Effects of similarity and history on neural mechanisms of visual selection

To investigate how the brain combines knowledge with visual processing to l ocate eye movement targets, we trained monkeys to search for a target defin ed by a conjunction of color and shape. On successful trials, neurons in th e frontal eye field not only discriminated the target from distracters, but also discriminated distracters that shared a target feature as well as dis tracters that had been the search target during the previous session. Likew ise, occasional errant saccades tended to direct gaze to distracters that e ither resembled the current target or had been the previous target. These f indings show that the frontal eye field is involved in visual and not just motor selection and that visual selection is influenced by long-term primin g. The data support the hypothesis that visual selection can be accomplishe d by parallel processing of objects based on their elementary features.