Car crashes on bends in fog - solved

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Why we are more likely to crash on a bend in fog or night have been discovered by scientists.

We do not watch the edges of the road as we drive, rather our brain processes the ground speed as the tarmac whizzes towards us.

This also explains how when bombing down a narrow hedge lined country lane in a low slung sports car we think we are going faster than we really are.

This sense of speed helps us stay on the road but fog or darkness interferes with how our brains processes what we see when behind the wheel.

The University of Leeds study could also explain how animals routinely move through the world by following demarcated paths, trails or runways.

When travelling across a ground surface we experiences the apparent perceptual motion of texture elements - often referred to as optic flow.

A wide variety of species are sensitive to optic flow during locomotion, including bees, flies, birds, desert ants and humans.

Associate Professor Dr Richard Wilkie who researches perception, action and cognition said: “Different species are sensitive to optic flow and one control solution is to maintain the balance of flow symmetry across visual fields.

“However, it is unclear whether animals are sensitive to changes in asymmetries when steering along curved paths.

“Flow asymmetries can alter the global properties of flow, in that flow speed, which may also influence steering control.”

The study by Leeds’ School of Psychology and the Institute for Transport Studies used a driving simulator to test whether human steering was influenced by visual speed signals.

The textured ground either side of the road - on the inside and outside of bends - was manipulated to move artificially faster or slower than the driving speed.

It found a driver’s steering responded to the average ground speed, irrespective of which side moved faster or slower.

This suggested human brain uses the ground movement signal from across the whole of the scene to guide steering, and not just the road edges.

Associate Professor Dr Wilkie added: “This research gives us not just an understanding of the way humans drive, but may also give an insight to how insects, for example, choose their flight paths.

“It is not just a case of looking at the road edges and steering accordingly.

“The brain processes information from the whole visual scene moving past the eyes, known as optic flow, in helping select a path.

“Results showed that rather than being influenced by changes in flow asymmetry,

steering responded to global flow speed.

“We conclude that the human brain performs global averaging of flow speed from across the scene and uses this signal as an input for steering control.”

The findings are surprising because road edges alone provide enough information for successful steering, but the brain also uses flow speed information to guide steering.

However he noted: “While asymmetric flow-speed conditions of the type simulated in this study are unlikely to occur naturally, the speed information from the global flow field can vary considerably across different real-world environments.

“Conditions where the quality of flow is degraded, for example the presence of fog or driving at night, can reduce the perceived locomotor speed, whereas increases in flow quality/quantity for example driving with a seated position close to the ground along narrow country lanes would increase perceived speed.

“Our findings indicate that such conditions could cause systematic steering errors even when there are clear visual markings for the position in lane and future steering requirements.”

The study was published in the journal Royal Society Open Science.

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