Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo


  • Simone Gori
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_271



An afterimage is an image that continues to be perceived after the physical stimulus that it originated from disappears from the observer’s visual field. The afterimage can be a result of an exposition to a grayscale pattern, a colored pattern, or even to a motion stimulus. There are different kinds of afterimages, for example, the positive one will be the same with the physical stimulus, while the negative one will result in the opposite in terms of luminance, colors, or direction of the physical stimulus that generates it.


In everyday experience it is not so uncommon to experience several types of aftereffects. The observation done by Addams [1] while watching the Falls of Foyers, near to the Loch Ness in Scotland, is probably the most famous description of the motion aftereffect outside a scientific laboratory. The motion aftereffect was already observed by Aristotle and Lucretius in the ancient times, but the description done by Addams remains the most cited example: if an observer watches a fall for about 60 s and, after that, she/he moves their gaze to the wood nearby, everything will seem to move upward. Now it is known that motion aftereffect can be so powerful that it can influence the direction of the illusory motion produced by static patterns [2] or even followed after only milliseconds of adaptation [3].

Possible Explanations

However, it is not just adaptation to motion that produces aftereffects. Although an afterimage can be easily experienced after looking at a prolonged grayscale image, the most popular afterimages are probably experienced after looking at colors. Staring at the fixation cross in Fig. 1 for more than 30 s and then moving the gaze to a white surface should produce a color negative afterimage: the disks will appear filled with the opposite colors of the original stimulus on the blank surface. The common opinion in the scientific community is that the afterimages result from neural adaptation, but adaptation is present throughout the visual system, which makes the neural substrate of these phenomena not so easy to isolate. For long, it was supposed that the afterimages were caused by fatigued cells in the retina responding to light. Then, if an observer will stare at the red color for enough time, the receptors in the retina responding to red will fatigue and will fire less. In color vision, it is generally believed that colors are represented along orthogonal opponent axes: yellow to blue and red to green. Consequently, when the observer will switch over to a white surface, after that the retina receptors for the red are adapted, the visual system will interpret that blank surface as filled with the red complementary color: green. This oversimplified explanation where all the color afterimages are explained at the retina level was successively challenged by several phenomena that required cortical elaboration [4]. In the 1960s it was shown that the rabbit visual cortex presented neural adaptation after prolonged exposition to a stimulus that was comparable to the duration of the aftereffects recorded during the psychophysical experiments [5]. This results, concordantly with other neuropsychological and psychophysical studies [4], moved the possible main physiological substrate of the afterimage in the primary visual cortex (V1). V1 is able to also explain the interocular transfer of the aftereffect, which is the possibility to adapt an eye and to observe some effects on the non adapted one.
Afterimage, Fig. 1

In order to experience a color negative afterimage, the reader should stare at the fixation cross shown for no less than 30 s and after try to move the gaze to a white surface. What should be seen on the blank surface are four circles filled with the opposite colors (the green should be now red, the blue yellow, the yellow blue, and finally the red green)

However, even if low-level cortical processes seemed perfectly appropriated in order to explain the afterimage, the discovery that the top-down processes are able to influence radically both the primary visual cortex and also some subcortical “stations” of the visual system, as the lateral geniculate nucleus (LGN), together with some new types of aftereffects that showed the influence of attention [6, 7],consciousness [8], or an effect that lasts for days, weeks, or even months, seemed to clearly reject an explanation in terms of the short-lived adaptation reported typically in single cells of V1. These effects all suggested that the final percept of the afterimages is probably a complex result of the interaction and the adaptation of several districts throughout the visual system from the retina to the high-level cortical areas. Recently it was shown that the color afterimage signals are generated in the retina, but they are modified by cortical processes [9]. In sum the retinal afterimages face the similar destiny of all retinal signals that in humans are virtually always heavily modulated by the cortex.

An interesting question that can be posed, however, is that whether the afterimages have a function or if they are just a side effect incurred as a minor consequence of having evolved such a complex and superb machinery known as the human visual system. The answer, as it was probably expected, seems to be that the afterimages and the neural adaptation in general are part of complex neural strategies evolved during thousands of years in order to improve our world perception (e.g. [10, 11]).

Breathing Light Illusion

Finally the afterimage (with color or in grayscale, it depends on which version is used) is also at the basis of the family of illusions composed of the breathing light illusion and the dynamic luminance-gradient illusion [12, 13, 14]. Approaching these patterns like the one in Fig. 2 by moving one’s head toward it makes the spot appear to become larger, more diffuse, and filled with white. On receding from it, the spot’s center remains white but the remainder appears smaller, darker, and sharper. The proposed explanation of the phenomenon is related to the superimposition of the afterimage on the physical stimulus during dynamical viewing [13, 14].
Afterimage, Fig. 2

A complex version of the breathing light illusion. Approaching the patterns by moving one’s head toward it makes the spot appear to become larger, more diffuse, and filled with white. On receding from it, the spot’s center remains white but the remainder appears smaller, darker, and sharper. In addition, in this specific pattern, an illusory rotation is perceived together with the typical illusory effect of the breathing light illusion. This illusory rotation is the same as experienced in the Rotating-Tilted-Lines Illusion [15, 16, 17, 18]

In summary the afterimages are interesting phenomena that helped to understand our brain mechanism, they are able to produce striking illusory effects, and the underlying mechanisms seem to be relevant in producing a more efficient perception of the world.



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© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.Department of Human and Social SciencesUniversity of BergamoBergamoItaly
  2. 2.Developmental Neuropsychology UnitScientific Institute “E. Medea”Bosisio Parini, LeccoItaly