Faster than the eye can see: blue cones respond to rapid flicker.

Flickering lights that are detected by the blue cones of the human visual system fuse to yield a steady sensation at much lower rates of flicker than do lights that are detected by the red or green cones. Yet, although blue-cone-detected lights flickering at 30-40 Hz appear to be steady, they are still able to interact with red- or green-cone-detected flickering lights to produce clearly detectable beats in the form of an amplitude modulation of the red- or green-cone flicker. Thus the blue cones produce a viable high-frequency flicker signal, as do the red and green cones, but one that is normally lost before it reaches sensation. The temporal-frequency response for the blue-cone beat interaction is similar in shape to the temporal-frequency response for directly detected red- or green-cone flicker. When measured through the same pathway (which we identify as the luminance pathway, since it is able to transmit high-frequency flicker), the response of the blue cones seems to be as fast as that of the other cones.