Treebeard was Right: Travelers are Less Rational than they’d like to Believe

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By Carla Voorhees

Dr. Tad Brunyé is a cognitive scientist at the U.S. Army Natick Soldier Research, Development and Engineering Center (NSRDEC) in Natick, Massachusetts. He is the recipient of the 2010 Presidential Early Career Award for Scientists and Engineers for his research examining the information Soldiers and civilians use when planning routes and navigating through environments.

Most people assume that if they look at a map they are able to make an easy and deliberate decision regarding which routes to take. Most husbands (including myself) spend a decent amount of their lives attempting to convince their wives of exactly that.

“Trust me, I know the way.”

“Trust me, this is the best way to get there.”

These types of statements are pretty well-founded. People are generally very confident in their route plans (even while shopping), and usually they have selected the route for pretty good reasons. Maybe it looked like the shortest route, most direct route, fastest route, or the route with the fewest number of turns. Or perhaps it looked like the route with the most right-turns, the one avoiding back-roads, or the one likely to have the least amount of traffic. These are all very rational factors to consider. They are based on quantifiable measures such as route length, traffic density and patterns, and number and direction of turns. There is nothing wrong with this strategy.

But what is actually happening under the hood, so to speak? Do these factors alone account for all route plans? What factors might people consider without their knowledge?

In the Lord of the Rings: The Two Towers, the bombastic Treebeard states “I always like going south. Somehow it feels like going downhill.”

Treebeard had an uncanny ability to predict at least one hidden strategy that people use when planning routes through environments: avoiding north-going routes. Studies in our laboratory show that about 70% of the time people prefer a south- rather than north-going route even though the competing routes are exactly the same length. Moreover, people think that heading north takes longer, burns more calories, and moves uphill relative to heading south. Of course, when we ask participants why they make these (somewhat irrational) decisions, they think about it for a while and respond that they have “no idea why” and are dumbfounded to learn about their behaviors.

So, while people generally do pretty well when planning routes, and think they have a pretty good handle on why they chose a particular route, the story is not that simple. Studies in our and others’ laboratories (see here, here, and here) suggest that the way we reason about and move through space is not only driven by explicit and conscious judgments of space such as “that route is longer” or “that route has too many turns.” Rather, people use a wide variety of strategies when making navigation decisions, some of which are completely outside of awareness. For instance, right-handers prefer to turn right, people with higher spatial skills will take more complex paths, and people overall have a bias away from selecting northbound paths.

These types of discoveries are critical to defining and characterizing the range of factors that affect navigation behavior, and hold promise in the development of predictive navigation models. When an enemy flees from a site of an attack towards a known safe-house, which path is he likely to choose? How can urban planners better design environments to accommodate high density traffic between frequented locations? In the event of a disaster, how can we predict the movement patterns of a population?

It is exactly these types of questions that can be answered by better understanding both the strategies we are aware of and the strategies that take place “under the hood” and aren’t consciously accessible to us.

The next time you’re planning a route, pause for a second and think about why you’ve chosen a particular path. You might be surprised to learn that Treebeard was correct: not all of your decisions are guided by rational thought.