When discrimination fails (or at least falters).

Pigeons learned 2 concurrent simultaneous discriminations in which the pecking of left keys versus right keys was reinforced depending on a color that appeared on one of the keys. When the reinforced choice was to peck directly at the color, accuracy was very high initially, but dropped noticeably with continued training. Partial reinforcement of these choices exacerbated the dropoff, sometimes causing accuracies to fall close to zero. By contrast, when the reinforced choice was to peck the alternate-key stimulus, accuracy was very low, initially, but remained high and stable following acquisition. Lowering the reinforcement probability, even to zero, for the latter choices had little effect on their accuracy but yielded increased accuracy on color-choice trials. These results resemble the ambiguous-cue effect and suggest the process of value transfer.