Euro-update 4: Sperm whale perception
Tuscany is about the last place you might think to go to speculate about the visual system of a whale, but when you're spending three weeks relaxing in a secluded villa, you have a lot of reading time. I've been reading Moby-Dick.
Herman Melville describes the sperm whale with almost obsessive detail in the book, from the shape of its tail to the nature of its skin.
In one chapter, devoted to contrasting the head of the right whale and the sperm whale, we find amazing speculation about both the human and sperm whale visual system. Remember, this was published in 1851:
Far back on the side of the head, and low down, near the angle of [a] whale's jaw, if you narrowly search, you will ... see a lashless eye....
Now, from this peculiar sideway position of the whale's eyes, it is plain that he can never see an object which is exactly ahead, no more than he can one exactly astern. In a word, the position of the whale's eyes corresponds to that of a man's ears; and you may fancy, for yourself, how it would fare with you, did you sideways survey objects through your ears. You would find that you could only command some thirty degrees of vision in advance of the straight side-line of sight; and about thirty more behind it. If your bitterest foe were walking straight towards you, with dagger uplifted in broad day, you would not be able to see him, any more than if he were stealing upon you from behind.
It may be that our vision system is so entwined with our nature that it wouldn't be possible to be human and have a vision system like a whale's. Melville latches on to a crucial implication:
The peculiar position of the whale's eyes, effectually divided as they are by many cubic feet of solid head, which towers between them like a great mountain separating two lakes in valleys ... must wholly separate the impressions which each independent organ imparts. 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.
That final claim might be overstating things a bit, but Melville moves on to discuss the implications of this arrangement in a fascinating analysis:
So long as a man's eyes are open in the light, the act of seeing is involuntary; that is, he cannot then help mechanically seeing whatever objects are before him. Nevertheless, any one's experience will teach him, that though he can take an indiscriminating sweep of things at one glance, it is quite impossible for him, attentively, and completely, to examine any two things -- however large or however small -- at one and the same instant of time; never mind if they lie side by side and touch each other. But if you now come to separate these two objects, and surround each by a circle of profound darkness; then, in order to see one of them, the other will be utterly excluded from your contemporary consciousness. 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 it is as marvellous a thing in him, as if a man were able simultaneously to go through two the demonstrations of two distinct problems in Euclid. Nor, strictly investigated, is there any incongruity in this comparison.
That's a fascinating question. Might a whale, unlike a human, be able to attend to two different objects simultaneously? How would the whale's conception of the world then differ from our own? Would other senses come into play? Why would it be adaptive for a whale to have a massive blind spot directly in front of its body?
Discuss.
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I would hazard that for those of us living in the profound blackness of the ocean depths, the whale-sonar ability is the primary sense, not sight, and for the sperm whale, an object directly ahead is probably food being hurtled at through the murk at a speed and distance that precludes vision. I guess the sight is only useful for locating close objects such as children.
"I guess the sight is only useful for locating close objects such as children."
I found that to be quite a strange remark until I realised you meant baby whales.
Horses and other land creatures have this same type eye arrangement. How do horses run when they can't see straight forward?
If, as some suggest, whales were once land animals who moved into and adapted to the sea, then maybe at that time their eyes were closer together. Over time, maybe the sonar sense developed and the eyes became less important.
Does anyone know if sonar has a 'field of vision'? Perhaps the eyes now only serve as a complement to sonar, or in angles where sonar does not serve.
A horse can look forward, else with horse blinkers it would be blind. Where we use it to help the horse to focus what's happening in front of it.
I think a better comparison would be a chameleon as it/some have independent eye movement. But still it choses to have a blind spot, where as the sperm whale will always have a blind spot.
I thought about this quite a while ago, not realizing Melville had raised the question. The whale's perceptual arrangement is similar to that of a bull and other land-based herbivores. How does a charging bull target something? I finally realized that the answer is just the opposite of an attacking carnivore. The carnivore, which has stereo vision, knows it is on course when the object is in the center of its visual field. The bull, on the other hand, knows it is on course when it cannot see the target! Only then is the target straight ahead. If the bull can see the target out of either eye, it changes course until it can no longer see the target. The primary sensory medium for the sperm whale is, of course, its echolocation, which is directed in front of it. Vision has presumably assumed a subordinate status. Between the two sensory modalities, the whale probably has something close to 360º awareness in the horizontal plane.
Both horses and chameleons have side-mounted eyes, but their skull structure allows them doesn't obstruct a forward view. They don't have, as Melville puts it, "many cubic feet of solid head" between their eyes.
Whale sonar is focused into a beam in the direction of the head. Presumably if there is a blind spot, it would just be 'behind the animal'.
Loved "Moby Dick". Amazing how someone that long ago observed wales so closely to come up with such knowledgeable conclusions
But I think natural selection adapted every creature to survive in its environment, and for the whale the sonar abilities are more important than eyesight. From my reading whales have a U-shaped iris in bright light which becomes a circle in darkness and allows for pretty good vision. But most whales depend on echolocation to "see" their surroundings, and I'm wondering if the eyes serve as only additional limited vision of if the eyes in some whales are a fairly useless appendage like our tonsils or appendix.
Humans have no problem integrating the slightly different images received through binocular vision.They also integrate the dual sonic images received by either ear. The sonic images provide information about the nature of the sonic space, if not the precise location of various sound sources within that space. So why do we assume there is a difficulty in integrating the input from a whales two eyes? What difference does the vaster distance between the two eyes make? It must mean that it takes longer to form a comparison. Or maybe there is no utility to such a comparison, so whale brains don't waste effort making one?
We are amazed at Melville's perspicacity in thinking through the problems associated with the whale's visual system, but we shouldn't be. He wrote in the great age of exploration of the natural world, when close observation of flora and fauna laid the foundation for scientific advances of the twentieth century, and of our own time. Do we imagine Melville to be a less skillful observer, or thinker, than, say Darwin?
the sight is not the primary sense for whale or creatures living in depth. I think the related experience for human is - probably lets say, touch. We can experience touch at multiple place at same time and form a right perception of whats going on.
So the eyes of whale forms two distinct images and they both get processed, a touch sensation for us, and whale take appropriate action to deal with both.
Considering that whales and dolphins sleep one brain hemisphere at a time, it may be that they are also only using one eye at a time. That's not to say that they can't at some point be fully awake, I don't think, but they are never fully asleep. Of course, Melville didn't know this, but it adds an interesting twist to it all. How often are whales binocular? The Siegel Lab at UCLA has done some interesting studies on sleep in whales and dolphins if anyone is interested.
rabbits are the best comparison, as they have essentially no binocular vision at all (except possibly for a thin strip overhead, in the 3rd dimension). clearly, there's some value to getting "better coverage" at the expense of coordinated vision and depth of field -- rabbits are very visual (although obviously they also supplement with sound as whales do with sonar) and clearly good at both running and dodging...
I think there may also be a difference between what is seen by the whale, and what is perceived. After all, human eyes have blind spots, and yet we perceive no holes in our visual fields. Our brains automatically fill in the missing information.
We humans also lack the ability to see behind us, which the whale can (at least partially) do. Would the whale think "all behind the human must be profound darkness and nothingness to him", which, of course, is not the case?