The discrete trial is the primary teaching method for a number of the behaviorally-based interventions used in teaching children with autism. In fact, Discrete Trial Training (DTT) is often synonymous with Applied Behavior Analysis (ABA), though that is a practice that should probably be discouraged, as they are two very different beasts.
Children with autism often face many deficits and difficulties in learning (Romancyzk in Maurice, 1996). Discrete-trial training can help to compensate for these difficulties.
Attention -- Many children with autism begin a program with rather short attention spans. In DTT, tasks are broken down into short, simple trials. At the start of a program, interactions may only be a few seconds in length. As the child's attention span increases, the length of the interactions increases accordingly.
Motivation -- Children with autism may not be as motivated to work as other children might be. DTT attempts to build this motivation by rewarding performance of desired behaviors and completion of tasks with tangible or external reinforcement (food, toys, time to play, etc.). That external reinforcement is paired with social praise with the hope that eventually praise will become as reinforcing as the treats, etc.
Stimulus control -- Discriminating between stimuli which we would like to think of as important -- teacher/parent requests, invitations from peers, important environmental cues (school bells, alarms, weather, etc.) -- and all the other "background" stimuli is often difficult for children with autism. In DTT the presented stimuli (typically instructions from a teacher or parent) are clear and relatively consistent. The child is given rewards only for behaviors in response to those stimuli so that eventually he comes to understand that certain stimuli are probably more deserving of his attention than others.
Generalization -- Generalization, the application of a behavior or skill across a number of environments or to a number of related behaviors, is typically quite difficult for children with autism. Consequently, the instructions in good DTT programs are designed to change over time, in content (the verbiage of the instruction) and context (who is giving the instruction, where and when it is being given).
Cause-effect learning and observational learning -- Children with autism typically have a great deal of difficulty in "picking things up" from their environments. To compensate then, DTT teaches skills and behaviors explicitly, without relying on these areas of difficulty.
Communication -- Often in children with autism, both expressive and receptive language are deficient. Teaching that relies on a great deal of verbiage from the teacher, then, is often too difficult for these children. The instructions given in discrete trials are simple, concrete, and clearly provide only the most salient information, especially at first. As the child progresses, and his receptive language becomes stronger, these instructions can become more complex.
Perspective taking and understanding of social and behavioral expectations -- While there is little built into the DTT structure to directly address deficits in social cognition and perspective taking, they are designed to avoid reliance on these deficient skills. Discrete trials can be designed to teach those deficient skills explicitly, however.
A discrete trial is a single cycle of a behaviorally-based instruction routine. A particular trial may be repeated several times in succession, several times a day, over several days (or even longer) until the skill is mastered. There are four parts, and an optional fifth, to a discrete trial.
the discriminative stimulus (SD)-- the instruction or environmental cue to which the teacher would like the child to respond
the prompting stimulus (SP)-- a prompt or cue from the teacher to help the child respond correctly (optional)
the response (R)-- the skill or behavior that is the target of the instruction, or a portion thereof
the reinforcing stimulus (SR)-- a reward designed to motivate the child to respond and respond correctly
the inter-trial interval (ITI)-- a brief pause between consecutive trials
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