Relative versus absolute reinforcement effects: Implications for preference assessments

We compared results obtained in two previous studies on reinforcer identifi cation (Fisher et al., 1992; Pace, Ivancic, Edwards, Iwata, & Page, 1985) b y combining methodologies from both studies. Eight individuals with mental retardation participated. During Phase 1, two preference assessments were c onducted, one in which stimuli were presented singly (SS method) and one in which stimuli were presented in pairs (PS method). Based on these results, two types of stimuli were identified for each participant: High-preference (HP) stimuli were those selected on 75% or more trials during both prefere nce assessments; low-preference (LP) stimuli were those selected on 100% of the SS trials but on 25% or fewer of the PS trials. During Phase 2, the re inforcing effects of HP and LP stimuli were evaluated in reversal designs u nder two test conditions: concurrent and single schedules of continuous rei nforcement. Two response options were available under the concurrent-schedu le condition: One response produced access to the HP stimulus; the other pr oduced access to the LP stimulus. Only one response option was available un der the single-schedule condition, and that response produced access only t o the LP stimulus. Results indicated that 7 of the 8 participants consisten tly showed preference for the HP stimulus under the concurrent schedule. Ho wever, when only the LP stimulus was available during the single-schedule c ondition, response rates for 6 of the 7 participants were as high as chose observed for the HP stimulus during the concurrent-schedule condition (1 pa rticipant showed no reinforcement effect). These results indicate that, alt hough the concurrent-schedule procedure is well suited to the assessment of relative reinforcement effects (preference for one reinforcer over another ), absolute reinforcement effects associated with a given stimulus may be b est examined under single-schedule conditions.