Feature head-start: Conjunction search following progressive feature disclosure.

When a colour/orientation conjunction search display is immediately preceded by a display that shows either the colour or the orientation of each upcoming search item, search is faster after colour-preview than after orientation-preview. One explanation for this feature asymmetry is that colour has priority access to attentional selection relative to features such as orientation and size. In support of this hypothesis, we show that this asymmetry persists even after colour and orientation feature search performance is equated.

Recognizing partially visible objects.

In two experiments we measured object recognition performance as a function of delay. In Experiment 1 we presented half of an image of an object, and then the other half after a variable delay. Objects were subdivided into top versus bottom halves, left versus right halves, or vertical strips.

Does previewing one stimulus feature help conjunction search?

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.

Search of jumping items: visual marking and discrete motion.

Watson and Humphreys (1997 Psychological Review 104 90-122) showed that when searching for a target, observers can ignore a previewed set of distractors (other items), effectively decreasing the number of relevant items in a difficult search display and thus speeding performance ('visual marking'). Other researchers have more recently investigated visual marking for continuously moving items, finding that shared features, and preserved inter-item spatial relationships, are helpful. Here, we tested whether visual marking occurs for a set of initial items that moves in one discrete jump (preserving shared features and inter-item spatial relationships).

Does partial difficult search help difficult search?

Olds, Cowan, and Jolicoeur (2000a, 2000b) showed that exposure to a display that affords pop-out search a target among distractors of only one color) can assist processing of a related display that requires difficult search. They added distractors of an additional color to the initial simple display and analyzed response time distributions to show that exposure to the initial display aided subsequent search in the difficult portion (this finding was called search assistance). To test whether search assistance depends on perceptual grouping of the initial items, we presented initial items that were more difficult to group (two colors of distractors, instead of just one).

The decay and interruption of interactions between search mechanisms.

The attentional mechanisms in the brain responsible for fast pop-out search and slower difficult search have been shown to interact. Even if pop-out search is interrupted, by the addition of extra distractors to an initially simple search display, the partial computations calculated by the mechanisms responsible for pop-out can facilitate subsequent difficult search ("search assistance"; Psychon. Bull.