FIGURE 9.

The simplest version of the START (Spectrally Timed Adaptive Resonance Theory) neural model. Adaptively timed learning maintains motivated attention within the temporal-amygdala-orbitofrontal feedback loop (Figure 8) at the same time that it inhibits activation of the orienting system. START hereby combines the reinforcement learning, motivated attention, and action processes of the CogEM model with adaptively timed inhibition of the ART orienting system A (Figure 7). A sensory cortical representation S_i⁽¹⁾ is activated by the CS input I_i, and then tries to activate its orbitofrontal cortical projection in S_i⁽²⁾. This happens while it also competes with other sensory representations and sends conditioned reinforcer signals to the drive representation, D, which plays the role of the amygdala in the model. Learning from S_i⁽¹⁾ to D is conditioned reinforcer learning, whereas learning from D to S_i⁽²⁾ is incentive motivational learning. The S_i⁽¹⁾-to-D-to-S_i⁽²⁾-to-S_i⁽¹⁾ feedback loops maintain motivated attention upon motivationally salient objects and events. A parallel branch from the sensory cortex S_i⁽¹⁾ goes to the hippocampus where a spectrum of cells responds at different rates (r_j, r_k, r_l) to the input signal T (see Figure 10). The population response of these cells supports correctly timed learning that can bridge the temporal gaps that occur during trace conditioning and delayed non-match to sample, among other paradigms. When the adaptively timed circuit is active, it maintains motivated attention via the feedback pathway (pathway D → S_i⁽²⁾ → S_i⁽¹⁾ → D) for an adaptively timed interval, while it inhibits activation of the orienting system (pathway D → A) in order to prevent distracting events from interfering with the adaptively timed response that is read out by S_i⁽²⁾ to acquire a valued goal. [Adapted with permission from Grossberg and Merrill (1992).]