Reward-amount effects may be investigated (a) by the "absolute method" of comparing groups one of which always receives a higher amount of reward for making the given response than does the other group, or (b) by the "differential method" of comparing the strengths of S-R connections learned by the same 5s when these connections are followed by different reward amounts. Under the differential method some quantitative differences in responses followed by different reward amounts are apparently always found (e.g., 2, 5, 16, 13); under the absolute method differences between groups are not found for all measures (4,11,12,14,15). Greene's data (5) suggest different outcomes for these two methods, but he did not stress this possibility. Meyer (13) indicated that training influenced amount-of-reward results, but his 5s were sophisticated rewardwise. The differences produced by these types of training have not been compared within one experiment; such was one purpose of this study.Recent experiments (6, 8, 9) on secondary reward (5 r ) strength-as inferred from resistance to extinction, or rate of new learning with only secondary rewards operative-have not shown it to vary with the amount of primary reward previously associated with the stimuli. These experiments all used the absolute method: only one amount of reward was associated with the stimuli for a given group of 5s. Since the procedures by which a stimulus becomes a discriminative stimulus or an S r are similar (3, 16), S r strength might vary with primary reward amount if the same 5s had different stimuli on a continuum associated with different amounts of reward. This would account for Wolfe's (19) positive results on the preference of different-colored tokens as a
In Experiment I, a four-ply multiple schedule was used to study the effects on rate of responding in rats of food, water, and food and/or water reinforcement under different deprivation conditions. Food and water were associated separately with different stimuli, the combination of which was associated with food and water together, or with food or water randomly. Rates in the presence of the combined stimuli were consistently intermediate to the rates generated by the separate stimuli, a result seemingly incompatible with a "summation" hypothesis. Experiment II was a simplified systematic replication of Experiment I, verifying the major findings.
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