Participants in a sensory deprivation experiment reported having hallucinations after just fifteen minutes.
They then put the participants, one by one, in a dark anechoic chamber which shields all incoming sounds and deadens any noise made by the participant. The room had a ‘panic button’ to stop the experiment but apparently no-one needed to use it.
Turns out when we have no external stimuli, we superimpose our own patterns. [via]