Distortions of posterior visual space
((F. Phillips, M. Voshell))
Skidmore College, Eye, Brain, and Vision Laboratories, Saratoga Springs, NY;
Purpose. The study of spatial vision is a long and well traveled road (which, of
course, converges to a point at the horizon). Its various distortions have been widely
investigated empirically, and most concentrate, pragmatically, on the space anterior to
the observer. The visual world behind the observer has received less attention and it is
this perspective that these experiments address.
Methods. An initial ‘field’ experiment using surveyed locations and physical poles ar-
ranged in a large pasture was followed by several experiments using a computer graphics
simulation of the ecological setup. A series of egocentric pointing tasks were performed
in which the subject was instructed to make a controlled observation of their posterior
visual space, after which they adjusted a mechanical pointer to indicate their perceived
direction to an object in that environment. Results. Subjects’ responses reflect system-
atic and consistent distortions in their perception of the visual world behind them. For
the various presentation and observation conditions the subjects consistently ‘spread’
their perceptual representation of their posterior space in a hyperbolic fashion. Direc-
tions to distant, peripheral locations were consistently overestimated by 5 to 10 degrees,
and variability increased as the target was moved toward the center of the observer’s
back.
Conclusions. The perceptual representation of posterior visual space is, no doubt,
secondary to the more immediate needs of the anterior visual world. Still, it is important
in some contexts including certain sports, such as rowing, and in vehicular navigation
(c.f. Voshell and Phillips in these proceedings). Our results show systematic perceptual
distortions in the posterior visual world when viewed statically. Investigations currently
underway examine these distortions when moving through and navigating this space.