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Patricia R. DeLucia; Judgments of time to contact when an approaching object is partially concealed by a static or moving occluder. Journal of Vision 2002;2(7):348. doi: 10.1167/2.7.348.
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© ARVO (1962-2015); The Authors (2016-present)
PURPOSE. Studies of time-to-contact (TTC) typically focussed on judgments of unoccluded approaching objects. DeLucia, et al. (ARVO ′00) reported that a stationary occluder can affect the object's optical size, and local tau margin derived from the unoccluded portion of the object; they also reported differences in TTC judgments of occluded and unoccluded objects. Effects of moving occluders on TTC judgments were measured here. METHOD. A computer-generated object approached the S while partially concealed by an occluder that was stationary, or moved leftward or rightward. The latter motions resulted in an increase and decrease, respectively, in the local tau margin. In one condition, the occluder nullified the object's optical expansion. Global tau was not affected by occlusion. Sixteen Os pressed a button when they thought the object would reach them; TTC estimates were measured. RESULTS. There were significant effects of the occluder's motion and interactions between motion and other variables such as the object's TTC and shape, p < .05. Generally, compared with stationary occluders, rightward-moving occluders resulted in smaller TTC estimates; occluders that nullified expansion resulted in greater estimates. Although such directional changes in TTC estimates are consistent with the local tau margin, the latter predicted a greater change in TTC estimates than was observed. CONCLUSIONS. Moving occluders can affect TTC judgments of approaching objects. Results are difficult to reconcile with explanations based on local or global tau. Effects of occlusion on TTC judgments must be considered in models of perceived collision. CR: None. SUPPORT: Texas Advanced Research Program.
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