Task-dependent switching of feedback controllers

The separation of distinct motor memories by contextual cues is a well known and well studied phenomenon of feedforward human motor control. However, there is no clear evidence of such context-induced separation in feedback control. Here we test both experimentally and computationally if context-dependent switching of feedback controllers is possible in the human motor system. Specifically, we probe visuomotor feedback responses of our human participants in two different tasks – stop and hit – and under two different schedules. The first, blocked schedule, is used to measure the behaviour of stop and hit controllers in isolation, showing that it can only be described by two independent controllers with two different sets of control gains. The second, mixed schedule, is then used to compare how such behaviour evolves when participants regularly switch from one task to the other. Our results support our hypothesis that there is contextual switching of feedback controllers, further extending the accumulating evidence of shared features between feedforward and feedback control.

Discrimination between Outcomes in Instrumental Learning: Effects of Preexposure to the Reinforcers

In two experiments rats received instrumental training with two response levers, one response being reinforced by sucrose solution and the other by sucrose pellets. Prior to a test session, on which both levers were made available in the absence of reinforcement, the rats were given free access to one of the reinforcers, a procedure known to reduce its value. It was found that the rats responded at a lower rate on the lever that had produced the now-devalued reinforcer, but that this effect was substantial only in rats that had received preexposure to the two reinforcers before instrumental training was begun (Experiment 1). Experiment 2 demonstrated that this effect was obtained only when presentations of the two reinforcers were presented according to an inter-mixed schedule during preexposure. It is suggested that this result constitutes an instance of the perceptual learning effect in which intermixed preexposure to similar events enhances their discriminability.

Extinction of Observing Behavior

The probability of observing-key responses for pigeons trained to observe during a mixed-fixed ratio 50 fixed-interval 2-min. schedule of reinforcement decreased sharply when only the mixed schedule or the corresponding multiple schedule was programmed. First session observing-key response probability values were greater in the mixed-schedule condition, suggesting that the mixed-schedule stimulus set the occasion for pecking the observing-key following reinforcement offset. In the mixed-schedule condition, the results for one bird suggested that stimuli associated with the early portion of each component controlled a relatively high response-rate; and, when the component was fixed-interval, stimuli arising from the organism's behavior controlled a pause which followed more than 50 responses. This post-response pause contributed to the determination of a relatively low response-rate in the fixed-interval component of the mixed-schedule.