Perception in Unusual Environments

Spatial Judgments

Distance judgments are affected by many factors, such as atmospheric visibility, the presence of intervening objects, and the direction of viewing. With horizontal viewing, observers increasingly underestimate far distances, particularly across featureless terrain. When looking up or down from a height, distances usually appear large and objects small. A well-known example is the moon illusion: The moon appears large and near on the horizon, but small and distant when up high. Slope judgments are also distorted, probably through distance foreshortening. When viewed from a height, distant downhill slopes appear too flat, a flat valley appears to rise, and facing uphill slopes appear too steep. The perceived horizontal is attracted toward the angle of the nearest frontal slope, affecting the perceived height of further hills. Observers looking over a gentle downhill slope judge horizontal eye level as too low and the opposite hilltop as too high; and vice versa when looking up a slope.

Atmospheric and Weather Effects

We are accustomed to the usual atmospheric visibility where we live. One of the cues used in judging distance is aerial perspective—the reduction of luminance and color contrast with distance. The light reflected from objects becomes more similar to that of the sky background as it travels through the atmosphere to reach the observer. In a misty atmosphere we overestimate distance, and in a clear atmosphere we underestimate it. Mist is particularly dangerous while driving, because distant objects are invisible or appear far away. An exceptionally clear atmosphere can be misleading for walkers, who think that distant land is close, and attempt to walk impossible journeys. They may also see baffling mirages.

Walking or skiing in a whiteout is hazardous. Walkers can lose their sense of orientation, and skiers can lose their sense of their own movement. If stationary skiers are surrounded by moving skiers, they may feel that they are moving in the opposite direction, apply an inappropriate correction and fall over in the same direction as the moving skiers.

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