YOU WILL WALK IN CIRCLES

Why Your Body Is Not a Compass

There is an old warning in navigation: take away a person's directional references and eventually he will begin to wander.

He may even walk in circles.

For generations, that idea was repeated more often than it was scientifically demonstrated. Then researchers put it to the test.

They sent people walking for hours through a large forest in Germany and across the Sahara. They also conducted controlled experiments in which people attempted to walk straight while blindfolded.

The results contain an important lesson for anyone who travels without GPS.

Your sense of straight ahead cannot be trusted indefinitely.

And the reason may not be what you think.

THE EXPERIMENT

In a 2009 study published in Current Biology, researchers Jan L. Souman, Ilja Frissen, Manish N. Sreenivasa, and Marc O. Ernst tracked people attempting to maintain a straight course through unfamiliar terrain.

Participants walked for several hours through a large, relatively flat forest. Others walked in the Sahara. Their movements were recorded using GPS.

The forest experiment produced a striking result.

Four participants walked while the Sun was obscured by clouds.

All four walked in circles.

Three repeatedly crossed their own previous tracks without realizing it.

Two other participants walked while the Sun was visible. Their tracks were dramatically different. They maintained an almost straight course, except during an initial period when the Sun was obscured.

That should get the attention of any navigator.

THEN THEY TRIED THE DESERT

The researchers also sent three participants walking through the Sahara.

Two walked during daylight. They deviated from their intended courses, but they did not begin walking in circles.

The third walked at night.

Initially, the full Moon was visible.

Then the Moon disappeared behind clouds.

After losing that celestial reference, the participant made several sharp turns that eventually carried him back toward the direction from which he had come.

The Sun and Moon were not necessarily telling these people exactly where to go.

They were providing something more fundamental.

An external directional reference.

Remove that reference and the human navigation system begins accumulating error.

IT ISN'T BECAUSE ONE LEG IS SHORTER

There is a familiar explanation for why people walk in circles.

One leg is supposedly longer or stronger than the other, causing a person to gradually turn toward one side.

It sounds plausible.

The researchers tested it.

Fifteen participants attempted to walk straight while blindfolded. Their paths were often astonishingly poor. Some walked in circles less than 20 meters in diameter.

But there was no consistent direction to the errors.

The average directional bias across the participants was not significantly different from zero. Only a minority showed a strong tendency to consistently turn in one particular direction.

The researchers also examined differences in leg strength and experimentally altered effective leg length.

Those biomechanical asymmetries did not explain the general circling behavior.

The problem appears to be more interesting than simply having a dominant or shorter leg.

YOUR BRAIN HAS TO ESTIMATE STRAIGHT AHEAD

When you walk, your brain is constantly estimating what “straight ahead” means.

Your vestibular system contributes information about motion and orientation. Proprioception tells your brain what your body and limbs are doing. Vision supplies information about movement relative to the environment.

Over short distances, this system can work remarkably well.

Over longer distances without an external directional reference, small errors accumulate.

The researchers concluded that the subjective sense of straight ahead can drift. Once that internal estimate begins moving away from actual straight ahead, a person can follow it into an increasingly curved path.

Eventually, that path can become a circle.

This is fundamentally a navigation error problem.

A one degree directional error may seem insignificant.

A slight tendency to drift around an obstacle may seem insignificant.

A small error in your subjective sense of straight ahead may seem insignificant.

But navigation errors accumulate with distance.

WALKING FARTHER DOES NOT NECESSARILY MEAN GETTING FARTHER

One of the most interesting results of the experiment is easy to overlook.

During the blindfolded walking trials, the average displacement from the starting point eventually leveled off at roughly 100 meters even though the participants continued walking.

Think about what that means.

They were still moving.

They were still expending energy.

They were still covering distance.

But additional walking was no longer producing equivalent useful displacement away from where they started.

That distinction matters in navigation.

DISTANCE TRAVELED is not the same thing as DISPLACEMENT.

And neither necessarily means PROGRESS TOWARD THE DESTINATION.

A lost person can walk for hours and work very hard while accomplishing remarkably little.

Walking farther does not necessarily mean getting farther.

THE SUN CHANGED EVERYTHING

One of the most interesting findings was how dramatically people performed when reliable external directional information was available.

When the Sun was visible, the forest participants maintained relatively straight courses even while negotiating vegetation and obstacles.

There is another important detail.

The Sun's azimuth changed substantially during the several hours they were walking.

If the participants had simply kept the Sun at exactly the same position relative to their bodies, their paths should have curved as the Sun moved.

They did not.

The researchers concluded that participants apparently compensated, at least partially, for the changing solar azimuth.

Exactly how they did that was not established.

The authors discussed several possibilities, including other visual information, landmarks, an internal sense of time, optic flow, and shadows. They specifically noted that participants may sometimes have used shadows rather than looking directly at the Sun.

That leads to an important navigation principle.

A celestial object does not have to point toward your destination to be useful.

The Sun, Moon, or stars can provide an external directional reference against which movement can be checked.

NAVIGATIONAL RECALIBRATION

Another useful finding was buried in the blindfolded experiments.

Participants did not remain blindfolded continuously. Between some trials they briefly regained visual information.

Their directional performance effectively reset toward straight again.

The researchers described external directional information as recalibrating the internal estimate of walking direction.

That is an excellent way to think about navigation in the field.

NAVIGATIONAL RECALIBRATION.

Every time you check your compass, you recalibrate.

Every time you establish another distant reference point, you recalibrate.

Every time you compare your map with a ridgeline, drainage, road, or terrain feature, you recalibrate.

The Sun can provide a reference.

A shadow can provide a reference.

The Moon can provide a reference.

Polaris can provide a reference.

Recognizable stars and constellations can provide references.

You are not simply checking where you are going.

You are preventing accumulated error from becoming your new definition of straight ahead.

THIS IS WHY INTERMEDIATE REFERENCE POINTS MATTER

Suppose your destination lies two kilometers away on an azimuth of 047 degrees.

You establish 047 degrees, put the compass away, and start walking.

That is poor technique.

Instead, use the azimuth to select a recognizable object along your line of travel.

Walk to it.

Then establish another reference.

Repeat.

The distant tree, rock, saddle, building, star, terrain feature, or other identifiable point becomes an external directional reference.

Each reference limits how long your internal estimate of direction is allowed to drift without correction.

THE TERRAIN IS ALSO WORKING ON YOU

The researchers discussed another possible contributor to curved travel: obstacles.

In actual terrain you rarely walk an uninterrupted straight line.

You go around vegetation.

You bypass rock outcrops.

You cross drainages.

You move around deadfall.

You contour across slopes.

You choose the easier side of obstacles.

If those deviations are not deliberately corrected, they accumulate.

A navigator who repeatedly favors one side of obstacles may introduce a systematic component into his route error.

Meanwhile, uncertainty in his subjective sense of straight ahead continues to accumulate.

These are different kinds of error, but both can move the navigator away from the intended route.

NOT ALL ERRORS BEHAVE THE SAME WAY

This distinction is important.

A compass with a consistent calibration error produces something resembling a systematic error.

A navigator who consistently bypasses obstacles on one side may create another systematic tendency.

But the researchers found little evidence for one universal left or right bias that explains human circling.

Instead, their results support a model in which variable errors accumulate in the subjective estimate of straight ahead.

Different errors require different countermeasures.

Known systematic errors can sometimes be corrected.

Variable errors must be repeatedly bounded by new observations.

This is one reason independent navigation information is so valuable.

Disagreement is information.

If your compass, terrain, celestial reference, and expected route geometry disagree, do not simply average the answers until they agree.

Find out why.

DARKNESS MAKES THE PROBLEM HARDER

At night, many of the visual references available during daylight disappear.

Terrain becomes indistinct.

Distant landmarks vanish.

Minor changes in slope become harder to recognize.

The horizon may disappear completely.

Your usable world contracts.

That makes celestial references particularly valuable.

Polaris can provide a northern reference.

The Moon can provide useful directional information when properly interpreted.

Recognizable constellations such as Orion can provide additional directional information when their geometry and movement are understood.

The important lesson is not to memorize dozens of tricks.

It is to understand why external references matter.

Your internal estimate of direction needs something outside itself against which it can be checked.

DON'T WAIT UNTIL YOU ARE LOST

A person does not necessarily become lost because of one enormous navigational mistake.

Failure can occur gradually.

A few degrees here.

A small obstacle deviation there.

A mistaken assumption about the terrain.

Another hundred meters without checking direction.

Then another.

Eventually, the navigator's internal picture of where he is and where he is going no longer corresponds to reality.

That is when seemingly reasonable decisions begin producing increasingly unreasonable results.

The solution is to interrupt the process early.

Navigation is a continuous process of measurement and correction.

Establish direction.

Move.

Observe.

Verify.

Correct.

Repeat.

A SIMPLE FIELD EXPERIMENT

You do not need to blindfold yourself or wander into the desert to demonstrate the principle.

Choose a safe, open area where your route can be observed and where there are no hazards.

Establish a distant reference point and walk toward it normally.

Then repeat the exercise using progressively shorter visual reference points.

Notice how much easier it becomes to introduce small directional changes when the useful reference becomes poor or disappears.

Another useful exercise is to walk an azimuth through broken terrain while recording every time you must deviate around an obstacle.

Afterward, reconstruct the route.

Look for patterns.

Do you tend to bypass obstacles on one side?

How accurately do you return to your original line?

How frequently do you check direction?

How far do you travel between independent references?

You may discover that your personal navigation errors have recognizable patterns.

That information is useful.

The advanced navigator is not someone who never makes errors.

The advanced navigator understands where those errors come from and builds methods that prevent them from accumulating.

YOUR BODY IS NOT A COMPASS

The experiments demonstrated that without reliable external directional references, humans have difficulty maintaining a fixed course over extended movement.

That does not make human navigation unreliable.

It tells us how human navigation needs to work.

A compass is an external reference.

A landmark is an external reference.

The relationship between map and terrain provides external information.

The Sun is an external reference.

The Moon and stars can provide external references.

Each gives the navigator another opportunity to compare what he thinks is happening with something independent of himself.

Never navigate entirely inside your own head.

Keep looking outside.

Keep measuring.

Keep recalibrating.

Read the sky. Rule the ground.

Source

Souman, J.L., Frissen, I., Sreenivasa, M.N., and Ernst, M.O. (2009). “Walking Straight into Circles.” Current Biology, Volume 19, pages 1538 to 1542. DOI: 10.1016/j.cub.2009.07.053

EMNAV develops analog navigation tools for situations where electronic navigation is unavailable, unreliable, or undesirable. Learn more about EMNAV field tools.