The authors describe the technique (developed by h.r. blackwell) selected to measure contrast sensitivity. It is basically a forced-choice task wherein a participant must respond to every possible occurrence of a target presentation. The target size, shape and position are known. The subject must indicate in which one of 4 well defined temperal intervals the randomly presented luminance increment has occurred. The apparatus consists of a large screen, a rear projection light and shutter arrangement and an electronic control and recording unit. Target presentation takes place at time intervals of 2.5 second. Equations are derived for calculating the detection probability after raw scores have been corrected. Contrast multipliers, which can be used to relate detectability to that of a standard, are given. Data obtained with the 25 participants, ranging in age from 25 to 40 who were involved in the investigation, are presented and discussed. (See also B 3411 and B 3412)
Abstract