Stimulus generalization is the tendency of a subject to respond to a stimulus or a group of stimuli similar but not identical to the original CS. For example, a subject may initially make the desired response when exposed to any sound (that is, to a generalized stimulus) rather than making such a response only to a specific sound. Such generalization can occur in both classical and operant conditioning (if a CS is used). However, a subject can be taught to discriminate among sounds and to respond only to a specific sound.