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DISPLAY SYSTEM DESIGN PROBLEMS 



two parts, (a) a photosensitive portion called the retina and {b) a control 

 system for positioning the eye. The following discussion will be limited to 

 a consideration of the retina and its characteristics that influence system 

 design. The response of the control system will not be considered in this 

 analysis because its characteristics manifest themselves as part of tracking 

 behavior. 



The major subdivisions of the retina that can influence design are (1) the 

 periphery and (2) the fovea or center portion. Each portion has important 

 characteristics. The center portion or fovea is color sensitive and has high 

 resolution properties. The periphery is sensitive to very small amounts of 

 light when the eye is dark-adapted. 



The basic characteristics of the eye will be considered in terms of their 

 effect upon the performance of a simple task, i.e. the detection and resolu- 

 tion of spots of varying size, color, and brightness under varying conditions 

 of background brightness, exposure time, and eye adaptation time. The 

 basic problem and the sensitive parameters to be considered are shown in 

 Fig. 12-15. 



Background 

 Brightness 



Spot Characteristics 

 Size 



Brightness 

 Color 

 Exposure Time 



Eye Adaptation 



Fig. 12-15 Sensitive Parameters of the Spot Detection and Resolution Problem. 



Visual acuity (i.e. the ability to resolve small visual angles) depends upon 

 the angular displacement from the fovea as shown in Fig. 12-16. At 10° 

 from the fovea on the nasal side, the visual acuity is 20 per cent of the value 

 that exists when the object falls on the fovea. (That is to say, the minimum 



