PERSPECTIVE EFFECTS IN FRONTAL SLOPE PERCEPTION
Observers usually judge slopes to be steeper than they are. However, according to perspective theory, distance foreshortening should make distant uphill slopes appear steeper and distant downhill slopes flatter. Experiments have shown that distant uphill slopes appear steeper than near slopes. Downhill slopes are also overestimated, but they are judged flatter when viewed from a height and greater distance than when viewed from ground level. When viewed from a height of 100 m, flat ground was estimated as sloping 6 deg uphill. These results support the distance foreshortening account, but contravene the changes in optical angle of the scenes - which should make distant uphill views appear flatter and distant downhill views steeper.