In three experiments, we measured recognition as a function of exposure duration for three kinds of images of common objects: component images containing mainly low-spatial-frequency information, components containing mainly high-spatial-frequency information, and compound images created by summing the components. Our data were well fit by a model with a linear first stage in which the sums of the responses to the component images equalled the responses to the compound images. Our data were less well fit by a model in which the component responses combined by probability summation. These results support linear filter accounts of complex pattern recognition.

Olds, Cowan and Jolicoeur [2000. Tracking visual search over space and time. Psychonomic Bulletin & Review (in press)] interrupted pop-out search by adding distractors to a display after a delay. They analyzed the response time distributions from conditions with different delays for interruption and showed that when pop-out search fails, its partially completed computations can be used to assist other, slower search processes. This paper demonstrates that expectancies, numbers of items and colors in the display, and color onsets do not explain those results. Finally, an experiment in which the target was moved mid-trial demonstrates that partial pop-out assists difficult search by indicating something about where the target is, or where the target is not.

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.

Weinterrupted pop-out search before it produced a detection response by adding extra distractors to the search display. Weshow that when pop-out for an orientation target fails because of this interruption, it nevertheless provides useful information to the processes responsible for difficult search. 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.Vision provides people with an enormous amount of information. Because it is impossible to process all ofthis information in detail, limited subsets must be quickly selected for further analysis. How is this selection performed? The mechanisms responsible for visual selection can be elucidated by data from search tasks. In a search task, observers determine whether or not a target appears among distractors (other items) in a complex display. Researchers classify search performance in terms of response time (RT) patterns. In pop-out search, RTs are fast, and RT for correct responses is virtually independent of the number of items in the display. In difficult search, RTs are much longer and generally increase linearly with the number of items (Treisman & Gelade, 1980). Pop-out search is possible for some target-distractor relationships but not others. Many researchers believe that early "preattentive" mechanisms in the brain perform pop-out search in parallel across the entire display; difficult search occurs when these mechanisms cannot detect the target and "attention" is required (Treisman & Gelade, 1980;Wolfe, 1994). Most work on attention implicitly assumes that preattentive processing is all-or-nothing (Treisman & Gelade, 1980;Wolfe, 1994), despite suggestions that processing could develop gradually (e.g., Wolfe, 1994, p. 229; Wolfe, Cave, & Franzel, 1989, p. 428).Olds, Jolicceur (2000a, 2000b) have shown, however, that pre attentive processing of color is not allor-nothing but can, in fact, be dissected both temporally and spatially. They interrupted pop-out search at interme- diate points in processing, and the results showed that even when pop-out search fails, its partially completed computations can be used to assist other, slower search processes. 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? In this paper, we investigate interactions be...

We examined the effects of previewing one aspect of a search display, in order to determine what subset of display information is most useful as a prelude to a search task. Observers were asked to indicate the presence or absence of a known target, in a conjunction search where the target was defined by the combination of colour and orientation (a yellow horizontal line presented among yellow vertical and pink horizontal distractors). In the colour preview condition of experiment 1, observers were first shown a 1 s preview of the locations and colours of the search items before the actual search set was presented. That is, search items first appeared as yellow and pink squares for 1 s, which each then turned into yellow and pink oriented lines (in the same locations) which comprised the display to be searched. In the orientation preview condition, observers were first shown a 1 s preview of the locations and orientations of the search items before the actual search display was presented. These two conditions were compared to a control condition consisting of standard conjunction search without any preview display. There was no effect of colour preview; there was a marginal effect of orientation preview, but in the opposite direction from what was expected reaction time increased for orientation preview searches. In experiment 2 these previews were compared to two spatial cueing conditions; in this experiment the colour preview did provide a small amount of help. Finally, in experiment 3 both previews were presented in succession, and increased facilitation was found, in particular when the colour preview preceded the orientation preview. These findings are discussed in relation to the literature, in particular the Guided Search model (Wolfe et al 1989 Journal of Experimental Psychology: Human Perception and Performance 15 419-433; Wolfe 1994 Psychonomic Bulletin & Review 1 202-238).