We propose to use the term 'facilitating' operant conditioning to refer to situations in which the behavior controls a stimulus (solid arrow) onto which the reinforcer is made contingent (solid arrow); i.e. there is no a priori contingency between a behavioral program and the reinforcer as in parallel operant conditioning. Of course, both stimuli feed back (dotted arrows) onto the animal. In such occasions, no 'pure' operant conditioning occurs but the operant process can facilitate learning about the stimulus/reinforcer relation.

Facilitating operant conditioning is brought about in the Drosophila flight simulator using the standard flight simulator (fs)-mode: the fly is flying in closed loop to make the rotational speed of the arena proportional to the fly's yaw torque. This enables the fly to stabilize the rotational movements of the panorama. The electric shutter opens whenever the fly brings one of the two pattern pairs into the frontal 90° sector of its visual field. The fly is punished by the heat beam and will eventually change its flight direction towards the other pattern, whereupon the shutter will close. After some minutes the fly will avoid the pattern previously associated with heat even when the heat is permanently switched off. In a similar manner flies can be trained to avoid one of two colors. The patterns are replaced by four identical vertical stripes. These denote the centers of four virtual quadrants. Whenever the fly turns the arena and enters a new quadrant, the color filter between the light source and the light guides changes the illumination of the entire arena from one color to the other. Training is conducted as in the pattern conditioning experiment: heat when the arena is illuminated with one color but not with the other. Flies quickly develop a preference for the unpunished illumination and keep that preference even when the heat is permanently switched off.