Life with a digital speedometer

In my cognitive psychology class and on this blog, I have criticized the digital speedometer as not being as instantly useful as an analog speedometer, where you can quickly judge the angle of the needle and get a sense of how fast you are driving. However, buying a car is surprisingly emotional, and cognitive design principles can get thrown out of the window. In short: I bought a 2008 Honda Civic, and I’ve been driving it for about a week. How’s the digital speedometer?

It’s… usable. I don’t think it’s better than an analog speedometer. I can glance down and read the number, and interpreting my speed does not really take that much longer than an analog display. So I can get along just fine with it.

I do, however, take issue with why Honda made the change (source: Honda Press Release for the 2006 Civics, PDF version):

And they state the reason clearly again in the same press release:

The two-tier instrument panel positions priority gauges like the speedometer up high in the driver’s field of vision.

So Honda wanted to put the speedometer - critical information, to be sure - closer to the driver’s field of view. It’s a valid design choice, but why not move the analog speedometer upwards? My guess is that a traditional circular analog display would have been too large and would have interfered with driving. Therefore, as a compromise, Honda made the speedometer digital to save space. It doesn’t take up as much space as an analog version, and it has the benefit of looking pretty cool.

The problem with this is twofold. The first problem is that our peripheral vision is really poor. Our sharpest vision is only 1 degree of visual angle (the width of your thumb an arm’s length away is 1-2 degrees). Everything outside of that area is not very sharp. We can get some information out of it - maybe the angle of a line (analog speedometer) - but reading (digital speedometer) gets fuzzy. So Honda put the display closer to the driver’s field of vision, but made it more difficult to read by going digital. To make matters worse, there’s a concept called the Useful Field of View (Ball et al., 1988). Essentially, the more focused we have to be at a central task, the less we can pay attention to peripheral objects and events. Driving is an attention-heavy task, so we have even less attention to take in information in the periphery.

The end result? I still have to move my eyes away from the road and down in order to read my speed. Moving critical information closer to the driver’s visual field is good idea, but the implementation failed because of lack of knowledge about vision and cognition. By not understanding peripheral vision or the effects of attention to a central task, the repositioned digital speedometer fails at its goal of being better. It’s not a bad design, per se, but it does not improve the driving experience.

How I stopped worrying and learned to love my GPS

So I’m spatially challenged. I can follow maps, but I have no ability to create my own mental map of an area. However, my inability to form anything above route-based knowledge is for another post. What is worth mentioning is that I finally offloaded the cognitive challenge of navigating to a new GPS device, the TomTom Go 720. Most everyone knows how GPS devices work. You enter in an address or Point of Interest, and it calculates the best way to get you there, giving you turn-by-turn real time instructions. It’s really great.

There was a rocky start, though, and there was a learning period where I had to learn to trust the device. The voice commands are fairly demanding: “Turn right at So-And-So Drive.” The map shows you exactly where to turn, and it gives so much useful information. But there’s a strange loss of control that comes with trusting the device, even though you are, of course, fully in control of the car. The task of deciding where to turn next had been replaced by the task of deciding whether or not to trust the system. Whether the device really knew where it was taking me, or whether I should trust what I know and take a potentially longer route.

Learning to trust the system is directly tied to the body of literature that researchers automation. You should be reliant on it; it’s there to help, and you did buy it. GPS systems are assistive devices in their current state: they give you advice, and you can choose whether or not to follow it. It makes the task of navigation easier, but it adds a whole new layer of decision making: do you follow the advice to turn there, or do you follow your gut? And if you are worried about the trustworthiness of the system, is it really helping? Are things better because you’ve offloaded a difficult task to a computer?

After a while, I got used to it - most people do. The answer, at least with me, was training. After a few instances of navigating to a new location or avoiding a roadblock or getting around traffic, I trusted the GPS to save my butt and get me to where I was going. I was trained to trust the system, and my interactions with the system trained it to be more useful to me. I changed the settings of the device to adapt to my learning style and it learned some of my Favorite Locations and a little more about my driving preferences. I learned to feel more comfortable with it. This piece of automation goes with me almost all the time, and after a rocky start, I learned to rely on it.

Of course, over-reliance can be a bad thing: http://www.timesonline.co.uk/tol/news/article707216.ece

2008 Honda Civic Dashboard

So, I am still recovering from the 2007 Human Factors & Ergonomics Society conference in Baltimore, MD. It was a long week, but it was a great learning experience. Today I wanted to focus on the 2008 Honda Civic Dashboard with the digital speedometer. I use this example when I teach Cognitive Psychology and talk about Human Factors:

Why is this a bad idea compared to using an analog speedometer with a needle? Well, let’s do a simple analysis:

• What are digital readouts good for? Precise information - exact numbers.
• What are analog readouts good for (like the tachometer)? Approximate information.

When you’re driving, how often do you need to know the exact speed you’re going? Rarely! It’s way more important to know whether your speed is \ versus | versus /. Even better, a quick glance downwards of an analog speedometer gets you a near-instant perception of the approximate angle of the needle and, therefore, a near-instant perception of speed.

A digital readout requires much more interpretation because the physical characteristics of the numbers 48 and 58 do not intrinsically mean as much to perception as \ versus | versus /. You have to think more about whether 48 or 58 is too fast? Of course, it’s not like that process takes more than 500 ms - 1 second. But when you’re going 58 mph, every second matters.

The moral of the story? With driving, rapid perception of information is good. And when that information gives you a rapid interpretation of information, that’s even better.