Arantes, J. & Machado, A. (2008).
Context effects in a temporal discrimination task: further
tests of the scalar expectancy theory and learning-to-time models.
Journal of the Experimental Analysis of Behavior, 90, 33-51.
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.
Key words: bisection procedure, context effect, temporal discrimination,
timing models, key peck, pigeon