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Yee Joon Kim, Marcia Grabowecky, Satoru Suzuki, Nava Rubin; Bistability of flicker vs. rotational apparent motion: Psychophysics and steady-state visual evoked potentials (SSVEP). Journal of Vision 2009;9(8):675. doi: 10.1167/9.8.675.
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A counter-phase flickering 8-arm radial pattern induces bi-stable alternations between perception of flicker (F) and rotational apparent motion (R). We studied the effect of stimulus parameters on the relative time spent seeing the rotational apparent motion, R/[R+F]. Results were then used to investigate how the averaged power spectra of steady-state visual evoked potentials (SSVEPs) in the stimulus-driven frequency bands varied as a function of the changing percept. Observers maintained the central fixation for the duration of each 1-min trial and continually indicated the periods of flicker perception and the periods of rotation perception by pressing buttons throughout a trial. In the behavioral experiment, two different contrasts, 80% and 100%, and four different flicker frequencies ranging from 2.5 Hz to 10 Hz were randomly intermixed in a factorial design. R/[R+F] increased as flicker frequency decreased, and as stimulus contrast decreased. Selecting (for each observer separately) parameters that induced approximately 50% rotational apparent motion, we recorded EEG and calculated SSVEP as a function of percept. The preliminary results suggest that SSVEP power at the 2nd harmonic of flicker frequency in posterior (occipital) electrodes changes according to perceptual state, yielding higher power during perception of flicker than during perception of rotational apparent motion. This is consistent with the phenomenological experience reported by observers, that the sense of flicker is reduced during periods of rotational apparent motion. Neurally, this could reflect greater phase locking in one perceptual state (F) than the other (R).
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