An image seen immediately after the intense stimulation of the eye by light has ceased. for about a second, the afterimage is 'positive' , and then it turns to 'negative', often with fleeting colors. The positive phase is due to after-discharge of the receptors of the retina; the negative phase is caused by loss of sensitivity of the receptors as a result of bleaching of the photo-pigments by the intense light. Afterimages can be annoying, but they are usually ignored or suppressed.

(c) Oxford University Press

Richard Gregory, Oxford Companion to the Mind.

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