Saliency maps for finding changes in visual scenes?

Sudden changes in the environment reliably summon attention. This rapid change detection appears to operate in a similar fashion as pop-out in visual search, the phenomenon that very salient stimuli are directly attended, independently of the number of distracting objects. Pop-out is usually explained by the workings of saliency maps, i.e., map-like representations that code for the conspicuity at each location of the visual field. While past research emphasized similarities between pop-out search and change detection, our study highlights differences between the saliency computations in the two tasks: in contrast to pop-out search, saliency computation in change detection (i) operates independently across different stimulus properties (e.g., color and orientation), and (ii) is little influenced by trial history. These deviations from pop-out search are not due to idiosyncrasies of the stimuli or task design, as evidenced by a replication of standard findings in a comparable visual-search design. To explain these results, we outline a model of change detection involving the computation of feature-difference maps, which explains the known similarities and differences with visual search

The multiple-weighting-systems hypothesis: theory and empirical support

Observers respond faster when the task-relevant perceptual dimension repeats across consecutive trials (e.g., color–color) relative to when it changes (orientation–color)—the phenomenon termed the dimension repetition effect (DRE). Similarly, when two (or more) different tasks are made to vary randomly across trials, observers are faster when the task repeats, relative to task changes—the phenomenon termed task-switch cost (TSC). Hitherto, the DRE and TSC effects have been discussed independently of each other. Critically, either effect was explained by assuming a single mechanism giving rise to DREs or TSCs. Here, we elaborate strong conceptual similarities between the DRE and TSC effects; we introduce the concept of criterion-specific intertrial sequence effects, with DREs and TSCs being different manifestations of criterion-specific effects. Second, we review available evidence suggesting that none of the single mechanism explanations can readily account for all the findings in the literature. Third, we elaborate on the multiple-weighting-systems (or MWS) hypothesis, a recently proposed account that postulates the existence of several, independent mechanisms sensitive to intertrial sequences. Finally, we test predictions derived from the MWS hypothesis in two novel experiments and discuss the results from both the single- and multiple-mechanism perspectives