Adults born deaf react more quickly to objects at the edge of their visual field than hearing people, according to groundbreaking new research by the University of Sheffield.
The study, which was funded by the Royal National Institute for Deaf People (RNID), has, for the first time ever, seen scientists test how peripheral vision develops in deaf people from childhood to adulthood.
Dr Charlotte Codina, from the University's Academic Unit of Ophthalmology and Orthoptics, led the research and found that children born deaf are slower to react to objects in their peripheral vision compared to hearing children. However, deaf adolescents and adults who have been without hearing since birth can react to objects in their peripheral vision more quickly.
The findings of Dr Codina's study, which were published in Development Science, showed that deaf children aged between five to 10 years old had a slower reaction time to light stimuli in their peripheral vision than hearing children of the same age. By the age of 11 and 12 however, hearing and deaf children react equally quickly and deaf adolescents between 13 and 15 reacted more quickly than their hearing peers.
The study tested profoundly deaf children (aged five to 15 years) using a self-designed visual field test, and compared this to age-matched hearing controls as well as to deaf and hearing adult data.
The children tested sat with their head positioned in the centre of a grey acrylic hemisphere into which 96 LEDs were implanted. The participants then had to watch a central glowing ring in which a camera was hidden to monitor their eye movements.
The LEDs were then each briefly illuminated at three different light intensities all in random order. The test was designed to be like a computer game and called the Star Catcher. If the LED flash occurred above, the child had to 'catch the star' by moving the joystick upwards, and if it occurred to the left they would have to move the joystick to that position. In this way, the team were able to verify that the child had seen the light and not just guessed, as has been the problem with previous visual field tests in children.
Dr Charlotte Codina, who undertook the study as part of her RNID-funded PhD said: "We found that deaf children see less peripherally than hearing children, but, typically, go on to develop better than normal peripheral vision by adulthood. Important vision changes are occurring as deaf children grow-up and one current theory is that they have not yet learnt to focus their attention on stimuli in the periphery until their vision matures at the age of 11 or 12.
"As research in this area continues, it will be interesting to identify factors which can help deaf children to make this visual improvement earlier."
RNID's Research Programme Manager, Dr Joanna Robinson, said: "This research shows that adults who have been deaf since birth may have advantages over hearing people in terms of their range of vision. For example, deaf people could be more proficient in jobs which depend on the ability to see a wide area of activities and respond quickly to situations, such as sports referees, teachers or CCTV operators.
"On the other hand, the findings suggest that parents of deaf children need to be aware that their child's initially delayed reaction to peripheral movements may mean they are slower to spot and avoid potential dangers such as approaching traffic."
- Charlotte Codina, David Buckley, Michael Port, Olivier Pascalis. Deaf and hearing children: a comparison of peripheral vision development. Developmental Science, 2010; DOI: 10.1111/j.1467-7687.2010.01017.x
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