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Author(s): Grossberg, S. | Schmajuk, N.A. |
Year: 1987
Citation: Psychobiology, 15, 195-240
Abstract: A real-time neural network model is developed to explain data about the acquisition and extinction of conditioned excitors and inhibitors. Systematic computer simulations are described of a READ circuit, which joins together a mechanism of associative learning with an opponent processing circuit, called a recurrent gated dipole. READ circuit properties clarify how positive and negative reinforcers are learned and extinguished during primary and secondary conditioning. Habituating chemical transmitters within a gated dipole determine an affective adaptation level, or context, against which later events are evaluated. Neutral conditioned stimuli can become reinforcers by being associated,~ ither with direct activations or with antagonisticre bounds within a previouslyh abituatedd ipole. Neural mechanisms are characterized whereby conditioning can be actively extinguished, and associatives aturation prevented, by a process called opponent extinction, even if no passive memory decay occurs. Opponent extinction exploits a functional dissociation between read-in a:tld read-out of associative memory, which may be achieved by locating the associativem echaniSJant dendritic spines. READ circuit mechanismsa rejoined to cognitive-emotionaml echanismsfo r associativel earning of conditionedr einforcersa nd of incentive motivation, and to cognitive-.in particular, adaptiver esonanceth eory-mechanismsf or activating and storing internal representationosf sensoryc uesi n a limited-capacity short-term memory( STM);f or learning, matchiJlg, and mismatching sensory expectanciesl, e ading to the enhancemenot r updatingo f STM; antI for shifting the focuso f attention toward sensoryre presentations whose reinforcement history ill consistent with momentary appetitive requirements. This total neural architecture is used to explain conditioning and extinction of a conditioned excitor; conditioning and nonextinction of a conditioned inhibitor; and properties of conditioned inhibition as a ""slave"" process and as a ""comparator"" process including effects of pretest deflation or inflation of the conditioning co~terl, of familiar or novel training or test contexts, of weak or strong shocks,a nd of preconditioltlingu nconditioned-stimulus-alone exposures.T he same mechanismsh ave elsewhere been used to explain phenomena such as blocking, unblocking, overshadowing l, a tent inhibition, supercolJditioningin, verted U in conditioninga s a functiono f interstimulus interval, anticipatory conditioned responses, partial reinforcement acquisition effect, learned heclplessnessa, and vicious-circle behavior. The theory clarifies why alternative models have been unable to explain an equally large data base.
Topics:
Biological Learning,
Models:
Other,
