A nurse is assisting with an admission interview for a client who has schizophrenia. He tells the nurse that he is receiving special audible messages from the Central Intelligence Agency that no one else is able to hear. The nurse should identify that the client is having which of the following alterations in perception?

c. Hallucination

In the scenario described, the client's experience of receiving special audible messages from the Central Intelligence Agency that no one else can hear indicates a hallucination. Hallucinations are perceptual disturbances in which a person experiences sensory perceptions without any external stimuli. They can occur in any sensory modality, such as hearing (auditory hallucinations), seeing (visual hallucinations), smelling (olfactory hallucinations), tasting (gustatory hallucinations), or feeling (tactile hallucinations).

In this case, the client is experiencing auditory hallucinations, as he is perceiving auditory stimuli (audible messages) that are not present in the external environment. Auditory hallucinations are most commonly associated with schizophrenia, although they can occur in other psychiatric disorders as well.

Derealization (option a) refers to a subjective feeling of unreality or detachment from the environment. It involves a perception that the external world is strange, distorted, or unreal. This is not the primary alteration in perception described in the scenario.

Illusion (option b) is a misinterpretation or misperception of a real sensory stimulus. It occurs when a person's perception of an actual stimulus is distorted or misunderstood. There is no indication of a misperception of a real stimulus in the scenario.

Depersonalization (option d) is a subjective experience of being detached from one's own body, thoughts, or emotions. It involves a feeling of being outside of oneself or observing oneself from a distance. This is not the primary alteration in perception described in the scenario.

Therefore, the correct answer is c. Hallucination, as the client's experience of receiving special audible messages that no one else can hear represents an auditory hallucination.