Cones change rod sensitivity

Steady-state (i), masking (ii), and moving-stimulus (iii) experiments all show that cones decrease rod sensitivity. The effect is larger for the transient conditions [(ii) and (iii)]. For (i) the steady adapting field test, rod sensitivity was measured as a function of eccentricity for two backgrounds, a 500 nm scotopic background and a 700 nm mesopic background which produced the same threshold as the 500 nm background at a single eccentricity. Since the eccentricity functions are of different shape for the two backgrounds, cones change rod sensitivity, (ii) Scotopically equal green and red fields have unequal masking effects upon test flashes seen by rods alone; the masking effect is much larger than the steady effect. (iii) Thresholds for rods centered within rotating vanes are higher if the vanes stimulate cones in addition to rods.