Quantity of reinforcement and fixed-interval performance

Abstract

Two groups (N = 5) of hybrid-strain rats were conditioned to press a lever on a fIXed-interval 3 min schedule of food reinforcement. For Although quantity or quality of reinforcement has often been varied in studies of free operant behavior (e.g., Collier & Meyers, 1961;Guttman, 1954), relatively few experimenters have studied the effects of these variables on responding maintained by a fIXed-interval reinforcement schedule. Hutt (1954), in a study of fIXed-interval responding, showed that mean response rate increased with increases in both the quality and the quantity of a liquid reinforcer. Similarly, Stebbins, Mead, & Martin (1959), using a within-S procedure, reported that the mean response rate on a fIXed-interval reinforcement schedule increased as the concentration of the sucrose reinforcer increased.Stebbins et al also reported that the distribution of responses within an interreinforcement interval depended on the sucrose concentration of the reinforcer. As sucrose concentration increased from 5% to 32%, the percentage of responses made early in the interreinforcement interval increased, and the percentage made late in the interval decreased. Since the mean response rate increased as well with greater sucrose concentration, the implication is that the increase in response rate occurred at least partly because the Ss made more responses early in the interreinforcement interval at the higher sucrose concentration.In the present experiment, a between-S procedure was used to study the effects of two quantities of reinforcement on fixedinterval responding. We were specifically interested in examining differences in the interreinforcement response distributions associated with the two reinforcement quantities. METHOD Subjects Ten male, hooded rats of a hybrid strain bred in our laboratory were the Ss. Each S was 90-100 days old at the beginning of the experiment and was placed on a 22-h food deprivation schedule one week before the first experimental session. Water was always available to an S except for the time it was in the experimental chamber. ApparatusThe experiment was run in a Skinner box (Lehigh Valley No. 1316) with interior dimensions of 7-1/2 in. x 12 in. x 8 in. A single response lever was located 1-3/16 in. above the grid floor and 1-1/2 in. from the right side of the box. The food hopper was located midway along the base of the front wall, and 45 mg Noyes pellets were used as reinforcement.Masking white noise was always present in the room in which the experimental chamber was located. All the programming and recording equipment was in an adjacent room. Procedure Each S was given one to three I-h sessions of continuous reinforcement in which each lever press produced one food pellet. The reinforcement schedule was then changed to fixed-interval 3 min. Two groups were randomly formed with five Ss in each. For the l-pellet group the reinforcement was one 45 mg pellet delivered immediately after the lever press. For the 3-pellet group the reinforcement consisted of three 45 mg pellets. One pell...

Quantity of reinforcement and fixed-interval performance: Within-subject effects

“…The size of the multiplier varied for individual Ss, but the phenomenon was basically the same for all Ss. DISCUSSION Response distribution, as measured by percentages, was not affected by reinforcement quantity either when individual Ss experienced only one quantity of reinforcement (Meltzer & Brahlek, 1968) or when they experienced two quantities of reinforcement. Apparently the results reported by Stebbins et al (1959), in which response distribution changed as a function of sucrose concentration, were caused by some factor other than exposure of individual Ss to different reinforcers.…”

“…There were several differences between the Stebbins et al (1959) and the Meltzer & Brahlek (1968) studies, one of which was that all Ss experienced all the different reinforcement magnitudes in the former study while each .S experienced only one reinforcement quantity in the latter. This experiment examined the effect of different reinforcement magnitUdes on FI performance in a within-S design.…”

“…Acceleration of response rate during the interval was a function of reinforcement quantity; but acceleration of response rate relative to the terminal rate of a S was not related to reinforcement quantity. Meltzer & Brahlek (1968) claimed that the response distribution during the interval might be a better index of the delay gradient than response rate. In that case, it could be concluded that the delay gradient was unaffected by quantity of reinforcement.…”

“…The Meltzer & Brahlek (1968) recently described the effects of different reinforcement quantities on the fixed-interval (FI) performance of two groups of rats. The Ss in both groups were reinforced on an FI 3-min schedule.…”

Rats show preference for delayed rewards on the radial maze

“…Thus, rats will run down a runway or press a bar faster for a larger amount of food than they will for a smaller amount (Meltzer & Brahlek, 1968;Roberts, 1969). Given a choice between responses leading to small or large rewards, animals choose the large reward (Clayton, 1964;Davenport, 1962).…”