The physiological function of removing all sensory stimuli, it has various psychological effects as well. This is commonly achieved by floating in a covered unlit tank filled with water. Of course, this isn't complete deprivation as you will still feel water, but with proper planning, control and will, you can achieve very close to a complete sensory deprivation. A friend and I are working up the nerve (boy that sounds ironic), time, and plan to doing this ourselves in an effort to achieve self-awareness and possibly even induce natural hallucinations. This is also a considerably step above such experiments as sleep deprivation.