Separating the Reinforcing and Discriminative Properties of Brief‐stimulus Presentations in Second‐order Schedules

Abstract

Pigeons' responses were maintained under multiple schedules to study properties of briefly presented stimuli. Responses in one component produced food according to a second-order schedule with fixed-interval components in which food or a brief stimulus occurred with equal probability. In the second component responses produced only the brief stimulus under a fixed-ratio schedule. Under various conditions the brief stimulus in the first component was (a) paired with food, (b) not paired with food, (c) partially omitted, or (d) scheduled simultaneously with the second-order schedule under an independent variable-interval schedule. Paired and nonpaired brief stimuli maintained similar response patterning in the second-order schedule. However, only paired stimuli maintained responses in the second component. The data suggest that nonpaired brief stimuli engender response patterning in second-order schedules as a result of their discriminative properties. When the stimulus is paired with food, these discriminative properties sometime mask a reinforcement effect, and no change in response patterning is observed. When the discriminative properties of the brief stimulus are absent, the reinforcing effects of pairing the brief stimulus with food may be observed.

Effects of medial prefrontal or anterior cingulate cortex lesions on responding for cocaine under fixed-ratio and second-order schedules of reinforcement in rats

“…Omission of the drug-associated light stimulus resulted in disruption of response rates and patterns in control rats, with a significant decrease in Ic values. These findings confirm previous studies that have demonstrated the ability of reinforcer-associated cues to maintain rates and patterns of responding under secondorder schedules using cocaine, heroin or food as reinforcers in monkeys and pigeons (Goldberg and Tang 1977;Kelleher and Goldberg 1977;Cohen et al 1979;Goldberg et al 1979;Cohen 1991) and sexual contact as a reinforcer in rats (Everitt et al 1987). The present study also showed changes in response patterns in the absence of changes in response rates, indicating that simple rates of responding may not be sufficient as an indicator of stimulus control over behaviour under the conditions tested here.…”

“…The acquisition of a new response with conditioned reinforcement is unaffected by cell-body lesions selectively of prelimbic parts of the medial prefrontal cortex (Burns et al 1993) and stimulus-reward learning assessed using a simple Pavlovian conditioning procedure is unimpaired by medial prefrontal cortex lesions similar to those studied here (Bussey et al 1997). The present paradigm does not distinguish clearly between the conditioned and discriminative stimulus effects of the cocaine-associated light stimulus (Cohen et al 1979), thereby confounding possible comparisons with previous work. Consequently, it cannot be ruled out that the present data are at least in part accounted for on the basis of impaired incentive-motivational control over responding.…”

Effects of Fixed‐time Shocks and Brief Stimuli on Food‐maintained Behavior of Rats

“…In second-order schedules of reinforcement, Cohen, Calisto, and Lentz (1979) found thai brief stimuli that maintained patterns of responding only had reinforcing effects when they had been paired with the reinforcer. In parallel, one would expect that the tone in the present study would not have acquired aversive properties because it was not paired with shock.…”

Conditioned Reinforcement: Experimental and Theoretical Issues

“…If such pairings are not required, it seems unlikely that the enhancements of response rate seen with such stimuli are in fact due to the conditioned value ofthe brief-stimuli, which presumably depends on their Pavlovian association with the primary reward. The experimental literature on the effects of paired versus unpaired brief-stimulus presentations is extremely complex, with no clear rationale for when the pairing operation will be critical (see Gollub, 1977, pp. 302-305 for a review; also see Cohen, Calisto, & Lentz, 1979, for an important subsequent study).…”