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Distance Perception
Dennis R. Proffitt
University of Virginia
ABSTRACT—Distance perception seems to be an incredible
achievement if it is construed as being based solely on static
retinal images. Information provided by such images is
sparse at best. On the other hand, when the perceptual
context is taken to be one in which people are acting in
natural environments, the informational bases for dis-
tance perception become abundant. There are, however,
surprising consequences of studying people in action.
Nonvisual factors, such as people’s goals and physiological
states, also influence their distance perceptions. Although
the informational specification of distance becomes re-
dundant when people are active, paradoxically, many
distance-related actions sidestep the need to perceive dis-
tance at all.
KEYWORDS—perception; vision; distance; action
Many of the oldest questions in psychology deal with percep-
tion—the means by which people know the world—and distance
perception has been one of the central conundrums. The ques-
tion is typically posed as follows: Given a two-dimensional ret-
inal image of a distant object, how can one perceive the distance
between oneself and the object? Stated this way, the perceptual
system appears to be confronted with a hard, perhaps impossi-
ble, problem. A way out of this difficulty is to consider the en-
vironmental and bodily contexts in which the retinal image is
embedded.
In fact, people are fairly accurate in perceiving distances.
Studies conducted in natural environments find that perceived
distance tends to be slightly underestimated when assessed by
verbal reports or visual matching tasks, whereas another de-
pendent measure, blindwalking, tends to be more accurate
(Loomis, da Silva, Fujita, & Fukusima, 1992). In blindwalking,
people view a target and then attempt to walk to its location while
blindfolded.
The research literature on distance perception is voluminous
and dense. I will not attempt to review it in this article. Instead, I
will develop current views of distance perception by taking the
core problem—how to derive distance from a two-dimensional
retinal image—and wrapping this problem in layers of context
that relate to both the perceiver’s body and the natural envi-
ronment in which perception takes place.
FROM IMAGES TO BODIES ACTING IN NATURAL
ENVIRONMENTS
The Image
Berkeley (1709/1975) noted that a point in space projects to a
point on the retina and that this retinal projection conveys no
information about the point’s distance from the eye (see Fig. 1).
From this, Berkeley concluded that distance perception could
not be based on optical information alone. It is now recognized
that, in complex natural environments, there is far more infor-
mation about distance than could be gleaned from Berkeley’s
situation of observing a point in a void.
The Image in an Eye
The retinal image exists in an eye having a sizable pupil. A lu-
minous point in space would illuminate the whole pupil and
thereby project an area of illumination (not a point) on the retina,
were it not for other optical structures. These structures, the
cornea and lens, bend light so that rays converge to a point on the
retina. The lens changes its curvature when focusing on objects
at different distances. This process, called accommodation, in-
forms the perceptual system about distance and is effective for
close objects.
Two Eyes
People, of course, have two eyes, and each eye must be directed
at the object of regard. The gaze angles for the eyes define
convergence, which effectively specifies distance for near ob-
jects. In addition, each eye has a slightly different perspective on
the scene, and this is the basis for stereo vision.
Eyes in a Body
The eyes exist within a body and this fact has profound conse-
quence for distance perception. Notice first that, for a standing
observer, the eyes have a constant elevation above the ground. In
many situations there exists optically specified distance infor-
mation that can be scaled to one’s eye height (see Fig, 2).
Address correspondence to Dennis Proffitt, Department of Psychol-
ogy, University of Virginia, P.O. Box 400400, Charlottesville, VA
22904; e-mail: drp@virginia.edu.
CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE
Volume 15—Number 3 131Copyright r2006 Association for Psychological Science
The Body in the Natural Environment
The natural environment presents nothing like the situation that
Berkeley described; Berkeley discussed a point being observed
in an otherwise empty environment. The natural environment
consists of a ground plane, which is typically littered with
objects. While the distance to a point viewed in a void is not
optically specified, the distance to an object on the ground is.
Gibson (1979) showed how distance perception is informed by
optical variables that are available to people when they are
situated in natural environments. In contrast to the way Berkeley
described the distance-perception problem—as an extent
through empty space (Fig. 1)—Sedgwick (1986), elaborating on
Gibson’s approach, represented the problem as depicted in
Figure 2. Here it is shown that if an object and perceiver are both
located on level ground, then the distance to the object is
specified by optical variables. The visual angle ais formed by
the gaze angle to the object relative to the straight-ahead view
coinciding with the horizon, or it can be derived from the gaze
angle relative to vertical. Given the visual angle aand the ob-
server’s eye height, I, then the distance, d, to the object is given
by the equation d5I/tan a. Expressed in words, the distance to
the object is a function of its angular elevation scaled to the
observer’s eye-height.
The importance of this formulation of the distance-perception
problem cannot be overstated, because it shows that, in most
viewing situations, the distance to an object is directly specified
by visual angles inherent in optical information. For this for-
mulation to work, objects and observers need to be on the ground
and the ground needs to be relatively level.
Gibson (1979) also noted that the natural environment con-
sists of surfaces having different textures; textures project to the
eye in lawful ways that relate to distance (Sedgwick, 1986). As
illustrated in Figure 3, the projected texture of the ground sur-
face—notice the tiles in the figure—becomes increasingly
compressed as it gets farther away, thereby forming a gradient of
density, which is informative about distance.
The Body in Action
An observer’s movement through the environment produces a
continuous change in perspective, which is highly informative
about distance. Figure 4 depicts a bird’s-eye view of an observer
who is initially, at T
1
, looking at an object that is straight ahead of
her. As she moves to the left, the visual angle to the object, b,
increases to her right. Between T
1
and T
2
, the observer will have
traversed a certain distance, d
t
. The initial distance to the object,
d, is given by the equation d 5d
t
/tan b. Expressed in words, the
distance to the target is a function of the distance traveled and
the change in the visual angle to the object.
Interim Summary
So far I have shown how distance perception becomes increas-
ingly well specified as aspects of the body and environment are
brought into the perceptual situation. It is very important to note,
however, that nothing has been said about how the perceptual
system responds to this available information, what its sensi-
tivities might be, or how different sources of distance information
are combined. These are tough problems, which are reviewed
extensively elsewhere (Cutting & Vishton, 1995; Proffitt & Cau-
dek, 2002; Sedgwick, 1986).
Fig. 1. The problem of distance perception distilled to its minimal rep-
resentation. A point in space projects its image into the eye. The retinal
image contains no information about the distance of the point from the eye.
Fig. 2. A person viewing a cone situated on the ground. The distance of the
cone from the observer, d, is specified by the visual angle, a, relative to her
eye height, I, by d5I/tan a.
Fig. 3. Texture gradient. As the ground plane recedes into the distance, its
texture, which in this situation consists of tiles, becomes compressed and
denser.
132 Volume 15—Number 3
Distance Perception
PURPOSIVE PERCEPTION
Embodied Perception
Distance perception is influenced by the body in many ways. I
have shown how distances are scaled to the body’s stature (eye
height) and informed by the optical consequences of locomotion
(motion perspective). Apparent distances are also influenced by
the energetic costs associated with performing distance-relevant
actions, the observer’s purposes, and the behavioral abilities of
the observer’s body (Proffitt, 2006).
Objects appear farther away as the energy required to act on
them increases. Viewing a target while wearing a heavy back-
pack causes its distance to appear greater relative to when no
backpack is worn (Proffitt, Stefanucci, Banton & Epstein, 2003).
When people throw balls to targets, targets appear more distant
when the balls are heavy than they do when the balls are light
(Witt, Proffitt, & Epstein, 2004). An especially compelling in-
stance of energetic influence on distance perception occurs
when people walk on a treadmill. Walking on a treadmill pro-
duces an adaptation in which the visual–motor system associates
forward-walking effort with remaining stationary. Given that the
system learns that effort is required to go nowhere, it follows that,
after treadmill adaptation, more effort will be required to walk a
prescribed distance. This anticipated increase in walking effort
evokes an increase in apparent distance: Objects appear farther
away after walking on a treadmill (Proffitt et al., 2003).
Purpose is also critical; effort’s influence on apparent distance
is specific to the intended action. Walking on a treadmill influ-
ences the apparent distance to an object only if people anticipate
walking to it. If, after a period of treadmill walking, a person
views a target with the intention of throwing a beanbag to it, then
its apparent distance is unaffected by the treadmill-walking
experience (Witt et al., 2004). Similarly, throwing a heavy ball to
a target influences its apparent distance only if people anticipate
throwing to it again, not if they intend to walk to it (Witt et al.,
2004). These studies show that people view intervening dis-
tances as ‘‘walkers’’ or ‘‘throwers’’ and that perceived distances
are influenced by the energy required to perform these actions.
The extent of one’s reach defines a special region, called near
or personal space (Cutting & Vishton, 1995). This extent can be
lengthened by holding a tool, and this expansion of near space
influences perceived distance. Witt, Proffitt, and Epstein (2005)
showed that target locations, which were within reach when
holding a tool (a conductor’s baton) but out of reach without it,
appeared nearer when the baton could be used to touch the
targets. Objects within reach have a unique immediacy; they can
be touched. Holding a tool extends reach and thereby confers an
immediacy and closeness to those objects that become touchable
through the tool’s use.
Visual Control of Action
Common sense suggests that many visually guided behaviors
rely on distance perception. When driving, for example, we may
notice that the car in front of us has stopped and that the distance
between ourselves and this car is rapidly decreasing; conse-
quently, we brake to avoid a collision. Such a situation appears to
be a case in which distance perception is of paramount impor-
tance, but this may not be so.
Lee (1976) noted that a time-to-contact variable that relates
the visually projected size of the stopped car to its rate of ex-
pansion in the field of view could be effectively used to control
braking without there being a need to know or perceptually
represent the distance to the stopped car. There is evidence that
people utilize this variable when braking (Yilmaz & Warren,
1995). What is important for our discussion is that when per-
forming actions on a distance, such as braking to avoid a colli-
sion, people may rely on optical variables that bypass the need
to take distance into account.
Another situation in which distance perception may be side-
stepped is that of baseball outfielders catching fly balls. Common
sense suggests that, to catch a fly ball, outfielders must know
where the ball is going to land and that knowing the distance to
this location is an important component in getting there effec-
tively. One account suggests, instead, that outfielders use a
visual-control heuristic in which they need only run so that the
path of the ball maintains a linear trajectory relative to their eyes
(McBeath, Shaffer, & Kaiser, 1995): If the trajectory curves, then
the fielder must run with a speed and in a direction that nullifies
the curvature. If fielders can run so as to maintain the ball’s
projected linear trajectory, then they will arrive at the location
where it can be caught without ever representing where they
were going.
Fig. 4. Motion perspective. The distance to the cone, d, is specified by the
change in the visual angle to the cone, b, and the distance, d
t
, that the
observer moved by d5d
t
/tan b.
Volume 15—Number 3 133
Dennis R. Proffitt
FUTURE DIRECTIONS AND CONCLUDING REMARKS
For moving observers in natural environments, distances are well
specified; requisite information abounds. I have provided only a
scant description of the optical and ocular-motor information that
is available. Far less is known about how this information is ac-
tually used; in this regard, perhaps the most difficult problem is
determining how information from different sources is combined.
An especially thoughtful discussion of this issue was provided by
Cutting and Vishton (1995), who noted that the utility of different
informational sources depends on distance. Accommodation and
convergence, for example, are most useful for near distances,
whereas occlusion (the obscuring of objects by other objects) is
equally useful for distances near and far.
Recent research has shown that apparent distances are in-
fluenced by the perceiver’s behavioral potential and the ener-
getic costs associated with intended actions. That perception is
subject to such influences raises the possibility that other factors
may be influential as well. What might these factors be?
Ongoing research from our lab indicates that emotional and
social factors are also influential (Proffitt, 2006). For example, in
her dissertation research, Stefanucci (2006) is finding that, when
people look down from a high balcony, they hugely overestimate
the distance to the ground. Moreover, the magnitude of this
overestimation is positively correlated with people’s fear of
heights. Other research indicates that the distance to objects
within personal space is influenced by social ownership (Schnall
et al., 2005). People at an outdoor cafe were approached and
asked to judge the distance to a soda can placed on the table
within their reach. In one condition, the can had been given to
the participants—it belonged to them—whereas in the other
condition, the can belonged to the experimenter. Participants
perceived the can to be closer when it belonged to the experi-
menter—and had invaded their personal space—than when it
was their own soda.
Another unresolved question deals with the role of distance
perception in the visual control of action. I discussed cases in
which the visual guidance of action has been found to rely on
control heuristics that bypass the need to represent distance. In
these cases, there seems to be a mismatch between the infor-
mation that is guiding people’s actions and the informational
bases for their explicit awareness. Baseball players, for example,
are oblivious to the nature of the visual heuristics that they use
when catching fly balls. Instead, their awareness is of the spatial
layout of the field, the flight of the ball, and the fact that they are
running to catch it. Being aware that they are running with the
intent to catch the ball engenders an assumption that they are
also aware of the location to which they are running. This lo-
cation, however, is not specified by the visual heuristic that is
controlling their running.
One way of reconciling this mismatch between the visual in-
formation that guides actions and that which supports explicit
awareness is to suppose that there exist functionally and ana-
tomically distinct visual systems (Goodale & Milner, 2004). By
such an account, the visual guidance system controls immediate
actions over short extents of time and space, whereas explicit
awareness is responsible for long-term planning. The two-visual -
systems account is controversial and should continue to motivate
research for some time to come. At stake is no less then the
definition of perception and its relationship to consciousness.
Should the unconscious, visual control of action be considered
an instance of perception? How does one distinguish between
behaviors that are guided by perception from those that are
controlled by visual information for which there is no conscious
access? These are fundamental questions of relevance through-
out psychology.
Recommended Reading
Cutting, J.E., & Vishton, P.M. (1995). (See References)
Loomis, J.M., da Silva, J.A., Philbeck, J.W., & Fukusima, S.S. (1996).
Visual perception of location and distance. Current Directions in
Psychological Science,5, 72–77.
Proffitt, D.R., & Caudek, C. (2002). (See References)
Sedgwick, H. (1986). (See References)
REFERENCES
Berkeley, G. (1975). An essay towards a new theory of vision. In M.R.
Ayers (Ed.), George Berkeley: Philosophical works including the
works on vision. London: J.M. Dent. (Original work published
1709)
Cutting, J.E., & Vishton, P.M. (1995). Perceiving layout and knowing
distances: The integration, relative potency, and contextual use of
different information about depth. In W. Epstein & S. Rogers
(Eds.), Handbook of perception and cognition, Vol 5: Perception of
space and motion (pp. 69–117). San Diego, CA: Academic Press.
Gibson, J.J. (1979). The ecological approach to visual perception. Boston:
Houghton Mifflin.
Goodale, M.A., & Milner, D. (2004). Sight unseen: An exploration of
conscious and unconscious vision. Oxford: Oxford University Press.
Lee, D.N. (1976). A theory of visual control of braking based on infor-
mation about time-to-collision. Perception,5, 437–459.
Loomis, J.M., da Silva, J.A., Fujita, N., & Fukusima, S.S. (1992). Visual
space perception and visually directed action. Journal of Experi-
mental Psychology: Human Perception & Performance,18, 906–
921.
McBeath, M.K., Shaffer, D.M., & Kaiser, M.K. (1995). How baseball
outfielders determine where to run to catch fly balls. Science,268,
569–573.
Proffitt, D.R. (2006). Embodied perception and the economy of action.
Perspectives on Psychological Science,1, 110–122.
Proffitt, D.R., & Caudek, C. (2002). Depth perception and the percep-
tion of events. In A.F. Healy & R.W. Proctor (Eds.), Comprehensive
handbook of psychology, Vol. 4: Experimental psychology (pp. 213–
236). New York: Wiley.
Proffitt, D.R., Stefanucci,J., Banton, T., & Epstein,W. (2003).The role of
effort in perceiving distance. Psychological Science,14, 106–112.
Schnall, S., Witt, J.K., Augustyn, J., Stefanucci, J.K., Proffitt, D., &
Clore, G. (2005). Invasion of personal space influences percep-
134 Volume 15—Number 3
Distance Perception
tion of spatial layout. Journal of Vision, 5, Abstract 198.
Retrieved April 25, 2006, from http://www.journalofvision.org/5/
8/198/
Sedgwick, H. (1986). Space perception. In K.R. Boff, L. Kaufman, & J.P.
Thomas (Eds.), Handbook of perception and human performance
(Vol. 1, pp 1–57). New York: Wiley.
Stefanucci, J.K. (2006). Looking down from high places: The roles of
altitude and fear in perceiving height. Unpublished manuscript,
University of Virginia, Charlottesville.
Witt, J.K., Proffitt, D.R., & Epstein, W. (2004). Perceiving distance: A
role of effort and intent. Perception,33, 577–590.
Witt, J.K., Proffitt, D.R., & Epstein, W. (2005). Tool use affects per-
ceived distance but only when you intend to use it. Journal of
Experimental Psychology: Human Perception and Performance,
31, 880–888.
Yilmaz, E.H., & Warren, W.H. (1995). Visual control of braking: A test
of the tau hypothesis. Journal of Experimental Psychology: Human
Perception and Performance,21, 996–1014.
Volume 15—Number 3 135
Dennis R. Proffitt
