A set of visual search experiments tested the proposal that focused attention is needed to detect change. Displays were arrays of rectangles, with the target being the item that continually changed its orientation or contrast polarity. Five aspects of performance were examined: linearity of response, processing time, capacity, selectivity, and memory trace. Detection of change was found to be a self-terminating process requiring a time that increased linearly with the number of items in the display. Capacity for orientation was found (...) to be about 5 items, a value comparable to estimates of attentional capacity. Observers were able to filter out both static and dynamic variations in irrelevant properties. Analysis also indicated a memory for previously-attended locations. These results support the hypothesis that the process needed to detect change is much the same as the attentional process needed to detect complex static patterns. Interestingly, the features of orientation and polarity were found to be handled in somewhat different ways. Taken together, these results not only provide evidence that focused attention is needed to see change, but also show that change detection itself can provide new insights into the nature of attentional processing. (shrink)

The effect of attention on perceived brightness and contrast was investigated in eight experiments. Attention was manipulated by engaging observers in an attention-demanding concurrent task or by directing attention to a location with a peripheral cue. In all of the dual-task manipulations, attention reduced the variability of responses. However, attention did not affect the brightness of stimuli, nor did it affect the amount of simultaneous brightness contrast. Results with peripheral location cues were similar; however, the effect of attention in these (...) experiments could be attributed to nonperceptual factors. The metaphorical “spotlight” of attention reduces observers' uncertainty about the brightness of a stimulus, but it does not “illuminate” in terms of brightness or contrast. (shrink)

Detection theory has been applied to a host of varied problems (for example, measuring the accuracy of diagnostic systems or reliability of lie detection tests) and extends far beyond the detection of signals. This book is a primer on the subject.

The issue of capacity limits in visual short-term memory (VSTM) has been an area of active research since the 19th Century (Cattell, 1886). A common metaphor suggests that VSTM is akin to a limited capacity urn, able to hold only three-to-six items (Cowan, 2001). The 11 experiments in this thesis explore implications of this metaphor. Experiments 1-4 suggest that items in VSTM are not stored as coherent objects, contrary to recent suggestions (Luck & Vogel, 1997; Vogel, Woodman, & Luck, 2001). (...) Experiments 5-6 contrast two distinct experimental techniques used to probe the structure of information encoded in VSTM. The "single-shot" technique measures sensitivity to differences across two sequential arrays (Luck & Vogel, 1997); the "flicker" technique measures response times to the detection of change, across multiple successive presentations of two alternate displays (Rensink, O'Regan, & Clark, 1997). It is shown that observers' underlying sensitivity to change, and by implication the structure of information encoded, is the same for these two techniques. Experiments 7-9 examine the relationship between observers' performance for detection and identification of change between two successive visual arrays. It is demonstrated that this relationship fails to meet basic assumptions inherent in the urn metaphor. An alternate model is proposed, which suggests that the capacity limit in VSTM is not determined by the number of items stored, but by the amount of information able to be extracted from a visual display. In Experiments 10-11, this alternative model is used to examine the short-term storage of visual information. Overall, the findings of the thesis are inconsistent with a model in which limits in the detection and identification of change are the result of a single process, which operates on a limited number of coherent objects held in a high-level memory store. (shrink)