Effects of similarity and history on neural mechanisms of visual selection.

To investigate how the brain combines knowledge with visual processing to locate eye movement targets, we trained monkeys to search for a target defined by a conjunction of color and shape. On successful trials, neurons in the frontal eye field not only discriminated the target from distractors, but also discriminated distractors that shared a target feature as well as distractors that had been the search target during the previous session. Likewise, occasional errant saccades tended to direct gaze to distractors that either resembled the current target or had been the previous target. These findings show that the frontal eye field is involved in visual and not just motor selection and that visual selection is influenced by long-term priming. The data support the hypothesis that visual selection can be accomplished by parallel processing of objects based on their elementary features.