Overriding stimulus-driven attentional capture

Theeuwes (1992) found a distracting effect of irrelevant-dimension singletons in a task involving search for a known target. He argued from this that selectivity is determined solely by stimulus salience; the parallel stage of visual processing cannot provide top-down guidance to the attentive stage sufficient to permit completely selective use of task-relevant information. We argue that in the task used by Theeuwes, subjects may have adopted the strategy of searching for an odd form even though the specific target form was known. In Experiment 1, we replicated Theeuwes’s findings. Search for a circle target among diamond nontargets was disrupted by the presence of a diamond nontarget that was uniquely colored. In two subsequent experiments, we discouraged the singleton detection strategy, forcing subjects to search for the target feature. There was no distracting effect of a color singleton in these experiments, even with displays physically identical to those of Experiment 1, demonstrating that top-down selectivity is indeed possible during visual search. We conclude that goal-directed selection of a specific known featural identity may override stimulus-driven capture by salient featural singletons.     

Adaptation in motion perception: Alteration of motion evoked by ocular pursuit

A new perceptual adaptation, an alteration in the perceived direction of motion given by ocular pursuit, is reported. When an object starts to move on a straight path, its displacement is initially given by a shift of its image on the retinas of the stationary eyes; then, after about 200 msec, the eyes start to track the moving object. The perception of motion that results from ocular pursuit was altered by causing ocular pursuit of a moving object to be preceded regularly by a displacement of the object’s image whose direction differed from the direction of the pursuit movement. This was arranged by changing the direction of the given motion at approximately the moment when image displacement changed into tracking. Prolonged exposure to such conditions resulted in a change of the tracked motion’s apparent direction, which became somewhat more like the direction of the preceding motion phase that was given by image displacement.     

The effect of two types of induced-motion displays on perceived location of the induced target

Using a pointing test, perceived location of a target seen in induced motion was evaluated under two display conditions. In one, a fixated, horizontally stationary spot was surrounded by a frame moving back and forth. As the frame moved to each side, its center shifted correspondingly with respect to the subject’s objective median plane. In the second display, the surround was constructed so that as it moved back and forth, its center remained in virtual alignment with the objective median plane. Although both conditions produced a substantial induced-motion effect, only the former produced significant shifts in the target’s perceived location. Furthermore, similar shifts were also obtained with a stationary, offcenter frame (Experiment 2). This suggests that the changes in perceived location obtained with the first induced-motion display were not derived from the induced motion per se, but, rather, from a frame effect produced when the surround moved to an off-center position. Implications for the relationship between perceived motion and position, as well as for two theories of induced motion, are discussed.     

Local processes in preattentive feature detection.

Sagi and Julesz (1987) claimed that for a target to be detected preattentively, it must be within some small critical distance of a nontarget. The independent effects of separation and display size, which were confounded in the Sagi and Julesz experiments, were examined. Experiments 1 and 2 revealed that in tasks requiring search for a color-defined target, target-nontarget separation had no effect on reaction time (RT). Display size, however, was inversely related to RT. Experiment 3 ruled out the possibility that the decreasing function of RT with display size was due to arousal caused by higher display luminance. When nontarget grouping was inhibited, (Exp. 4) it was found that RT no longer decreased with increasing display size. This suggests that nontarget grouping may have been the cause of the improved performance at larger display sizes. Experiments 5 and 6 extended the results to line segments, the stimuli used by Sagi and Julesz.     

Aging of attention: Does the ability to divide decline?

Previous research has yielded conflicting results regarding the relationship between adult age and the ability to divide attention between two concurrent tasks. At least some of the inconsistency is probably attributable to methodological variations, such as the manner in which divided-attention ability has been assessed, how single-task performance has been considered, and the degree of control over relative emphasis placed on each task. Two experiments employing procedures sensitive to these concerns were conducted in which a speeded decision task was performed during the retention interval of a letter-memory task. The results of both experiments indicated that there were relatively few age-related influences on dual-task performance vis-à-vis those on single-task performance.     

Evaluating a treatment without extinction for elopement maintained by access to stereotypy

Elopement is a common and potentially dangerous form of problem behavior. Results of a functional analysis found that the elopement of a child with autism was maintained by access to stereotypy in the form of door play. We implemented functional communication training and contingency-based delays dependent on the absence of elopement and increased the amount of time the participant waited prior to engaging in stereotypy. We also conducted treatment-extension probes, with the participant waiting up to 10 min without elopement.