ABSTRACT
A real-time neural network model is described in which reinforcement helps to focus attention upon and organize learning of those environmental events and contingencies that have predicted behavioral success in the past. The same mechanisms control selective forgetting of memories that are no longer predictive. Computer simulations of the model reproduce properties of attentional blocking, inverted-U in learning as a function of interstimulus interval, primary and secondary excitatory and inhibitory conditioning, anticipatory conditioned responses, attentional focusing by conditioned motivational feedback, and limited-capacity short-term memory processing. Qualitative explanations are offered of why conditioned responses are forgotten, or extinguish, when a conditioned excitor is presented alone but do not extinguish when a conditioned inhibitor is presented alone. These explanations invoke associative learning between sensory representations and drive, or emotional, representations between sensory representations and learned expectations of future sensory events, and between sensory representations and learned motor commands. Drive representations are organized in opponent positive and negative pairs (e.g., fear and relief), which are modeled by recurrent gated dipole, or READ, circuits. Cognitive modulation of conditioning is regulated by adaptive resonance theory, or ART, circuits that control the learning and matching of expectations and the reset of sensory short-term memory in response to disconfirmed expectations. Disconfirmed expectations interact with opponent mechanisms to regulate selective forgetting. Unless expectations are disconfirmed, memory does not passively decay, yet does not saturate due to cumulative learning over successive learning trials. To achieve selective forgetting, the read-in and read-out of learned memories are functionally dissociated within the opponent READ circuit. Such dissociation may be achieved by using dendritic spines as a site of associative learning. The selective forgetting mechanism is called opponent extinction.
