We propose to call situations in which the CS is only paralleling the appearance of the US, i.e. the change in a behavioral program primarily determines reinforcer presentation 'parallel' operant conditioning. In such cases, both the significant stimulus (i.e. the reinforcer or US) and the insignificant one (i.e. the CS) are controlled in the same way by the behavior of the animal (solid arrows) and both feed back on the animal (dotted arrows). The animal is thus provided with the opportunity to simultaneously learn to modify a behavioral program and about the (temporal) relation between CS and US.

In the Drosophila flight simulator, parallel operant conditioning is brought about using the switch (sw)-mode setup. The tethered fly is heated whenever the fly's yaw torque is in one half of its range (approximately corresponding to either left or right turns). The heat is switched off as soon as the torque passes into the other half (henceforth: yaw torque sign inversion). During yaw torque sign inversion the two visual cues are exchanged. For colors as visual cues, the panorama contains no patterns and the only the illumination of the arena is changed from green to blue or vice versa. For patterns as visual cues, one of the four T-shaped patterns is presented stationarily in front of the fly. Whenever the range of the fly's yaw torque passes into the other half, the arena is turned by 90° to bring the other pattern orientation in front.