after-image

af·ter·im·age

, after-image (af'tĕr-im'ăj) Persistence of a visual response after cessation of the stimulus.

after-image

A visual negative impression of a bright object or light, which persists for a few seconds after the gaze is shifted or the eyes closed. Persistence of a positive image after moving the eyes implies a potentially serious neurological defect.

after-image

Visual sensation persisting after the original stimulus has been removed. If observed in darkness following stimulation by a high intensity, brief duration light source, seven different after-image phases are frequently noted. The first phase, also called Hering's after-image, is a positive after-image and it is followed by a negative after-image. After a short interval (less than half a second) a second positive after-image, called Purkinje after-image or Bidwell's ghost, appears, the character of which depends upon the conditions of adaptation, the colour of the stimulus and the retinal region stimulated (best in the periphery). Afterwards, a second negative after-image is sometimes observed followed by a third positive after-image, called Hess after-image. After a long dark interval, a third negative after-image may appear followed after another long dark interval by a fourth positive after-image. If the light stimulus is of moderate intensity, the last phases will be absent. See Emmert's law; after-image test; after-image transfer test.
complementary after-image An after-image in which the colour is complementary to the colour of the original stimulus.
Hering's; Hess after-image See after-image.
homochromatic after-image An after-image in which the colour appears the same as in the original stimulus.
motion after-image See waterfall after-effect; Plateau's spiral.
negative after-image An after-image in which the light areas of the original stimulus appear dark, the dark areas appear light and the coloured areas appear in a complementary colour.
positive after-image An after-image that appears the same as the original stimulus.
Purkinje after-image See after-image.

After-image

Aft´er-im`age

after-image

af·ter·im·age

after-image

after-image