Review : An Immense World (I)

It's time to review another book about animal senses. This time I'm going to try and minimise any philosophical discussions and keep things as brief as I can.

... I tried, I really tried. But I still ended up having to split this one in two. In this first post, I'll give the obligatory review and cover what Yong says about some more familiar, everyday senses : smell, vision, pain and hearing. In the next post I'll look at the weirder, more exotic senses : sonar, electromagnetic, and hydrodynamic.

The Review Bit

I was a bit worried that being of such a similar topic, Ed Yong's An Immense World would be a bit too similar to Jackie Higgin's Sentient. It's not. There is some overlap, but the two are largely complementary, each providing content that the other misses. Yong is sometimes a bit more skeptical than Higgins, but more focused on the senses of animals themselves. Whereas Higgins' goal is explicitly to make comparisons with human abilities, concentrating heavily on their raw capabilities, Yong tries to grasp the animals' own experiences, which Higgins only touches on here and there. Yong tries very hard to work out not just what animals are capable of, but what's actually important and relevant to them.

Yong can sometimes be just a tad accusative and judgemental ("the once-popular series Game of Thrones"), but also has a more emotive writing style without sacrificing one whit of detail or being overly-schmultzy. Conversely, Higgin's greatest strength is explaining the agonising efforts required to do real, hard science, examining the research process itself in a thoroughly engaging way, whereas Yong largely sticks to reporting the current findings (though he does summarise the process by which these were obtained and doesn't shy away from controversy).

If I had to choose, I'd give it to Yong. Though not as in-depth as Higgins, he still conveys the uncertainty of the scientific process sufficiently well, and describes additional senses that Higgins, thanks to her own remit of comparisons with humans, does not. And, though he does have one or two throwaway remarks which are just plain silly (and some parts where I strongly disagree), I find his writing style just a nudge... better. I happily give this one an outstanding 9/10.

Right, so what's the most interesting stuff in this wonderful book ?

The Umwelt

This is a very useful concept of, quite simply, the sensory experience of the world. There is only one external world, but everything perceives this differently. You might recall my own amazement at how butterflies can perform astonishing feats of precision agility despite having much worse vision than most humans; the book doesn't look at this example directly, but provides a good many clues to understanding how this is possible.

Different umwelts mean that no organism has a unique claim on a special knowledge of reality itself. Photons perform supremely well in some situations but are useless in others. Just because vision is our primary sense in no way gives it any special claim to be observing the "true" reality, and the attempt to grasp other umwelts is intrinsically fascinating, however limited it must be.

This did make me wonder if the analogy can be useful culturally. Human sensory umwelts are mostly similar to each other, but our cultural ones - especially politically - can seem at times to be totally different. What to one person seems like a laudable improvement can be to others a terrible corruption; or more basically, an obsessive football fan experiences an entirely different world to a virtuoso violinist. Perhaps this doesn't offer anything more than the standard filter bubbles / echo chamber analogy, but it did make me wonder.

Smell

I have to mention this if only because Yong answers Higgin's irritatingly-unanswered question : are dogs really much better at smelling than we are ? Higgins gets bogged down in quantification and fails to come up with a clear answer, whereas Yong says it directly : yes. He emphasises that trying to quantify it is a mistake. Knowing how many neurons an animal dedicates to smell, or even how complex or large its sensory apparatus is, doesn't really tell you much about how much of its unwelt is smell-based. Dog behaviour, however, unarguably demonstrates that smell is much more important to dogs than people, even if the human sense of smell is traditionally underrated.

Imaging

Animal vision is weird. Although it's been reported, motion blindness in humans is incredibly rare. But apparently in spiders it's perfectly normal for some eyes to be unable to register motion at all. In animals with larger numbers of eyes, they don't all just provide imaging of different areas but do qualitatively different tasks : some give different resolution, some are dedicated to motion, some are different to different wavelengths, some are better are seeing high contrast features, some are specialised for low-light conditions, etc.

Scallops take this to extremes. They may have a sort of "distributed vision" system which each eye contributes only a small part of the whole. But weirdly, their brains are so simple it could be that they don't actually perceive vision at all - rather they've outsourced all vision-related tasks to the eyes themselves. The eyes might be triggering the appropriate response (seek food, close shell, etc.) without any processing by the brain. Yong likens this to our sense of touch, in that this too doesn't build up a 3D picture of the world around it. But it's a bit of an odd comparison, and perhaps better would be the taste buds in our internal organs - they register something but we don't perceive their stimuli. To be fair, the idea of "nociception" - sensations which are registered but are consciously unperceived - is dealt with elsewhere.

Still, I'm not much persuaded that scallops could exist in a world of perpetual blindsight. Likewise some animals appear to create colours they themselves cannot perceive, while many animals appear to have abilities we would expect to require high resolution optics even though they don't. 

This suggests there may be compensating factors (beyond their additional senses). While human vision is pretty near the top of the tree in terms of angular resolution, we're mediocre in terms of processing speed : dogs are about 25% faster, birds can be more than twice as fast, while insects can be almost six times as fast as us. So many animals have, in effect, a lot longer to scrutinise a scene and work out what they're seeing. For a fly, we may appear as nothing more than a blur, but it can take its time to work out whether that blur is approaching dangerously or just passing by.

One other example of how the different umwelt can affect our understanding of behaviour : cows. Unlike humans they perceive their visual field with equal resolution and attention across their whole field of view. So they don't turn their heads to watch passers-by not because they're lazy or uncaring, but because they just don't need to.

Remember that next time you're out in the countryside. Even if they don't turn to look at you, the cows are always watching.

Colour

Initially I thought that Yong gave a very nice overview of colour perception. I felt stupid for not realising that colour is generated in the same way was astronomers define colour : by subtracting one wavelength band from another. And two of the three wavebands that humans are sensitive to are surprisingly similar, which makes me wonder why we didn't evolved to sense more different wavelengths - an obvious question that Yong strangely doesn't raise.

... and thinking about it now, I got carried away (this is one reason I find doing these write-ups so useful). Yong also says in a throwaway statement that colour and wavelength are interchangeable but this is just not true at all*. Sure, there may well be a strong correlation between wavelength and experiential colour, but it can't possibly be the whole story, and so by the same token, neither can opponency (waveband subtraction). Yong doesn't much mention illusions either. 

* Similarly he claims audio frequency has a perfect correlation with perceived pitch. I'm not sure about this. However, he mentions this in the section on smell, noting that there's no way to match chemistry with perceived odour, so he does at least recognise the key aspect of qualia.

In fact, the more I think about it the worse this gets. Someone pointed out recently that after-image colour illusions are the result of activity in the eye which continues after the original stimulus. So Yong contradicts himself by saying that colour perfectly correlates with wavelength and then describing it as opponency, and also fails to demonstrate how this works given that there are plenty of examples in which the brain creates different colours from the same input signal. At the least, colour is not uniquely generated by instantaneous local signals : the perceived colour of one small region is affected both by what we saw previously and what we continue to see in the surroundings. Yong doesn't mention any of this.

But let's move on. While it's well-known that some animals can see wavelengths we cannot, Yong reveals that UV vision is downright common - in fact, it's the norm. I wonder if the shorter wavelength also helps compensate for their otherwise poor resolution, since the shorter wavelength means a smaller diffraction limit, but Yong doesn't mention this.

More dramatically, since colour is (I guess at least in part) formed by opponency, the more wavebands you're sensitive to, the more colours you perceive. Dogs and cats are dichromats (they don't see in black and white, but they do see fewer colours than us), humans are mainly trichromats, but a few of us and some animals can see four wavebands - which would give them the potential of seeing hundreds of times more colours than we can.

That sounds pretty awesome, but Yong pours a bit of cold water on this. Amazingly, gene therapy can allow trichromatic male squirrel monkeys to become tetrachromats, with resulting tests showing that indeed they could perceive new colours. But it didn't change their day-to-day behaviour very much. Likewise the handful of tetrachromatic humans don't seem to be going around continuously staggering with awe and their kaleidoscopic explosion of unimaginable rainbows, because for them, it's normal. Without colours having some known meaning, seeing new colours is apparently no big deal.

Of course Yong also covers the mantis shrimp. Popularised by the Oatmeal because it has no less than twelve colour receptors, sadly the comic was premature. Tests show it's not great at distinguishing colours at all. The latest theory about what's going on is that it might be sensing colours in a totally different, in some ways simpler way : each waveband doesn't overlap much with the others, so it might be seeing just twelve discreet colours instead. True, it can see circularly polarised light, but apparently the only things it needs this for are for other mantis shrimp - otherwise, this remarkable sort of vision isn't actually much of a perceptual breakthrough; its view of the world is certainly different to ours, but not especially advantageous.

As in Sentient, it's clear that sensory organs can be repurposed and might not always work the way we think we do. For instance, while the heat sensors of beetles work remarkably like photomultiplier tubes - turning minute signals into substantial ones - those sensors are unrelated to their eyes and function completely differently. How do they actually perceive this ? 

Snakes are even more of a challenge. They have heat-sensitive pits of such fidelity that their heat sense alone is enough to guide them to a specific body part of their prey when blindfolded. But while infra-red is just a longer wavelength of light, again the pits don't seem to have anything to do with their eyes. Do they perceive images from the pits directly ? Does the brain combine it as another colour with the visual signals from their eyes somehow ? Or do they sense it in a completely different way altogether, not forming an image of any kind ? We just don't know.

Pain

Yong notes throughout that animals sense what they need to sense. We've already seen examples where animals can sense but not perceive, and pain and temperature exemplify this. The pain we feel from spicy foods just isn't experienced by some animals at all, possibly because they simply don't need to sense that. Likewise temperature. Our sense of what's warm and cold is not an absolute; in all likelihood, animals that live in conditions that feel unsuitable to us don't feel so to them.

Here Yong makes another of his extremely silly statements. He says that the "unfortunate persistence of dualism" is responsible for people equating "subjective" with "woolly" and "imagined". I think this is just stupid. If anything, dualism would be more ready to accept that a subjective experience is no less valid or real than a physical one. Likewise, he says that the complexity of the brain may impose a lower limit on brain size below which consciousness is just not possible, which I think is very far from convincing (Planta Sapiens is next on my reading list).

The moral question here is of course which animals feel pain. Here Yong is much more cautious. I frequently see knee-jerk claims on the internet that of course all animals can feel pain, but we ourselves don't automatically register all damaging sensations as pain - and for the important reason that this can help us extricate ourselves from danger before the pain becomes distracting.

Because we know that we can sense some things without consciously perceiving them, it is entirely credible to suggest that some animals might have no conscious experience of pain at all. Yong errs strongly on the side of caution, noting that while crabs have apparently rudimentary nervous systems, their behaviour clearly suggests they experience pain nonetheless; squid appear to feel the effects of injuries with their whole body even when the damage is localised. About the only firm conclusion here is that the experience of many animals is clearly different to our own. The sentiment I get from this section is that we should presume but verify that animals can feel pain, and shouldn't expect it to be the same as our own - after all, many of their other senses are demonstrably different.

Hearing

Perhaps one of the clearest examples of the importance of the umwelt comes from the treehopper. These little insects produce a veritable plethora of extraordinary sounds, from rumble like an alligator to a "half moo, half scream", or a "hooting monkey with mechanical clicks". And like wandering into a silent disco, we're totally oblivious to the whole thing - not because the sounds are too faint or the wrong frequency, or because they're rare or exotic, but because they transmit them through the surface vibrations of plants rather than through the air.

When you realise an animal has all this extra information on which to base its decisions, you can't help but re-evaluate its behaviour in terms of intelligence. Yong doesn't dwell much on cognition in the book but he makes a couple of interesting remarks here. First, he describes in some detail how spiders respond to vibrations on their webs. But he also notes that spiders are fully capable of adjusting their webs to respond differently to different prey : e.g., when hungry they can increase the sensitivity to smaller items. There's an interplay here : the sensitivity of the web determines what the spider will hunt, but the spider can itself decide what the sensitivity should be. So I might be willing to cautiously revise my earlier opinion that a spider's web does not count as extended cognition.

Second, while songbirds typically have regular calls consisting of repetitive sequences, that's apparently not always what's important to them. Just as sight operates at different frequencies, so too does sound, with birds being able to distinguish very much finer structures in the sound than we can. Apparently, for some species it's this fine structure which they're listening to, not anything as crude as the major order of the notes. So while it's often claimed that no animal species has a true human-like language, this may only be a human bias in us examining things which are important from our perspective : what matters to the animals can be completely imperceptible to us. They have a wealth of different and extra information they're sending and receiving, and it's this we need to consider, not what we experience with our own senses.

Not that we should go nuts with this. Some responses do seem to be purely instinctual; while I found Higgin's claims about pheromones to be lacking in detail, Young says that some crickets have a hearing system wired directly to automatically produce responses to the song's of the opposite gender. At least some behaviours have no real thought (or at least no agency or choice) behind them at all.

Those are the familiar sorts of senses, then. I've glossed over smell because Yong doesn't really add anything new to Higgins. And I'm leaving touch for the next post, as some animals use this in such a radically different way that it's barely recognisable in terms of the kind of touch we're familiar with. Already, though, we can see that animal umwelts can be dramatically different from our own, with a running theme being that this is dependent on what animals need to be able to sense : penguins probably don't feel cold in Antarctica but rather feel normal; animals that suffer no great harm from losing a limb or a tail probably don't feel the agonising pain that we would in a comparable situation. Next time I'll look more at how radically different the umwelt can really be.