Neural Mechanisms of Fixation Choice While Searching Natural Scenes

Northwestern University, Evanston IL

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Abstract

Project Summary/Abstract The overall goal of these experiments is to understand how the brain controls where we look. To accomplish this, it is important to study brain activity and behavior under conditions that closely approximate those in the real world. All of the proposed experiments will use awake behaving rhesus monkeys as subjects. This work focuses upon the frontal eye field (FEF), a region of cerebral cortex shared by both human and non-human primates that is closely involved in the control of purposive voluntary eye movements. A great deal is known about the FEF's role in controlling single saccades to a small number of potential targets. However, its role in the generation of eye movement strategies involving continuous series of self-generated eye movements in a rich natural environment is poorly understood. The experiments described in this proposal use semi-chronic arrays of microelectrodes to record single neuron activity from the FEF while monkeys search for targets in natural scenes. The power of this design is that one can observe the activities of many single neurons while the monkey makes series of self-guided eye movements in search of the target. Preliminary experiments suggest that the activities of FEF neurons are directly related to the development and execution of eye movement strategies to optimize these search movements. The activities seen are related to 1) planning efficient search movements, 2) selecting the location of the search target, and 3) controlling both exploratory and goal-directed saccades. The Aims of this proposal will use this preliminary data as a foundation to 1) Understand both the behavioral mechanisms and underlying neural activity responsible for planning efficient eye movements during visual search; 2) Understand the process of target recognition and selection; and 3) investigate differences in neural activity between exploratory eye movements (used to survey the visual environment) and exploitative eye movements (that capture the ultimate target of the search). Specifically, this aim will look at how visual space is represented during these different types of eye movements. The contributions of these three aims will be significant because they spearhead the use of natural scene search to study how the FEF is involved in eye movement strategies, including the development of both the data analysis and the experimental techniques needed to do so. This will lead to a deeper understanding of the FEF, the generation of real world eye movement strategies, and the data analysis techniques needed to make sense of complicated multivariate data.