ABSTRACT
A working definition of the word ‘virtual’ may be found in any dictionary, and will be something along the lines of ‘having the essence or effect, but not the appearance or form of’. Extending this definition to virtual reality seems quite appropriate. This chapter considers in detail two ways in which a virtual world may differ from the real one. Temporal aliasing and misaccommodation are contrasting examples of current knowledge about the effects of visual display technology on perception. The images used to simulate motion in virtual environments paradoxically do not usually contain any motion. Cathode ray oscilloscopes and liquid crystal displays on which virtual images are usually displayed are updated at a finite rate. The extraction of motion from sequences of static images can be considered the result of cognitive processes. The appearance of motion reversals may readily be explained by either motion energy detection or feature matching systems.
