There is a difference between the way the brain of healthy older adults perceive color than younger adults, finds a new study by UCL researchers. New research compared how younger and older pupils reacted to different aspects of color in the environment.
The result of the study on the brains of the elderlywas published in Scientific Reports
The brains of healthy older adults perceive colors differently than young adults
The team studying the brains of older adults recruited 17 healthy young adults with an average age of 27.7 years and 20 healthy older adults with an average age of 64.4 years. Participants were placed in a darkened room and shown 26 different colors for five seconds each, while researchers measured the diameter of their pupils.
The pupils constrict in response to increased brightness and color chroma (coloration). The colors shown included dark, muted, saturated, and light shades of magenta, blue, green, yellow, and red, along with two shades of orange and four grayscale colors.
Using a highly sensitive eye-tracking camera, which recorded pupil diameter 1,000 times per second, the team found that the pupils of healthy older adults constricted less in response to color chroma than young adults. This was especially noticeable for the green and magenta hues perceived by the brain. However, both younger and older adults had similar responses to the “lightness” of a color shade.
The study is the first to use pupillometry to show that as we age, our brains become less sensitive to the intensity of colors in the world around us.
The study's findings also complement previous behavioral research that has shown that older adults perceive surface colors as less colorful than young adults.
Lead author Dr Janneke van Leeuwen (UCL Queen Square Institute of Neurology) explained: “This work challenges the long-held belief among scientists that color perception remains relatively constant throughout life, and instead suggests that colors slowly fade as they occur. we grow old. Our findings may also help explain why our color preferences may change as we age and why at least some older people may prefer to dress in bright colors.
Researchers believe that as we age there is a decline in the body's sensitivity to color saturation levels within the primary visual cortex, the part of the brain that receives, integrates and processes visual information transmitted by the retinas.
Previous research has also shown that this is a feature of a rare form of dementia called posterior cortical atrophy (PCA), in which significant difficulties and abnormalities in color perception may be due to a significant decline in the brain's sensitivity to certain color tones. (especially green and green). magenta) in the primary visual cortex and its connected networks.
Co-corresponding author Professor Jason Warren (UCL Queen Square Institute of Neurology) noted: “Our findings could have broad implications for how we adapt fashion, furniture and other color 'spaces' for older people, and potentially also for our understanding of aging brain diseases, such as dementia.
“People with dementia may show changes in color preferences and other symptoms related to the visual brain: to interpret them correctly, we must first evaluate the effects of healthy aging on color perception. Further research is therefore needed to delineate the functional neuroanatomy of our findings, as higher cortical areas may also be involved.”
Red, orange, yellow, green, blue, indigo and purple – the colors of the rainbow are well known to anyone who remembers “Roy G. Biv”. However, scientific research has long shown that such colors are not inherent in the physical world, but rather the result of how our brain processes light.
A further study, co-authored by a University of Chicago neuroscientist, identifies those neural networks, specifically the areas of the brain that code the colors we actually see.
“We were able to show where it occurs in the visual pathway, which is relatively early,” said Prof. Steven Shevell, a leading researcher on color and brightness perception. “It's like a road map showing where to look for the neural circuits that cause the transition from early neural representations of the physical world to our mental world.”
Using brain scans and a new “switch rivalry” technique, he and his co-authors found that the primary visual cortex, which is the first stage of cortical visual processing, does not accurately represent the colors we experience. On the other hand, the higher areas of the visual path follow the hues we actually see. The article was published in the Proceedings of the National Academy of Sciences.
Building on previous work from Shevell's lab, they conducted their experiments with a technique that rapidly switched back and forth between two different wavelengths of light. Although the change occurred six times per second, viewers saw a sustained color (green) for several seconds before the perceived color changed to another color (magenta).
After examining the fMRI scans, Shevell and his colleagues found that activity in higher areas of the visual cortex matched the colors seen by the study subjects. These findings mark an important step in explaining the transition from encoding the physical light entering our eyes to the perceptual experience of seeing color.
The study is the result of an international collaboration with Insub Kim and Won Mok Shim of Sungkyunkwan University, as well as Sang Wook Hong of Florida Atlantic University. Hong, Ph.D.'05, studied with Shevell as a graduate student at UChicago.
“It's always satisfying to do great work that none of the collaborators could have accomplished alone,” said Shevell, the Eliakim Hastings Moore Distinguished Service Professor of Psychology, Ophthalmology and Visual Sciences.
Shevell, who directs the Institute for Mind and Biology at the University of Chicago, previously published on the use of ri
valry for switches in a 2017 paper, which he co-authored with Anthony D'Antona, Ph.D. Christiansen.
That work revealed a similar color perception phenomenon, but did not identify which areas of the brain were responsible.
Now, Shevell hopes that these new findings could lead to research that clarifies how different regions of the visual pathway make the transition to human color perception.
“We can focus and do experiments in those areas to understand how this happens,” he said. “We haven't been able to show how the transitions happen. We have proven that they happened. We want to understand how it happens.”
There are hundreds of thousands of distinct colors and shapes that a person can visually distinguish, but how does the brain process all this information? Scientists previously believed that the visual system initially encoded shape and color with different groups of neurons and then combined them much later. But a study by Salk researchers shows that there are neurons that respond selectively to particular combinations of color and shape.
“New genetic sensors and imaging technologies have allowed us to more thoroughly test the connection between visual circuits that process color and shape,” says Edward Callaway, senior author and professor in Salk's Systems Neurobiology Laboratory. “These findings provide valuable insights into how visual circuits are connected and organized in the brain.”
Similar to the sensor in a digital camera, light-sensitive cells in the eye (photoreceptors) detect wavelengths of light within specific ranges and at particular locations. This information then travels through the optic nerve to neurons in the visual cortex that interpret the information and begin to decipher the content of the image. Scientists have long thought that color and shape were extracted separately and then combined only in the higher brain centers, but Salk's new research shows that they are combined much earlier.
“The goal of our study was to better understand how the visual system processes the colors and shapes of visual stimuli,” says co-first author Anupam Garg, MD/Ph.D of the University of California at San Diego. student in the Callaway lab. “We wanted to apply new imaging techniques to answer these long-standing questions about visual processing.”
The researchers used imaging technology combined with genetically expressed sensors to study the function of thousands of individual neurons involved in color and shape processing in the primary visual cortex. During long recording periods, approximately 500 possible color and shape combinations were tested to find the stimulus that best activated each visually responsive neuron.
The team found that visual neurons responded selectively to color and shape along a continuum: while some neurons were activated only by a specific color or shape, many other neurons responded simultaneously to a particular color and shape, contrary to long-standing notions. data on how visual processing works.
“Our brain encodes visual information efficiently using intelligently designed circuits. Contrary to what is taught in class – that color and shape are processed separately in the early visual cortex and then integrated later by unknown mechanisms – the brain encodes color and shape together in a systematic way,” says Peichao Li, co-first author and post researcher -PhD in the Callaway laboratory.
“For the past 20 years, I have wanted to know how the visual system processes color, so this discovery is really exciting for me,” says Callaway, who holds the Vincent J. Coates Chair in Molecular Neurobiology. “This discovery lays the foundation for understanding how neural circuits carry out the calculations that lead to color vision. We look forward to building on these findings to determine how neurons in the visual cortex work together to extract colors and shapes.”
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