In earlier studies with rats, the effectiveness of the auditory element of a tone--light discriminative stimulus was enhanced when the conditioned incentive value of the compound was negative rather than positive. The present experiment systematically replicated these results in pigeons trained to press a treadle in the presence of a tone--light compound under food-reinforcement or shock-avoidance schedules. Positive incentive value was conditioned to the compound by associating it with either food or relative safety from shock. The compound was made negative in other groups by associating it with shock or the absence of food. When tone and light were presented separately following this training, control by the auditory element was significantly enhanced in the conditions designed to make the compound negative rather than positive. The similarity of this constraint on learning in rats and pigeons suggests that it involves a fundamental attentional and incentive-motivational process with widespread species generality.