What is an example of a substitution impairment in articulation?

In articulation disorders, substitution impairment refers specifically to the replacement of one speech sound with another. The example of saying 'w' for 'r' clearly illustrates this concept, as it demonstrates the speaker replacing the correct sound /r/ with an incorrect sound /w/. This phonetic alteration affects the clarity and intelligibility of speech when the intended sound is not produced accurately, leading to potential misunderstandings.

Options involving dropping the initial sound of a word or adding extra sounds refer to other types of speech errors, such as omissions and distortions, respectively. Not pronouncing sounds correctly may encompass a broad category of speech errors, but it does not specifically define the clear act of substitution as presented in the example provided. Substitution impairments are characterized by the consistent replacement of one phoneme by another, which is precisely what is illustrated in the correct choice.