Attentuation of the differential outcomes effect by extraneous reward

• In delayed matching to sample, a short-term memory task, matching is more accurate when correct choices produce rewards of different amounts (differential outcomes).
• The magnitude of the differential outcomes effect is attenuated when rewards for an extraneous task are arranged in the retention interval.
• Both the differential outcomes effect, and its attenuation by extraneous rewards, is predicted by White and Brown's (2014) reinforcement context model.

The reinforcement context model for performance in delayed matching to sample tasks (White and Brown, 2014) predicts the course of forgetting based on the assumption that rewards for extraneous behavior compete with rewards for accurate matching and increase as a linear function of retention-interval duration. In the differential outcomes effect, greater matching accuracy occurs when correct choices produce different outcomes, which the model assumes have greater reward effectiveness than same outcomes. The model was tested in the present experiment with pigeons by arranging an additional task during the retention interval of a delayed matching to sample task, center-key pecking rewarded by food delivered at variable intervals. This additional source of extraneous reward resulted in attenuation of the differential outcomes effect as predicted by the model. The model was supported by satisfactory quantitative fits to the forgetting functions for same and different outcome conditions with and without additional extraneous reward.