Discrete Trial Teaching and Discrimination Training

Organize the teaching room so there are no unnecessary distractions for the child

Organize the teaching room so it is comfortable for the child and for the teacher

Know the exact goal for each program

Know exactly which instructions to give to the child

Know exactly what constitutes a correct response

Know exactly what teaching materials to use

Have teaching materials ready, well organized and within the teacher’s reach

Select a number of reinforcers to use during teaching and have them within reach

Antecedent Stimulus (the Task)

Each trial starts with the presentation of the antecedent stimulus. The antecedent stimulus consists of the interventionist presenting an instruction and some sort of task to the child. For example, the teacher shows the child a car and asks “What is it?” The question and the car together constitute the antecedent stimulus, and this antecedent stimulus is meant to evoke a particular answer from the child. The antecedent stimulus need not include a verbal question; it can be any situation which the child needs to respond to, such as seeing some other children playing a game (then the response could be to ask to join) or seeing some crayons and paper (for which the response could be to draw).

For each exercise, the antecedent stimulus is always carefully defined and it should be explicitly written as a part of the child’s program description. Moreover, if stimulus cards are used, sometimes it is helpful to write the instruction that the teacher is supposed to give to the child on the back of each stimulus card. For example, if teaching the child to name colors, the teacher shows the child a blue color card, and asks, “What color?” The instruction “What color?” could be written on the back of the color card so that the teacher remembers to say, “What color?” instead of, for example, “What color is the card?” or “What color do you think this is?”

When presenting an antecedent stimulus, the teacher should:

1.	Simplify the language used as the instruction to match it to the child’s language level. For example, for early learners, “Car” or “Give me car,” instead of “Can you give me the car?” or “Do you know which one is the car?”
2.	Present tasks that are appropriate for the child’s skill level (i.e., ensure prerequisite skills are already in place)
3.	Use a natural, friendly, and clear voice
4.	Use the exact type of stimulus material and wording that has been decided for the particular task being taught
5.	Give the child 3–5 s to respond before any consequences are given
6.	Present the instruction only once within each trial

Prompt

The purpose of the prompt is to help the child produce the correct response after the antecedent stimulus has been presented (MacDuff et al. 2001). For example, the teacher might say “Clap,” and then manually guide the child’s hands to produce a clap. This is known as a physical prompt. If the antecedent stimulus is a question requiring a verbal answer, the teacher could model the correct answer so that the child can imitate it. For example, the teacher would present a doll and ask, “What is this?” and a verbal prompt would be to say “Say doll” immediately after saying “What is this?” Obviously, this prompt requires that the child is already able to imitate speech. Other types of prompts include pointing prompts (e.g., pointing to the object car after saying “Touch car”), position or proximity prompts (e.g., putting the car closer to the child than the other stimuli), time delay (e.g., across trials gradually delaying the onset of the prompt after providing the S^D, with the hope that the child might produce the correct response before the prompt is given), and modeling prompts (e.g., the teacher shows the child the correct response).

All prompts must eventually be faded so that the target response is produced by the antecedent stimulus only. For example, initially the teacher might manually guide the child to clap, but then over successive trials the teacher can let go of the child’s hands earlier and earlier until the child can clap independently. Such fading of prompts is one of the cornerstones of effective DTT.

When prompting the teacher should:

1.	Provide the prompt as specified in the teaching program, which typically means that the prompt is presented immediately after the S^D. However, other strategies for prompting can be used, such as presenting the prompt together with the S^D or gradually, over successive trials, increasing the time between the S^D and the prompt
2.	Use the least intrusive prompt necessary to produce the correct response
3.	If a particular prompt is not effective, use a more intrusive prompt in the next trial
4.	Refrain from using non-intentional prompts such as always looking at the correct stimulus, orally mimicking the correct verbal response, or always leaving the correct stimulus in the same place, etc.

Response

It is important to remember that responses are meaningful only in combination with a specific antecedent stimulus. For example, it would be pointless to teach a child to simply clap randomly in all situations. What is important, however, is that the child can clap as a response to other children clapping or when someone is asking him/her to clap.

The target response is always defined in observable behavioral terms, as precisely as possible, and written down as part of the child’s program description. During DTT, the child’s response can be:

Correct: A correct response without prompt occurs within 3–5 s of the presentation of the antecedent stimulus.

Prompted: A correct response with prompt occurs within 3–5 s of the presentation of the antecedent stimulus.

Incorrect: The child’s response does not meet the criteria required in the response definition, or it occurs more than 5 s after the presentation of the antecedent stimulus.

No response: The child does not respond to the antecedent stimulus in any particular way. This can be due, for example, to lack of motivation or lack of attention. No response does not necessarily indicate that the child cannot perform the task.

The teacher should:

1.	Allow the child 3–5 s to respond
2.	Observe if the response is correct, incorrect, prompted, or if it is a no response
3.	Refrain from repeating the instructions or talking about other things while waiting for the child to respond

Reinforcer, S^R (the Consequence)

To increase the likelihood that the child will produce the target response given the specified antecedent stimulus, responses are differentially reinforced. This means that the child is presented with a desired item or activity as quickly as possible after the target correct response has been performed. Reinforcers can be verbal praise, tickling, favorite toys, games, or snacks. Which stimuli function as reinforcers depends on the child’s interests, and hence may vary greatly across children. Some children may like to watch YouTube movies while others prefer bouncing on the trampoline. Moreover, the extent to which a particular stimulus functions as a reinforcer also depends on motivational variables such as deprivation and satiation . Therefore, which stimuli function as reinforcers for each child will vary from time to time. For example, if the child has not played with bubbles for a while (deprivation), blowing bubbles might be highly reinforcing. However, after blowing bubbles a number of times (satiation), bubbles might temporarily lose their reinforcing properties until the child has again not seen the bubbles for a while.

There are a number of different ways to identify reinforcers for a particular child, such as (a) asking the parent and teachers what the child likes to do (e.g., Fisher et al. 1996); (b) observing what the child is playing with or doing when he/she participates in an unstructured activity; and (c) letting the child sample different items, by, for example, presenting various items to the child and observing which items he/she chooses (Roane et al. 1998; Cote et al. 2007). An ideal procedure is to provide the student with an opportunity to make a physical choice between two or more reinforcers at the beginning of each block of trials and to use the chosen stimulus as the reinforcer for that block of trials.

Sometimes reinforcement needs to be given when the child produces approximations of the target response. This is called shaping and is a technique from behavior analysis that teaches the child the target response by reinforcing successive approximations to it. For example, if the child is learning vocal imitation of the sound “Ah,” then initially any kind of vocalization on the part of the child is reinforced. Gradually, over successive trials, only vocal sounds are reinforced, and when the child reliably emits vocal sounds during 80–90 % of the trials when the discriminative stimulus (S^D) “Ah” is presented, only those sounds that approximate the sound “Ah” are reinforced. Finally, only the sound “Ah” is reinforced, and this continues until the child emits the sound “Ah” during 80–90 % of the trials where the S^D “Ah” is presented.

Social stimuli such as a smile and praise are almost always a powerful reinforcer for the behavior of typically developing children. One of the characteristics of children with autism spectrum disorder (ASD) is that many such social stimuli do not function as reinforcers, and this probably affects their learning and development in a negative way. To establish (or strengthen) social stimuli as reinforcers for the behavior of children with ASD, the presentation of tangible reinforcers (e.g., favorite toys, snacks, or activities) is always paired with the presentation of social stimuli such as verbal praise (e.g., “Good job!”) and smiles. The rationale is that social stimuli alone will eventually become reinforcing through a process called classical conditioning.

To avoid the child satiating on reinforcers and losing his/her motivation for learning, it is important that the teacher identifies a number of different reinforcers for each individual child, and that the teacher presents different reinforcers on successive trials (i.e., the teacher varies the way he/she praises the child across trials and the teacher uses different tangible reinforcers across successive trials). In addition, it is important to save the stimuli that are likely to be the strongest reinforcers for when the student performs a particularly difficult task.

Another way to avoid satiation can be to use a token economy system. In a token economy, correct responses produce tokens. Tokens can be check marks, stickers or happy faces, and the like. Whenever the child has collected a set number of tokens (e.g., ten tokens) the child can exchange the tokens for a backup reinforcer. The backup reinforcer must be a very potent reinforcer, such as watching a video for a few minutes, eating a favorite snack, or playing a favorite game.

It is important to note that behaviors taught in DTT are of little use if the child does not use them outside of the DTT setting. During DTT, the behaviors are usually maintained by arbitrary reinforcers; that is, by reinforcers that are not related to the behavior being taught (e.g., the child is reinforced with small bites of a cracker for playing with a doll in a specific way). Moreover, in DTT these reinforcers are typically delivered at a high frequency. This type of reinforcement is not provided in natural settings, and hence, the child may fail to perform newly learned skills in everyday life if specific measures are not taken to ensure generalization and maintenance.

To help the child transfer skills learned in DTT to natural settings, the teacher can:

Reduce the frequency of artificial reinforcers used in DTT after the child has begun mastering a particular skill.

Observe whether or not a particular behavior learned in DTT is maintained by natural reinforcers in natural settings. For example, if the other children in the preschool play a particular game and the child in treatment finds interaction with peers reinforcing, then playing that particular game after learning it in DTT will likely be naturally reinforced by the other children.

Whenever a behavior learned in DTT is not performed or maintained in the natural settings, the teacher must design a system for presenting the artificial reinforcer, at least for a while, to ensure that the behavior is performed and maintained in this setting. Often, a token economy system is used for this purpose, where the child receives tokens for performing specific behaviors in the natural setting. These tokens can later be exchanged with favorite activities such as playing a computer game, etc.

For more thorough discussions of reinforcement, see the chapter dedicated to variables that impact reinforcer effectiveness and for a thorough discussion of teaching and generalizing skills in the natural environment, see the chapter dedicated to natural environment training in this volume.

When using reinforcers (S ^R) the teacher should:

1.	Present the S^R as quickly as possible after the correct response occurs
2.	Observe the child to see whether he/she is “enjoying” the S^R, as indicated by consuming and/or interacting with it. If not, alternative reinforcers should be considered
3.	Pair tangible S^R with social stimuli such as praise and smile
4.	Vary the tangible S^R across trials
5.	Vary the social S^R across trials

Generalization

After the child has learned a particular skill, generalization occurs when the child uses the new skill in a somewhat different way than the way it was taught. For example, generalization has occurred if the child names all dogs that he or she meets as “Dog” and not the specific examples of dogs that were used during teaching. If the child does not generalize, which is often the case, then generalization must be explicitly taught. This is done by expanding, one by one, the examples of dogs that function as antecedent stimuli for saying “Dog,” until the child generalizes to all dogs. This procedure is called multiple exemplar training or “training sufficient exemplars” (see chapter on teaching cognitive skills in this volume). When the student is able to exhibit the skill in the presence of untrained stimuli (e.g., new examples of dogs that were never taught), it is called stimulus generalization. In addition, the child must learn to generalize across settings (or situations). That is, the child must learn to use the word “Dog” outside the teaching room, such as in other rooms and places in the preschool, at home, at the playground, in the car, etc. Moreover, the child must also use the label “Dog” when with other teachers, with parents and siblings, and with other children, which is called generalization across people. Finally, the child must be able to maintain (remember) the skill over time, and this often requires the skill to be occasionally rehearsed (e.g., once a week or once a month).

It is particularly important to address generalization when using DTT. Although DTT is highly effective in teaching new skills, the particular structure of this teaching procedure differs in many ways to how the child learns and behaves in real life settings. These differences may challenge generalization, and hence the teacher must not assume that the child will automatically perform new skills learned in DTT in other places and with other people. It is possible that the child will learn a number of new skills in the one-to-one setting with a particular teacher in the room where the teaching takes place, but subsequently fail to use these skills at home, with parents or siblings, playing with other children or even with other preschool teachers. With careful planning and monitoring of generalization, the child can learn to respond adequately to the full range of naturally occurring situations.

When using DTT, generalization should be addressed by:

1.	Assessing whether the child can perform the new skill when exposing him/her to other materials found in daily life (e.g., different pictures or different objects of an item learned)
2.	Assessing whether the child can perform the new skill in new places (e.g., home, playground, other places in the preschool, etc.)
3.	Assessing whether the child can perform the new skill for other adults (e.g., different teachers and parents)
4.	Assessing whether the child can perform the new skill for other children
5.	Assessing whether the child can maintain the skill over time

Other Teaching Procedures Often Used in Conjunction with DTT

In addition to DTT, children typically participate in other types of instructional or play activities, performed in groups or individually, depending on the child’s needs. Since the skills learned in DTT are initiated by the teacher, DTT has been criticized for making the child passive and teacher dependent, resulting in generalization difficulties and lack of spontaneity. This criticism is valid in the sense that DTT is not the most effective way to teach all type of skills. For that and other reasons, two other behavior analytic teaching procedures called incidental teaching and natural environment teaching are often used in conjunction with DTT. Virtually all contemporary comprehensive EIBI programs for children with autism implement a combination of DTT and naturalistic behavioral teaching strategies (see chapter on naturalistic teaching strategies in this volume for a thorough treatment of the topic).

Areas of Application and Scientific Support

Many intervention packages for children with developmental delays, especially autism, include DTT together with other behavior analytic techniques (Eikeseth 2009). Much of the support for DTT is indirect in the sense that those programs that have received much research interest and have been shown to be highly effective in teaching children language skills and adaptive behaviors (Reichow 2011) have used DTT alongside other techniques. An example of this is EIBI, which was pioneered by Dr. O. Ivar Lovaas (Lovaas 1987, 2003). A recent meta-analysis analyzing nine peer reviewed, controlled outcome studies on EIBI, found a large effect size (1.10) for change in IQ scores and a moderate effect size (0.66) for change in adaptive behavior scores (Eldevik et al. 2009).

Although these findings are based solely on children with autism, there are indications that EIBI including DTT might be effective for children with intellectual disabilities (Eldevik et al. 2010), and for children with severe intellectual disabilities and pervasive developmental disorders (Smith et al. 1997).

Intensity of DTT

There is an extensive and ongoing debate about what constitutes the optimal intensity of DTT. Most likely, the optimal intensity or amount of DTT for a particular child will depend on several factors, including the child’s level of functioning. Children with little or no language or who lack basic skills such as motor or vocal imitation need more DTT than children who need to learn more subtle social skills such as peer interaction. Having said this, it should be noted that intervention programs that have included a large portion of DTT combined with other one-to-one behavior analytic teaching procedures have yielded the largest effects (Eldevik et al. 2010).

Imitation

One of the skill areas most commonly and successfully taught using DTT is imitation (e.g., Coe et al. 1990; Lovaas et al. 1966, 1967; Young et al. 1994). This entails gross motor imitation (e.g., clapping when someone else claps), fine motor imitation (e.g., copying a sign-language sign), vocal imitation of phonemes (e.g., repeating consonant-vowel combinations), words and phrases (e.g., repeating novel words and sentences), as well as imitation of complex play skills (e.g., playing like other children). Imitation is gradually made more difficult by moving, for example, from clapping to imitating various play behaviors, such as filling a car with gas. Imitation skills in each area (such as gross and fine motor imitation) are taught until the child achieves generalized imitation (i.e., the child imitates novel movements or sounds on the first attempt without prior practice on that specific imitation). Imitation is not only useful in natural settings, such as when learning new words and behaviors from peers and adults, but is also used as an effective prompt in other DTT exercises.

Language

DTT can be used to teach both receptive and expressive language (also see chapter on verbal behavior in this volume). Receptive language includes responding to and the comprehension of verbal instructions (Lovaas 2003). Examples of this could be to point to different objects when they are named, or following instructions such as “Clap” or “Jump.” Receptive language is usually built up from simple discriminations such as these to more complex instructions such as “Get the big red ball from the living room.” The effectiveness of using DTT to teach receptive language has been shown in multiple studies on a wide range of language skills (Lovaas 1977; Risley et al. 1972).

There is often a need to teach the child to use words, even if he/she can understand them when they are spoken by someone else. Expressive language is the production of verbal statements, such as naming objects or answering questions. As with receptive language, expressive language is first taught at a simple level and is then made gradually more difficult, up to telling stories, asking questions, or engaging in small talk (McGee et al. 1984). DTT can also be used to teach children grammar. For instance, the child can be taught to correctly use plurals (Baer et al. 1972), grammatical tense, pronouns (Lovaas 1977), adjectives (Risley et al. 1972), and answering Wh-questions (Jahr 2001). It should be noted that all the techniques that are used to teach children spoken language can just as easily be used to teach sign language (Carr 1979).

Vocal imitation is a necessary prerequisite to teaching expressive language, as this is frequently used as a prompt to help the child produce the target verbal response (Baer et al. 1972; Risely et al. 1972). As with receptive language, many studies have shown the effectiveness of using DTT to teach expressive language (Lovaas 1977; Howlin 1981).

Play skills

Teaching children play skills is often an area of high priority . Enabling a child to play is important because it makes social interaction with peers both easier and more rewarding for the child, and it also decreases time spent in stereotypic behaviors (Lovaas 2003). Children with autism very often lack basic skills for cooperating with peers, but this may be taught (Downs and Smith 2004). Play skills are taught like any other skills, by presenting the child with an antecedent stimulus (usually the play materials) and prompting a target response. When presenting the child with a new game or new play material, this novel activity is usually not rewarding to the child by itself, and it is important that the teacher uses reinforcers when teaching the child the play behaviors. Eventually, some play activities may become intrinsically reinforcing to the child and are thus maintained without the use of other types of reinforcers .

Most play activities require a large number of independently taught responses, both verbal and nonverbal. Playing with dolls can be broken down into a number of smaller responses such as dressing, feeding, and talking with the doll (and countless more). The child is taught each of these responses separately through prompting and differential reinforcement. Subsequently, they are chained together so that, for example, putting on one sock is an S^D for putting on the other sock, which in turn is the S^D for putting on the dress, etc. .

The type of play skills usually taught initially includes playing with cars, trains, and dolls, doing insert and jigsaw puzzles, lotto, drawing, and ball games. It is important to include typically developing peers in the play activity as quickly as possible after the child has learned to perform the play activity with the teacher. The child must also be taught how to initiate play with other children, comment on what their peers are doing, and take on different roles in pretend play.

Two studies have reported on the effectiveness of teaching children play using DTT alone. Coe et al. (1990) reported successful teaching of a simple ball game to three children with autism or Down’s syndrome. Jahr et al. (2000) taught cooperative play to six children with autism, all of whom mastered cooperative pretend play and generalized to novel settings and peers .

Daily living skills

Another high priority in DTT programs is to teach the child age appropriate self-help skills (also see chapter on independent living skills in this volume). As with play, these skills can be broken down into component behaviors which are taught independently and subsequently chained together to form a particular self-help skill. Common daily living skills that can be taught with DTT include: using utensils, drinking from a cup, dressing and undressing, and washing hands. As in the play exercises described above, the child is presented with an antecedent stimulus in the form of a situation requiring action or an instruction. The child is then prompted, verbally, manually, or by modeling, to perform the target behavior. The prompts are slowly faded until the child responds correctly without help. Some daily living skills may become automatically reinforcing and maintain themselves (such as undressing to go to bed and listen to a story), while others (such as cleaning one’s room) often require continued reinforcement from a teacher or parent.

Matson et al. (1990) taught a number of different self-help skills (tying shoes, brushing teeth, combing hair, putting on pants, shirt, and socks, and eating and drinking) to four children with mental retardation, three of whom also had autism. A majority of the skills were successfully mastered by the children and maintained at follow up several months later. The authors note that mastering the complete sequence of skills most likely helps maintain the sequence because of naturally occurring positive consequences (i.e., tying shoes to go outside to play).

Reducing stereotypic and problem behaviors

Many children with developmental delays exhibit stereotypic and maladaptive behaviors, sometimes dangerous to themselves or to peers. DTT may concomitantly decrease problem behaviors in the child, by both strengthening incompatible behaviors and by making teaching situations highly rewarding (Dib and Sturmey 2007). In addition to this, DTT aims to increase communicative skills in children, which in turn might decrease problem behaviors by giving the child more adaptive alternatives to tantrums or problem behaviors to get what he/she wants (Matson et al. 1996; Smith 2001).

Other curriculum skills

DTT must be combined with an appropriate and comprehensive curriculum for the child to make maximum gains. The content of the curriculum is comprehensive and addresses all areas of deficit and must be individually tailored for each child’s needs. The key components of the curriculum are described elsewhere (Leaf and McEachin 1999; Lovaas 1977, 2003; Lovaas et al. 1981; Maurice et al. 1996, 2001; chapter on linking curriculum to assessment in this volume), and are only summarized below.

Beginning curriculum

Each child’s curriculum is individualized and comprehensive, teaching skills in all areas of development. Beginning skills included prerequisites in the areas of attention, communication, social initiations, and play. Examples include sitting in a chair, responding to simple instructions such as “come here” and “wave bye-bye,” requesting favorite items, pointing, joint attention, matching identical objects, imitating gross motor actions or imitating actions with objects, imitating sounds and words, identifying and naming objects, playing independently with toys, and basic interactive skills such as rolling a ball to and from an adult.

Intermediate curriculum

Intermediate skills include further language training such as identification and naming of abstract concepts, parallel play, turn taking, imitating sentences, early academic skills such as identifying letters and numbers, drawing imitation and tracing, and self-help skills such as dressing and undressing, toilet training, drinking from an open cup, and increasing the range of food and drink taken.

Advanced curriculum

Once these skills are acquired, more advanced skills are addressed, such as conversation and asking questions, advanced pretend play and cooperative play, social-emotional skills such as theory of mind and perspective taking, advanced academic skills, self-management and self-control skills, observational learning, and learning in the classroom environment.

Alternatives to DTT

DTT differs from another commonly used behavior-analytic technique known as pivotal response training (Koegel & Koegel 2006). DTT stresses the need to build a complete behavioral repertoire in a systematic and incremental manner, behavior by behavior, while pivotal response training aims to identify and teach key (pivotal) behaviors which are assumed to automatically lead to spontaneous learning. Pivotal response training is designed as an alternative to DTT and hopes to achieve similar results with less intervention (Koegel & Koegel 2006).

Pivotal response training differs from DTT in that it is less structured, both in regard to where the training takes place and what is being taught. Pivotal response training is more dependent on initiations from the child in natural settings. This takes advantage of the momentary motivation of the child (e.g. wanting a cookie or a specific toy) and teaching a relevant response in that situation (e.g., “Say ‘cookie’!”) (Delprato 2001). However, pivotal response training can most likely neither achieve the same number of repetitions for any particular response as DTT, nor teach discriminations that are hard to master for a particular child (see discrimination training below).

Reviewing studies comparing DTT to other normalized and less structured interventions, Delprato (2001) reported larger gains for children who received more informal behavior analytic interventions. It is likely that different teaching techniques are differentially effective for different children (Schreibman et al. 2011). For example, DTT is likely to be more efficient for teaching basic learning skills (such as generalized motor and vocal imitation) and discriminations. Normalized interventions are likely to be more efficient for teaching generalized language use and to expand a basic behavioral repertoire that may have to be taught using DTT (Smith 2001). However, it is worth noting that, to date, no comprehensive outcomes studies have been published on EIBI programs that make exclusive use of naturalistic teaching strategies. Put another way, every single published controlled outcome study evaluating EIBI has contained a large proportion of DTT, usually combined with some amount of incidental teaching and/or natural environment training .

Discrimination Training

Discrimination training is an important element of DTT. Discrimination training is concerned with the way training stimuli and prompts are presented, and how prompts are subsequently removed . For example, if the child has learned to name a red block “Red,” and a blue block “Blue,” the child has learned to discriminate the colors red and blue, and the procedure used to establish this discrimination is called discrimination training.

What constitutes the optimal procedure for discrimination training may vary across children. Moreover, it may vary within the same child depending on which skills are being taught. Some skills are complex to learn and hence may require an elaborate discrimination training procedure involving many steps and a high number of training trials, whereas other skills are easier for the child to learn and might be effectively taught in considerably fewer trials. The teacher must always seek to use the discrimination training procedure which leads to mastery most quickly, and, typically, the more complicated and elaborate discrimination training procedure used, the more trials it takes to complete. We will start with a description of the most basic discrimination training procedure .

Basic Procedure: Teaching Language Comprehension

The following description of discrimination training is illustrated with a receptive language program, which is designed to teach the child to select particular objects (or pictures) upon hearing the name of the objects. This program is commonly known as receptive labels (Lovaas 2003), or manded stimulus selection (Michael 1985). Table 12.1 provides a summary of the teaching stages outlined below.

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