The effects of size and brightness on the speed of identifying number of range rings

Abstract

Abstract : There is an optimal display size for identifying the total number of range rings. The effect of size is not pronounced, however, except at small visual angles. In general, it seems best to use visual angles between 20 and 60 degrees. The effect of visual angle is much more severe with large total numbers than with small total numbers. For example, changing the visual angle from 28 degrees to approximately 3.5 degrees increases identification time almost by a factor of two when 10 rings are used. A similar change in visual angle for two rings increases identification time less than 10 per cent. There is a suggestion that, at a constant visual angle, identification time is faster with a larger diameter display with the observer farther away than with a smaller diameter display with the observer closer. The optimum screen brightness is approximately 10 apparent foot candles, although the effect of brightness is small over a wide range of brightnesses. The effect of increasing the total number of rings is much more severe than any of the effects due to differences in size or brightness, except when very small visual angles are used with large numbers of rings. Individual differences in speed of identification are large, and selection of observers for this type of perceptual task may be the best means of increasing efficiency. (Author)