STUDIES OF DISPLAY SYMBOL LEGIBILITY

Abstract
The purpose of this study was to determine the effects on the legibility of capital alphabetic letters of: (a) two simulated TV rasters with horizontal, linear scan constructions of 11 and 5 lines per letter height and a solid (continuous) construction of infinite lines per letter height, (b) two visual exposure times of 0.03 and 0.003 second, and (c) two letter strokewidths of 16% and 28% of letter height. Four subjects identified the letters presented singly in a tachistoscope under all combinations of these conditions. Legibility was measured three ways: by information transmitted (in bits), by errors in identification, and by verbal reaction time. The results showed that for the 0.03second exposure time, the letters constructed with 11 lines were as legible as solid (continuous stroke) letters, but the line construction was less legible at 0.003-second exposure. At both exposure times, the 5-line construction was less legible than the solid construction. With 5-line construction and 0.003-second exposure, the wide stroke-width gave better legibility than the narrow width. Confusion between specific letters varied for both line constructions and stroke-widths. The possible effects on legibility of changes in brightness, contrast and letter geometry introduced by the experimental conditions are discussed. It was concluded that the legibility of letters generated by a horizontal kinear scan construction is highly dependent upon apparently minor differences in letter geometry. (Author).

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