Evaluation of stimuli along a hierarchy under additive and geometric progressive-ratio schedules




Amini, Meaghan Latifi

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This study was primarily intended as a comparative investigation of the difference between participants' responses to a task under two progressive-ratio schedules (i.e., geometric and additive). Furthermore, the study served as an examination of the variations in response levels across an array of preferences (HP, MP, LP) under the two increasing schedule requirements. Three individuals, all males, ranging between the ages of 16 years old and 28 years old participated in the study. The study utilized a MSWO preference assessment to identify the stimuli for each participant. The three identified stimuli were categorically ranked as HP, MP, and LP to be analyzed during three independent reinforcer assessments. An alternating treatment design was conducted to assess the stimuli. The additive and geometric progressive ratio schedules were conducted in a single-operant arrangement for each reinforcer assessment. The dependent variables collected during the reinforcer assessment were: (a) the breakpoint, (b) responses per minute, and (c) the cumulative number of responses. The data were further analyzed using mean breakpoint, average response per minute, total tasks correct, cumulative number of tasks completed, and sessions terminated. The results of the study support the suggestion of Glover et al. (2008): namely, that individuals with ASD may vary their response levels across a hierarchy of stimuli under increasing schedule requirements. The results for two of three participants are consistent with the research on reinforcer assessments under progressive ratio schedules. The results derived from 2/3 participants’ assessments support the notion that HP stimuli yields a higher mean BP compared to either the MP and LP reinforcer (DeLeon et al., 2009; Call et al., 2012; Glover et al., 2008). In addition, the MP stimuli supported higher mean break points than the LP stimuli for 2/3 participants (see also Call et al., 2012). The findings for one participant are consistent with previous findings found in the literature. One participants’ response on tasks corresponded with the ranking of the stimuli. The HP stimulus supported higher mean BP, more total responses, and the highest accuracy of task completion. In regard to the results of the PR schedule, for 2/3 participants, the highest BP was obtained during the geometric schedule. However, across all 3 participants, considerably more responses were observed under the additive schedule for the differing levels of preferred stimuli.


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