In the Unit on Perception and Action we investigate how visual inputs are transformed into perception and behavior. Most of our research has been focused on the frontal eye field (FEF), an area in the prefrontal cortex that converts visual information into eye movement commands. We have shown that FEF combines visual inputs with cognitive knowledge to form a priority map of visual space that identifies the location of the most important objects in the visual scene to guide gaze. During the past year we have extended this finding to show that spatially selective signals in the frontal cortex enhance visual processing leading to object recognition (ref. 1) and the formation of complex object representations in the visual cortex (ref. 2). We also described mechanisms by which FEF neurons cooperate and compete to select targets for saccades during visual search (ref. 3). In ref. 1 we investigated the link between neuronal activity in the frontal eye field and the enhancement of visual processing associated with covert spatial attention. We found that FEF activity was correlated with performance accuracy and reaction time in monkeys manually reporting the identity of a visual search target in the absence of eye movements. Chemical inactivation of FEF produced spatially selective perceptual deficits that were correlated with the effectiveness of the inactivation and were strongest on trials that require a voluntary attention shift. These results demonstrate a strong functional link between FEF activity and covert spatial attention, and suggest that spatial signals from FEF directly influence visual processing during the time that a stimulus to be identified is being processed by the visual system. In ref. 2 we addressed the question of how we locate and identify objects in complex natural environments by simultaneously recording single neurons from two brain regions that play different roles in this familiar activity the frontal eye field, an area in the prefrontal cortex that is involved in visual spatial selection, and the inferotemporal cortex (IT), which is involved in object recognition in monkeys performing a covert visual search task. Although the monkeys reported object identity, not location, neural activity specifying target location was evident in FEF before neural activity specifying target identity in IT. These two distinct processes were temporally correlated implying a functional linkage between the end-stages of where and what visual processing and indicating that spatial selection is necessary for the formation of complex object representations associated with visual perception. In ref. 3 we investigated the role of spike rate versus spike timing in visual target selection. We simultaneously recorded activity from multiple frontal eye field neurons and asked whether they interacted to select targets from distractors during visual search. When both neurons in a pair selected the target and had overlapping receptive fields, they cooperated more than when one or neither neuron in the pair selected the target. Elevated spike timing coincidences occurred at the time of attentional selection of the target by both neurons. Decreased spike timing coincidences occurred between neurons with spatially non-overlapping receptive fields at the time of attentional selection of the target by one of the neurons. These results provide evidence for dynamic and task-dependent cooperation and competition among frontal eye field neurons during visual target selection. These studies have extended our understanding of visual processing. We have shown that the frontal eye field provides top-down cognitively-derived signals that modulate ongoing visual processing. We also have identified two separate and dissociable cognitive processes within the frontal eye field, visual selection and saccade preparation. Both of these processes are crucial for normal vision and for interacting with the world. With this knowledge we can design experiments to investigate the flow of sensory information through the brain as it is transformed into perception and action. This work helps us understand the mechanisms of how the brain focuses attention to make perceptual decisions and guide behavior, which is necessary to be able to understand and treat eye movement and attention-related disorders in humans.
