Cue relevance effects in conjunctive visual search: cueing for location, color, and orientation.

Performance in visual search tasks where the target differs from distractors by a conjunction of features can improve when a precue signals observers to limit their search by attending to a subset of elements. The current experiments were designed to study the temporal characteristics of precueing the location or feature (color or orientation) of targets in color-orientation conjunctive searches. Color (sensory or symbolic), location, or orientation precues preceded the search stimulus with cue-to-stimulus onset asynchrony (SOA) in the range of 50-750 ms. The stimuli consisted of elements formed by combining horizontal/vertical and red/green features. Observers responded to the presence/absence of an odd element in an "odd-man-out" paradigm. Reaction time and accuracy were used as measures of performance. Color and location precues improved search performance. The magnitude of improvement did not vary as the SOA changed. The color and location cues exhibited their effects in guiding visual search even at 50 ms after cue onset. However, orientation precue did not facilitate nor inhibit the search processing. These results indicate that in conjunctive search it takes at most 50 ms after cue onset for the visual system to exert the guidance effects using color and location precueing. We speculate that color may be a stronger feature than orientation for segmenting the search elements, thus facilitating visual search.