A stimulus that pinpoints the exact moment that the behavioral criterion (for that approximation) is met. The "bridge", as it is often referred to, (often a clicker, whistle or word) communicates to the subject that it has performed correctly and often signals that additional reinforcement is on the way. It "bridges" the gap between the time the correct response is given and the time the additional reinforcer is delivered. It is a stimulus that can act as both an SD (See cue or discriminative stimulus) and a secondary reinforcer.
A stimulus that can act as both an SD and a secondary reinforcer. It pinpoints the exact moment of reinforcement in a desired behavior. The "bridge" (often a clicker, whistle or word) communicates to the subject that it has performed correctly and signals that reinforcement is forthcoming. It "bridges" the gap between the time the correct response is given and the time the reinforcer is delivered.