Abstract
Detecting a change in a scene is easy when motion cues are available to draw attention to the location of the change. However, when visual contact with the scene is even briefly disrupted, as in the flickering task of Rensink, O'Regan, and Clark (1997), change detection becomes difficult. A brief mask intervening between alternate versions of a photographed scene slowed change detection markedly relative to immediately successive presentations. The difficulty in the flickering task was attributed to the requirement of focused attention to maintain image components in memory for comparison and the need to direct attention serially to different components until the area of change became the focus of attention. However, attention was not manipulated directly.
The present series of experiments tested whether limiting the attentional resources available would disrupt change detection by having participants perform concurrent n-back or number-repetition control tasks. Experiments 1 and 2 examined the effects on change detection when alternate forms of the images switched every 320 ms. Experiment 1 allowed the use of motion cues, in that alternate forms of images were presented in immediate succession. Change-detection performance was equivalent for the two concurrent tasks. Experiment 2 removed motion cues by using the flickering task with a mask between alternate forms. Change detection performance was adversely affected by concurrent performance of the n-back task relative to the control. Experiment 3 replicated two presentation conditions from the Rensink study, using a 640 ms image alternation rate. In addition to the mask between alternate forms, in one condition, the presentation time of each form was divided by a mask. In both versions of the task, concurrent performance of the n-back task slowed change detection. Overall, the results support the conclusion that attention is important for change detection when motion cues are not available.