The Ganzfeld Effect

The Ganzfeld effect is a phenomenon of perception caused by exposure to unstructured stimuli. Unstructured stimuli in the form of white noise and or a uniform field of light can cause your brain to actually hallucinate. This effect is the result of the brain amplifying neural noise in order to look for the missing visual signals. The noise is interpreted in the higher visual cortex, and gives rise to these hallucinations. The video linked will provide more information about this phenomenon and you can see two people share their experience trying it out themselves.