BEHAVIORAL CONTRAST WHEN RESPONSES ARE MAINTAINED BY UNSIGNALED DELAYED REINFORCEMENT

Resumen

 Positive and negative behavioral contrast were studied in pigeons when keypecking was maintained by a variable-interval (VI) schedule with a 1- or 2-s unsignaled delay prior to each reinforcer. In three different conditions, extinction (defined as removing the reinforcer) alternated with the VI schedule. These extinction conditions were programmed as 20-s blackouts of the chamber, 100-s blackouts of the chamber, or 20-s changes in the color of the response key. Adding extinction in any of these forms increased response rates maintained by the delayed-reinforcement contingency (positive contrast), and removing extinction decreased these response rates (negative contrast). Differential behavioral contrast did not occur systematically across pigeons as a function of the different extinction conditions. The results extend to responding maintained by delayed reinforcement the range of circumstances under which behavioral contrast occurs. The role of contingencies controlling low response rates and different types and durations of stimuli in generating behavioral contrast are discussed.