A weight lifted?

Imagine the biggest hill in your home town. Now try to guess how steep it is, where 0° would be completely flat and 90° would be vertical. (In Champaign, that’s easy — we have no hills.) Go ahead. Make an estimate before reading further.

What did you guess? 60°? 45°? 30°? The odds are good that you massively overestimated the steepness of the hill (Proffitt et al, 1995). People judge 5° slopes to be more than 20°. Our intuitive judgments about absolute distances and slopes are terribly inaccurate.

The steepest road in the United States, Canton Street in Pittsburgh, has a slope of approximately 20° (37ft of elevation change for every 100ft of distance — trig finally comes in handy).

view of Canton Road

Canton Road in Pittsburgh (from Lildobe at en.wikipedia)

If you’ve run the Boston marathon, you might think Heartbreak Hill is huge, but it ascends at just over 2.5 degrees relative to a completely flat road (about 27m elevation change over 600m distance).

image of heartbreak hill

Heartbreak Hill photo by http://flickr.com/photos/tatler/

The famed Alpe d’Huez climb in the Tour de France averages just 7.8°, but it’s particularly tortuous because of it’s length and the altitude at the finish. The hills seem much bigger because we’re fatigued.

Research over the past 15 years by Dennis Proffitt and colleagues examined just that experience: When we’re tired, hills seem steeper (see Bhalla & Proffitt, 1999). People judge hills to be steeper when wearing a heavy backpack or after jogging. Proffitt and colleagues argue that these overestimates are actually misperceptions—we really see the hill differently when we’re fatigued, and our physiological state at least partly determines our conscious perception. A jogger viewing a 5° hill before a run estimates it to be just over 21°. After jogging, they judge it to be nearly 28°.

But do people really perceive the hill differently or do they just say that they do? People intuitively understand the Heartbreak Hill effect—we know that climbing hills is harder when we’re tired or when we’re carrying a heavy bag.

A recent series of experiments suggests that the effect of backpacks on slope judgments was due to such intuitions rather than to an effect of physiological changes on conscious perception (Durgin et al, 2009). As in the earlier studies by Proffitt and colleagues, Durgin et al had subjects wear a backpack and estimate the slope of a ramp. In the standard backpack condition, subjects were left to their own devices to guess why they were being asked to carry a weight. Unlike the earlier studies, Durgin et al added a critical control condition: Subjects were told that the backpack contained electromyographic equipment designed to measure their ankle muscles. To make the deception complete, they attached electrodes to the subjects’ ankles had had a fan noise come from the backpack. With this explanation for the backpack, subjects no longer need to wonder why the experimenter made them wear a backpack, so they would be less likely to look for some reason.

If slope estimates are due to the effect of physiology on conscious judgments, then it shouldn’t matter what explanation subjects were given—the backpack weighed the same in both conditions. But Durgin et al found that those who fell for the ruse gave estimates no different from those who weren’t wearing a backpack at all. In other words, the effect of wearing a backpack was due to the intuitions of the subjects that weight should affect slope judgments and not due to the weight itself. When they had no reason to guess that the experimenters were interested in the effect of weight on slope judgments, their judgments were unaffected by the weight. Although other evidence provides some support for the effects of physiological state on judgments, in this case, the effect appears to be one of experimental and social context on judgments.

Proffitt, D. R. P., Bhalla, M., Gossweiler, R., & Midgett, J. (1995). Perceiving geographical slant. Psychonomic Bulletin & Review, 2, 409-428

Bhalla M, & Proffitt DR (1999). Visual-motor recalibration in geographical slant perception. Journal of experimental psychology. Human perception and performance, 25 (4), 1076-96 PMID: 10464946

Durgin, F., Baird, J., Greenburg, M., Russell, R., Shaughnessy, K., & Waymouth, S. (2009). Who is being deceived? The experimental demands of wearing a backpack Psychonomic Bulletin & Review, 16 (5), 964-969 DOI: 10.3758/PBR.16.5.964

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