A person hears voices that speak to him in the absence of any external sitmuli. This is an example of :

Hallucination

People with schizophrenia may have hallucinations, i.e. perceptions that occur in the absence of external stimuli. Auditory hallucinations are most common in schizophrenia. Patients hear sounds or voices that speak words, phrases and sentences directly to the patient (second-person hallucination) or talk to one another referring to the patient as s/he (third-person hallucination).