2ND-ORDER PARALLEL-PROCESSING - VISUAL-SEARCH FOR THE ODD ITEM IN A SUBSET

Visual search tasks in which participants searched for an odd element in a subset of items were investigated. Participants searched for an i tem of odd orientation in the red subset. The target was a led line of X degrees, distracters were green fines of X degrees and red lines of Y degrees. The orientations, X and Y, changed on every trial. In this task, orientation information was useful only after color had been us ed to select the relevant subset. Results show that response time (RT) and error data were different from standard color X orientation conju nction searches (Experiment 1). RT X Set Size functions had slopes nea r 0 ms per item (Experiment 2). The selection of the subset appeared t o take 200-300 ms (Experiments 2 and 3). Subset selection was based on properties of the relevant subset, not the irrelevant subset (Experim ent 4). It was more difficult (perhaps impossible) to select a subset defined by 2 colors (Experiment 5). Random variation in an irrelevant dimension did not disrupt subset search (Experiment 6).