Sequential sampling from memory underlies action selection during abstract decision making

The process of deciding what a sensory stimulus is and how to act on that decision seem distinct, yet they appear to be coupled at the neural level. Neurons in the parietal cortex of monkeys represent both the integration of evidence toward a decision and the behavior used to report the decision. This raises the possibility that monkeys evaluate sensory percepts in terms of their motor affordances rather than their abstract identity. It is not clear how monkeys can evaluate sensory percepts when unaware of the motor actions they bear upon. We investigated this by training monkeys to make perceptual decisions about the direction of motion in a noisy random-dot display. They learned to associate leftward and rightward with two colors, and to select from a pair of colored targets, which were displayed after the motion at unpredictable locations. Surprisingly we found that monkeys postpone decision formation until the pertinent motor actions are revealed. Neurons in parietal cortex represent the accumulation of evidence sampled from short term memory of the motion display. The findings demonstrate that abstract decisions are framed in terms of their motor affordances and highlight the capacity for integration of evidence from memory.