ABSTRACT
This chapter considers in some detail the limits of visual perception in present technology for man-machine communication. The restriction to visual perception has been chosen because almost all output data are presented visually. The chapter explores some future developments in man-machine dialogues, including the use of speech as an output medium. Especially in vision some perceptual limits are essential to the functioning of technical products. Visual limitations may show up in the first place with computer output information which has to be read - so, essentially, they are limitations in reading. The chapter describes the consequences of each requirement to establish the resulting limits for reading. The concept of visibility which just has been dealt with could be defined as referring to threshold levels of contrast and/or size, i.e. below a certain text-background contrast or a certain letter size the letters concerned remain invisible at the prevailing adaptational state of the eye.
