Abstract
The threshold luminance of test field (13.2′ in diameter) presented with a rectangular inducing field (180.9′×18.9′) was measured by the constant method. A parafoveal test field whose center was located within 2° below a fixation point was used. The effect of retinal separation between test and inducing fields was examined in Exp. I, changing it from 0.27° to 2.31°. The effect of inducing luminance (-1.9 to 0.5 log mL) was examined in Exp. II, and that of inducing area (9.4′ to 56.6′ in width) in Exp. III. The results for three Ss were compared with those previously obtained using a ring-shaped inducing field and they were analysed and discussed from the viewpoint of the stray-light hypothesis.