Suppose, for example, 
that the object shown on the 
left in this figure is 12 inches 
square and seen at a distance of 
10 feet. If perceived size were 
governed only by visual angle, 
the square viewed at 30 feet 
would appear to be one-third 
the size of the one at 10 feet, or 
a square of 4 inches to a side, 
because visual angle is 
inversely proportional to 
distance. If distance is taken 
into account, however, then 
we have

Perceived size
      = perceived distance x visual 
           angle

Perceived size of near square 
       = 10 x visual angle

Perceived size of far square 
       = 30 x visual angle/ 3
       = 10 x visual angle

Thus, the diminution of an 
object’s visual angle with 
distance would be exactly 
compensated for by the 
increase in its perceived 
distance, as long as the latter is 
perceived accurately.