Temporal properties of visual search in pigeon target localization

To examine the mechanisms and time course of visual search behavior, we rewarded 6 experienced pigeons for locating and pecking at an odd target region randomly embedded in a larger rectangular array of contrasting distractor elements. On two-target test trials, a flanking secondary target region was briefly presented (100, 250, or 500 ms) after display onset with stimulus onset asynchrony values of 0, 50, 100, 175, 250, 375, 500, 1000, 2000, and 3000 ms. Two types of interference effects were possibly identified with target localization accuracy. One type occurred early in processing, where the secondary target appeared to interfere with search behavior, perhaps involving mechanisms similar to inhibition of return. A second type of interference was isolated that appeared to be time locked to responding and might occur at a postsearch stage of processing. Several possible connections of these effects to established mechanisms in human visual search and attention are suggested.