People with psychosis are said to lack insight when they have a poor awareness that they are mentally ill and don't think they need to get help. Lack of insight is associated with poorer outcomes and worse adherence to treatment while improved insight has been linked to better treatment compliance and less hostility. A team of researchers led by Guillem Lera from the Hospital de la Ribera in Valencia looked into the links between insight and auditory hallucinations in a study of 168 psychotic patients. They found that patients with persistent auditory hallucinations had significantly less insight than patients with occasional or no hallucinations. The further away the hallucinations were thought to come from the less insight people had. The patients who heard voices 'in their head' showed better insight than those who heard voices coming from outside themselves.
Lera, Guillem ... [et al] - Insight among psychotic patients with auditory hallucinations
Journal of Clinical Psychology, 67(7), 1-8