In the Neuroscience book edited by Purves et al. (page 232), it can be reading: “The reason for this unusual arrangement (rods and cones are active in the “dark” and inactive in “light”) compared to other sensory receptor cells is not known”!
I think the reason is this:
In the Neuroscience book edited by Purves et al. (page 232), it can be reading: “The reason for this unusual arrangement (rods and cones are active in the “dark” and inactive in “light”) compared to other sensory receptor cells is not known”!
I think the reason could be this:
To human beings can “see” places where come from few photons as a cave entrance or not “visible” photons from black painted surfaces, use the following trick:
1.- When none or few visible photons are reaching the retina (“dark”), rods and cones are active and releasing their transmitter.
¿Why? They are producing the sensation of “Darkness” because black is a positive sensation; the blind eye does not “see black”; it “sees nothing” (W. Ganong in Medical Physiology, 22 edition, page 163).
2.- When some but still few photons reach the retina ("weak light"), rods will inactive and produce the sensation of nocturnal vision (without color sensation). However, cones keep still active.
3.- When a lot of photons reach retina ("strong light"), cones also will inactive and produce the sensation of diurnal vision with color sensations, while rods will saturate.
In other worlds, “dark” is working as a “background”, “filling” or “stuffing” in the visual field, otherwise, poor illuminated areas or objects will see, not “dark”, but invisible!
In poetic words: “Photons write on the retina, as a chalk on a blackboard”!
We must say, instead "being in the dark or light", being in absence or presence of weak or strong amounts of photons! Ja, ja, ja.
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