Illusion helps demystify the way vision works

For the first time, research shows that a certain kind of visual illusion, neon color spreading, works on mice. The study is also the first to combine the use of two investigative techniques called electrophysiology and optogenetics to study this illusion. Results from experiments on mice settle a long-standing debate in neuroscience about which levels of neurons within the brain are responsible for the perception of brightness.

We're all familiar with optical illusions; some are novelties, while some are all around us. Even as you look at the screen in front you, you are being fooled into thinking that you're seeing the color white. What you're really seeing is lots of red, green and blue elements packed so tightly together it gives the impression of being white. Another example is a fast rotating wheel or propeller, which can briefly look like it's reversing direction while it's accelerating to full speed. In any case, it might be surprising to know that optical illusions are not just fun to look at but can also be a useful tool to learn more about eyes, nerves, minds and brains.

Associate Professor Masataka Watanabe from the Department of Systems Innovation at the University of Tokyo is on a mission to understand more about the nature of consciousness. It's a vast subject area so naturally there are many ways to explore it, and amongst other things, he uses optical illusions. His most recent research looked at whether a certain kind of illusion that works on humans would also work on mice. And it turns out, it does. But why is this significant?

"Knowing this kind of illusion, called a neon-color-spreading illusion, works on mice as well as humans, is useful for neuroscientists like myself, as it means that mice can serve as useful test subjects for cases where humans cannot," said Watanabe. "To really understand what goes on inside the brain during perceptual experiences, we need to use certain methods that we cannot use on people. These include electrophysiology, the recording of neural activity with electrodes, and optogenetics, where light pulses enable or disable firing of specific neurons in a living brain."

Watanabe's experiment was the first of its kind to make use of both electrophysiology and optogenetics at the same time in animal test subjects exposed to the neon-color-spreading illusion, which allowed his team to see precisely what structures within the brain are responsible for processing the illusion.

"After a visual stimulus lands on the eye, it's carried to the brain by nerves and is then received by a series of layers of neurons called V1, V2 and so on, where V1 is the first and most basic layer, and V2 and above are considered higher layers," said Watanabe. "There is a long-standing debate in neuroscience about the role higher levels play in the perception of brightness and it was not an easy thing to study. Our experiment on mice has shown us that neurons in V1 responded not just to the illusion, but also to a nonillusory version of the same kind of pattern shown. But only when the illusory version was shown to the mice did neurons in V2 also play a crucial role: that of modulating the activity of neurons in V1, thus proving that V2 neurons do in fact play a role in the perception of brightness."

Read more at Science Daily

Heat stress from ocean warming harms octopus vision

While climate change has led to an increase in the abundance of octopuses, heat stress from projected ocean warming could impair their vision and impact the survivability of the species.

"We found several proteins important for vision that were affected by thermal stress," says Dr Qiaz Hua, a recent PhD graduate from the University of Adelaide's School of Biological Sciences.

"One of them is a structural protein found in high abundance in animal eye lenses to preserve lens transparency and optical clarity, and another is responsible for the regeneration of visual pigments in the photoreceptors of the eyes.

"The levels of both of these proteins were significantly reduced under projected ocean warming conditions, which suggests that octopus vision is likely to be impaired under thermal stress."

Octopuses are highly visual animals, with 70 per cent of the octopus brain dedicated to vision -- which is 20 per cent more than in humans.

"The primary functions of vision include but are not limited to visual acuity, discrimination of brightness, depth perception, motion detection and polarisation, and it is crucial for detecting predator and prey as well as for communication," says Dr Hua.

"Having impaired vision will affect an octopus's chances of survival in the wild through increased predator risk as well as lower foraging success."

To make this finding, the research team, including academics from the University of South Australia, University of California Davis, and the South Australian Research and Development Institute's aquatic sciences division, exposed Octopus berrima embryos to different temperature treatments, a control 19°C exposure, 22°C to model current summer temperatures, and 25°C to model projected summer temperatures.

"The future-projected temperature was based on the Intergovernmental Panel on Climate Change's projected increase of about 3°C of warming by 2100," Dr Hua says.

In addition to impaired vision, Dr Hua found increased ocean water temperatures would have a negative effect on octopus broods.

"We found a high mortality rate under future warming conditions. Out of three replicate octopus broods, none of the eggs hatched for two of them and less than half of the eggs hatched for the remaining brood," Dr Hua says.

"In the broods where none of the eggs hatched, the mothers died naturally while the eggs were still in early development stages.

"Because maternal care of embryos occurs in octopuses, global warming could have a simultaneous impact on multiple generations, with the low survival rate of the embryos caused by the direct effect of thermal stress as well as the indirect effect of thermal stress on the mothers.

"Our study shows that even for a highly adaptable taxon like octopuses, they may not be able to survive future ocean changes."

Other effects of higher temperatures which have been observed in octopuses include a higher metabolic rate, reduced size at maturity, and even a range shift in the distribution of some species.

"We hope that future research would examine a combination of environmental stressors including ocean acidification, warming, and deoxygenation," Dr Hua says.

Read more at Science Daily

Vision via sound for the blind

Australian researchers have developed cutting-edge technology known as "acoustic touch" that helps people 'see' using sound. The technology has the potential to transform the lives of those who are blind or have low vision.

Around 39 million people worldwide are blind, according to the World Health Organisation, and an additional 246 million people live with low vision, impacting their ability to participate in everyday life activities.

The next generation smart glasses, which translate visual information into distinct sound icons, were developed by researchers from the University of Technology Sydney and the University of Sydney, together with Sydney start-up ARIA Research.

"Smart glasses typically use computer vision and other sensory information to translate the wearer's surrounding into computer-synthesized speech," said Distinguished Professor Chin-Teng Lin, a global leader in brain-computer interface research from the University of Technology Sydney.

"However, acoustic touch technology sonifies objects, creating unique sound representations as they enter the device's field of view. For example, the sound of rustling leaves might signify a plant, or a buzzing sound might represent a mobile phone," he said.

A study into the efficacy and usability of acoustic touch technology to assist people who are blind, led by Dr Howe Zhu from the University of Technology Sydney, has just been published in the journal PLOS ONE.

The researchers tested the device with 14 participants; seven individuals with blindness or low vision and seven blindfolded sighted individuals who served as a control group.

They found that the wearable device, equipped with acoustic touch technology, significantly enhanced the ability of blind or low-vision individuals to recognise and reach for objects, without causing too much mental effort.

"The auditory feedback empowers users to identify and reach for objects with remarkable accuracy," said Dr Zhu. "Our findings indicate that acoustic touch has the potential to offer a wearable and effective method of sensory augmentation for the visually impaired community."

The research underscores the importance of developing assistive technology in overcoming the challenges such as locating specific household items and personal belongings.

By addressing these day-to-day challenges, the acoustic touch technology opens new doors for individuals who are blind or have low vision, enhancing their independence and quality of life.

Read more at Science Daily

Scientists achieve promising results towards restoring vision in blindness caused by cellular degeneration in the eye

A preclinical study using stem cells to produce progenitor photoreceptor cells -- light-detecting cells found in the eye -- and then transplanting these into experimental models of damaged retinas has resulted in significant vision recovery. This finding, by scientists at Duke-NUS Medical School, the Singapore Eye Research Institute and the Karolinska Institute in Sweden, marks a first step towards potentially restoring vision in eye diseases characterised by photoreceptor loss.

"Our laboratory has developed a novel method that enables the production of photoreceptor progenitor cells resembling those in human embryos," said Assistant Professor Tay Hwee Goon, first author of the study from Duke-NUS' Centre for Vision Research. "Transplantation of these cells into experimental models has yielded partial restoration of the retinal function."

The degeneration of photoreceptors in the eye is a significant cause of declining vision that can eventually lead to blindness and for which there is currently no effective treatment. Photoreceptor degeneration occurs in a variety of inherited retinal diseases, such as retinitis pigmentosa -- a rare eye disease that breaks down cells in the retina over time and eventually causes vision loss -- and age-related macular degeneration, a leading cause of vision impairment worldwide.

Asst Prof Tay and her team developed a procedure to grow human embryonic stem cells in the presence of purified laminin proteins that are involved in normal development of human retinas. In the presence of the laminins, stem cells could be directed to differentiate into photoreceptor progenitor cells responsible for converting light into signals that are sent to the brain.

When these cells were transplanted into damaged retinas, the preclinical models showed significant recovery of vision. A diagnostic test called electroretinogram also identified significant recovery in the retinas via electrical activity in the retina in response to a light stimulus. The transplanted cells established connections with surrounding retinal cells and nerves in the inner retina. They also survived and functioned for many weeks after transplantation.

Moving forward, the team hopes to refine their method to make it simpler and achieve more consistent results than earlier attempts to explore stem cell therapy for photoreceptor cell replacement.

"It is exciting to find these results, which suggest a promising route towards using stem cells to treat those forms of visual deterioration and blindness caused by the loss of photoreceptors," said Dr Helder Andre, Head of Molecular and Cellular Research from Karolinska Institute's Department of Clinical Neuroscience and a senior author of the study.

Associate Professor Enrico Petretto, Director of the Centre for Computational Biology at Duke-NUS and the study's bioinformatics analysis lead, added: "Our method may also be useful for understanding the molecular and cellular pathways that drive the progression of macular degeneration, perhaps leading to the development of other therapeutic approaches."

The next challenge for the researchers is to explore the efficacy of their method in models of photoreceptor degeneration that more closely match the human condition.

"If we get promising results in our future studies, we hope to move to clinical trials in patients," said Professor Karl Tryggvason, from Duke-NUS' Cardiovascular and Metabolic Disorders Programme, and the corresponding author of the study. "That would be an important step towards for being able to reverse damage of the retina and restore vision."

Read more at Science Daily

Eye-opening discovery about adult brain's ability to recover vision

A discovery about how some visually impaired adults could start to see offers a new vision of the brain's possibilities. The finding that the adult brain has the potential to partially recover from inherited blindness comes from a collaboration between researchers in the University of California, Irvine School of Biological Sciences and the School of Medicine. Their paper appears in Current Biology.

The team was examining treatment for Leber congenital amaurosis, known as LCA. The term refers to a group of inherited retinal diseases distinguished by severe visual impairment at birth. The condition, which stems from mutations in any of over two dozen genes, causes degeneration or dysfunction in the retina's photoreceptors.

Administering chemical compounds that target the retina, called synthetic retinoids, can restore a notable amount of vision in children with LCA. The UCI team wanted to find out if the treatment could make a difference for adults who have the condition.

"Frankly, we were blown away by how much the treatment rescued brain circuits involved in vision," said Sunil Gandhi, professor of neurobiology and behavior and the corresponding author. Gandhi is a fellow of UCI's Center for the Neurobiology of Learning and Memory and a member of the Center for Translational Vision Research. "Seeing involves more than intact and functioning retinae. It starts in the eye, which sends signals throughout the brain. It's in the central circuits of the brain where visual perception actually arises." Until now, scientists believed that the brain must receive those signals in childhood so that central circuits could wire themselves correctly.

Working with rodent models of LCA, the collaborators were surprised by what they found. "The central visual pathway signaling was significantly restored in adults, especially the circuits that deal with information coming from both eyes," Gandhi said. "Immediately after the treatment, the signals coming from the opposite-side eye, which is the dominant pathway in the mouse, activated two times more neurons in the brain. What was even more mind-blowing was that the signals coming from the same-side eye pathway activated five-fold more neurons in the brain after the treatment and this impressive effect was long-lasting. The restoration of visual function at the level of the brain was much greater than expected from the improvements we saw at the level of the retinae. The fact that this treatment works so well in the central visual pathway in adulthood supports a new concept, which is that there is latent potential for vision that is just waiting to be triggered."

The finding opens exciting research possibilities. "Whenever you have a discovery that breaks with your expectations about the possibility for the brain to adapt and rewire, it teaches you a broader concept," Gandhi said. "This new paradigm could aid in the development of retinoid therapies to more completely rescue the central visual pathway of adults with this condition."

Read more at Science Daily

Colorblind fish show experts how vision evolved

After decades of studying color vision in mice, new research in zebrafish has allowed experts at the University of Tokyo to uncover how some animals regulate their ability to see blue light. The results, published in Science Advances, allow researchers to better understand the evolutionary history and current control mechanisms of color vision.

"In 1989 when I began studying the evolution of vision, the textbooks said that light sensitivity and color differentiation all came from the same protein. Since then, our group identified color-sensitive proteins, mapped their evolution between species, and now understand their regulation," said Emeritus Professor Yoshitaka Fukada from the University of Tokyo Graduate School of Science.

As new color-sensitive cone cells grow in the eye, controlled patterns of gene activity mean that each cell differentiates and produces one type of protein specialized to detect a specific range of light wavelengths. The ancestor of all animals with a backbone could differentiate four different color wavelengths of light: near-ultraviolet, blue, green and red.

Over millennia, some ancestor species lost the genes responsible for one or two of those color-detecting proteins. Sometimes, a descendant species eventually recreated a color-specific protein by duplicating, then mutating a remaining gene.

Genome sequencing allows researchers to study the evolution of color vision genes while gene editing tools can reveal how those genes are regulated. Studying mice has allowed experts to understand how violet- and red-wavelength sensitivity are regulated, but mice evolved without the ability to differentiate the blue and green wavelengths. Lack of convenient gene editing tools meant regulation of blue and green color sensitivity remained unknown.

In 2019, Fukada's research team, now led by Lecturer Daisuke Kojima, combined the relatively new gene editing tools and color vision studies in zebrafish, a species with all four color-sensitive proteins. Microscope images of normal zebrafish retinas, the light-sensitive membranes lining their eyeballs and connected to their brains by their optic nerves, show a vibrant arrangement of fluorescently labeled cone cells in a distinct pattern of violet-, green-, red-, blue-, red-, green- and violet-detecting cells.

Researchers first identified three genes -- six6b, six7, and foxq2 -- common only in species with all four color vision proteins. Then, they genetically modified zebrafish to reduce the activity of those genes.

Previously, the UTokyo researchers observed that reducing expression of six6b and six7 -- either in combination or individually -- eliminated both blue and green vision in zebrafish. Zebrafish without blue and green vision had difficulty finding food, indicating the importance of full-color vision for their survival.

It was their most recently published results that allowed researchers to understand how blue and green sensitivities are distinguished by different foxq2 activity. In cone cells that will detect blue light, six6b and six7 activate foxq2. Then foxq2 activates gene expression of the blue-sensitive protein and blocks expression of green-sensitive proteins. Retinas of zebrafish lacking normal foxq2 gene expression do not have cone cells sensitive to blue light, instead packing together a shorter pattern of violet-, green-, then two red-, green- and violet-detecting cone cells.

The combination of molecular genetic studies in single species with comparative genomic studies of multiple species gives researchers additional confidence in their map of color vision regulation.

Read more at Science Daily

Study shows how our brains sync hearing with vision

Every high-school physics student learns that sound and light travel at very different speeds. If the brain did not account for this difference, it would be much harder for us to tell where sounds came from, and how they are related to what we see.

Instead, the brain allows us to make better sense of our world by playing tricks, so that a visual and a sound created at the same time are perceived as synchronous, even though they reach the brain and are processed by neural circuits at different speeds.

One of the brain's tricks is temporal recalibration: altering our sense of time to synchronize our joint perception of sound and vision. A new study finds that recalibration depends on brain signals constantly adapting to our environment to sample, order and associate competing sensory inputs together.

Scientists at The Neuro (Montreal Neurological Institute-Hospital) of McGill university recruited volunteers to view short flashes of light paired with sounds with a variety of delays and asked them to report whether they thought both happened at the same time. The participants performed this task inside a magnetoencephalography (MEG) machine, which recorded and imaged their brain waves with millisecond precision. The audio-visual pairs of stimuli changed each time, with sounds and visual objects presented closer or farther apart in time, and with random orders of presentation.

The researchers found that the volunteers' perception of simultaneity between the audio and visual stimuli in a pair was strongly affected by the perceived simultaneity of the stimulus pair before it. For example, if presented with a sound followed by a visual milliseconds apart and perceived as asynchronous, one is much more likely to report the next audio-visual stimulus pair as synchronous, even when it's not. This form of active temporal recalibration is one of the tools used by the brain to avoid a distorted or disconnected perception of reality, and help establish causal relations between the images and sounds we perceive, despite different physical velocities and neural processing speeds.

The MEG signals revealed that this brain feat was enabled by a unique interaction between fast and slow brain waves in auditory and visual brain regions. Slower brain rhythms pace the temporal fluctuations of excitability in brain circuits. The higher the excitability, the easier an external input is registered and processed by receiving neural networks.

Based on this, the researchers propose a new model for understanding recalibration, whereby faster oscillations riding on top of slower fluctuations create discrete and ordered time slots to register the order of sensory inputs. For example, when an audio signal reaches the first available time slot in the auditory cortex and so does a visual input, the pair is perceived as simultaneous. For this to happen, the brain needs to position the visual time slots a bit later than the auditory ones to account for the slower physiological transduction of visual signals. The researchers found that this relative delay between neural auditory and visual time slots is a dynamic process that constantly adapts to each participant's recent exposure to audiovisual perception.

Their data confirmed the new dynamic integration model by showing how these subtle tens-of-millisecond delays of fast brain oscillations can be measured in every individual and explain their respective judgments of perceived simultaneity.

In autism and speech disorders, the processing of the senses, especially hearing, is altered. In schizophrenia as well, patients can be affected by perceived distortions of sensory inputs. The neurophysiological mechanisms of temporal recalibration described in this study may be altered in these disorders, and their discovery may reveal new research goals to improve these deficits.

Read more at Science Daily

Vision scientists discover why people literally don't see eye to eye

We humans may not always see eye to eye on politics, religion, sports and other matters of debate. But at least we can agree on the location and size of objects in our physical surroundings. Or can we?

Not according to new research from the University of California, Berkeley, recently published in the Proceedings of the Royal Society B: Biological Sciences journal, that shows that our ability to pinpoint the exact location and size of things varies from one person to the next, and even within our own individual field of vision.

"We assume our perception is a perfect reflection of the physical world around us, but this study shows that each of us has a unique visual fingerprint," said study lead author Zixuan Wang, a UC Berkeley doctoral student in psychology.

The discovery by Wang and fellow researchers in UC Berkeley's Whitney Laboratory for Perception and Action has ramifications for the practices of medicine, technology, driving and sports, among other fields where accurate visual localization is critical.

For example, a driver who makes even a small miscalculation about the location of a pedestrian crossing the street can cause a catastrophe. Meanwhile, in sports, an error of visual judgment can lead to controversy, if not a fiercely disputed championship loss.

Take, for example, the 2004 U.S. Open quarterfinals, in which tennis icon Serena Williams lost to Jennifer Capriati after a series of questionable line calls. An umpire incorrectly overruled a line judge who called a backhand hit by Williams as in, resulting in an apology to Williams by the U.S. Tennis Association.

"Line judges need to rule on whether the ball is outside or inside the parameters. Even an error as small as half a degree of visual angle, equal to a sub-millimeter shift on the judge's retina, may influence the result of the whole match," said Wang, a die-hard tennis fan.

Researchers sought to understand if different people see objects in their surroundings exactly the same way. For example, when glancing at a coffee cup on a table, can two people agree on its exact position and whether its handle is big enough to grip? The result of a series of experiments suggest not, though there's an upside.

"We may reach for a coffee mug thousands of times in our life, and through practice we reach our target," Wang said. "That's the behavioral aspect of how we train ourselves to coordinate how we act in relation to what we see."

In the first task to test visual localization, study participants pinpointed on a computer screen the location of a circular target. In another experiment looking at variations of acuity within each person's field of vision, participants viewed two lines set a minimal distance apart and determined whether one line was located clockwise or counterclockwise to the other line.

And in an experiment measuring perception of size, participants viewed a series of arcs of varying lengths and were asked to estimate their lengths. Surprisingly, people perceived the exact same arcs to be bigger at some locations in the visual field and smaller at other locations.

Overall, the results showed remarkable variations in visual performance among the group and even within each individual's field of vision. The data were mapped to show each study participant's unique visual fingerprint of perceptual distortion.

"Though our study might suggest that the source of our visual deficiencies can originate from our brain, further investigations are needed to uncover the neural basis," said Wang.

"What's also important," she added, "is how we adapt to them and compensate for our errors."

Read more at Science Daily