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The term "operant conditioning" is used here to describe a type of associative learning in which there is a contingency between the presentation of response and reinforcer. This situation resembles most closely the classic experiments of Skinner (1938), where he trained rats and pigeons to press a lever in order to obtain a food reward ("Skinner-Box"). In such experiments, the subject is often able to generate a variety of motor-outputs. The experimenter chooses a suited output (the response R, e.g. pressing a lever) at t1 to pair it with an unconditioned stimulus (US, e.g. a food reward). Often a discriminative stimulus (SD, e.g. a light) is present when the R-US contingency is true. After a training period (at t2), the subject will show enhanced R - the conditioned response (CR, e.g. pressing a lever) - even in absence of the US if the R-US association has been memorized. The subject is said to have learned about salient contingencies between its own behavior and some part of the world. Such instrumental or operant conditioning is opposed to Pavlovian or "classical conditioning", as described above (1.2), where producing a response has no effect on US presentations. This fundamental difference has an important temporal consequence: whereas it is per definitionem of no value for the subject to make any associations during classical conditioning - it will receive the US anyway - operant behavior provides the subject with a means to optimize its situation already during acquisition. In other words: classical conditioning can be perceived as passive learning from events in the past, while operant conditioning implies learning to behave in the present and the future.
This view is reflected in the work of Wolf and Heisenberg (1991), who have further analyzed the process of operant conditioning in Drosophila and propose a basic model of operant behavior (Fig. 2):
Fig. 2: General model of operant behavior. The brain generates a large variety of motor-outputs and cross-correlates them with one or several sensory inputs. If, for a certain combination, the correlation is sufficiently positive, the fly can manipulate this sensory input according to its needs. The long external arrow coupling 'rotatory control maneuvers' and 'temperature', depicts the situation of a fly in the Drosophila Flight Simulator. (From: Wolf and Heisenberg, 1991)
According to Wolf and Heisenberg (1991) operant behavior is the active choice of one out of several output channels in order to minimize the deviations of the current situation from a desired situation (1-4). Operant conditioning in these terms is expressed by persisting activation of this channel after the situation has changed (5). Mutant analyses in Drosophila have shown that these processes can also be genetically distinguished (Eyding, 1993; Weidtmann, 1993).
For more information on operant conditioning see the documents on various properties of operant conditioning.
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