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Maximilian Bruchmann, Kathrin Thaler, Philipp Hintze; Magnetoencephalographic correlates of visible persistence in transient random-dot stimuli. Journal of Vision 2013;13(9):40. doi: 10.1167/13.9.40.
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© ARVO (1962-2015); The Authors (2016-present)
Visible persistence (VP) refers to the perceived presence of a stimulus after its physical offset. Typically, it lasts for several tens of a second and is most prominent in briefly presented stimuli. To create an extreme case of VP, we successively presented two matrices of 600 d05; 600 randomly black and white pixels, where all pixels in an annulus-shaped region reversed polarity between the matrices while all other pixels remained identical. On the transition of the first to the second matrix the luminance flip created the perception of an annulus with an abrupt onset and a gradual offset lasting on average about one second. In a magnetoencephalographic study we presented 19 participants repeatedly with such single-transient-random-dot-stimuli and let them judge the subjective duration of visible persistence on each trial. Based on these trial-by-trial judgments we split the data post-hoc into trials with physically identical stimulation but subjectively short and long durations of VP. We therefore avoided confounding phenomenal differences with physical differences between experimental conditions. We compared evoked fields as well as time-frequency responses. Source analyses of evoked fields indicated that before stimulus onset a parietal cluster was more active in trials with long compared to short perceived durations, signaling a positive influence of attention on VP. This interpretation was supported by differences in the power of oscillations in the alpha-band between short and long trials, also located in parietal areas. Additionally, frontal electrodes showed differences in gamma-activity, suggesting that small eye movements contributed to the maintenance of a conscious percept in the absence of physical stimulation. We discuss the strength and limitations of our approach to obtain objective results about a subjective phenomenon.
Meeting abstract presented at VSS 2013
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