Visibility on Cathode-Ray Tube Screens The Effect of Size and Shape of Pip*

Abstract

The area and contour of a stimulus have been indicated experimentally as factors in its visibility. In order to evaluate the role of such factors in radar presentation, an experiment was conducted to determine the effect upon visibility of changes in the size and shape of a radar pip. A wide range of beam widths (which determine the angular dimension of the pip) and pulse lengths (which determine its radial dimension) was investigated at each of three test field brightnesses. Resuits show that visibility, on a decibel scale, is a linear function of the logarithm of beam width at each of the three brightness levels used. For the dim background visibility is also a linear function of the logarithm of pulse length. For the brighter backgrounds, on the other hand, visibility is shown to be a curvilinear function of the logarithm of pulse length. It is suggested that the reason for the difference between an increase in beam width and an increase in pulse length lies in the time factor. Doubling the beam width, for example, results in a greater increase in the time during which the pip is exposed to the eye than does a corresponding increase in the pulse length.