Control of vocal production in budgerigars (Melopsittacus undulatus): selective reinforcement, call differentiation, and stimulus control.

Budgerigars were trained to make a specific call using a real-time automated call recognition system and food reward. Calls produced by the bird were followed by food only if they were similar enough to a template call. The selective reinforcement of a particular call type increased the similarity of the bird's call to the template and decreased overall call variation, including call duration. After the birds' performance reached asymptote (i.e. the calls became matched to the template with no further increase in similarity), a call differentiation procedure was introduced. This procedure consisted of both matching-to-template and non-matching-to-template trials. In order to receive food in non-matching-to-template trials, the birds had to produce a call that was sufficiently different from the template call. This procedure resulted in a `new' call emerging from the first template call which occurred gradually rather than abruptly. In the third procedure, called two-template matching training, the birds had to match their calls to the first template call (signaled by illuminating the left LED) and to the second template call (signaled by illuminating the right LED). The calls produced in both first and second template call trials were well controlled by the position of the LED. These results extend the effects of selective reinforcement, differential reinforcement, and stimulus control on response topographies to the domain of vocalizations in budgerigars.