec after stimuli offset. Phase decoding of the perceptual outcome in AM trials was significant for theta-band activity in the right intraparietal sulcus. Prestimulus theta-band connectivity between V5/MT and intraparietal sulcus best predicted AM perceptual outcome. For both tasks, phase effects found could not be accounted by concomitant variations in power. These results show a strong relationship between specific spatiotemporal binding windows and specific oscillations, linked to the information flow between different areas of the “where” and “when” visual pathways.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience 1–12.
Published: 04 April 2023
Abstract
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The brain organizes the continuous flow of sensory input by parsing it into discrete events. In the case of 2 flashes separated by a brief ISI, for example, perception may be of a single flash or 2 distinct flashes, depending on the ISI but also on the speed of processing. A number of studies have reported evidence that participants with a higher EEG peak alpha frequency are able to detect the presence of 2 flashes separated by short intervals, whereas those with slower alpha report only 1 flash. Other studies have not found this correlation. We investigated potential factors that might mask the relationship between individual alpha frequency and visual perception. We recorded resting-state EEG from a large sample of participants ( n = 50) and measured the temporal resolution of visual perception with the 2-flash fusion task. We found that individual alpha frequency over posterior channels predicted the 2-flash fusion threshold, in line with previous studies, but this correlation was significant only when taking into account the steepness of the psychophysical curve of the 2-flash task. Participants with a relatively shallow psychophysical curve, likely reflecting high sensory and/or decision noise, failed to show this relationship. These findings replicate previous reports of a correlation between alpha frequency and visual temporal resolution, while also suggesting that an explanation of two-flash fusion performance that neglects the role of internal noise might be insufficient to account for all individual differences.