The measurement that people tend to use here is cycles per radian, and it defines how well a given eye can discriminate between two lines next to each other. An eagle is up over 8,000 cycles per radian. A human eye registers an impressive 4175. A cat is down around 570. And researchers working with minke whales estimate that it is down with the rabbits and elephants at around 230.
Though it's probably not advisable to attempt a translation from this visual acuity to the more familiar units from your optician's office, I'm going to do it anyway. If normal human good vision is 20/20, a whale might rank somewhere like 20/240. That sounds pretty bad, but if you, like me, have a glasses prescription of -5.00, you almost certainly have worse visual acuity than a normal minke whale. (Of course, you can see colors, so count your blessings.)
But it's not easy to make the comparison between human vision and whale vision. It's definitely weirder than that. One fascinating aspect of cetacean eye anatomy is that it appears that whales don't have one central area for higher-resolution imaging like humans. Instead, they appear to have two areas of dense cell concentrations, according to a 2007 paper in the Anatomical Review. These match up with a strange feature of the cetacean pupil: It closes like a smiling mouth, and when it's very tightly constricted, it has two small circular areas that remain open.
Contrast that with the way our eyes work: when they constrict, the larger circle of our pupillary opening simply becomes a smaller circle, still focused on the on the fovea. For a whale using its eyes, two distinct spots would be in the best focus. I think that is impossible to imagine what it might be like to have two centers to one's vision.
Trying to imagine what a whale might see becomes even more difficult when we take into account the actual eye positioning for most whales. Whale eyes are located on the sides of their heads. This is roughly the opposite of our own visual system. We have two eyes facing forward with a ton of visual field overlap. Or as Herman Melville wrote in Moby Dick, "For what is it that makes the front of a man -- what, indeed, but his eyes?" His narrator is staring at a sperm whale head, a lifeless version of the same creature that Austin the photographer encountered.
Looking at the eyes, placed on opposite sides of the head, Ishmael wonders about the whale mind relative to our own:
How is it, then, with the whale? True, both his eyes, in themselves, must simultaneously act; but is his brain so much more comprehensive, combining, and subtle than man's, that he can at the same moment of time attentively examine two distinct prospects, one on one side of him, and the other in an exactly opposite direction? If he can, then is it as marvellous a thing in him, as if a man were able simultaneously to go through the demonstrations of two distinct problems in Euclid. Nor, strictly investigated, is there any incongruity in this comparison.
It is no surprise that we use the same word for refracting light into a particular location as we do for directing our consciousness to a particular idea or object: focus. We focus our attention. But what if there are multiple points of focus -- not just the two eyes, but the two focal points on the retina. To grasp after Melville's question, how could an organism make sense not just of its visual surroundings, but, its own sense of coherence or conscious unity? (I imagine the 90s sitcom, Herman's Head, in which four separate characters live within one guy's mind.)
There is just so much difference to try to cross with a human mind.
I asked Peichl and Johnsen to speculate on what it might be like to have an eye on either side of your head, dual monocular vision.
"Perhaps the two eyes get very different parts of the visual field and environment. I don't know how they integrate that," Peichl said. "Usually in the brain... there is a high connectivity that connects the two hemispheres and makes that into a perceptual unity of just one continuous visual field. Something like that probably also exists in whales because they have to have some kind of perceptive unit of their environment, a unitary percept of their environment."
And Johnsen: "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.