Abstract
We examined the effect of varying the distractor ratio on behavioural performance and eye movements during search for two possible conjunctive targets defined by differences in color and orientation that were matched for saliency. As in previous studies, search was facilitated and there were increases in fixations towards the target when unequal groups of distractors were presented - eye movements were also directed towards the minority subset of distractors sharing either the colour or orientation with the target. However, it was clear that first fixations were not positioned directly towards display stimuli, suggesting that items were processed in parallel rather than serially, with subsequent fixations becoming more accurate in their positioning. Fixations were directed more towards the centre of smaller colour groups whether they contained the target or not, with no similar bias for items with the same orientation. These data suggest that small groups defined by colour are selected together, with search remaining within the selected group when it contained the target (signalled by a local orientation disparity) or shifted to the larger colour group when the target was not present in the smaller color group. The results point to differences in color- and orientation-grouping in conjunction search.