Differential outcome effect in the horse

Three horses were trained with a discrimination task in which the color (bl ue or yellow) of a center panel signaled the correct (left or right) respon se (lever press). Reinforcing outcomes for the two correct color-position c ombinations (blue-left and yellow-right) were varied across phases. Discrim ination performance was better when the combinations were differentially re inforced by two types of food (chopped carrot pieces and a solid food pelle t) than when the combinations were randomly reinforced by these outcomes or when there was a common reinforcer for each of the correct combinations. H owever, the discrimination performance established by the differential outc ome procedure was still 80% to 90% correct, and an analysis of two-trial se quences revealed that the stimulus color of the preceding trial interfered with discrimination performance on a given trial. Our demonstration of the differential outcome effect in the horse and its further analysis might con tribute to more efficient control of equine behavior in the laboratory as w ell as in horse sports.