Academic journal article The Psychological Record

Postreinforcement Pause Duration Varies within a Session and with a Variable Response Requirement but Not as a Function of Prior Revolutions

Academic journal article The Psychological Record

Postreinforcement Pause Duration Varies within a Session and with a Variable Response Requirement but Not as a Function of Prior Revolutions

Article excerpt

Learning more about the factors that influence postreinforcement pause (PRP) duration is important in the experimental analysis of behavior, particularly with respect to understanding differences between qualitatively different reinforcers. PRP duration can index changes in the value of a reinforcing consequence; however, it can also reflect inhibitory postreinforcement effects and/or excitatory stimulus effects (Bonem & Crossman, 1988; Perone & Courtney, 1992; Schlinger, Derenne, & Baron, 2008). The current study investigated the effect of a variable response requirement and number of revolutions on PRP duration in rats responding on levers for the opportunity to run in a wheel as a reinforcer.

It is commonly believed that PRPs tend to be minimal or nonexistent on variable-ratio (VR) schedules (Schlinger et al., 2008), although this appears to be a function of the size of the lowest ratio value in a schedule (Schlinger, Blakely, & Kaczor, 1990). The unpredictable nature of the requirement leads animals to respond more quickly following the termination of a reinforcer. In contrast, when the requirement is fixed, animals typically pause for a long period following the termination of a reinforcer--the duration of the pause varying with the response requirement (Schlinger et al., 2008). While minimal or very short pauses have been demonstrated on VR schedules using conventional reinforcers, they have yet to be shown with wheel-running reinforcement. With the exception of Premack, Schaeffer, and Hundt's (1964) study that used fixed-ratio (FR) schedules, most studies of wheel-running reinforcement have used fixed-interval (FI) schedules (e.g., Belke, 2000; Belke & Dunbar, 1998; Belke & Hancock, 2003; Collier & Hirsch, 1971) and response-initiated variable-interval (VI) schedules (e.g., Belke, 1997; Belke & Heyman, 1994). Response-initiated VI schedules have been used because the longer PRPs following the termination of wheel running would either time out or greatly reduce the programmed reinforcement interval, particularly in the case of short average-duration VI schedules (Belke & Dunbar, 1998). Requiring a response to initiate the reinforcement interval ensures that the schedule is experienced as programmed rather than as a continuous reinforcement schedule. Regardless of this point, PRPs have yet to be described with VR schedules using wheel-running reinforcement. Showing that PRPs are shortened when the ratio requirement is changed from fixed to variable would be a small contribution but consistent with Collier and Hirsch's (1971) conclusion that wheel running generates schedule effects similar to those with more conventional reinforcers.

Of greater importance is the need to understand the relationship between revolutions and PRP duration. If a revolution is considered the unit of value with wheel running, then this relationship would be equivalent to that between reinforcer magnitude and PRP duration with more conventional reinforcers. Because revolutions vary with duration of opportunity to run, the relationship between revolutions and PRP duration should be similar to that between wheel-running reinforcer duration and PRP duration. This latter relation has been investigated with wheel-running reinforcement.

Previous research has shown that as wheel-running reinforcer duration increases, PRP duration increases. Premack et al. (1964) showed that pause duration on a FR 10-lick schedule increased as duration of a contingent opportunity to run increased from 2 s to 30 s. Belke (1997) showed that median PRP duration on a tandem FR 1 VI 30-s schedule (i.e., a response-initiated VI schedule) increased as the duration of an opportunity to run increased across 30 s, 60 s, and 120 s. Belke and Dunbar (1998) found a similar systematic relationship for rats responding on FI schedules with wheel-running reinforcer durations of 15 s, 30 s, and 90 s.

Although a relationship between wheel running as a reinforcer and PRP durations is clearly evident, assessment of the relative role of excitatory effects and inhibitory aftereffects (e. …

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