Reaction time drifts identify objects of attention in pigeon visual search

Three pigeons searched for a unique target form among 31 identical distractors, and search reaction time (RT) was measured. Within experiments, target and distractor on each trial were drawn from the same small set of forms that differed from each other by simple features. Correlations across sessions among RTs to the various form pairs were analyzed. Experiment 1 indicated drifts of attention between the top of the forms, where a gap might appear, and the bottom, where a line might appear, and also suggested drifts of attention to the line as a target feature. Experiment 2 indicated similar drifts between the top and bottom of the forms and between small differences and large differences in target features. Attention to intraform location appeared relatively independent of attention to target features. The method provides a new way to identify functionally separable aspects of stimulus processing and to describe their temporal properties.