Attentional processing in pigeons: A test of composite stimulus control

Additive Summation occurs when greater responding is produced by simultaneous presentation of two independently trained, reinforcement-associated stimuli than by either presented alone. The current experiments further investigate additive summation using the composite-stimulus analysis viewing the contribution of "on" and "off" states of discriminative stimuli in determining stimulus control. Several studies investigating variables involved in producing additive summation have had limited success replicating this effect with pigeons using a single stimulus modality. The present study applies predictions of the composite-stimulus analysis to visual modality control using a touch-screen computer monitor. Pigeons were trained to peck the screen when presented with two independent reinforcement-associated right triangles that formed a square when compounded. During testing the stimuli and their compound were presented in 18 randomized blocks. Five of six pigeons met the operational definition of additive summation, supporting predictions from the composite-stimulus analysis of stimulus control.