Temporal Discrimination and External Clock

Abstract

Six experiments investigated the role of an external timing stimulus or 'clock' within both temporal discrimination and temporal differentiation procedures. The external clock used was selected so as to minimize the amount of non-temporal information available to the subject. Also investigated was the role played by stimulus content in duration discrimination. Experiments 1 to 5 used a temporal discrimination procedure. Pigeon's key pecks were reinforced following one of two durations of blackout. Duration control was measured using generalization gradients. The external clock was generally found to weaken duration control. Experiment 6 examined the role of an external clock within a temporal differentiation procedure. Three types of external clock were examined in a fixed interval 20-s schedule. The external clocks differed according to the amount of non-temporal information available to the subject. The results from this experiment indicated that the amount of non-temporal information available to the subject was an important variable in the amount of stimulus control acquired by the external clock. The overall results were placed within a two-dimensional stimulus control framework, and were taken to indicate that external clocks acted in much the same way as any other external discriminative stimulus. The role of stimulus content in duration discrimination was also interpreted with a two-dimensional stimulus control framework, although a second interpretation based on the role of an internal clock was suggested. These results indicated the important role played by stimulus content in duration discrimination and its implications for models of animal timing.