Investigating the Step Size in a Progressive-Ratio Schedule of Reinforcement for Young Children Diagnosed with Autism

Kathryn R. Glodowski, Chelsea B. Hedquist, Jeffrey R. Miller, Amanda L. Buchmeier, & Kevin P. KlattPsychology Department, University of Wisconsin- Eau Claire

Therapists who provide behavioral therapy to young children with autism need to identify preferred items in order to potentially use the items as reinforcers in a therapy session. Therapists use reinforcers to teach appropriate and functional skills. Many researchers have previously used a variety of preference assessments to gauge which items the child prefers relative to other items (Pace, Ivancic, Edwards, Iwata, & Page, 1985; Fisher et al., 1992; Windsor, Piche, & Locke, 1994; DeLeon & Iwata, 1996). Research has shown that preference assessments may not be accurate indicators of which items will function as reinforcers under increasing response requirements (Tustin, 1994; DeLeon et al., 1997). More recently, researchers discovered implementing a progressive-ratio schedule of reinforcement results in a more accurate determination of which items will function as reinforcers for children with autism under increasing response requirements (Roane, Lerman, and Vorndran, 2001). A progressive ratio schedule consists of an increase in the response requirement after each obtained reinforcer. Eventually the participant stops responding, and researchers take note of the last completed requirement, also called the break point. Researchers demonstrated the break points indicate differentiated preferences between stimuli (Hodos, 1961). Currently, studies conducted in the applied setting have either used an additive step size or a non-systematic step size with no specified ‘rule’ to the increase in response requirement. Roane (2008) urged more researchers to systematically examine the step size of a PR schedule. There are two systematic types of step sizes past researchers have used, additive and geometric. The current study examined the differences in break points, total responses, total reinforcement obtained, and session length in both an additive step size PR schedule and a geometric step size PR schedule for a young child with characteristics similar to autism.

Introduction

Participant and Setting. One child, Derek, with developmental delays similar to autism participated in the study. Derek was 17 months old at the time of the study and was receiving approximately 4 hours of behavior therapy at a University based program. Sessions for all participants were conducted in a therapy room (2.1 m by 4.6 m) located at a University based program. Sessions ranged from 2 to 5 minutes, 3-4 days per week, for 3 weeks. Participant Responses. Derek was instructed to engage in behaviors acquired from previous behavior therapy (maintenance) which included two gross motor imitations (clap, point, and tap table) as well as three oral motor imitations (blow, tongue out, and raspberry tongue).Preference Assessment. Researchers selected 4 items to use during the preference assessment based on reports of people familiar with Derek. Researchers set out the items on a table in the therapy room before each session and had the participant select one item. The selected item was used as the potential reinforcer during the entire session. Progressive Ratio Schedule. Researchers implemented a progressive-ratio schedule of reinforcement with either an additive step size or a geometric step size depending on the condition. The PR schedule started at an FR2 each session and after each obtained reinforcer, researchers increased the response requirement either by adding two to the previous requirement or doubling the previous requirement. Additive Step Size Condition. The response requirement progressed as follows: FR2, FR4, FR6, FR8, FR10, etc., increasing after each obtained reinforcer. Researchers terminated the session after the participant either engaged in behaviors alternative to the instructed behavior for 30 seconds, or after the occurrence of problem behavior.Geometric Step Size Condition. The response requirement progressed as follows: FR2, FR4, FR8, FR16, FR32, etc., increasing after each obtained reinforcer. The termination criterion for this condition was the same as in the additive condition.Data Collection. The first author gave the participant the instructions and collected data for three dependent variables. The first dependent variable was the break point, defined as the last completed response requirement. The second dependent variable was the total reinforcement obtained which was calculated by adding either the total amount of time spent with the reinforcer (in seconds) or the total amount of consumed reinforcers. The third dependent variable was the overall session length, which was calculated by starting a stop watch at the time of the first instruction and stopped when the termination criterion was met. Experimental Design. An alternating treatments design was used to evaluate the differences between conditions for the break point, total reinforcement obtained, and total session length. Only one condition was conducted per session with only one session per day for 2-4 days per week for 3 weeks. Researchers randomly selected the order of the conditions with no more than two of the same condition being conducted in a row.Interobserver Agreement (IOA) and Procedural Integrity (PI). IOA and PI were calculated for 100% of the sessions for both conditions. For the additive condition, IOA was 100% for break point, 100% for total responses, 100% for total reinforcement obtained, and 100% for session length. For the geometric condition, IOA was 100% for break point, 100% for total responses, 100% for total reinforcement obtained, and 83% for session length. For the additive condition, PI was 100% and for the geometric condition PI was 100%.

Method

Results

Discussion

We would like to thank UWEC’s Office of Research and Sponsored Programs

for supporting this research.

Figure 1 depicts the total responses in each session for both conditions. Figure 2 depicts a bar graph of the average total responses for both conditions. The total responses in the additive condition ranged from 19-26 with an average of 22.75 and the total responses in the geometric condition ranged from 12-38 with an average of 21.67. Figure 3 depicts the break point across all sessions for both conditions. Figure 4 depicts a bar graph of the average break point for both conditions. The break point in the additive condition ranged from 6-8 with an average of 7.5 and the break point in the geometric condition ranged from 4-16 with an average of 8.67. Figure 5 depicts the total reinforcement obtained in each session across all sessions for both conditions. Figure 6 depicts a bar graph of the average total reinforcement obtained for both conditions. The total reinforcement obtained in the additive condition ranged from 3-4 with an average of 3.75 and the total reinforcement obtained in the geometric condition ranged from 2-4 with an average of 3. Figure 7 depicts the session length for each session across both conditions. Figure 8 depicts a bar graph of the average session length for both conditions. The session length during an additive condition ranged from 2.37 minutes to 4.37 minutes with an average of 3.33 minutes and the session length during a geometric condition ranged from 1.43 minutes to 4.73 minutes with an average of 2.84 minutes.

The results indicate only slight differences in total responses, the break points, total reinforcement obtained, and the session length between an additive step size PR2 schedule and a geometric PR2 schedule for a child with characteristics similar to autism. More differences may be seen when children respond to gain access for differently preferred items, when required to engage in easier responses and when a PR schedule that is more sensitive to smaller break points is implemented. Future research could examine whether differences occur in total responses, break points, total reinforcement obtained, and session length between an additive and geometric step size PR schedule when using a less preferred item as the potential reinforcer. Future research could also examine if differences occur when altering the difficulty of the response type. The geometric step size could potentially be more useful when examining responding of easier response types due to the fast-increasing response requirements. Future research could also examine a PR schedule potentially more sensitive to smaller break points. A PR schedule that is more sensitive to smaller break points could possibly be a PR1 schedule with an additive step size.

Figure 1. Total responses across sessions. Figure 2. Average responses per condition.

Figure 3. Break points across sessions. Figure 4. Average break points per condition.

Figure 5. Total reinforcement across sessions. Figure 6. Average reinforcement per condition.

Figure 7. Session length across sessions. Figure 8. Average session length per condition.