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Won Mok Shim, Patrick Cavanagh; Attention shift induced by apparent motion can cause position compression. Journal of Vision 2004;4(8):575. doi: 10.1167/4.8.575.
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Purpose: Flashes presented just before a saccade are mislocalized toward the saccade target (presaccadic compression: Ross, Burr, & Morrone, 1998). We examined whether there is attention-based compression effect in the absence of eye movements. An apparent motion display was used to induce attention shifts analogous to a saccadic eye movement with the assumption that attention is captured initially by the first item in the motion sequence and then drawn over to the second item. Methods: Observers fixated the center of the display while apparent motion between two discs was repeated in upper or lower visual field. On the third cycle of the apparent motion, a test flash was presented beyond the location of the second disc in the direction of motion. The test was presented for 15ms at one of seven possible SOAs (time interval between the onset of the fist disc of the apparent motion and the test flash). To reduce the integration of the flashes into the apparent motion sequence, an additional flash was displayed on the apparent motion path simultaneously with the test flash. The task was to determine whether the test flash appeared left or right of a reference flash which remained on the screen during the trial. Results: The test flash presented beyond the location of the second disc was mislocalized back toward the second disc. The compression effect increased with SOA after the offset of the first disc, peaked between 100ms and 200ms SOA, and gradually decreased thereafter. Conclusion: The perceived position of the test flash ahead of the second disc underwent compression in spite of the lack of eye movements. We propose that a shift of attention induced by apparent motion may play a role in the bidirectional compression effect.
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