Previous research has documented the utility of PPD for individuals with ASD (Walker, 2008
), but the use of IF in instructional trials with children with ASDs has not been thoroughly examined (Werts et al., 1995
). The current results showed that (a) PPD with IF was as effective as PPD no IF, (b) PPD with IF doubled the number of words learned when compared with PPD no IF, and (c) PPD with IF was about twice as efficient as PPD no IF in terms of the amount of time required per skill acquired. These results are similar to previous research on IF conducted with other populations (Werts et al., 1995
) and provide generality to the conclusion that IF is an effective and efficient instructional practice when educating young children with ASD.
We examined the efficiency of IF by comparing the acquisition of target behaviors when IF was not presented (PPD no IF) and when IF was presented during the consequent event of correct responses (PPD with IF). Because the behaviors associated with the stimuli presented as IF (Sets 3 and 6) demonstrated mastery during the subsequent probes, the participants likely acquired the behaviors through their presentation during the preceding comparisons. Thus, learners could have potentially acquired four behaviors in PPD with IF and two behaviors in PPD no IF.
We can extrapolate these data with reference to two measures to illustrate how this increased efficiency might affect learning in other situations. With reference to the average number of sessions needed to acquire target behaviors, 10 sessions (one session per day for 2 school weeks) would be needed to result in the acquisition of two skills using PPD no IF, but four skills could be taught over the same number of sessions using PPD with IF. With reference to the amount of instructional time needed to teach four behaviors, approximately 145 min would be required when using PPD no IF, and approximately 74 min would be necessary when using PPD with IF.
Although the results from the present study are robust, one must take into consideration certain limitations when interpreting the findings. We conducted this study under one set of conditions using a small sample of participants with developed verbal and imitative repertoires. These factors limit the generality of the findings to the larger population of children with autism, and it is unclear if one could achieve replication under different circumstances (e.g., group instructional format, older children, nonimitative children, children with more severe autism). Future research should examine participant attributes and environmental conditions to determine the necessary elements for the greatest probability of success and to whom and what conditions generalizations can be made.
The data from the third probe showed maintenance of previously acquired behaviors across the 2-week period during which they were not presented (i.e., during the second comparison). Data from the maintenance probe (fourth probe) showed that previously acquired behaviors were maintained after 2 months at a much lower level (an average of 58% to 92% across participants). These levels of maintenance are lower than those obtained in previous studies on IF (e.g., Holcombe et al., 1993
); thus, further work is needed to identify methods that would promote response maintenance over extended periods.
Research should continue to examine the efficiency of IF. In this study, PPD with IF provided the opportunity to acquire four target behaviors per condition (two directly instructed and two through IF), whereas PPD no IF provided the opportunity to acquire only two behaviors. Thus, the outcomes of this comparison may have been influenced by a ceiling effect of PPD no IF (i.e., we provided fewer opportunities). Comparisons of teaching PPD with IF (two targets and two IF) to PPD no IF with four target behaviors may offer a more balanced comparison of the efficiency of these procedures.
Future studies should also consider examining IF as part of a standardized curriculum to identify target behaviors. A curriculum would allow the researcher to identify conceptually and sequentially related stimulus classes and relations between stimulus classes and would allow the manipulation of relations to examine conditions under which the procedure is most effective.
One interesting finding of the current study was the more rapid acquisition of the stimuli during the second comparison condition (i.e., mastery in 8 to 11 sessions vs. 15 to 27 sessions during the first comparison). Future research should examine this phenomenon of more rapid learning following the initial exposure to teaching procedures, which is consistent with the theory of learning sets proposed by Harlow (1949)
. Research is needed to determine whether priming events or other preintervention techniques can be used to provide similar gains in efficiency.
Given that the responding of individuals with ASD often fails to generalize across important contexts, PPD with IF might be a useful instructional arrangement for promoting generalized responding. For example, IF could be used to present multiple exemplars of the target stimuli (e.g., if the target response is to name a picture of a bear [a black bear], the IF stimuli might be pictures of other bears [grizzly, polar, and panda bears]). Similarly, if the behaviors being targeted follow a pattern (e.g., naming numerals 41 though 49, as in Paul's first exposure to the study), then directly teaching some numbers (e.g., 41, 44, and 48) and presenting others as IF (e.g., 42, 43, 47) may allow the student to generate a prescriptive rule (i.e., the 4 should be said “forty,” and then the name of the second numeral should be said). This arrangement may produce generalization to those numerals not taught directly or presented through IF (i.e., 45, 46, and 49). Thus, it is possible that individuals with autism could increase the efficiency of learning, conceptualized as greater generalization (M. Wolery et al., 1992
), in addition to more rapid learning when using PPD with IF when the target behaviors have similar patterns.
Our procedures did not permit us to determine when the participants acquired the IF responses. It is clear when to introduce a new skill during direct instruction; however, it is unclear when to introduce novel IF. Future research might include probes of the IF stimuli during instruction to examine the acquisition process and thus potentially increase teaching efficiency by allowing a teacher to include additional IF after a student has mastered earlier relations. One previous study included daily probes of the IF responses, and results suggested that students acquired IF stimuli prior to the target responses that received direct instruction (Anthony, Wolery, Werts, Caldwell, & Snyder, 1996
Finally, the behavioral process by which IF results in acquisition is unclear. In this and nearly all previous studies, each target stimulus was associated with a specific IF stimulus (Werts et al., 1995
). One possibility is that the pairing of a specific IF stimulus with a specific target behavior or stimulus resulted in some form of associative learning. Results of a study by Werts, Caldwell, and Wolery (2003)
, however, are inconsistent with this hypothesis. Multiple IF stimuli were presented after each target response, eliminating a one-to-one correspondence between a given target behavior and a given IF stimulus; nonetheless, students acquired the responses to these IF stimuli. It is also possible that the participants in this study acquired the IF responses due to a repertoire of generalized imitation (Baer, Peterson, & Sherman, 1967
) or through observational learning (Bandura, 1977
). The evaluation of IF with more novice learners and those with less developed imitative repertoires may help to determine whether imitative repertoires are necessary for the acquisition of IF responses.