Context effects in a temporal discrimination task: further tests of the scalar expectancy theory and learning-to-time models

Pigeons were trained on two temporal bisection tasks, which alternated every two sessions. In the first task, they learned to choose a red key after a 1-s signal and a green key after a 4-s signal; in the second task, they learned to choose a blue key after a 4-s signal and a yellow key after a 16-s signal. Then the pigeons were exposed to a series of test trials in order to contrast two timing models, Learning-to-Time (LeT) and Scalar Expectancy Theory (SET). The models made substantially different predictions particularly for the test trials in which the sample duration ranged from 1 s to 16 s and the choice keys were Green and Blue, the keys associated with the same 4-s samples: LeT predicted that preference for Green should increase with sample duration, a context effect, but SET predicted that preference for Green should not vary with sample duration. The results were consistent with LeT. The present study adds to the literature the finding that the context effect occurs even when the two basic discriminations are never combined in the same session.Research was supported by a grant from the Portuguese Foundation for Science and Technology (FCT) to Armando Machado. Joana Arantes was supported by a Ph.D. scholarship from the Portuguese Foundation for Science and Technology (FCT). We thank John Staddon, Randolph Grace, and Luı´s Oliveira for helpful comments on earlier versions of the paper, and Alexandra Lima for assistance with data collection.