How a Whale sees

Note it says how A whale sees, not how THE whale sees. Though it appears we are similar…monochrome…shades of black and white.

Killer_Whale_Eye

Killer Whale Eye by ~annlo13
Source deviantART http://bit.ly/10tMFia

Coming eye-to-eye with a whale, we know what we see. We know how we see, too. Light passes into our eyes through the cornea, which actually does most of the focusing for our eyes. Then it moves through the aqueous humor, to the lens, which finishing up concentrating the light on the retina. The retina is packed with photoreceptors, the cones, which detect color, and the rods, which do not pick up color but are more sensitive in dim light. Specialized ganglion nerve cells pick up excitations from the light-sensitive cells and filter them for contrast (quite seriously: kind of like hitting the “enhance” button in Instagram). This is a wonderful operation. Leo Peichl at the Max Planck Institute for Brain Research, gave a great illustration of how important the ganglions’ processing is.

“The ganglions sort of throw away the information about absolute light intensity,” Peichl told me. “That’s why we can read a book or newspaper at bright sunlight or candlelight, even though at bright sunlight, the black of the letters emits more light than the white paper would in candlelight.” In either situation, you see black letters on white paper, even though the raw unfiltered light information is vastly different. (Though obviously, you remain aware that it is brighter outside at noon than next to a candle light.)

That is the technical aspects, now for the interesting part.

Whales, unlike nocturnal rodents or ourselves, see the world in monochrome. Leo Peichl at the Max Planck Institute for Brain Research co-authored a paper with the nearly tragic title, “For whales and seals the ocean is not blue.” Indeed, the first thing that we can know for sure about how whales see the world is that it exists only in shades of gray. The water we see as blue they would see as black. “They do want to see the background. They want to see animals on the background. And the animals on the background are reflecting light that’s not blue,” Johnsen explained. If we try to imagine what that might look like, Johnsen said perhaps we could picture a grayscale photograph of people wearing fluorescent clothes under a black light.

When it comes to the optics of whale eyes, the first difference we should note is that its cornea — the outermost layer of the eyes — doesn’t help it nearly as much as ours helps us. We live in air, which has a different refractive index than the material of the cornea. When light enters our cornea, it bends inward. You know how pencils appear to bend when you put them in a glass of water? That’s refraction, and our eyes exploit it to help focus photons on the central part of our retinas. Johnsen told me roughly 70 percent of the work of focusing light on our eyes is done by the cornea before the light even reaches the lens. But that’s a clever terrestrial trick. In water, the refractive index of the cornea and water are roughly the same, which means that marine mammals don’t get that pencil-going-into-water light bending help. “The lens has to do everything in the whale eye,” Peichl said. While our lenses are flattish, theirs are circular in order to provide sufficient focus.

An eye on each side of the head presents further interesting details.

 “They have two completely independent fields of view. God knows what they do with that. The internal perception, how do they represent that? Is it like two screens in their head? Do they stick it together? We don’t deal with that because we don’t have a region of our field of view that’s like that,” he said. “For all we know, they represent sonar information as vision. We think they hear a bunch of clicks, but for all we know, it is represented in a visual spatial form in their heads.”

Then he said something that’s key to understanding what we can know about the vision, and maybe the minds of whales: “All we really know is what they can’t do.” They don’t have binocular vision. They couldn’t read the big E on a chart at the eye doctor’s office. Their ocean is not blue.

But when it comes to what it’s like *inside* those big heads, we’re almost no further along than Melville’s guess more than 150 years ago.

“The whale, therefore, must see one distinct picture on this side, and another distinct picture on that side; while all between must be profound darkness and nothingness to him” he wrote. “Man may, in effect, be said to look out on the world from a sentry-box with two joined sashes for his window. But with the whale, these two sashes are separately inserted, making two distinct windows, but sadly impairing the view.”

 


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