T- maze learning as a joint function of probability and magnitude of reward

Abstract

Rats were trained on a position discrimination. The experimental design involved simultaneously manipulating per cent and magnitude reward given for the correct response. Learning-rate was found to be a negatively accelerated growth function of reward magnitude for both of the reward schedules used. The results are interpreted as support for the treatment of reward magnitude as a special case of reinforcement probability. ProblemIn a previous study (Clayton, in press) three groups of rats received either 1, 2, or 4 pellets for the correct position response in a T-maze and no reward for an error. Analysis of the resulting performance suggested the following relationship between learning-rate and reward magnitude:where J ~ is the learning-rate parameter associated with r reward pellets. Equation (1) says, generally, that J r is a negatively accelerated growth function of J l' where M is a parameter effecting the growth-rate and asymptote of the curve.The present study was stimulated by an assumption regarding reward magnitude made recently by Estes & Suppes (1959). Following a Guthrian treatment of reward magnitude and distinguishing between reward and reinforcement, Estes & Suppes have suggested reward magnitude is but a special case of rei n for c e men t pro b a b i 1 i t Y in that an increase in magnitude merely increases the probability of the reinforcing event. Within this framework Equation (1) may be conceived as the relationship between learning-rate and reinforcement probability. However, a second variable affecting reinforcement probability should be reward probability, or reward schedule. In the previous study the correct response was always rewarded. The present study sought to determine the effect on the relationship between learning-rate and reward magnitude when the correct response was sometimes nonrewarded. The hypothesis tested was that if Equation (1) relates learning-rate to reinforcement probability, it should hold (with possible changes in M) regardless of whether the correct response was always rewarded.A second purpose of this study was to provide an independent check on Equation (1) with different reward magnitudes to make certain the obtained function is not specific to the particular amounts used previously. For these reasons reward magnitude was factorially manipu-

Faster rates of discrimination learning with centrally elicited reinforcement than with food.

“…Based on an extensive review of the earlier literature, Pubols (1960) concluded that for independent-groups designs, incentive magnitude influences the speed of responding but not the number of trials required to learn a discrimination. More recently, however, several experiments have reported faster discrimination learning with large reinforcement magnitudes (Clayton & Koplin, 1964;Cross & Boyer, 1964;Cross, Rankin, & Wilson, 1964;Waller, 1968). Were incentive factors to have played a role in the present results, one would expect that the large differences between the food-and ICS-reinforced groups in acquiring the discrimination would be accompanied by differences in the speed of running for these reinforcers.…”

Effects of magnitude of reward in spatial and brightness discrimination tasks.

“…The purpose of this study was to provide a parametric evaluation of the effect of reward magnitude on discrimination learning. Previous studies involving a position discrimination indicated that choice performance was directly related to reward magnitude (e.g., Clayton & Koplin, 1964). However, studies of brightness discrimination have produced apparently contradictory results.…”

Role of delay in magnitude of reward effects in discrimination learning in the rat.

“…Until recently, effects of reward magnitude on speed of learning have been consistently reported for spatial discriminations (e.g., Clayton & Koplin, 1964), but inconsistently for brightness discriminations (McKelvey, 1956;Schrier, 1956). Waller (1968), using identical apparatus and procedures for the two task types, found large effects of reward magnitude independent of task.…”