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Kornmeier Juergen, Bigalke Heiko W, Bach Michael; Ambiguous Figures: Effects of ISIs in discontinuous stimulus presentation on EEG components. Journal of Vision 2005;5(8):702. doi: 10.1167/5.8.702.
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© ARVO (1962-2015); The Authors (2016-present)
Background. When observing an ambiguous figure, our percept suddenly changes while the figure stays unchanged. In previous EEG experiments we found an early occipital correlate of the perceptual reversal, suggesting that disambiguation is initiated during early visual processing. Orbach et al. (1963) showed that with discontinuous presentation of the Necker cube the duration of inter stimulus intervals (ISI) interacts with the reversal frequency. In the present experiment we investigated the effect of ISI duration on the associated EEG/ERP components.
Methods. An ambiguous “Necker lattice” appeared repeatedly for 800 ms with 4 randomly changing ISIs (ms: 14; 43; 130; 390) between successive presentations. Subjects indicated whether they perceived a “reversal” or two identically oriented Necker lattices (“stability”). EEG was recorded from 13 channels in 12 subjects; the difference traces between reported “reversal” and “stability” (reversal minus stability) were analyzed separately for each ISI.
Results. With all ISIs a highly significant parietal/central distributed ERP negativity (“Reversal Negativity”, RN) occurred after a very early occipital positivity (“Reversal Positivity”, RP, at 130 ms). Both components confirmed previous findings. The latency of the RN (ms: 370; 338; 298; 276) was negatively correlated with the ISI duration. The RP was independent of the ISIs except for the longest ISI, when the RP overlapped with the RN.
Discussion. We interpret the early RP as a correlate of an initial transient bottom-up interaction of multiple neural representations preceding a perceptual reversal. The RN would indicate perceptual steps after ambiguity has been resolved. The negative correlation of the RN's latencies with ISIs suggests neural hysteresis accompanied with the reorganization of a biased perceptual system. This hysteresis may be stronger, the closer in time the previous percept was.
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