Pigeons’ Memory for Time: Assessment of the Role of Subjective Shortening in the Duration of Comparison Procedure

In Experiment 1, pigeons were trained with a 1-s baseline s-c delay in a duration comparison procedure to peck one key if a comparison duration (c) was 1-s shorter than a standard duration (s), and another key if c was 1-s longer than s. The duration pairs used prevented pigeons from relying on the absolute duration of c on some trials (comparison common) while on other trials they could rely on the absolute duration of c (comparison unique). Pigeons were then tested with equal duration pairs at extended s-c delays of 1, 2, 4, and 8 s. Long responding increased as a function of s-c delay length and at the 8-s s-c delay responding was indicative of a reliance upon the absolute duration of c. In Experiment 2, no-standard probe testing was used to assess whether responding was controlled by the absolute duration of c at the 8-s s-c delay. Long responding on comparison common durations of c was significantly higher than 8-s s-c delay testing, which suggested that the memory of s was still impacting long responding. In Experiment 3, pigeons were trained with white vertical lines superimposed onto the keys to make the trial presentation phase distinct from the intertrial interval (ITI). Extended s-c delay testing with equal duration pairs revealed similar s-c delay functions to Experiment 1 when the lines were present throughout the s-c delay, but not when the lines were absent from the s-c delay. Taken together, these results suggest that subjective shortening can account for the increase in long responding on comparison common trials in Experiment 1 and line-present test trials in Experiment 3