Discrimination of compound stimuli involving the presence or absence of a distinctive visual feature.

Pigeons learned a free operant, go/no-go discrimination between stimuli produced by rapid alternation of different features on the response key. The 0 degrees -B compound consisted of a vertical black line on a white background (the 0 degrees feature) alternated with a blank white field (the B feature), with successive 0.75-sec feature on periods separated by 0.20-sec dark periods. Pecks at the alternating 0 degrees and B features were recorded separately. When pecks at the 0 degrees -B compound were reinforced and pecks at the B-B stimulus (repeated brief presentations of the B feature) were extinguished, the birds pecked more at the 0 degrees feature than at the B feature in the 0 degrees -B compound; subsequently, decremental line-tilt generalization gradients were obtained. When pecks at B-B were reinforced and pecks at 0 degrees -B were extinguished, the rate of pecking at the 0 degrees feature decreased to a low level much more rapidly than did the rate of pecking at the B feature in the 0 degrees -B compound; incremental line-tilt gradients were obtained. Following training with pecks at 0 degrees -B reinforced and pecks at 0 degrees -0 degrees extinguished, incremental line-tilt gradients were obtained, whereas the gradients were decremental following training with 0 degrees -0 degrees reinforced and 0 degrees -B extinguished.