Research Reveals People Overestimate Slants, Heights
12, 1999 -- Steep
hill? It's probably not as steep as you think it is.
appear steeper than they actually are. For example, everyone judges
hills with only a seven-degree slant as extremely steep. The tendency
to overestimate steepness is even greater for elderly people, people
carrying a heavy load and people who are tired, of low fitness or
in poor health.
are findings of University
of Virginia research probing how people perceive and think about
space. Part of the first systematic studies on people's perception
of everyday geographical inclines, the results were published recently
in the national periodical, Journal of Experimental Psychology:
Human Perception & Performance.
a series of experiments on perceptual bias led by psychology professor
Dennis R. Proffitt, participants consistently judged a hill with
a 10-degree slant to be about 30 degrees. Their guesses for a five-degree
hill averaged 20 degrees. When told that their estimates were off
by more than 15 degrees -- and that by law the steepest public road
in Virginia can have no more than nine degrees in inclination --
most participants were incredulous.
look at a 10-degree hill, typically judged to be about 30 degrees
by verbal estimates and visual matching, and to be told that it
is actually 10 degrees is an astonishing experience for anyone unfamiliar
with the facts of geographical slant overestimation," said Proffitt,
the Cavalier Distinguished Teaching Chair at U.Va.
with depth perception, perception of geographical slant involves
juggling spatial considerations making judgments about how steep
hills and other inclines are in relation to a "normal" flat, horizontal
surface. In the experiments 130 U.Va. students reported their judgments
of inclines in three different ways. A verbal report was a simple
estimate in degrees of the hill's incline. Participants made their
judgments while standing at the base of hills, looking directly
ahead at them.
gain a visual estimate, participants used a disk with an angle that
could be adjusted to represent the hill's incline. Judgments based
on touch (called "haptic judgments") were made by using a tilt board
with a flat palm rest, the tilt of which could be adjusted to match
experiments were conducted. They showed that hills appear steeper
when people carry a heavy load, are fatigued by running, are not
physically fit, are elderly or in poor health. The verbal and visual
judgments grossly overestimated incline, while haptic judgments
were significantly more accurate. The results are described in "Visual-Motor
Recalibration in Geographical Slant Perception" by Proffitt and
Mukul Bhalla, associate professor of psychology at Loyola University
New Orleans, in the journal's August issue.
from being a problem, the exaggeration of slant perception actually
helps people ascend hills, said Proffitt, who noted that earlier
work showed that overestimates of pitch are even more pronounced
when people view steep hills from the top rather than the bottom.
overestimates are functional. They help people pace themselves when
ascending hills and may even prevent people from undertaking climbs
that would be too difficult. In a similar vein, as anyone in San
Francisco can tell you, descending steep hills is difficult. So
overestimates encourage people to be cautious," he said.
study participants' verbal and visual overestimates reflect their
awareness of how challenging hills can be to climb, Proffitt believes.
"The highly exaggerated estimates of slant show that human perceptions
are not simple reflections of reality, although most people tend
to assume they are," he said. "However, the visually guided actions,
reflected in the haptic response, are accurate and unaffected by
fatigue, load, fitness, age, and health. Our visually guided actions
are accurate even though our conscious awareness may be distorted."
other experiments investigating how people perceive heights, the
U.Va. researchers found that the larger real objects are outdoors,
the greater is the overestimate of their height. The
findings were published in the July issue of the national journal,
studies involving 230 U.Va. students investigated why people experience
very small vertical-horizontal distortions when viewing photographs
and line drawings, but tend to vastly overestimate vertical extent
when viewing real objects outdoors. For example, when viewed in
person, the Rotunda at the University of Virginia appears elongated
vertically when compared to Thomas Jefferson's illustration showing
the building's horizontal and vertical dimensions are physically
six experiments involving 230 U.Va. students, participants viewed
objects presented in line drawings or in photographs and found that
there was only a small overestimation of their vertical extent.
These same objects were also viewed in an outdoor setting and in
a 3D virtual reality scene shown in a head-mounted display. In these
situations the vertical overestimation was about twice as large
as that found when viewing the two-dimension images.
with the studies on geographical slant, these findings demonstrate
that our everyday perceptions often exhibit large distortions of
which we are generally unaware," Proffitt said.
are invited to observe and participate in 3D virtual-reality experiments
and outdoor distance-judging experiments. To arrange such, contact
Dennis Proffitt at (804) 924-0655 or firstname.lastname@example.org.
Ida Lee Wootten