Talking while driving is not a recommended habit for safe driving. But researchers at Fujita University of Health Sciences, Japan, have identified the exact mechanism that hinders vehicle driving. Speaking while driving delays eye movements, according to a new study published by Japanese scientists in the journal PLOS One.
“The results indicate that the cognitive demands associated with speech interfere with the neural mechanisms responsible for triggering and controlling eye movements, which represent the critical first step in visual and motor processing during driving,” explains professor and head of the study at the institution, Shintaro Uehara, in a press release.
According to the researchers, this is particularly important because around 90% of the information used while driving is acquired visually. Thus, any delay in the start or end of eye movements can trigger a cascading effect, leading to slower recognition of hazards, lower accuracy of visual scanning, and delayed motor responses.
In the study, they asked 30 healthy adults to perform rapid eye movement tasks from the center to the periphery of vision in three different conditions: speaking, listening, and a third without performing any other parallel activity for comparison. Participants were instructed to look as quickly and accurately as possible at a peripheral visual target.
In the oral simulation, volunteers had to answer general knowledge questions, while in the oral simulation, they listened to excerpts from a Japanese novel. The experiments were conducted on three different days in random order.
After testing, the researchers observed that speaking produced “clear and consistent” delays in three components considered essential: the time needed to initiate the eye movement after the target appeared (reaction time), the time needed to reach the target (movement time), and the time needed to stabilize gaze on the target (adjustment time).
The same thing did not happen in the listening sessions and those without parallel activities. To scientists, this suggests that the act of speaking generates cognitive effort to seek out and produce verbal responses which, in turn, create significant interference in gaze control mechanisms.
“These delays seem small when considered in isolation, but, during driving, they can accumulate and lead to slower detection of hazards and a delay in the initiation of physical responses,” they said in a note.
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