Hebbian learning for deciding optimally among many alternatives (almost)


Reward-maximizing performance and neurally plausible mechanisms for achieving it have been completely characterized for a general class of two-alternative decision making tasks, and data suggest that humans can implement the optimal procedure. A greater number of alternatives complicates the analysis, but here too, analytical approximations to optimality that are physically and psychologically plausible have been analyzed. All of these analyses, however, leave critical open questions, two of which are the following: 1) How are near-optimal model parameterizations learned from experience? 2) How can sensory neurons' broad tuning curves be incorporated into the aforementioned optimal performance theory, which assumes decisions are based only on the most informative neurons? We present a possible answer to all of these questions in the form of an extremely simple, reward-modulated Hebbian learning rule for weight updates in a neural network that learns to approximate the multi-hypothesis sequential probability ratio test.

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