Control of the temporal location of schedule-induced attack in pigeons.

Pigeons were exposed to complex fixed-ratio schedules to assess whether the temporal location of schedule-induced attack was controlled by the discriminative properties of food or by the aversive aftereffects of food withdrawal. When exposed to a multiple fixed-ratio 25 fixed-ratio N schedule in which either fixed-ratio component occurred with equal probability according to a quasi-random sequence and in which the value of N ranged from 115 to 150 across subjects, all pigeons exhibited post-food attack against a rear-projected conspecific target predominantly at the signalled onset of the higher-valued ratio component. Exposure of subjects to a mixed fixed-ratio 25 chained fixed-ratio 25 fixed-ratio N-25 schedule, however, resulted in a shift of attack to the signalled onset of the fixed-ratio N-25 component rather than following food. A chained fixed-ratio 25 fixed-ratio N-25 schedule induced attack predominantly after food delivery rather than at the onset of the fixed-ratio N-25 component. These findings show that the temporal locus of schedule-induced attack is primarily controlled by a stimulus, whether food delivery or key color change, that reliably precedes a relatively long period of reinforcer unavailability.