ABSTRACT
Adults perceive their surroundings as a continuous spatial whole, from near to far distance, which includes those parts to the side and behind them and not immediately visible, as well as those parts at which they are looking. But a great variety of information is included in the schemata on which perception of and reaction to the total spatial framework is based. Many different processes may come into play in perceiving and assessing the various aspects of these. Thus the disparate images
of the two eyes are involved in perceiving the location and three-dimensional solidity of near objects, together with shadows on their sides and the shadows they cast. The continuous perspective changes in size, brightness and surface texture which Gibson (I950a) termed 'gradients' are the principal aspects contributing to perception of the 'ground' on which objects are situated; but also they enable the location of these objects to be made, and hence judgments as to their distance. Normally all these and other percepts corroborate each other and provide redundant information as to the appearance and lay-out of the surroundings; and the more information available, the more accurately can judgments of the distances of objects be made. Thus Luria and Kinney (1968) found that whereas absolute distances of objects up to fifteen feet could be made accurately when the full surroundings were visible, distances were increasingly over-estimated when targets were viewed in a large empty room; and still more when they were seen monocularly through a circular opening in a screen, with walls and floor draped in black. Again, Gruber and Dinnerstein (1965) showed that absolute, though not relative, judgments of distance over about forty-eight feet were more accurate both when observers could actually perceive the lighted corridor in which the objects were situated, and also when they were given previous knowledge of its dimensions, than when this information was not available.
