Abstract
Evidence for timing during Pavlovian trace and delay conditioning trials was sought by exposing pigeons to differentially cued trial durations of 18, 24, and 60 sec. For a delay group, one of three visual patterns (CSs) was presented on a key for the entire trial; for a trace group, each CS was 12 sec in duration, creating trace gaps of 6, 12, or 48 sec. Intertrial interval duration was 48 sec. The most informative data were provided by measures of time spent proximal to the CS (proximity). Stimulus control was evident in that proximity was inversely related to trial duration for both groups. Evidence for timing was obtained from the relation of relative proximity during each CS to relative elapsed trial time for individual birds. The obtained superposition of the three functions for each bird is consistent with a scalar timing process and implies that subjects learned the temporal relation between each CS and the unconditioned stimulus. Associative status of the CSs differed between groups and among CS-US intervals, as reflected in proximity data during a higher-order test in which the CSs served as reinforcers. The results are consistent with a two-dimensional model of Pavlovian conditioning according to which the associative strength accruing to a CS is orthogonal to the temporal information encoded for that stimulus.