Saccades and covert shifts of attention during active visual search: spatial distributions, memory, and items per fixation.

Target detection during active visual search was examined. The chance corrected spatial distribution of target detection was found to be symmetrically distributed around the point of fixation and, unexpectedly, was independent of the proximity of fixations to the display boundaries. Memory was found to play a very limited role in target detection, but a significant role in the guidance of eye movements. A model of covert shifts was used to estimate the number and spatial distribution of shifts required to explain observed performance. An increase from one to five shifts per fixation across increasing array set size as estimated by two different methods was inconsistent with unchanging fixation durations, suggesting that multiple covert shifts are not occurring during the fixations in active search.