8: Compressed Fence Illusion
Now look down the fence as it extends westward (downhill). Compare the apparent width of the 1st segment of the fence (the distance between the posts) and the 10th segment. Do they appear equal in width or does the 10th look considerably narrower? Most people report that the 10th appears narrower.
This illusion occurs because we tend to under-estimate long distances. We estimate the distance from the 1st to the 2nd post accurately because they are at short range. We under-estimate the distance from the 9th to the 10th post because of the tendency to under-estimate relative distances at long distances.
This is a well-known phenomenon called “depth compression.” You can experience this quite strikingly when hiking outdoors. Large distant mountains appear much closer than they actually are.Back to Map Next