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Jack Grinband, Joy Hirsch, Vince P. Ferrera; Functional imaging of categorical decision processes. Journal of Vision 2005;5(8):923. doi: 10.1167/5.8.923.
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© ARVO (1962-2015); The Authors (2016-present)
Current models of decision making have suggested that the frontal and parietal cortices contain neurons that underlie volitional choice. However, a locus of categorical decision making has not been conclusively identified. The identification of brain regions with activity specific to categorization is complicated by general task related activity that is correlated with, but is distinct from, decision specific activity. These ancillary processes include working memory, attention, motor planning, and motivation. To dissociate decision related activity from general task related activity, we designed a categorical decision making task that required subjects to classify a vertical line segment as “long” or “short” using one of two learned criteria that varied from trial to trial. In this task, decision uncertainty, defined by distance from the criterion, is parametrically modulated while the stimulus set, categorization rule, and response set all remain constant. In addition, we attempted to equalize attention and working memory load, as well as task difficulty, by equating psychophysical functions across trial type and across subjects. Rapid event-related fMRI on human subjects was used to identify areas of the brain that have general task related and/or decision specific activation. We found that the medial frontal gyrus, anterior insula, and posterior parietal cortex showed general task related activation. However, only the medial frontal gyrus and anterior insula showed additional activity modulated by decision uncertainty. In fact, after accounting for general task related variance, posterior parietal cortex showed no additional modulation related to decision uncertainty. These data suggest that a specific network of areas in the frontal cortex (i.e. a “decision triangle”) is directly involved in categorization and volitional choice.
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