ABSTRACT
Can you see in the dark: the dark of a light-tight room? Possibly not, but you can have an experience like seeing. Impressions of colour and shape can be provided in various ways, including by electrical stimulation of the eye or by a blow to the head. A procedure more acceptable to observers involves dark-adapting them, and then briefly switching the lights on and then off. A quite vivid experience of the room will follow, sometimes so strong that it is difficult to believe that the room is still dark. This after-image is positive, and appears one to three seconds after the light is switched off.
