Matching to Sample in ABA refers to a procedure where a stimulus is presented and taught to match a secondary stimulus (such as the word “car” and a picture of a car).  When the two stimulus are correctly matched, a reinforcer is given to increase future likelihood  of the stimulus matching to occur again.

Reflexive is also called identity matching.  This is the act of the subject matching the primary stimulus to the target stimulus.  Showing a picture of a bird and the child saying “bird.”

Symmetrical refers to the two way relationship of matching.  For example, show a picture of a bird and say “bird.”  Point to the picture of the bird, and the subject says “bird.”

Transitive this occurs when the equation if A = B and if B = C, then A = C.  In other words one stimulus is matched to a second stimulus.  The second stimulus is matched to the third stimulus.  By this relationship, the subject learns that the first stimulus and third stimulus are also matching.  For example, if you say “bird” and show a child a picture of a bird, then you show a picture of a bird and match it to a real bird in a cage, the relationship of saying bird for the caged animal is acquired.

When a learner can match two stimuli that are equivalent due to a relationship with a third stimulus, this is called transitivity.

In mathematics and logic, transitive relation is described in a similar manner.

Stimulus Equivalence has been achieved when ALL reflexive, symmetrical and transitive matching has been learned.

Equivalence Class is the collection of stimuli that evoke the same behavior.  Once an equivalence class has been established, it remains functional long after training.  For example, if a child has learned to be cry in the presence of dogs, this may transfer to crying when seeing a cat as well because they are both fluffy animals in the same stimulus class.  Teaching a behavior in the presence of a stimulus that is a member of a stimulus class should generalize over to the other members in the stimulus class.  When adding a new item to a stimulus equivalence class, the new item must be conditioned to at least one stimulus in the equivalence class.

In an Arbitrary Stimulus class, the stimuli do not look alike but the share the same response.  For example, “3+3”, “half a dozen” and “number of kids in the Brady Bunch” all equal 6!