Discrete Trial

Applied Behavior Analysis
Helping children with autism

DISCRETE TRIAL

Discrete trial: Any operant whose response rate is controlled by a given opportunity to emit the response. Each discrete response occurs when an opportunity to respond exists. Discrete trial, restricted operant, and controlled operant are synonymous technical terms. (Contrast with free operant.) Cooper Heron Heward Applied Behavior Analysis p694

A discrete trial has four parts. An S^D, response, consequence, and an inter trial interval. When put together they form a discrete trial. An S^D is short for discriminative stimulus. A stimulus is an object or event that has an effect on the behavior of an individual. A discriminative stimulus alters the probability of a response depending upon its presence or absence. The stimulus is discriminative.

So for example lets suppose that you hear the door bell ring and you open the door and your friend is at the door. The door bell is the S^D, you opening the door is the response, and seeing your friend is the consequence. The inter trial interval is the time until your friend rings your door bell again.

Many people make the mistake of calling an S^D an instruction. As you see in the example above the door bell is a stimulus however not an instruction.

In a home applied behavior analysis program for a child with autism a discrete trail may be used to teach a student a few skills. For example a teacher might say to a student "touch head" this is the S^D, the student touches his head and this is the response, the teachers then says "good job" and this is the consequence, the time the teacher waits to give a new S^Dis the inter trial interval. If the teacher had to help the student in order for the student to respond correctly this is called a prompt. The teacher would say touch head and immediately after saying touch head she might guide the students hand to his head.

Many people take data when running discrete trials. On the data sheet if the student's response is independent the teacher would put a plus but if the response was prompted she would put a P or other symbol to indicate a prompted response. If the response is incorrect the data sheet would have a minus. Typically a criteria is set for each target between 80-100% across x amount of trials before you start teaching the new target. In the data sheet section are data sheets you can use if you are running a discrete trial home program.