AN INVESTIGATION OF SCOTOPIC THRESHOLD VERSUS ILLUMINANCE CURVES FOR THE ANALYSIS OF COLOR MATCHING DATA

Stiles developed a method for estimating whether rod-photoreceptor act ivity contributed to color-matching data. This method requires knowled ge of the rod threshold at the illuminance levels of lights being view ed. Stiles suggested that the Aguilar and Stiles scotopic threshold-ve rsus-illuminance (TVI) curve could serve as a convenient approximation of the rod threshold. Stiles' method was intended for use in color-ma rching experiments where the stimuli are presented side by side, but, in the Aguilar and Stiles experiment, detection thresholds were measur ed for temporally, pulsed lights. This study, compares rod-sensitivity with detection and side-by-side adjustment tasks. The illumination le vel of the rest and background light was kept below the absolute thres hold of the short-wavelength sensitive cones, because there is evidenc e that cone signals may interact with the scotopic TVI function. The t hreshold data fell mainly within the range of the Aguilar and Stiles o bservers. There were two notable deviations from the Aguilar and Stile s curve (1) consistent with previous reports, the scotopic TVI functio n had a slope shallower than the Aguilar and Stiles curve when measure d with a short-wavelength background (2) thresholds measured from a da rk surround with a spatial adjustment task were higher than the Aguila r and Stiles thresholds even though the slopes were the same. (C) 1996 John Wiley & Sons, Inc.