Visual adaptation

Visual adaptation is the temporary change in sensitivity or perception when exposed to a new or intense stimulus, and the lingering afterimage that may result when the stimulus is removed. These continuous small adjustments reflect the neural coding process of the visual system, and exist so the brain can attempt to "normalize" the visual experience.[1]

## Research

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The aftereffects of exposure to a visual stimulus or pattern causes loss of sensitivity to that pattern and induces stimulus bias. An example of this phenomenon is the "lilac chaser", introduced by Jeremy Hinton. The stimulus here are lilac circles, that once removed, leave green circles that then become the most prominent stimulus. The fading of the lilac circles is due to a loss of sensitivity to that stimulus and the adaptation to the new stimulus. To experience the "lilac chaser" effect, the subject needs to fixate their eyes on the cross in the middle of the image, and after a while the effect will settle in. Visual coding, a process involved in visual adaptation, is the means by which the brain adapts to certain stimuli, resulting in a biased perception of those stimuli. This phenomenon is referred to as visual plasticity; the brain's ability to change and adapt according to certain, repeated stimuli, altering the way information is perceived and processed.[2]

Lilac Chaser from Jeremy Hinton's experiment

The rate and strength of visual adaptation depends heavily on the number of stimuli presented simultaneously, as well as the amount of time for which the stimulus is present. Visual adaptation was found to be weaker when there were more stimuli present. Moreover, studies have found that stimuli can rival each other, which explains why higher numbers of simultaneous stimuli lead to lower stimulus adaptation. Studies have also found that visual adaptation can have a reversing effect; if the stimulus is absent long enough, the aftereffects of visual adaptation will subside. Studies have also shown that visual adaptation occurs in the early stages of processing.[3] While longer stimulus durations can induce perceived aftereffects, even short fixations have been shown to induce rapid adaptation that can bias neural responses and perception at subsequent fixations.[4]

## Face recognition

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Perceptual adaptation plays a big role in identifying faces. In an experiment conducted by Gillian Rhodes, the effect of face adaptation was investigated, along with whether visual adaptation affects the recognition of faces. The experiment found that perceptual adaptation does, in fact, affect face recognition. Individuals tend to adapt to common facial features as early as after five minutes of looking at them. This suggests that humans adapt to common facial features, leaving neural resources and space to identify uncommon characteristics and features, which is how humans identify specific faces on a case-by-case basis.[5]

Perceptual aftereffects for face recognition occur for several different stimuli, including gender, ethnicity, identity, emotion, and attractiveness of a face. The fact that this distinction occurs, implies that face recognition is a process that happens on a higher level and later on in the visual encoding, rather than early on within visual adaptation. The fact that the aftereffects in face recognition in particular are so strong, suggests that it is for the purpose of regulation of how processes work. This provides a sense of constancy in an individual's perception, while adapting to differences and possible versions of a stimulus allows for constancy and stability, and makes it easier to adapt to variations in a stimulus, while recognizing commonalities. These face perception cues are encoded in an individual's brain for extended periods of time, ensuring consistency over the individual's lifespan. A young person would perceive stimuli the same way as an older individual.[6]

## Body size adaptation

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Visual aftereffects have also been demonstrated in bodies. Individuals who are exposed to images of low fat (or low muscle) bodies have been shown to perceive subsequently-presented bodies as higher fat (or higher muscle) than they really are (and vice versa).[7] Individuals who are less satisfied with their bodies have been shown to direct more visual attention to thin bodies, resulting in stronger adaptation to thin bodies,[8] suggesting that visual adaptation may provide a mechanism for the association between exposure to thin media portrayals of bodies and body size misperception.[9][10]

Body size adaptation effects are thought to be higher-level aftereffects.[11]

## References

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1. ^ Webster, Michael A. (2015-11-18). "Visual Adaptation". Annual Review of Vision Science. 1 (1): 547–567\. doi:10.1146/annurev-vision-082114-035509. ISSN 2374-4642. PMC 4742349. PMID 26858985.
2. ^ Webster, Michael (19 May 2011). "Re: Adaptation and Visual Coding". Journal of Vision. 11 (5). JOV Journal of Vision: 3. doi:10.1167/11.5.3. PMC 3245980. PMID 21602298.
3. ^ Blake, Randolph; et al. (30 January 2006). "Re: Strength of early visual adaptation depends on visual awareness". Proceedings of the National Academy of Sciences. 103 (12): 4783–4788\. Bibcode:2006PNAS..103.4783B. doi:10.1073/pnas.0509634103. PMC 1400587. PMID 16537384.
4. ^ Niemeyer, James E.; Paradiso, Michael A. (2017-02-01). "Contrast sensitivity, V1 neural activity, and natural vision". Journal of Neurophysiology. 117 (2): 492–508\. doi:10.1152/jn.00635.2016. ISSN 0022-3077. PMC 5288473. PMID 27832603.
5. ^ Rhodes, Gillian (12 May 2010). "Re: Perceptual adaptation helps us identify faces". Vision Research. 50 (10): 963–968\. doi:10.1016/j.visres.2010.03.003. PMID 20214920.
6. ^ Clifford, Colin (23 August 2007). "Re: Visual Adaptation: Neural, psychological and computation aspects". Vision Research. 47 (25): 3125–3131\. CiteSeerX 10.1.1.331.1993. doi:10.1016/j.visres.2007.08.023. PMID 17936871. S2CID 6711382.
7. ^ Sturman, Daniel; Stephen, Ian D.; Mond, Jonathan; Stevenson, Richard J; Brooks, Kevin R. (2017-01-10). "Independent Aftereffects of Fat and Muscle: Implications for neural encoding, body space representation and body image disturbance". Scientific Reports. 7 (1): 40392. Bibcode:2017NatSR...740392S. doi:10.1038/srep40392. ISSN 2045-2322. PMC 5223140. PMID 28071712.
8. ^ Stephen, Ian D.; Sturman, Daniel; Stevenson, Richard J.; Mond, Jonathan; Brooks, Kevin R. (2018-01-31). "Visual attention mediates the relationship between body satisfaction and susceptibility to the body size adaptation effect". PLOS ONE. 13 (1): e0189855. Bibcode:2018PLoSO..1389855S. doi:10.1371/journal.pone.0189855. ISSN 1932-6203. PMC 5791942. PMID 29385137.
9. ^ Challinor, Kirsten L.; Mond, Jonathan; Stephen, Ian D.; Mitchison, Deborah; Stevenson, Richard J.; Hay, Phillipa; Brooks, Kevin R. (2017-10-27). "Body size and shape misperception and visual adaptation: An overview of an emerging research paradigm". Journal of International Medical Research. 45 (6): 2001–2008\. doi:10.1177/0300060517726440. ISSN 0300-0605. PMC 5805224. PMID 29076380.
10. ^ Brooks, Kevin R.; Mond, Jonathan; Mitchison, Deborah; Stevenson, Richard J.; Challinor, Kirsten L.; Stephen, Ian D. (January 2020). "Looking at the Figures: Visual Adaptation as a Mechanism for Body-Size and -Shape Misperception". Perspectives on Psychological Science. 15 (1): 133–149\. doi:10.1177/1745691619869331. ISSN 1745-6916. PMID 31725353.
11. ^ Brooks, Kevin R.; Clifford, Colin W. G.; Stevenson, Richard J.; Mond, Jonathan; Stephen, Ian D. (June 2018). "The high-level basis of body adaptation". Royal Society Open Science. 5 (6): 172103. Bibcode:2018RSOS....572103B. doi:10.1098/rsos.172103. ISSN 2054-5703. PMC 6030264. PMID 30110427.

## Further reading

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* Stratton, George M. (1897). "Upright Vision and the Retinal Image". Psychological Review. 4 (2): 182–7\. doi:10.1037/h0064110.
* Richard L. Gregory (30 Oct 1997). Eye and Brain : The Psychology of Seeing. Oxford University Press. ISBN 978-0-19-852412-0.