Researchers Discover New Type of Eye Movement
A team of scientists at the University of Tübingen in Germany has discovered a new type of eye movement that is synchronized with blinking.
Researchers : The newly-discovered movement, named blink-associated resetting movement (BARM), helps to reset the eye after it twists when viewing a rotating object. It is like avoiding tiny rotations of a camera to stabilize the image we perceive.
We don’t notice the eye resetting in this way because it happens automatically when we blink.
“We were really surprised to discover this new type of eye movement and it was not what we had anticipated from the experiment,” said Mohammad Khazali, a researcher in the Department of Cognitive Neurology at theUniversity of Tübingen and lead author of a paper about the results available online in the journal eLife.
“We had expected to find that another, already well-known type of eye movement is synchronized to blinking.”
Although it is brief, blinking creates an interruption in our visual perception. We spend up to a tenth of our waking hours blinking but hardly notice it.
It serves an essential role in lubricating the eye and may even provide the brain with small, frequent mental breaks.
Khazali and his colleagues sought to investigate whether a reflexive, involuntary eye movement called torsional optokinetic nystagmus (tOKN) occurs at the same time as blinking.
The theory was that this reflex also creates a break in the visual system so synchronizing them minimizes downtime.
The researchers assessed the eye movements of 11 subjects using tiny wires attached to the cornea and with infrared video tracking.
The participants’ eye movements were tracked as they viewed a rotating pattern of dots. As their eyes twisted to follow the dots, they frequently reset, via tOKN, to avoid moving beyond the mechanical limits of the eye muscles.
However, this resetting was imperfect and the eyes gradually twisted until the muscles couldn’t twist any more. This varied between subjects from three to eight degrees of rotation.
Once they reached their maximum, the eyes reset so they were no longer twisted at all. This happened at the same time as blinking.
“The eye’s sharpest vision is enabled by a spot on the light-sensitive sheet of the retina called the fovea and this needs to stay balanced to ensure objects of interest can be scrutinized in an optimum way,” Khazali said.
The frequency and size of the movement is determined by how far the eyes have deviated from a neutral position. It helps to reduce strain in the eyes as they move to assess the world around us.
In further experiments, the team discovered that it even occurs when the eye is not tracking a rotating object.
“To discover such a ubiquitous phenomenon in such a well-studied part of the human body was astonishing to us and we’re very grateful to the volunteers who took part in the study,” Khazali said.
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