WERNICKE'S DEFINITION OF HALLUCINATIONS AND ILLUSIONS

In 1900 the German neurologist Carl Wernicke (1848-1904) defined hallucinations and *illusions as follows: "Hallucinations are sensory perceptions that arise without the stimulation of the sense organ in question by an external object, merely as a consequence of internal stimuli, [whereas] illusions are false perceptions, failures to appreciate genuine objects of perception that are actually available."

Wernicke, C. (1900).Grundriss der Psychiatrie. Leipzig: Verlag von Georg Thieme.