Scripps Institution of Oceanography

SIO Reference 60-31. Systematic data relating target size to the contrast necessary for detection at various levels of adapting luminance have heretofore been limited to 6 and lower. In many practical situations, however, larger target subtenses are involved, and the solution of visibility problems by established nomographic means has been impossible owing to lack of input visual performance data for large targets. The hypothesis has been advanced that the limiting target situation might reasonably be equivalent to the instance in which the entire visual field is divided, as it becomes fatuous to speak of targets larger than can be accommodated in the binocular visual field.An experiment was performed which yielded data for both the upper limiting circular target size of the previously used data of the Tiffany research (6°) and for a "split field" in which the target comprised a luminance increment on one half of the visual field. Six levels of background luminance were studied; those for which the classical data had not reached a terminal value of contrast.