Geoffery Schultz, a student of [Ronald] Melzack, has recently conducted a study showing that visual hallucinations need not be caused by psychopathology but may result from the disruption of sensory input among patients suffering eye damage. The neuromatrix, in Melzack's theory, overfires its output messages in the absence of stimulation from external sources (or temping feedback), and creates images – often fantastic or exaggerated – that may be experienced as real.