AN EXPERIMENT ON THE ASSESSMENT OF BRIGHTNESS UNDER, ‘ FREE-CHOICE ’ AND ‘ FORCED-CHOICE’ CONDITIONS BY A GROUP OF OBSERVERS

Abstract

An experiment is reported in which thirty-four subjects simultaneously made a series of assessments of the subjective brightness of a test patch in dark surroundings, indicating their estimates by the assignment of numbers chosen by themselves. Estimates made under these ‘ free-choice ’ conditions gave a relation between luminance and subjective brightness closely corresponding to the law previously found to relate sound energy level to subjective loudness

When the subjects were given stated numbers to be assigned to the highest and lowest luminances, the relation was distorted but apparently not. basically changed. The results can be interpreted as a demonstration that, under the experimental conditions, a basic relation exists between subjective brightness and the luminance of the stimulus which is distorted but not wholly suppressed when false information is given during its determination