110 rats were trained under a series of variable-interval schedules of sucrose reinforcement (0.6 M, 50 μl), covering a wide range of scheduled interreinforcement intervals. Response and reinforcement rates recorded during the last five sessions of exposure to each schedule were used to fit Herrnstein's (1970) hyperbolic ‘response strength’ equation to the data from each rat The equation accounted for >80% of the data variance in 90%, and >90% of the variance in 60% of the sample. The distribution of the values of Rmax, the asymptote of the hyperbolic curve, did not depart significantly from normality. However, the distribution of the values of KH, the reinforcement rate needed to maintain the half-maximum response rate, was markedly skewed; logarithmically transformed values of KH conformed to a normal distribution. The data provide further support for the applicability of Herrnstein's equation to variable-interval performance; it is suggested that studies involving comparison of the parameters of the equation between groups of subjects should adopt logarithmic transformation of the values of KH.
Herrnstein’s equation for the rates of responding during concurrent schedules