In the 1950s, Donald Hebb at McGill University conducted the first systematic studies of sensory deprivation — paying college students to lie in a chamber with goggles, cotton gloves, and foam cuffs blocking most sensory input, for as long as they could stand.

What Happened

Participants were expected to enjoy the rest. Most lasted only two or three days despite being paid generously. After a few hours, cognitive deterioration began: inability to concentrate, solve simple problems, or think coherently. Hallucinations emerged in most subjects — initially light patterns, then complex scenes, voices, and eventually complete alternative realities.

The Brain Without Input

The brain doesn't wait passively for external input. Deprived of normal sensory data, it generates its own — and those self-generated signals are experienced as external reality. Hallucination is what happens when the brain's prediction machine runs without corrective feedback from the world.

Applications and Misapplications

• Used by military and intelligence agencies to understand interrogation vulnerability
• Led to development of modern float tank therapy (much milder — tactile input present)
• Informed understanding of sensory processing in psychosis and extreme isolation

Reference:

Wikipedia: Sensory Deprivation

https://en.wikipedia.org/wiki/Sensory_deprivation