MECHANISMS OF VISUAL ATTENTION
Current theories of visual attention generally fall within one of two broad classes: Late Selection theories and Early Selection theories. They are typically seen as exhaustive alternatives. In this paper, however, I argue that these theories are inadequate. Several studies are reviewed that provide strong evidence for parallel stimulus identification. Such findings are consistent with predictions of late selection theory. On the other hand, experiments are presented here that do not support the central claims of late selection. It is shown that when subjects must report a stimulus item according to its location, selection of that item occurs early in stimulus processing, prior to identification. In order to reconcile these findings, several logically distinct issues in visual attention must be clarified. I distinguish between the issues of (1) parallel versus serial identification of stimulus items, (2) the temporal locus of selection, (3) voluntary control over stimulus processing, and (4) capacity limits. Several experiments are presented that investigate the nature of capacity limits on multi-stimulus identification. Specifically, capacity limits are evidenced by a superior performance when multiple stimuli are presented in successive frames compared to simultaneous presentations. The performance advantage for successive presentations is found to be an increasing function of the interval between successive frames. There is no effect, however, of predictability of stimulus exposure sequence. Effects of stimulus exposure sequence and predictability are used to argue against various forms of reallocatable capacity limits. A formulation is proposed which attributes capacity limits to the disruptive effects of spurious activation of letter detectors by multiple stimuli. Finally, a theoretical alternative to early and late selection theories is presented which integrates many findings reported here and in the literature.
BADGIO, PETER C, "MECHANISMS OF VISUAL ATTENTION" (1986). Dissertations available from ProQuest. AAI8703176.