Scotopic sensitivity to ON and OFF stimulus transients

The luminance of a large diffuse field, viewed peripherally, was temporally modulated near absolute detection threshold. The field luminance either increased abruptly and decreased gradually (ON stimulus) or increased gradually and decreased abruptly (OFF stimulus). For all wavelengths shorter than 620 nm, sensitivity to the ON stimulus was greater than to the OFF. The spectral sensitivity curves obtained indicate that rods and/or their associated neural pathways are more sensitive to ON stimulus transients than to OFF.