Rate of reinforcement and session duration as determinants of within-session patterns of responding

Abstract

Rats pressed levers for Noyes pellets or keys for sweetened condensed milk reinforcers delivered by multiple schedules. Session length and baseline rates of reinforcement were varied in two experiments. Rates of responding increased during the early part of the session and then decreased for both responses and reinforcers, as weIl as for all subjects and values ofthe independent variables. Changes in response rates across the session sometimes exceeded 500%. Response rates peaked approximately 20 min after the beginning of the session, regardless of session duration, when subjects responded on a multiple variable intervall-min variable intervall-min schedule. The function was flatter for longer sessions than it was for shorter sessions. The function was flatter, more symmetrical, and peaked later for lower rates ofreinforcement than for higher rates of reinforcement. The function appeared early in training, and further experience moved and reduced its peak. Variables related to reinforcement exerted more control over some aspects ofthis function than did variables related to responding. These within-session patterns ofresponding may have fundamental implications for experimental design and theorizing. 160Absolute rate of responding is one of the primary dependent variables in operant psychology. Given its importance, it is surprising that little is known about the way in which response rates change across experimental sessions.Preliminary infonnation on this topic was provided by McSweeney, Hatfield, and Allen (1990). In their study, rats pressed levers for Noyes pellets or pressed keys for sweetened condensed milk delivered by a multiple variable interval l-min variable interval l-min (multiple VI l-min VI l-min) schedule. The components ofthe multiple schedule alternated every 5 min. Rates of responding increased for the first 20 min of the 6O-min experimental session and then decreased. This bitonic function occurred for both responses and both reinforcers, as well as for each subject. The change in response rate was large. For example, the rate of keypressing averaged 15.7 and 27.5 responses per minute for the first and last 5 min of the session, respectively. It averaged 70.0 responses per minute at its peak.The bitonic functions reported by McSweeney et al. have many implications. First, they imply that the rate of responding averaged across the session-one of the primary dependent variables in operant psychologymasks large and reliable regularities in animal behavior, at least in some cases. Therefore, this molar measure must This research was panially supported by NIMH Grant MH 42466. The author wishes to thanklohn Hinson for his comments on an early version of Ibis manuscript and Cam Melville for bis help in conducting the experiments. Reprints may be obtained from F.

Dynamic changes in reinforcer effectiveness: Satiation and habituation have different implications for theory and practice

“…Rate of responding often increases to a peak and then decreases, but it sometimes only increases or only decreases within a session (e.g., McSweeney, 1992;McSweeney, Hatfield, & Allen, 1990). These changes occur in steadystate behavior.…”

“…For example, altering characteristics of the reinforcers such as their rate of delivery (McSweeney, 1992;McSweeney, Roll, & Cannon, 1994;McSweeney, Roll, & Weatherly, 1994;McSweeney & Swindell, 1999a; . At this time, changes in the effectiveness of the reinforcer appear to be the major, but not the sole, determinant of within-session changes in responding.…”

“…We argue that habituation contributes to these changes, not that it is the sole contributor. Swindell, & Weatherly, 1999), the behavioral interactions observed during multiple schedules (McSweeney, Kowal, Murphy, & Isava, in press;McSweeney, Murphy, & Kowal, 2003, 2004bMcSweeney, Swindell, Murphy, & Kowal, 2004;Swindell, McSweeney, & Murphy, 2003), some results that are usually attributed to behavioral economics (McSweeney & Swindell, 1999a;, and the bitonic relation between rate of responding and rate of reinforcement (e.g., McSweeney, 1992 Reducing the effectiveness ofa problematic reinforcer. Many behavioral problems occur because a reinforcer is too strong and maintains too much be-havior (e.g., obesity, smoking, drug consumption).…”

Economic context and pigeons’ risk-taking: an integrative approach

“…Few studies have examined the effects of session length on relative measures such as choice. The current literature base has focused primarily on session length effects upon within-session responding using multiple variable-interval schedules (McSweeney 1992;McSweeney, Roll & Cannon 1994), and has indicated systematic decreases in responding with longer session lengths, although response peaks were found to be independent of the session length. Although some experiments have…”

Effect of Unsignaled Delay to Reinforcement on Within-Session Responding

“…Reinforcers were scheduled at a probability of 0.0667 (VI 15-s schedule) or 0.0167 (VI 60-s schedule) every 1 s, depending upon the condition. These schedules of reinforcement were chosen because they typically produce different within-session patterns of responding (e.g., McSweeney, 1992). After a reinforcer was scheduled, the next response initiated an unsignaled delay of 0.04, 0.20, 1.00, 5.00, or 25.00 s. These particular delays were chosen because they were multiples of five and well represented the range of delays typically used in research on delayed reinforcement (e.g., Byrne et aI., 1998;Williams, 1976).…”