Saccade target selection during visual search.

Five experiments are reported in which eye movements were recorded while subjects carried out a visual search task. The aim was to investigate whether an accurate initial target directed saccade could be programmed. In experiments 1-2, subjects moved their eyes to targets defined by colour, which were presented with seven non-targets in a circular array. Accurate saccades with short latencies were common but errors sometimes occurred and search for an "oddity" target, defined exclusively by difference in colour from a homogeneous set of distractors, was particularly error prone. In Experiment 3, occasional trials contained double targets. First saccades sometimes landed at an intermediate position between the targets. In Experiments 4 and 5, targets were presented with 15 distractors in two concentric rings of 8. Targets specified by shape could be located accurately with a single saccade. Search for a colour-shape conjunction was more difficult but targets in the inner ring were located frequently with a single saccade. The results suggest that the control of the initial eye movement during both simple and conjunction searches is through a spatially parallel process.