Children who have been operated on after many years of suffering from blindness must first learn how to use their “new” sense of sight. A German-Israeli research team investigated how the brain integrates the new visual signals with the information from the other senses. The group of scientists observed Ethiopian children and adolescents whose cataracts were successfully operated on in the Hawassa Referral Hospital during the first few weeks and months following their operations. Ulm University, the Hebrew University of Jerusalem and the Padeh Medical Center in Tiberias (Israel) were involved in the study, which was published in the journal “Current Biology”.
In developing countries, cataracts are one of the main causes of blindness. This eye disease is partially congenital, but it is also caused by malnutrition and poor living conditions in childhood. The disease can be treated with surgery, in which the pathologically clouded lens is replaced with an artificial lens. Most families, however, cannot afford such eye operations. In Ethiopia, Israeli doctors from the Padeh Medical Center in Tiberias have been working since 2014 on helping young people with cataracts to (re)gain their vision after many years of blindness. Since 2016, a German-Israeli joint project has been investigating how children, adolescents and young adults who have been successfully treated in the Hawassa Referral Hospital are coping with their newly restored sensory organs. Researchers from the supporting scientific project at the Hebrew University of Jerusalem and Ulm University are investigating how the children with recent operations learn to see again over the course of time. “We want to find out when and how the brain succeeds in meaningfully linking the visual impressions with the information from the other senses,” explains Professor Marc Ernst, head of the Department of Applied Cognitive Psychology at Ulm University, who played a leading role in the study. Researchers from the fields of neurobiology, cognitive psychology, ophthalmology and medical imaging analysed in particular how the brain aligns the senses of sight and touch.
A lot happens in the brain before visual sensory stimuli become coherent images
What is it like for someone who has been blind from childhood when they are suddenly able to see? The surgical restoration of vision happens rather quickly, but a lot has to happen in the brain before visual sensory stimuli become coherent images of the world. The aim of this study, which was conducted in Ethiopia, was to clarify what exactly happens in the brain of these patients.
Dr Irene Senna, a scientist in Professor Ernst’s department, has been on site in Hawassa a total of seven times since 2016, for two to three weeks at a time, and has been personally involved in conducting investigations. The Italian cognitive psychologist was surprised at first by the reaction of the recently operated children and young adults. Senna had primarily expected great joy and tremendous excitement. As it turned out, reality looked completely different. The most common reaction among the subjects to the surgical restoration of their sight was a feeling of being overwhelmed. “The bright light of the sun is like a shock for many of them. The newly operated patients first need to learn how to correctly interpret the visual input and put the new signals into the right relationship with the world as they know it,” relates Senna. Along with Elena Andres from the Hebrew University, she is one of the first authors of the study.
Over time, the sense of sight becomes more and more relevant
How long does the brain take to learn to process visual information in a way that is compatible with the world? Is the brain of an older child or a young adult even still capable of doing so? In order to answer these questions, the German-Israeli research team studied 30 children, adolescents and young adults between the ages of 8 and 19 at the Hawassa Referral Hospital and in schools for the blind in Shashamane and Sebeta. At different points in time following the operation, they recorded whether and to what extent the subjects relied on their newly acquired sense of sight. The subjects were asked to estimate the size of objects that they could simultaneously touch with their hands. They were also shown realistically sized images as well as enlarged or shrunken images of objects in order to create visual distortion.
The result was that within a few weeks or months following the operation, the combination of visual and tactile information yielded multisensory balancing behaviour that was comparable to that of a control subject with normal vision. Over the course of time, the sense of sight becomes more and more relevant, especially when it is trained accordingly in relation to the world – ie in combination with other sensory experiences. “The level of success of multisensory integration does not depend only on age, but also on intensive experiences with the world in which all of the other senses are also used,” says Professor Ehud Zohary from the Hebrew University of Jerusalem, who coordinated the study with Prof Ernst.
Study results demonstrate the importance of rehabilitation and training
The results of the study, which were published in the journal Current Biology, are thus not only concrete evidence of the plasticity of the brain. They also lead us to the conclusion that appropriate training and rehabilitation measures are very important for improving therapeutic success rates. A follow-up study is already addressing which types of exercises this could include and what such rehabilitation for people with surgically-restored vision could look like. This project was funded by the German Research Foundation (DFG) as a German-Israeli project cooperation (DIP), which was applied for jointly by Ehud Zohary and Marc Ernst. The participating institutions include Ulm University, the Hebrew University of Jerusalem and the Padeh Medical Center in Tiberias (Israel), which performed the eye surgeries..
Development of multisensory integration following prolonged early-onset visual deprivation; Irene Senna, Elena Andres, Ayelet McKyton, Itay Ben-Zion, Ehud Zohary and Marc O. Ernst, in: Current Biology, Available online 16 September 2021,
Text and mediacontact: Andrea Weber-Tuckermann