Attention shifts to salient targets.

To investigate the role of salience in fast visual search, time courses for the detection and identification of salient targets were measured in six subjects, using texture-like line arrays. Single lines were made salient from luminance contrast, motion contrast, or by an added circular cue that is known to attract focal attention. Three major findings are reported: (1) Identification of target orientation required longer presentations than detection of the saliency effect itself, consistent with the model that target salience attracts focal attention for target analysis. (2) Different saliency mechanisms produced similar effects, suggesting that salience from feature contrast is functionally equivalent to salience evoked from a visual cue. (3) Circular cues were most effective when presented close to the target; performance in target identification decreased when the diameter was enlarged so that the cue was presented farther away and on a different spatial scale. All together, these findings suggest that popout targets in visual search may be detected fast and independent of set size because (a) they are salient and attract focal attention, and (b) their salience is produced on the same spatial scale and at the same location in the visual field where target properties are encoded.