Whether or not the person providing the prompt or probe can identify the likely response is probably dependent upon whether or not they are capable of being controlled by the same controlling variable with which the supplementary stimulation is said to sum. Two people may both be looking at an aardvark, for example, and one of them cannot remember the name. So the other says, “It begins with an ‘a.’” That is an example of a prompt because the provider is also stimulated by the primary variable and could emit the response.
A discriminative stimulus with the following features:
It is a supplementary stimulus
The person providing the supplementary stimulus can identify the response that the speaker is likely to emit
It is a supplementary stimulus
The person providing the supplementary stimulus cannot identify the response that the speaker is likely to emit
Whether the controlling relationship is formal or thematic
Who provides the supplementary stimulus (either another person or the speaker him or herself)