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Comment by bbctol | Hacker News Reader

The gaps between animal understanding and human awareness are just as fascinating as the similarities, and I'm glad that someone's reminding us to push back on the "They're just like us!" narrative of how animals minds must work. One of the more influential texts I read in college was Daniel Povinelli's work on whether or not chimpanzees understand weight, basically concluding: they don't, at all. Scientists tried for thirty years to train chimpanzees to recognize weight as a separate property of an object, and failed spectacularly.

It's such a basic component of what it is to be aware of the world, and yet it's complex enough it seems a uniquely human faculty. Chimpanzees can sort objects by color, size, or shape, but not weight! how similar to humans can their internal experience be? (Or, of course, what aspects of the world are we missing that would be obvious to a slightly more complex intelligence?)

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Interestingly it's pretty easy to fool humans regarding weight too! [1]

Not necessarily trying to debunk your point, but it's just interesting to realize that things we take as "simple" can actually be quite complex -- like that we (at least partially) use visual information to judge the weight of an object. Often perceptual priors are very unintuitive. What is "natural" or "often seen in nature" heavily biases our perception of the world in order to resolve conflicting sensory information -- "light comes from above", "things that look the same have the same density", "the ground is perpendicular to gravity", etc. (This last one leads to the "magnetic hill" illusion which is very cool to experience! [2])

It's not surprising that animals can have trouble with these things, since we do too! Highly recommend looking up videos of people showing magic tricks to dogs ;)

[1]: https://en.wikipedia.org/wiki/Size%E2%80%93weight_illusion

[2]: https://en.wikipedia.org/wiki/The_Magnetic_Hill_(Canada)

I've always thought that humans don't perceive weight; instead, they perceive density.

Carry a heavy load of shopping and you'll perceive weight, not density. It doesn't matter how big the bag is; what matters is that the handles are cutting into your fingers...

... or, for a more HN-friendly example, astronauts on the space station would not experience any difference in space to being on earth - objects in orbit have no weight, but do have density.

Are you suggesting that chimps would persist in trying to carry something that's too heavy for them, because they don't understand the concept of "weight", as tested for by some study? I haven't read the study, but I'm pretty skeptical about that.

My thought is that, just as accounts of past decades have tended to place too much emphasis on avoiding anthropomorphism (i.e., imbuing animals with human traits), they have also erred, and probably continue to err, in the converse, thinking that human behavior is much more "rational" and "consciously controllable" than it actually is. In other words, animals are more like us than scientists thought forty or fifty years ago, and we also are more like them than previously thought (i.e., we are not as rational as we think).

> Carry a heavy load of shopping and you'll perceive weight, not density. It doesn't matter how big the bag is; what matters is that the handles are cutting into your fingers...

Pedantically, that's really pressure, not weight or density. (Though weight is a more direct contributor to pressure than density is.)

Actually, pedantically, "weight" is a "force", so it makes perfect sense to say we perceive weight when we carry something. Our arms must provide an equal and counteracting force to sustain the weight of objects we carry. "The weight of an object is usually taken to be the force on the object due to gravity. . . . " https://en.wikipedia.org/wiki/Weight

> Actually, pedantically, "weight" is a "force", so it makes perfect sense to say we perceive weight when we carry something.

Yes, but the "handles cutting into your fingers" is pressure not force.

We're getting a little silly here, but I think it's both force and pressure. Any force will exert a corresponding pressure (which is merely "force per unit area"). To say that we don't feel the force of weight except as a pressure is getting overly pedantic; we don't generally think of carried objects as exerting a certain pressure on us, we think of them as being more or less "heavy", i.e., as having weight. Okay, the explanation for specific case of fingers being cut (while getting no cut in other cases) depends on the weight being applied to small area. . . :) But it is still perfectly true that the weight of the object cuts the fingers.

Actually what the illusion I linked to shows is that we "perceive" density by estimating it visually, and this can trump what our muscles and skin tell us about the weight of the object by means of pressure. So the answer is "both": we estimate density and weight, and what we perceive is a combination of the two, adjusted (biased) by our priors.

Specifically, a larger object with the same actual density but the same visual appearance will feel "lighter" when compared. And it's a very strong illusion, in the sense that it works even if you know what's happening.. it's very hard to shake the feeling that the larger object is lighter even though they actually weigh the same.

> Or, of course, what aspects of the world are we missing that would be obvious to a slightly more complex intelligence?

Also, there are surely aspects of the world we miss which are probably clear to chimps or even insects.

Richard Hamming said "Just as there are odors that dogs can smell and we cannot, as well as sounds that dogs can hear and we cannot, so too there are wavelengths of light we cannot see and flavors we cannot taste. Why then, given our brains wired the way they are, does the remark, Perhaps there are thoughts we cannot think, surprise you?"

Because Turing completeness?

But certainly, there are no doubt emotions, habits, moral concepts, and even "thoughts" that are thoroughly foreign to humans. Not impossible, just foreign.

Turing completeness requires infinite discrete time steps and memory.

Like tuned instruments for a specific context. It's so natural for a fly system to swerve around in all direction, avoid many obstacles and land somewhere like it's tuesday.

Very surprising, I'll have to read that. I'm sure any moving lifeform has an understanding of weight since moving involves shifting one. Maybe it's just a very hard question to formulate to non humans ..

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