Japanese Scientists Prohibit Talking to Drivers 0 13

Conversations while driving have long been considered a serious source of distraction; however, the exact mechanisms through which they interfere in the earliest stages of visual processing remain poorly understood. It has previously been shown that mental load can slow down braking and reduce situational awareness, but the question of whether conversation affects the basic processes of eye movement that precede any physical reaction has remained open.

Now, researchers from Fujita Health University have shown that conversation creates sufficient cognitive load to slow down key eye reactions that depend on immediate visual assessment of the road situation. The work, published in the journal PLOS ONE, traced how conversation alters the temporal characteristics of gaze movements. This is particularly important as about 90% of the information necessary for driving comes through vision. Any delays in initiating or completing eye movements can lead to later recognition of hazards, less accurate road views, and delayed motor responses.

To study this issue, the researchers recruited 30 healthy volunteers who performed saccadic eye movement tasks from the center to the side in three modes: talking, simply listening, and without an additional task. Participants were required to shift their gaze to a peripheral target appearing in one of eight directions as quickly and accurately as possible. In the talking mode, they answered general and biographical questions adapted from the Wechsler Intelligence Scale, as well as specially prepared tasks. In the listening mode, participants listened to excerpts from the Japanese novel "I Am a Cat." The order of conditions was randomized across three separate sessions.

Almost all participants experienced stable delays in three key parameters during conversation: reaction time (the onset of eye movement), gaze movement time to the target, and stabilization time on the target. No such effects were observed in the listening or control modes, indicating that it is the necessity to speak and formulate responses that significantly interferes with gaze control systems. Although these delays may seem minimal, they can accumulate while driving, slowing hazard detection and delaying the initiation of protective actions. Even hands-free conversation can create a mental load that disrupts the neural processes that initiate and direct eye movements. Since drivers often need to shift their gaze to pedestrians, objects, and road obstacles, such delays highlight the risks of conversations in high-visual-load situations.

At the same time, the researchers emphasize that conversation is not the only or main factor in reduced reaction. Many cognitive and perceptual processes affect driving quality, including distraction and competition between simultaneous tasks. Nevertheless, the work shows that conversation interferes at an early, pre-cognitive stage of visual processing – even before recognition and decision-making – and thus can subtly impair driving in ways that drivers themselves do not realize.