Evidence accumulation and the moment of recognition: dissociating perceptual decision processes using fMRI

Decision making can be conceptualized as the culmination of an integrative process in which evidence supporting different response options accumulates gradually over time. We used functional magnetic resonance imaging (fMRI) to investigate brain activity leading up to and during decisions about perceptual object identity. Pictures were revealed gradually and subjects signaled the time of recognition (TR) with a button press. We examined the timecourse of TR-dependent activity to determine how brain regions tracked the timing of recognition. In several occipital regions, activity increased as stimulus information increased, independently of TR, suggesting a role in lower level sensory processing. In inferior temporal (IT), frontal and parietal regions, a gradual buildup in activity peaking in correspondence with TR suggested that these regions participated in the accumulation of evidence supporting object identity. In medial frontal cortex, anterior insula/frontal operculum, and thalamus, activity remained near baseline until TR, suggesting a relation to the moment of recognition or the decision itself. The findings dissociate neural processes that function in concert during perceptual recognition decisions