Troxler effect

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The Troxler effect, demonstrated using Gaussian color noise : when the center of the fully resolved image is fixed from a short distance, the color differences seem to disappear after a few seconds.

The Troxler effect is a phenomenon of visual perception described by Ignaz Paul Vitalis Troxler in 1804 , which occurs as a result of local adaptation of retinal areas.

The adaptation of the eye is a physiological process of adapting the retina to the stimulus intensity. When adaptation processes are restricted to circumscribed areas of the retina, one also speaks of local adaptation. Retinal areas adapt to persistent or recurring stimuli of similar intensity in such a way that their sensitivity decreases. Images projected onto the same areas of the retina without any significant changes in stimulus therefore produce neuronal excitation patterns, the signal strength of which is progressively reduced. After a while, this can lead to the loss of the perceptibility of visually unchanged or repeated objects in the same place: the Troxler effect.

If you look at the picture for a long time, the colored circles fade after about 20 seconds, provided eye movements are suppressed. Some viewers see a moving light green circle instead of the gap as a successive contrast .

Of course, this also applies to those structures of the retina that are superimposed on the photoreceptor layer and through which light passes before it reaches the sensory cells. For example, the delicate blood vessels of the retina are projected onto the position of the receptors and displayed, mostly without being visually perceived.

If you make a diaphragm by piercing a small hole in a piece of paper with a needle and looking through this hole, and you let the opening rotate in front of the eye in a circle with a radius of one centimeter around a center, you change the angle by changing the angle of incidence Conditions of perception. The veins of the eye cast shadows on the retina during the rotational movement, which the brain can perceive again through the movement of these shadows.

In daily life the occurrence of local adaptation is prevented by permanent microsaccades of the eye. The phenomenon appears more clearly in the case of peripheral stimuli due to the larger receptive fields in the retinal periphery . The larger a receptive field, the lower the relative impact of a microsaccade.


  • Troxler, IPV (1804). About the disappearance of given objects within our field of vision. Ophthalmic Library, 2 (2), 1-53.
  • Herbert Kaufmann (Ed.): Strabismus. With the collaboration of Wilfried de Decker et al. Enke, Stuttgart 1986, ISBN 3-432-95391-7 .