ABSTRACT
For the adult observer the visually perceived environment is by and large a stable place. Objects remain more or less the same in their “intrinsic” properties of size, shape, color, and brightness and in their orientation, position, and state of movement (including their stationariness) as the observer moves about the environment and ambient light changes in its composition and intensity. But there is a paradox in all this. The representation of intrinsic and relational characteristics at the eyes is far from stable. The size and shape of the retinal images vary with the distance and bearing of the observer from the object. Furthermore their colors and luminances change with the wavelength composition and intensity of light. Likewise, the representation of orientation, position, and motion varies as the observer changes posture and position and scans the environment with eye and head movements.
