PARIS SCIENCES & LETTRES (PSL)
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The myth of multitasking, and other inattention stories

A very slow-moving driver normally has a 180 degree field of vision. At 90 kilometres per hour, the field of vision is halved, because the human brain can only deal with a limited amount of information at once. What if we add a phone conversation?

11
December 2017
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lire en français
Executive Summary

Recent discoveries on inattentive driving tell us a lot about the very specific workings of the brain. Sensory information – seeing, hearing, tasting or thinking – can only be used if it is first stored for a few seconds in the short-term memory. This storage operation consists of four cerebral stages, allowing information to be processed and prioritized: encoding, storage, retrieval and execution. The “cognitive load”, i.e. the quantity of conscious attention mobilized for one or more tasks, is a double-edged sword. When it is too high, it can trigger “inattentional blindness,” but this can also happen if the cognitive load is too low: a person doing a routine task tends to go into autopilot, and stop seeing the key markers in their environment. Advocates of simply banning telephones while driving have another target, which they call the myth of multitasking.

One day in January 2004, at around 4 pm, in Grand Rapids (Michigan), a 20-year-old woman went through a red light, while talking on her mobile phone.

She hit a car, which wasn’t the first through the crossroads, but the third or fourth. So when she jumped that red light, she really jumped it!

The police investigation concluded that the driver had never even touched the brake, and that she was driving at 48 miles per hour. The accident cost a 12-year-old boy his life. Several witnesses categorically said that the young woman wasn’t looking down, and that she wasn’t dialing a number nor writing a text message. They saw her looking straight ahead through the windscreen, just talking on her mobile phone (to her church, as she later explained in her trial), when she drove past four cars and a school bus waiting at the lights in the lane next to hers.

According to researchers, this was a classic case of “inattentional blindness”: a consequence of the cognitive distraction caused by a telephone conversation. Drivers may well be looking through the windscreen, but their brain doesn’t process all the environmental information about the road environment: information which might help them monitor their surroundings effectively, identify potential risks and anticipate unexpected hazards. Drivers who talk while behind the wheel look at objects, but they don’t see them. The American National Safety Council considers that drivers using telephones “miss” 50% of the visual information they could access if they were totally focused on the road ahead. This is similar to the phenomenon of “tunnel vision,” often triggered by panic and characterized by a loss of peripheral vision, with only central vision being retained, giving a narrow and circular view of the landscape.

The faster the vehicle is going, the more information the brain receives, forcing it to eliminate certain peripheral data. 

The telephone conversation adds to a cognitive load already intensified by speed (especially if the conversation is complex or highly emotional). A stationary or very slow-moving driver normally has a 180 degree field of vision. At 90 kilometres per hour, the field of vision is halved, because the human brain can only deal with a limited amount of information at once. The faster the vehicle is going, the more information the brain receives, forcing it to eliminate certain peripheral data. This means that a driver going fast might not see the child about to cross the road, or the car coming out at a junction.

In 1989, in a final thesis at France’s Higher National School of Landscape, entitled “The Landes road, or the search for an aesthetics of safety” (La route landaise ou la recherche d’une esthétique de la sécurité), a student by the name of Bertrand Richard explained that: “at high speed, the detailed field of vision covers an angle of around 4 degrees. The gaze leaves this focal point for just 5 to 10% of the overall observation time. This can be even less on long, straight sections, where its rapid sweeps of the road’s surroundings last a few tenths of a second.”

Moreover, all humans have what we call a “blind spot” in their vision: this is the only point on the retina that does not see, because it has no photoreceptors. It is located where the optic nerve joins the eye.

Professor Claude Darras, of the ParisTech Higher Optical Institute, emphasizes the connection in the brain between three crucial phenomena involved in the act of seeing: light, sight, and vision. Light is a carrier of information that allows us to “know” and “act.” Sight is the sum of all the light information reaching the brain. Finally, vision is the capacity of the visual strategies, and the interpretation and use of the information decoded by the brain. Vision works in conjunction with all the other senses, but in humans, it is dominant, particularly at night in the form of scotopic vision (in low light conditions) or mesopic vision (at dawn and dusk). Well-designed public lighting can have a positive impact on drivers’ brains.

Processing information

All of these discoveries on inattentive driving are connected to the very specific workings of the brain. Sensory information – seeing, hearing, tasting or thinking – can only be used if it is first stored for a few seconds in the short-term memory. This storage operation consists of four cerebral stages, allowing information to be processed and prioritized: encoding, storage, retrieval and execution.

Encoding is the fundamental operation by which the brain decides where to focus its attention. It goes without saying that distractions compromise encoding. Human brains have a very limited attention capacity, and very little of the information present in front of us is fully analyzed. To deal with distraction, which is an information overload, the brain will automatically select what to expel from the field of vision. These choices are partly conscious and controllable, but partly unconscious and uncontrollable. The brain of a driver who is talking at the wheel can subconsciously suppress a detail about the road, especially if this detail is unexpected, such as a dog crossing.

The “cognitive load” (the quantity of conscious attention mobilized for one or more tasks) is a double-edged sword. When it is too high, we have seen that it can trigger “inattentional blindness,” but this can also happen if the cognitive load is too low: a person doing a routine task tends to go into autopilot, and stop seeing the key markers in their environment. The brain is a powerful but malicious tool. The expectation that certain events will happen tends to inhibit the perception of other possibilities. Who can honestly say they’ve never spent ages looking for a familiar item, when it was perfectly visible, just next to its usual place?

As well as inattentional blindness, advocates of simply banning telephones while driving have another target, which they call the “multitasking myth.” Driving a vehicle and talking are both intellectual tasks. These advocates argue against the highly fashionable idea that some people can do several tasks requiring concentration at the same time. The brain can juggle between different activities very quickly, but this sequencing only looks like simultaneity. In reality, the brain executes just one action at a time. When it skips from task to task, its attention is also skipping back and forth. This is costly in terms of cerebral concentration, which the neurosciences can now see and measure. Our attention is a precious and rare thing. Let’s treat it like one.

This article is an excerpt from Stéphane Marchand's last book, Les Secrets de votre cerveau (Fayard, 2017)

Stéphane Marchand
Chief Editor, Paris Innovation Review