Relative size judgments were collected for two objects at 30.5 m and 2
3.8 m from the observer in order to assess how performance depends on
the relationship between the size of the objects and the eye level of
the observer. In three experiments in an indoor hallway and in one exp
eriment outdoors, accuracy was higher for objects in the neighborhood
of eye level. We consider these results in the light of two hypotheses
. One proposes that observers localize the horizon as a reference for
judging relative size, and the other proposes that observers perceive
the general neighborhood of the horizon and then employ a height-in-vi
sual-field heuristic. The finding that relative size judgments are bes
t around the horizon implies that information that is independent of d
istance perception is used in perceiving size.