Temporal context and conditioned reinforcement value.

Abstract

The effectiveness of a stimulus as a conditioned reinforcer depends on the temporal context of reinforcement, that is, the overall rate of reinforcement in the situation. The dominant view has been that context determines the learned value of a stimulus directly, according to delay-reduction theory. By contrast, the contextual choice model (CCM) maintains that value is independent of context and incorporates the effects of context on choice in the framework of the matching law. The authors report 2 experiments with pigeons as subjects that use transfer tests to assess the value of stimuli in the concurrent-chains procedure. Results strongly support the assumption of CCM that pigeons learn the temporal relations between events independently of context but that context modulates the expression of that learning as choice.

Failure to obtain value enhancement by within-trial contrast in simultaneous and successive discriminations

“…If the value of a stimulus in a simultaneous discrimination is not enhanced by following a relatively effortful response requirement, the apparent discrepancy noted in the introduction between the work ethic effect in pigeons and the findings of Grace and Savastano (2000) is resolved. However, there is evidence that after training on multiplechain schedules, a preference does emerge for the terminallink stimulus that follows a longer initial link (O'Daly, Angulo, Gipson, & Fantino, 2006;O'Daly, Meyer, & Fantino, 2005).…”

“…The advantage of random, nondifferential reinforcement is that responding can be maintained indefinitely over multiple test sessions, as compared with probe trials that always end in nonreinforcement (cf. Grace & Savastano, 2000). There is no reason to expect that such reinforcement would bias responding one way or the other, so any preferences found can be interpreted as baseline transfer.…”

“…After baseline training, the relative value of terminal-link stimuli was assessed using different types of transfer tests. Grace and Savastano (2000) found that choice in the transfer tests was accurately predicted by the assumption that stimulus value was determined by the reinforcer delay signaled by the stimulus and unaffected by the duration of the prior initial link, contrary to DRT.…”

“…In contrast to DRT, these models assume that the learned or conditioned value of a terminal-link stimulus is determined by the reinforcer delay signaled by that stimulus. Grace and Savastano (2000; see also Grace & Savastano, 1997) attempted to test directly whether the conditioned value of terminal-link stimuli depends on context by training pigeons on two different concurrentchains procedures in each session. After baseline training, the relative value of terminal-link stimuli was assessed using different types of transfer tests.…”

Preference and resistance to change in concurrent variable-interval schedules

“…They also suggested, instead, that the relative value of the two VI 40-sec components would be better assessed by arranging them as terminal links in concurrent chains to test the relative reinforcing strength in a manner used by Grace and Savastano (1997). Although that initial study produced ambiguous results, a subsequent study by Grace and Savastano (2000) has shown clearly that preference assessed in probe trials after training in concurrent chains is controlled by the absolute value of the terminal link schedules, regardless of the level of initiallink preference associated with them. For example, in Experiment 1 of their study, the initial-link schedules during Component A were VI 15-sec versus VI 15-sec with terminal links of VI 10-sec versus VI 20-sec; during Component B, the initial-linkschedules were VI 30-sec versus VI 30-sec, with terminal links of VI 20-sec versus VI 40-sec.…”