Examination of the influence of contingency on changes in reinforcer value.

This study examined how the amount of effort required to produce a reinforcer influenced subsequent preference for, and strength of, that reinforcer in 7 individuals with intellectual disabilities. Preference assessments identified four moderately preferred stimuli for each participant, and progressive-ratio (PR) analyses indexed reinforcer strength. Stimuli were then assigned to one of four conditions for 4 weeks: fixed-ratio (FR) 1 schedule, escalating FR schedule, yoked noncontingent (NCR) delivery, and restricted access. Preference assessments and PR schedules were then repeated to examine changes in selection percentages and PR break points. Selection percentages decreased for all NCR stimuli but increased for most of the restricted stimuli. There were no systematic changes in selection percentages for either of the contingent stimuli. Break points increased, on average, for all conditions, but the increase was highest for the restricted stimuli and lowest for the NCR stimuli. These results are discussed in relation to recent basic research addressing the influence of effort on stimulus value.