Foot-eye coordination: studying how vision adapts while walking

Neuroscientists from the university have established a link between shifts in visual perception and the cadence of our steps while walking. Understanding how vision shifts as we walk could help develop early diagnostics for neuromuscular or psychiatric illness and understand changes in mobility as we age.

The research, published in Nature Communications, revealed that the brain processes vision in a rhythmic manner, rising and falling in sensitivity in a cycle that corresponds to the rhythm of our steps. When swinging from one step to the next, human perception is good and reactions fast. During footfall, however, our vision is not as sharp and reactions are slowed.

Lead author Dr Matthew Davidson said the research findings revealed the relationship between perception and movement and could bridge the gap between experimental psychology and natural, everyday behaviour. The study also confirms the understanding of the visual brain sensing the environment in a strobe-like way; our perception takes regular samples of the world before stitching them together to create a seamless experience. The study found that shifts in our visual perception have important perceptions for understanding human behaviour.

The research was conducted by Dr Matthew Davidson with colleagues Professor David Alais and Professor Frans Verstraten from the University of Sydney. The study extends earlier research that showed that perception of vision and sound is cyclic, with the brain taking approximately eight samples per second. Alais said the critical new finding in this study is that these oscillations in the brain’s sampling of the world slow down when walking to match the step cycle.

“Humans take about two steps per second when walking and generally keep to a consistent rhythm. 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,” Alais said.

Davidson added that using VR technology enabled the researchers to discover that vision moves through a good and bad phase on every step. It is unclear why the brain’s perceptual processes are so closely linked to walking. The researchers tracked 45 subjects walking back and forth along a 10-metre path in a virtual environment. During each walk — lasting about nine seconds — subjects were required to respond to between zero and eight visual stimuli, with their eye and head movements tracked along with gait and walking information. Of the 45 subjects, insufficient data was collected for seven subjects. In the datasets for 38 subjects, reduced perception at footfall was recorded 83% of the time.

“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,” Alais said.

The researchers now plan to study whether the perception of sound and touch also modulate as we walk. “An obvious question is whether these oscillations in perception are more pronounced in the elderly given difficulties with balance and coordination as we age. It also raises the exciting possibility that we could develop cheap and easy diagnostic tests using VR headsets or use this information to develop tests for early onset of neuro-muscular disorders or some psychiatric illnesses, which can manifest in abnormal gaits,” Davidson said.

Image credit: iStock.com/Zbynek Pospisil