Whether it’s catching a baseball, learning to drive, or simply picking up an object, most of us are familiar with the concept of hand-eye coordination. But have you ever stopped to think about foot-eye coordination? Using virtual reality (VR) technology, new research is illuminating how the brain’s visual processing falls in step with our movements as we walk.
“This work reveals a previously unknown relationship between perception and movement,” said lead author Dr Matthew Davidson of the University of Sydney in a . “It bridges a gap between experimental psychology and our natural, everyday behaviour.”
Even if you’re not striving towards the oft-touted goal of , the average person still takes many steps per day, accompanied by lots of head-turning and eye movements as we take in the world around us. We experience all of this as a smooth, continuous process – but in order to achieve this effect, the brain is doing a lot of work behind the scenes.
“We are consciously aware of a seamless stream of vision but this is deceptive. I use the analogy of a duck swimming on a pond. Beneath the smooth motion on the surface there is a lot cycling activity beneath,” Dr Davidson said.
These cycles of activity were revealed in from the same lab. Rather than constantly receiving visual information from the eyes and from the ears, a snapshot is taken about eight times per second.
What Davidson and colleagues have now discovered is that this process of sampling the environment slows down when we’re , to match our pace.
“Humans take about two steps per second when walking and generally keep to a consistent rhythm,” explained co-author Professor David Alais. “The reported oscillations in visual sensitivity also occur at about two cycles per second and are locked to the step cycle.”
“In some participants these rhythmic oscillations occur at four cycles per second but these were also locked to the step cycle.”
This finding was only possible thanks to advances in . Forty-five volunteers wearing VR headsets and carrying handheld controllers were asked to take short walks along a 9.5-meter (31-foot) virtual track. During the walks or while standing still, the subjects were asked to respond to a varying number of random visual stimuli.
The researchers were able to monitor their eye and head movements, as well as their walking gait. Between each step, sharpens and reaction times are heightened. At the point when each foot falls back to the floor, visual perception is not so great.
As to why this happens, Professor Alais has some theories. “One possible explanation is that vision becomes secondary to motor control while your foot is grounded and the next step is planned. Once you are in the swing phase between footfalls, the brain switches back to prioritising perceptual sampling of the world, creating an ongoing perceptual rhythm that harmonises with your step rate.”
The team is planning further work to follow up on some of the unanswered questions. It’s hoped that this technology could also be used to help spot signs of some neurological and psychiatric conditions that can manifest as a .
Without our brains’ ability to complete the picture for us, our view of the world around us would be very different. How it manages this has been a mystery for the ages.
“This was once a question for philosophers,” said co-author Professor Frans Verstraten, “but with access to technology neuroscientists have been able to shed light on how the gaps get filled in.”
The study is published in .