Multiple-schedule interactions and discrimination

Abstract

Pigeons received variable-interval (VI) reinforcement for keypecking during randomized presentations of seven line-orientation stimuli forming a continuum ranging from horizontal (0 deg) to vertical (90 deg). Each line presentation lasted for 30 sec and was preceded and followed by 30-sec time-outs. After responding stabilized, only responding in the two extreme stimuli (0 and 90 deg) was reinforced. As discrimination training proceeded, strong behavioral contrast and dimensional contrast effects appeared. However, only marginal local effects (local contrast and local dimensional effects), exerted by one line-orientation component upon a second, appeared, indicating that behavioral and dimensional contrast may be independent of parallel local effects. An attempt was made to apply Blough’s (1975) quantitative model of operant generalization and discrimination to the present discrimination procedure. However, this model did not predict the generalization gradient shape that was experimentally obtained. This experiment also yielded two serendipitous findings: (1) Positive behavioral contrast appeared in an extinction-related stimulus (time-out) when other stimuli were switched from reinforcement to extinction (hitherto, positive behavioral contrast had been observed only in responding to a reinforcementrelated stimulus when other stimuli were switched from reinforcement to extinction), and (2) final responding was higher in the presence of an extinction stimulus that had always been an extinction stimulus than it was in the presence of other extinction stimuli that had previously been paired with VI reinforcement.