Molecular and molar analyses of fixed-interval performance.

Fixed-interval performances of rats were described either in terms of the individual intervals of the session or in terms of a single average interval constructed for the entire session. Responding in the individual intervals usually followed break-and-run and single response patterns rather than the scalloped pattern that emerged when the results were averaged. There was, however, a reasonable correspondence between the quarter-life values calculated from individual intervals and those calculated from the averages. According to the pattern exhibited by the average interval, the probability of a response increased as the interval elapsed. The same conclusion was indicated by more molecular analyses of the conditional probabilities of pause terminations. The results showed that descriptions of fixed-interval data in terms of overall averages reveal aspects of performance that are not immediately apparent within individual intervals.