DISCRIMINATION OF COMPOUND STIMULI INVOLVING THE PRESENCE OR ABSENCE OF A DISTINCTIVE VISUAL FEATURE 1

Pigeons learned a free operant, go/no‐go discrimination between stimuli produced by rapid alternation of different features on the response key. The 0° –B compound consisted of a vertical black line on a white background (the 0° 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° and B features were recorded separately. When pecks at the 0°–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° feature than at the B feature in the 0°–B compound; subsequently, decremental line‐tilt generalization gradients were obtained. When pecks at B—B were reinforced and pecks at 0°–B were extinguished, the rate of pecking at the 0° feature decreased to a low level much more rapidly than did the rate of pecking at the B feature in the 0°–B compound; incremental line‐tilt gradients were obtained. Following training with pecks at 0°–B reinforced and pecks at 0°–0° extinguished, incremental line‐tilt gradients were obtained, whereas the gradients were decremental following training with 0°–0° reinforced and 0°–B extinguished.