Subject: How does sensory deprivation work?

I am doing a school project on sensory deprivation. When I do a websearch, I 
get two contradictory results: sensory deprivation as a form of punishment or 
torture, normally in prisons; and sensory deprivation as a form of relaxation 
therapy. What changes sensory deprivation from a pleasant experience to 
torture? Does it involve length of time involved; which sense is deprived (eg. 
the therapeutic use focuses more on depriving proprioception and touch, whereas 
the torture technique seems to work more on sight and sound); or some other 
factor I'm not thinking of?

Re: How does sensory deprivation work?