When Luke is driving Kee and Theo to a boat on the coast, the car’s heads-up-display shows him the car’s speed with a translucent red number and speed gauge. There are also two broken, blurry gauges showing unknown information.

Suddenly the road becomes blocked by a flaming car rolled onto the road by a then unknown gang. In response, an IMPACT warning triangle zooms in several times to warn the driver of the danger, accompanied by a persistent dinging sound.

It commands attention effectively

Props to this attention-commanding signal. Neuroscience tells us that symmetrical expansion like this triggers something called a startle response.  (I first learned this in the awesome and highly recommended book Mind Hacks.) Any time we see symmetrical expansion in our field of vision, within milliseconds our sympathetic nervous system takes over, fixes our attention to that spot, and prompts us to avoid the thing that our brains believe is coming right at us. It all happens way before conscious processing, and that’s a good thing. It’s evolutionarily designed to keep us safe from falling rocks, flying fists, and pouncing tigers, and scenarios like that don’t have time for the relatively slow conscious processes.

Well visualized

The startle response varies in strength depending on several things.

• The anxiety of the person (an anxious person will react to a slighter signal)
• The driver’s habituation to the signal
• The strength of the signal, in this case…
  • Contrast of the shape against its background
  • The speed of the expansion
• The presence of a prepulse stimulus

We want the signal to be strong enough to grab the attention of a possibly-distracted driver, but not strong enough to cause them to overreact and risk control of car. While anything this critical to safety needs to be thoroughly tested, the size of the IMPACT triangle seems to sit in the golden mean between these two.

And while the effect is strongest in the lab with a dark shape expanding over a light background, I suspect given habituation to the moving background of the roadscape and a comparatively static HUD, the sympathetic nervous system would have no problem processing this light-on-dark shape.

Well placed

We only see it in action once, so we don’t know if the placement is dynamic. But it appears to be positioned on the HUD such that it draws Luke’s attention directly to the point in his field of vision where the flaming car is. (It looks offset to us because the camera is positioned in the middle of the back seat rather than the driver’s seat.) This dynamic positioning is great since it saves the driver critical bits of time. If the signal was fixed, then the driver would have his attention pulled between the IMPACT triangle and the actual thing. Much better to have the display say, “LOOK HERE!”

Readers of the book will recall this nuance from the lesson from Chapter 8, Augment the Periphery of Vision: “Objects should be placed at the edge of the user’s view when they are not needed, and adjacent to the locus of attention when they are.”

Improvements

There are a few improvements that could be made.

• It could synchronize the audio to the visual. The dinging is dissociated from the motion of the triangle, and even sounds a bit like a seat belt warning rather than something trying to warn you of a possible, life-threatening collision. Having the sound and visual in sync would strengthen the signal. It could even increase volume with the probability and severity of impact.
• It could increase the strength of the audio signal by suppressing competing audio, by pausing any audio entertainment and even canceling ambient sounds.
• It could predict farther into the future. The triangle only appears once the flaming car actually stops in the road a few meters ahead. But there is clearly a burning car rolling down to the road for seconds before that. We see it. The passengers see it. Better sensors and prediction models would have drawn Luke’s attention to the problem earlier and helped him react sooner.
• It could also know when the driver is actually focused on the problem and than fade the signal to the periphery so that it does not cover up any vital visual information. It can then fade completely when the risk has passed.
• An even smarter system might be able to adjust the strength of the signal based on real-time variables, like the anxiety of the driver, his or her current level of distraction, ambient noise and light, and of course the degree of risk (a tumbleweed vs. a small child on the road).
• It could of course go full agentive and apply the brakes or swerve if the driver fails to take appropriate action in time.

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Despite these improvements, I believe Luke’s HUD to be well designed that gets underplayed in the drama and disorientation of the scene.