Rat toys, reinforcers, and response strength: An examination of the Re parameter in Herrnstein's equation.

The response-strength equation is a mathematical model used to explain responding on variable-interval (VI) schedules. This equation has two fitted parameters, k and Re. Empirical research suggests that k is a measure of motor performance and Re is a measure of background sources of reinforcement relative to the arranged reinforcer. This experiment examined the interpretation of the Re parameter by augmenting the background reinforcement with a qualitatively different source of background reinforcement. Rats were food deprived and received sucrose solution for lever responding. Each experimental session consisted of a series of seven VI schedules, providing reinforcement rates that varied between 20 to 1200 h(-1). Occasionally, cardboard tubes were introduced into the experimental chambers in order to provide the rats with another source of reinforcement distinct from the lever-response specific sucrose reinforcer. The k parameter did not change systematically as a result of the experimental manipulations, but Re was significantly larger when tubes were introduced into the chambers. These results are consistent with the interpretation that k and Re measure two independent and experimentally distinguishable parameters and that Re is a measure of reinforcement of background sources to the arranged reinforcer.