Psychonomic Bulletin & Review2001, 8 (4), 713-720
"Time course of amodal completion revealed by a shape discrimination task"
RICHARD F. MURRAY, ALLISON B. SEKULER, andPATRICK J. BENNETT
GENERAL DISCUSSION
The finding that amodal completion can affect performance in perceptual tasks, but only if given enough time,is consistent with earlier reports. Our estimates of the time required for completion ranged from 46 to 114msec, and averaged to 75msec.Although our results clearly indicate a time course for completion, our estimate of its duration should not be taken as a fixed constant of visual processing. It is becoming increasingly clear that the time required for completion is not fixed but varies with task and stimulus.
Sekuler and Palmer’s (1992) first primed-matching studyfound amodal completion to require 100-200msec;however, in a later primed-matching study, Guttman and Sekuler (2001) found that completion time varied fromless than 75msec to over 200msec, depending on howmuch of the stimulus was occluded. Shore and Enns (1997) manipulated the amount of occlusion in theirstimuli, and they also found shorter completion times forsmaller amounts of occlusion. Using performance in a shape discrimination task as a measure of completion,Ringach and Shapley (1996) found amodal completionto require 120-170msec. This is longer than the estimate we found using similar methods, but their stimuli werevery large (17°×17°) and highly occluded (80%), so if completion time increases with the amount of completion required, a longer time course would be expected(Guttman & Sekuler, 2001; Shore & Enns, 1997). Although it is difficult to compare the completion times obtained in different studies directly, the fact that studies with different methods and stimuli all conclude thatamodal completion has a rapid but measurable time course provides converging evidence and makes it unlikely that the time course is an artifact of the methodsemployed.
"Time course of amodal completion revealed by a shape discrimination task"
RICHARD F. MURRAY, ALLISON B. SEKULER, andPATRICK J. BENNETT
GENERAL DISCUSSION
The finding that amodal completion can affect performance in perceptual tasks, but only if given enough time,is consistent with earlier reports. Our estimates of the time required for completion ranged from 46 to 114msec, and averaged to 75msec.Although our results clearly indicate a time course for completion, our estimate of its duration should not be taken as a fixed constant of visual processing. It is becoming increasingly clear that the time required for completion is not fixed but varies with task and stimulus.
Sekuler and Palmer’s (1992) first primed-matching studyfound amodal completion to require 100-200msec;however, in a later primed-matching study, Guttman and Sekuler (2001) found that completion time varied fromless than 75msec to over 200msec, depending on howmuch of the stimulus was occluded. Shore and Enns (1997) manipulated the amount of occlusion in theirstimuli, and they also found shorter completion times forsmaller amounts of occlusion. Using performance in a shape discrimination task as a measure of completion,Ringach and Shapley (1996) found amodal completionto require 120-170msec. This is longer than the estimate we found using similar methods, but their stimuli werevery large (17°×17°) and highly occluded (80%), so if completion time increases with the amount of completion required, a longer time course would be expected(Guttman & Sekuler, 2001; Shore & Enns, 1997). Although it is difficult to compare the completion times obtained in different studies directly, the fact that studies with different methods and stimuli all conclude thatamodal completion has a rapid but measurable time course provides converging evidence and makes it unlikely that the time course is an artifact of the methodsemployed.
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