In the relaxation response, herbert benson says, "Many people who meditate several hours everyday for weeks at a time tend to hallucinate"(172). The cause for this, according to benson, is ei-ther the pre-selection of the already psy-chologically disturbed practitioners seeking therapeutic effects from meditation or "sen-sory deprivation" due to prolonged meditation. I am intrigued in his diagnosis of sensory deprivation as the cause, which i suspect is inappropriate in that at least it is an over-generalization. Benson's assumed or implied mechanism of hallucina-tion is that as the meditator undergoes prolongged period of concentration-dominaed meditation he/she experiences progressively narrowing scope of consciousness to the point both internal and external sensory in-puts are shut off, hence sensory deprivation. In Buddhist meditation, we need to differen-tiate at least two basic categories, namely samatha (concentration or stillness) and vipassana(insight or discernment), which applies to the theravada, Chinese and tibetan traditions. While what Benson says might happen only to samatha practitioners, the likelihood of such occurrence is not big because in practice there are very few buddhist meditations without alternating insight at times. In the Diagnostic and statistical manual of Mental disorders Ⅳ, hallucination has undergone a change from being defined as a mental disorder cross-culturally to a normal mental state in some cultures and religions. The revision of the definition, however, requires that the subjects in study be able to demonstrate the capability of normal functioning professionally and socially.
