Answer:
The differential outcomes effect (DOE) is a theory in behaviorism, a branch of psychology, that shows that a positive effect on accuracy occurs in discrimination learning between different stimuli when unique rewards are paired with each individual stimulus. The DOE was first demonstrated in 1970 by Milton Trapold on an experiment with rats.[1] Rats were trained to discriminate between a clicker and a tone by pressing the left and right levers. Half of the rats were trained using the differential outcomes procedure (DOP), where the clicker was paired with sucrose and tone with food pellets. The remaining rats were trained with only sucrose or only food pellets. The rats trained with the DOP were significantly more accurate than those trained with only one type of reinforcement (common outcome). Since then it has been established through a myriad of experiments that the DOE exists in most species capable of learning.