Perception & Cognition
Cues for Visual Space Perception
(Summary 1998, J.S.Longstaff)

Monocular Focus
(Accommodation)

  • The visual image of an object is focused within a single eye by the bulging or flattening of the lens created by circumferential tension around the lens by the ciliary muscle.
  • The more tension in the ciliary muscle to focus on an object, the closer it is perceived.
Binocular Focus
(Vergence)
  • A visual image is focused between two eyes by convergent or divergent eye movements.
  • More muscular tension is required for converging eye movements.
  • The more tension to bring an object into binocular focus, the closer it is perceived to be.
Binocular Disparity
  • Two eyes view the environment from slightly different points, receive different images.
  • Two images are integrated into a unitary image in the brain.
  • The more disparity between the two images, the closer an object is perceived to be.
Motion Parallax
  • The closer an object is to the viewer, the faster its visual image will move past and the more its image will change (eg. a new viewpoint) when the observer moves (eg. turning the head or travelling).
  • When a person moves, objects whose visual images move farther are perceived as being closer than objects whose visual images move less far.
Occlusion
  • Objects farther from the observer will disappear from view (occlusion), or appear into view (disocclusion) from behind objects closer to the observer as a result of the objects’ or the observers’ motion.
  • Proximity of several objects, closest, close, less close etc. is given from occlusions.
Size / Distance
Relationship
  • An object which is close to the observer will fill a larger visual angle than the same object far from the observer (a fundamental principal to many others)
  • When an object gradually fills a larger and larger visual angle, it is perceived as moving directly towards the observer. The bigger it gets, the closer it is.
Linear Perspective
  • Parallel lines appear to converge with increasing distance from the viewer, thus:
  • Lines or surfaces which appear to be parallel are perceived to have a constant distance from the eye.
  • lines or surfaces which appear to converge towards the same point or line are perceived to be parallel and moving away from the eye.
Slope of Regard
  • The visual projective line towards an object (the “line of regard”) in the lower visual field will be directed more and more steeply downward as the object becomes closer.
  • The reverse is true for objects in the upper visual field.
  • The analogous effect occurs for objects in the right or left visual field.
Texture Gradients
  • As a uniform texture becomes further away from the eye, the texture’s visual image will gradually become more dense.
  • Texture can occur on the object or in the environment (untextured object on a textured floor).
  • If the visual image of a textured surface is uniform, the surface will be perceived as being at a constant distance from the eye.
  • If the visual image of a textured surface gradually becomes more dense, the surface will be perceived as gradually moving away from the eye.
Velocity Gradients
  • An object travelling at a constant speed far from an observer will move across the visual field slower than an object travelling at that same speed closer to the observer.
  • An object travelling on an angle toward the observer at a constant speed will gradually move across the visual field faster and faster.
Knowledge of
Object Sizes
  • Previous knowledge about the sizes of objects will influence the perception of how close or how far they are perceived to be from the viewer.
  • A mouse filling a large visual angle will be perceived as being close, whereas a truck filling that same size visual angle is perceived to be farther away.
Knowledge of
Object Distances
  • Previous knowledge (or perceptions) of the distance of an object from an observer will influence judgements of how big the object is perceived to actually be.
  • When objects are known or perceived to be the same distance from the observer, then objects filling a large visual angle will be perceived to be larger than objects filling a smaller visual angle.
   


REFERENCES:
  • Gibson, J. J. (1966). The Senses Considered as Perceptual Systems. Boston: H. Mifflin.
  • Sedgwick, H. A. (1986). Space perception. In Handbook of Perception and Human Performance. Vol. 1. Sensory Processes and Perception, edited by K. R. Boff, L. Kaufman, and J. P. Thomas (pp. 21.1–21.57). NewYork: John Wiley.