Tracking visual search over space and time

Abstract

Visual perception consists of early preattentive processing and subsequent attention-demanding processing. Most researchers implicitly treat preattentive processing as a domain-dependent, indivisible stage. We show, however, by interrupting preattentive visual processing of color before its completion, that it can be dissected both temporally and spatially. The experiment depends on changing easy (preattentive)selection into difficult (attention-demanding) selection. We show that although the mechanism subserving preattentive selection completes processing as early as 200 msec after stimulus onset, partial selection information is available well before completion. Furthermore, partial selection occurs first at locations near fixation, spreading radially outward as processing proceeds.Vision affords an enormous amount of information about the world, only a small fraction of which is submitted to detailed analysis. Thus, before anything else, perception must sift the incoming information to identify portions likely to merit further processing. This process must be fast enough that the organism can respond adaptively to dynamic environments. In this paper, we investigate how visual selection occurs, using data from a search task. In visual search tasks, observers determine whether or not a target appears in a complex display; data from search tasks are an effective probe ofthose visual features to which the early mechanisms that subserve selection are sensitive.

Partial orientation pop-out helps difficult search for orientation

“…At intermediate SOAs, the advantage of proximity to fixation is evident from the general trend of lower RTs and errors for targets nearer fixation than for those farther from fixation. This eccentricity effect for stimuli involving partial pop-out has not been shown before, except by Olds et al (2000aOlds et al ( , 2000b for color stimuli.…”

“…That is, partial pop-out assists difficult search. This interaction has also been found for color stimuli (Olds, Cowan, & Jolicoeur, 2000a, 2000b. These results indicate that interactions and/or overlap between the mechanisms responsible for pop-out and the mechanisms responsible for difficult search may be quite general in early visual selection.…”

“…If so, we can conclude that the mechanisms responsible for pop-out and difficult search are independent of each other and operate without interacting (as in race models and mixture models; see Olds et al, 2000b, for further discussion). Otherwise, we can conclude that there is some interaction (or overlap) between the processes responsible for pop-out and the processes responsible for difficult search.…”

“…The results of these experiments provide basic constraints that must be satisfied by any model of early vision and visual selection. Because all visual processing is affected by which portions ofthe visual field these early mechanisms select for further analysis, it is important to determine the nature ofeach selection mechanism, as well as interactions between the mechanisms.All of the results of Olds et al (2000aOlds et al ( , 2000b were based on experiments in the color domain. Are the results specific to color, or can they be generalized to other stimulus dimensions?…”

“…All of the results of Olds et al (2000aOlds et al ( , 2000b were based on experiments in the color domain. Are the results specific to color, or can they be generalized to other stimulus dimensions?…”