Temporal Memory of Interfood Interval Distributions with the Same Mean and Variance

The time of occurrence of reinforced lever responses of rats depends on the characteristics of the distribution of times from food to the next available food. Two groups of 10 rats were trained, in counterbalanced order, on two variable-interval schedules of reinforcement that were equated for the mean, standard deviation, and range of the intervals from food to the next available food, but which differed in shape. The differences in the shape of the interfood interval distributions resulted in differences in the distribution of interfood intervals, of postreinforcement pauses, the function relating response rate to time since food, and the power spectra of times of response. Quantitative timing models, such as scalar timing theory and a multiple-oscillator model, differ in their assumptions about the nature of the internal clock and the representation of time in memory. The multiple-oscillator model and scalar timing theory accounted for different features of the data.