RELATIONSHIP BETWEEN RESPONSE RATE AND REINFORCEMENT FREQUENCY IN VARIABLE‐INTERVAL SCHEDULES: III. THE EFFECT OF d‐AMPHETAMINE

Abstract

Four rats were exponsed to variable-interval schedules specifying a range of different reinforcement frequencies. The effects of two doses of d-amphetamine (1.6 and 3.2 μmol/kg) upon performance maintained under each schedule were examined. In the case of each rat, the response rates observed under control conditions (no injection or injection of the vehicle alone) were increasing, negatively accelerated functions of reinforcement frequency, the data conforming closely to Herrnstein's (1970) equation. In each rat, d-amphetamine (3.2 μmol/kg) significantly reduced the value of the constant R_max, which expresses the theoretical maximum response rate. In each rat, the value of K_H, which expresses the reinforcement frequency needed to obtain the half-maximal response rate, was also reduced, although this only achieved statistical significance in the case of one rat. When the proportional change in response rate in the presence of the drug was plotted against the response rate under control conditions on double logarithmic co-ordinates, linear functions of negative slope were obtained; in each rat the slope was steeper and the value of the control response rate at which d-amphetamine exerted no effect was lower in the case of the higher dose (3.2 μmol/kg) than in the case of the lower dose (1.6 μmol/kg).