'Pure' operant conditioning is a situation in which only the animal's behavior controls and is modified by, a biologically significant stimulus (reinforcer). No other sensory stimuli are contingent upon the presentation of the reinforcer and no sensory feedback besides the reinforcer is delivered to the animal about its behavior. The feedback loop (dotted arrow) between the reinforcer and the fly's behavior is closed, while the animal controls the reinforcer in a feed forward relation (solid arrow).

In the Drosophila flight simulator, pure operant conditioning is brought about using the yaw torque learning setup: The tethered fly is heated by an infrared lightsource whenever the fly's yaw torque is in one half of its range. The heat is switched off as soon as the torque passes into the other half. In this paradigm, the fly has no external stimuli that might serve as predictors of reinforcement. The arena is still illuminated from behind, but there are no patterns attached to it. This situation is totally unrealistic for the fly: one half of the yaw torque range (approximately corresponding to either left or right turns) is coupled to the heat source. There is no place one could think of where, say, right turns keep the fly away from a heat source and right turns constantly lead to life threatening heat. Neither do the fly's senses provide any information other than about its own behavior. Nevertheless, without extensive training, Drosophila keeps its yaw torque in the 'safe' range. So the central nervous system of the fly has to compare the temporal pattern of the thermoreceptor signals with efference copies of all or many of its motor-outputs. Any significant coincidence leads to modulation of the motor-output in order to keep the sensory input in the desired range. If, after such a training period, the heat is permanently switched off, the fly remembers the part of the yaw torque range that previously had not been heated (s. Fig) and not only stays in this range but also preferentially returns to it after excursions into the other half. Drosophila has been operantly conditioned.