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Ambiguous stimuli can look different in different contexts. Here we demonstrate that subjective appearance of motion depends not only on current visual input but critically on which aspects of the context are attended. Observers fixated a central oblique test grating flanked by two pairs of orthogonally oriented context gratings arranged in a cross (+) configuration. Each context pair could induce the test stimulus to appear to switch from diagonal motion to either horizontal motion (due to one context pair) or vertical motion (due to the other). Spontaneous switching between these motion states was observed under free viewing. We demonstrate that observers can voluntarily select between specific states when cued to attend selectively to one or other context pair in an alternating manner. Concurrent reports of perceived test stimulus motion depended specifically on which context was currently attended, indicating a high degree of “cued-control” over subjective state via attended context. Further experiments established that the perception was nevertheless still constrained by physical stimulus context as well as by attentional selection among that context. Moreover, the attentional control evident here did not seem reducible solely to local contrast gain modulation of the attended vs. ignored context elements. Selective attention to different parts of the context can evidently resolve the ambiguity of the test grating, with integration arising selectively for those components that are jointly attended. Such selective integration can result in substantial voluntarily controlled changes in phenomenal perception.
|Subjects:||B Philosophy. Psychology. Religion
R Medicine > RE Ophthalmology
|Divisions:||School of Social Sciences > Department of Psychology|
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