{"id":28694,"date":"2023-06-19T11:00:29","date_gmt":"2023-06-19T09:00:29","guid":{"rendered":"https:\/\/www.sciencefocus.com\/?p=145963"},"modified":"2023-06-19T11:38:29","modified_gmt":"2023-06-19T09:38:29","slug":"scientists-have-finally-solved-the-mystery-behind-this-optical-illusion","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/rss_feed\/scientists-have-finally-solved-the-mystery-behind-this-optical-illusion\/","title":{"rendered":"Scientists have finally solved the mystery behind this optical illusion"},"content":{"rendered":"

A new breakthrough study has discovered how ‘simultaneous contrast’ pictures trick your eyes. <\/p>

By Thomas Ling\n \t\t<\/p>

Published: Monday, 19 June 2023 at 12:00 am<\/p>

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See the image above? It\u2019s playing tricks on your eyes: despite initial appearances, the bar in the middle of the picture is actually a singular shade of grey \u2013 it only appears<\/em> lighter at one end due to the background gradient.<\/p>\n

Such \u2018simultaneous contrast\u2019 illusions like this have long fascinated scientists, with many pondering why these pictures so easily trip us up. However, a new breakthrough study from the University of Exeter may now have unravelled the mystery: high-contrast optical illusions are caused by limitations in our eyes<\/a>, rather than more complex neurological processes involving context and prior knowledge.<\/p>\n

In simpler terms, it\u2019s not your brain\u2019s processing power that\u2019s to blame, but rather the hardware of your visual system.<\/p>\n

\u201cThis throws into the air a lot of long-held assumptions about how visual illusions work,\u201d Dr Jolyon Troscianko<\/a> \u2013 one author of the study, published in PLOS Computational Biology<\/em> \u2013 said.<\/p>\n

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The two grey bars in the middle of this figure are the same grey, but the one on the left (surrounded by more black bars) appears darker. Image credit: Jolyon Troscianko<\/span><\/figcaption><\/div>\n

As previously discovered, our eyes communicate with the brain by adjusting how fast their neurons fire. However, as Troscianko explained, \u201cThere is a limit to how quickly these neurons can fire, and previous research failed to consider how this limitation might impact our perception of colour.\u201d<\/p>\n

In the study, researchers created a computer model that mimicked the \u2018limited bandwidth\u2019 of the human eye, replicating the way we perceive visual information. When this model was exposed to \u2018simultaneous contrast\u2019 illusions, the researchers observed that the model would become overwhelmed by the presence of high contrasts, resulting in a distorted perception of the image.<\/p>\n

\u201cOur model shows how neurons with such limited contrast bandwidth can combine their signals to allow us to see these enormous contrasts, but the information is \u2018compressed\u2019 \u2013 resulting in visual illusions,\u201d said Troscianko.<\/p>\n

The model, the researchers say, shows how different neurons have evolved to become finely tuned at processing subtle variations across a range of colours. \u201cFor example, some neurons are sensitive to very tiny differences in grey levels at medium-sized [ranges], but are easily overwhelmed by high contrasts,\u201d said Troscianko.<\/p>\n

\u201cMeanwhile, neurons coding for contrasts at larger or smaller scales are much less sensitive, but can work over a much wider range of contrasts, giving deep black-and-white differences.\u201d<\/p>\n

In future, scientists hope to use the computer model to explore the colour perception of animals with different vision neuron bandwidths to humans.<\/p>\n

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