In a conditional discrimination, pigeons’ responses on a right key were reinforced in the presence of a 0° line orientation, and responses on a left key were reinforced in the presence of any of five other orientations, 15° through 75°. Variable-interval schedules of reinforcement for right and left responses were changed over five experimental conditions. Values for a measure of discriminability of 0° from other orientations increased as orientation difference increased. Sensitivity of the choice between right and left in the different orientations, to reinforcers for right and left responses, changed with orientation difference. The effect of reinforcers in one component of a conditional discrimination on responding in another may therefore be modulated by the discriminability of the stimuli signaling the components.