An inexpensive method to study response variability in acquisition and extinction of operant behavior

To examine operant response variability in detail, a lever was attached to the Thumbstick of a videogame controller, which functions as a joystick. The controller was mounted outside of a standard rodent operant chamber with the lever extending into the chamber. Movement of the lever was restricted to a vertical downward distance of 2 cm.

Food pellet delivery was used as reinforcement of lever movement. Criteria for reinforcement were that the lever should be held between two criteria distances, one from the top resting position of the lever and one from the end position of full movement, and the holding response should last a certain duration. Apparatus construction and development of algorithms for response detection and display in graph format as actograms are described in detail. The use of the equipment is illustrated with two demonstration experiments that examined response variability in extinction and during acquisition.

The recording method allows for display of considerable detail regarding variability in real time with a resolution of 100 ms. For example, for Experiment 1, extinction of a relatively “simple” operant generated considerably new response forms with very little repetition of the form of the previously reinforced operant.