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Christopher R. L. Cantor, Clifton M. Schor; How well can we discriminate between stimulus onsets and offsets?. Journal of Vision 2011;11(11):1214. doi: 10.1167/11.11.1214.
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It is well established that our visual systems are sensitive to the sudden appearance or disappearance of a visual object, and that we can judge the temporal order of such visual events with millisecond precision. Much of the literature on this topic has focused on whether stimulus onsets or offsets are processed faster, or whether the onset or offset of neural firing offers a more reliable substrate upon which to build representations of transient visual events. We asked whether observers could distinguish a pair of temporal envelopes applied to a simple visual object. Each pair contained onsets and offsets such that that average energy of the stimulus remained the same, but their temporal structure was exactly opposite (e.g. a disc briefly appearing with a temporal pattern that flashed ON-OFF-ON or OFF-ON-OFF). At long durations, the transient structure of this stimulus is obvious, but as the duration decreases below ∼130 ms observers lose their ability to distinguish the temporal structure (direction) of the transient modulation, without ever losing the ability to detect the modulation itself (the phenomenon is not contrast dependent). We believe that the early visual system may combine timing signals originating in the ON and OFF channels, sacrificing the ability to discriminate between different kinds of visual events in order to produce reliable estimates of when they occurred.
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