Effects of Increment Size and Reinforcer Volume on Progressive Ratio Performance

Abstract

The progressive ratio schedule requires the subject to emit an increasing number of responses for each successive reinforcement. Eventually, the response requirement becomes so large that the subject fails to respond for a period of 15 min and thereby terminates the session. This point is arbitrarily defined as the "breaking point" of the subject's performance. The measure is quantified in terms of the number of responses in the final completed (i.e., reinforced) ratio run of the session. Previous work has shown that this measure varies as a function of several motivational variables and may thus be useful as an index of reinforcement strength. The present study is an extension of that work. The subjects were four rats. In the first experiment, the effects of the size of the increment by which each ratio run increased were studied. In two additional experiments, the volume of a liquid reinforcer was varied using both large and small ratio increments. The results indicate that the number of responses in the final completed ratio run increases as a function of the size of the ratio increment. However, the number of reinforcements obtained by the animals per session declines sharply. When large ratio increments are used, the number of responses in the final ratio increases as a function of the volume of the reinforcer, but when small increments are used, progressive satiation results in a decline in performance with the larger volumes of liquid.In order to make precise comparisons between behaviors maintained by different reinforcers, an experimenter must be able to make some statement as to the relative strength of each reinforcer. This Using this index, orderly relationships have been obtained (Hodos, 1961) between the breaking point of behavior and such variables as the concentration of a liquid reinforcer and the degree of food deprivation. The purpose of the present investigation is two-fold: (1) to study the effects of variation in the size of the ratio increment on progressive ratio performance, and, (2) to extend the earlier findings by determining whether the breaking 387

A novel procedure for assessing the effects of drugs on satiation in baboons: effects of memantine and dexfenfluramine

“…In addition to comparing commodities, BPs have been shown to vary systematically as a function of the stimulus qualities of the commodity or magnitude of the commodity. In general, increasing the amount of commodity delivered per reinforcement increases the BP for that commodity (e.g., Dantzer 1976;Hodos 1961;Hodos and Kalman 1963;Sclafani and Ackroff 2003;Reilly 1999), but Brennan et al (2001) reported an inverted-U function with BP increasing and then decreasing at the highest concentration of a sucrose solution. Given the greater BP for highly palatable food (candy) in monkeys and the role that such food plays in the development of obesity (e.g., Blundell and Finlayson 2004) it was of interest to develop procedures for measuring satiation on both palatable and standard food intake.…”

“…The response schedule requires that an incremental number of operant responses be made for each commodity delivery or reinforcer, i.e., a progressive ratio (PR). Responding was recorded during a long-single session, in which the animals were given ample time to complete the ever-increasing response requirement, with the session ending when no responses had been made for a long period of time, e.g., 15 min (Hodos and Kalman 1963). The value of the completed response requirement prior to the cessation of responding provided the PR breakpoint (BP).…”

“…Thus, food BPs are dynamic and can be used as tools to understand normal and disordered eating behavior. Hodos and Kalman (1963) cautioned that PR schedules with too small an increment in response requirement or too large a reinforcer magnitude could result in satiation thus confounding the estimate of reinforcer strength. Because it takes longer to complete the response requirement as the PR value gets larger, the interval between reinforcer deliveries necessarily gets larger, and the satiating effects of the food already eaten decreases.…”

Effects of hippocampal damage on reward threshold and response rate during self-stimulation of the ventral tegmental area in the rat

“…Addi-tionally, when sucrose pellets were substituted for the grain-based pellets, breakpoints of lesioned rats were differentially increased as compared to controls. As progressive ratio breakpoints are believed to reflect the amount of effort an animal will exert to obtain a reinforcer [22,23,35,53], these results were interpreted as indicating that the lesion had enhanced the incentive motivational properties of the delivered food pellets. Given the well known involvement of the NACC in rewarded behavior (see Ref.…”

Effects of chemotherapeutic agents 5-fluorouracil and methotrexate alone and combined in a mouse model of learning and memory

“…In the progressive ratio procedure, the effects of drugs can be evaluated on two measures of reinforcing efficacy: breakpoint and response rate. The breakpoint is defined as the ratio at which the subject stops responding or the highest ratio completed if a timeconstrained session is used (Hodos 1961;Hodos and Kalman 1963), thus, lower breakpoint values can indicate lower reinforcing value for a reward. Performance under PR schedules of food delivery is considered to reflect the efficacy or motivational strength of food because increases in either deprivation level or reinforcer magnitude increase break points (Hodos and Kalman 1963), and effects on motivation can be separated from overall suppression of response rate (see Stafford et al 1998 for review).…”