Research has demonstrated that most-to-least (MTL) and least-to-most (LTM) prompting are effective in helping children with Autism Spectrum Disorders acquire a variety of new skills. However, when directly compared to one another, the efficiency and efficacy of the prompting procedures have been variable. The inconsistencies in the literature could be due to selecting prompt topographies that do not promote correct responding. To address this, the present study began by assessing different prompt topographies and then compared most-to-least (MTL) and least-to-most (LTM) prompt-fading with only prompt topographies that were potent enough to promote correct responding. The subsequent comparison of prompt-fading procedures revealed that MTL prompting was more effective and efficient than LTM prompting for all three participants. Further implications for practice and future research are discussed.Keywords Least-to-most . Most-to-least . Prompt . Prompting . Prompt-fading Children with autism spectrum disorders (ASDs) often require prompts to learn new behaviors and prompt-fading strategies to transfer stimulus control from the prompt to the naturally occurring discriminative stimuli. Two of the most commonly used prompt-fading procedures are most-to-least (MTL) and least-to-most (LTM) prompting (Libby et al., 2008). These procedures employ the same prompt topographies, including verbal, gestural, and physical prompts; however, they differ in the order in which the prompts are presented. MTL fading sequences order prompt topographies from the most intrusive (e.g., physical prompts) to the least intrusive (e.g., verbal). In LTM fading, prompt sequences are arranged in the opposite order.Both MTL and LTM prompting can effectively improve independent responding when compared to baseline levels of responding or control procedures (for a review, see Demchak 1990). A few studies have directly compared the effectiveness and efficiency of these two popular procedures (Libby et al. 2008;McConville et al. 1998;Walls 1981). In all of these studies with the exception of Libby et al. (2008), MTL and LTM procedures were similarly effective; however, efficiency outcomes were variable across participants and different measurements of efficiency.Of the aforementioned studies, Libby et al. (2008) conducted the most systematic analysis and comparison of MTL and LTM procedures. In the first experiment, a direct comparison of the procedures revealed that three of five participants met a mastery criterion with both procedures, whereas the other two participants only met a mastery criterion with the MTL procedure. Therefore, overall, the MTL procedure was more effective than the LTM procedure in this experiment. Efficiency data, on the other hand, were variable across dependent variables. The LTM procedure was more efficient for the three participants who met a criterion with this procedure when considering trials to criterion; however, the MTL procedure was more efficient for all participants when considering errors to criterion....

After training conditional discriminations among selected stimuli from two perceptual classes, the emergence of novel relations involving other members of both classes was assessed using cross-class probes. The cross-class probes were presented using one of four different testing schedules. In the 2/9 test, nine different probes were presented in each of two test blocks. In the 6/3 test, three different probes were presented in each of six test blocks. In the 18/1-RND test, each of the 18 cross-class probes was presented in separate test blocks. In the 2/9 and 6/3 tests, the cross-class probes were presented in a randomized order within test block. In the 18/1-RND test, the cross-class probes were presented in a randomized sequence. In the 18/1-PRGM test, however, the cross-class probes were presented in a programmed order (i.e., the values of the stimuli in each cross-class probe were changed systematically in the succession of probe presentations). About 55% of the linked perceptual classes emerged during the 2/9, 6/3, and 18/1-RND tests. Thus the number of different probes in a test block did not influence the emergence of classes as long as the probes were presented in a random order. Virtually all classes emerged during the 18/1-PRGM test. Thus at least one ordered introduction of different cross probes resulted in the reliable emergence of linked perceptual classes. Mechanisms responsible for linked perceptual class formation are discussed along with the relation of these classes to other complex categories.

When the stimuli in one perceptual class (A`) become related to the stimuli in another perceptual class (B`), the two are functioning as a single linked perceptual class. A common linked perceptual class would be the sounds of a person's voice (class A`) and the pictures of that person (class B`). Such classes are ubiquitous in real world settings. We describe the effects of a variety of training procedures on the formation of these classes. The results could account for the development of naturally occurring linked perceptual classes. Two perceptual classes (A`and B`) were formed in Experiment 1. The endpoints of the A`class were called anchor (Aa) and boundary (Ab) stimuli. Likewise, the anchor and boundary stimuli in the B`class were represented as Ba and Bb. In Experiment 2, the A`and B`classes were linked by the establishment of one of four cross-class conditional discriminations: AaRBa, AaRBb, AbRBa, or AbRBb. Results were greatest after AaRBb training, intermediate after AaRBa and AbRBa training, and lowest after AbRBb training. Class formation was influenced by the interaction of the anchor/ boundary values and the sample/comparison functions of the stimuli used in training. Experiment 3 determined whether class formation was influenced by different sets of two cross-class conditional discriminations: AaRBa and AbRBb, or AaRBb and AbRBa. Both conditions produced equivalent results. Similarities were attributable to the use of anchor stimuli as samples and boundary stimuli as comparisons in each training condition. Finally, the results after joint AaRBa and AbRBb training were much greater than those produced by summing the results of AaRBa training alone and AbRBb training alone. This same synergy was not observed after joint AaRBb and AbRBa training or either alone.