A color x color conjunction can be searched in 'parallel

Purpose. It has been proposed that wheieas some between-dimension conjunctions (color x orientation: a red vertical target unong red tilted and blue vertical distractors) can be searched in a parallel fashion, within- dimension conjunctions (color x color: a green & red square among green & blue and blue & red squares) are necessarily searched in a serial self-terminating fashion. We explored the effects of distractor grouping and practice on a within-dimension conjunction search task to see if it could be searched in parallel. Methods. Thirty observers searched for .1 red & green target amid 3, 7, 11 or 15 distractors, which was present in half of the tri.ils. Observers were assigned to one of two experimental conditions: In the first condit:on, the distractors (red & blue and blue & green) shared a simple feature (blue color). In the second condition, the distractors were red & blue and green & yellow, ie they did not share that simple feature. Observers performed 4 experimental blocks of 320 trials each. BT and accuracy were the dependent variables. Results. Search time decreased progressively from the first to the fourth session; detecting the presence of the target was faster than detecting its absence; and, search time increased as the display contained more items. More importantly, in the first condition, with practice, observers detected the target in a parallel fashion. In contrast, in the second condition observers detected the target ir a serial fashion regardless of practice. Conclusions. The differential effects of p ractice between these two experimental conditions could be explained in terms of distractor grouping induced by the shared color of the distractors. If distractors can be perceptually grouped and observers are given some practice with the display, attention could be guided to a target defined by the conjunction of the colors of two parts. This finding has implications for the structure of the parallel stage of processing of visual search mocels. According to Wolfe et al. (1990, 1994), the distinction between withm-dimension and between-dimension conjunctions constrains the structure of the parallel stage of processing of visual search models.