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Vincent Ferrera, Marianna Yanike, Carlos Cassanello; The role of monkey frontal eye field in visual categorization. Journal of Vision 2008;8(6):374. https://doi.org/10.1167/8.6.374.
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The frontal eye field (FEF) is a region of prefrontal cortex that is involved in linking visual stimuli to motor responses. FEF is thought to select visual targets for eye movements. However, it is not known whether FEF is capable of playing a role in categorizing visual stimuli independently of a specific motor response. To investigate this, we developed a speed categorization task in which monkeys were presented with a random dot motion stimulus. They were required to make a saccadic eye movement to one of two targets to indicate whether the stimulus is “fast” or “slow”. The task was designed so that monkeys associated the speed categories with the colors of the response targets (“fast” = green, “slow” = red). The locations of the response targets were randomized. Hence, the categorical decision was independent of the motor response. The category boundary was determined arbitrarily by the computer and the monkeys learned it by trial and error. Once the monkeys had learned one boundary speed, the boundary was shifted to a new speed and the monkeys learned the new boundary. After learning, monkeys were able to shift rapidly between the two category boundaries. We recorded from 67 FEF neurons from two monkeys. Activity during stimulus presentation was significantly modulated by stimulus speed in 24 (36%) neurons. Activity changed significantly when the category changed in 28 (42%) cells (2-way ANOVA, p [[lt]]0.05). Some cells encoded both the physical speed of the stimulus and its category, which could be considered a categorical representation. Others simply showed enhanced firing to all stimuli of one category, but were not affected by stimulus speed. These results demonstrate that FEF activity is influenced by stimulus category and suggest a possible threshold model for categorical decision-making.
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