Qualitatively different reinforcers and parameters of Herrnstein's (1970) response-strength equation

Previous research that compared the estimated parameters (i.e., k and R-c) from Herrnstein's (1970) hyperbolic matching law equation within the same individuals responding for qualitatively different consummatory reinforcers (i.e., water and sucrose solution) found similar asymptotic response rates (k). The present study compared these parameters within subjects responding on levers for consummatory and nonconsummatory reinforcers. Male Wistar rats responded on a lever in a running wheel on a series of tandem FR 1 VI schedules for either 0.1 ml of a 15% sucrose solution or the opportunity to run for 15 sec. Herrnstein's hyperbola was fit to response and reinforcement rates from each session. Results showed that k values were significantly higher for sucrose than for wheel-running reinforcement. On average, R-e was lower for sucrose than for wheel-running reinforcement, though not significantly lower. The results of the present study appear to violate the assumption of the constancy of k in Herrnstein's matching law analysis.