Human Actors Shouldn't Be Able to Speak Alien Languages

Isn't a little weird that humans can speak Na'vi? Or that aliens can learn to speak English? Or, heck, Klingon! The Klingon language is weird, but every single sound is used in human languages.

Of course, there's an obvious non-diegetic reason for that. The aliens are played by human actors. Actors wanna act. Directors want actors to act. It's less fun if all of your dialog is synthesized by the sound department. But while it is an understandable and accepted trope, we shouldn't mistake it for representing a plausible reality.

First, aliens might not even use sound to communicate! Sound is a very good medium for communication--most macroscopic animals on Earth make use of it to some extent. But there are other options: electricity, signs, touch, light, color and patterning, chemicals. Obviously, a human actor will not, without assistance, be able to pronounce a language encoded in changing patterns of chromatophores in skin, nor would a creature that spoke that language have much hope of replicating human speech. But since sound is a good and common medium of communication, let's just consider aliens that do encode language in sound.

The argument was recently presented to me that aliens should be able to speak human languages, and vice-versa, due to convergent evolution. An intelligent tool-using species must have certain physical characteristics to gain intelligence and use tools, therefore... I, for one, don't buy the argument that this means humanoid aliens are likely to start with, but supposing we do: does being humanoid in shape imply having a human-like vocal tract, or a vocal tract capable of making human-like noises? I propose that it does not. For one thing, even our closest relatives, the various great apes, cannot reproduce our sounds, and we can only do poor approximations of theirs. Their mouths are different shapes, the throats are different shapes, they have different resonances and constriction points. We have attempted to teach apes sign languages not just because they lack the neurological control to produce the variety of speech sounds that we do, but also because the sounds they can produce aren't the right ones anyway. Other, less-closely-related animals have even more different vocal tracts, and there is no particular reason to think they would converge on a human-like sound producing apparatus if any of them evolved to be more externally human-like. We can safely assume that creatures from an entirely different planet would be even less similar to us in fine anatomic detail. So, Jake Sully should not be able to speak Na'vi in his human body, and should not be able to speak English in his avatar body--yet we see Na'vi speaking English and humans speaking Na'vi all the time in those movies.

And that's just considering creatures that make sounds in essentially the same way that we do: by using the lungs to force air through vibrating and resonant structures connected with the mouth and nose. Not all creatures that produce sound do so with their breath, and not all creatures that produce sound with their breath breathe through structures in their heads! Intriguingly, cetaceans and aliens from 40 Eridani produce sound by moving air through vibrating structures between internal reservoirs, rather than while inhaling or exhaling--they're using air moving through structures in their heads, but not breath!

Hissing cockroaches make noise by expelling air from their spiracles. Arguably, this should be the basis for Na'vi speech as well: nearly all of the other animals on Pandora breathe through holes in their chests, with no obvious connection between the mouth and lungs. They also generally have six limbs and multiple sets of eyes. Wouldn't it have been cooler to see humanoid aliens with those features, and a language to match? But, no; James Cameron inserted a brief shot of a monkey-like creature with partially-fused limbs, no operculi, and a single set of eyes to provide a half-way-there justification for the evolution of Na'vi people who are just like humans, actually.

Many animals produce sound by stridulation. No airflow required. Cicadas use a different mechanism to produce their extremely loud songs: they have structures called tymbals which are crossed by stiff ribs; flexing muscles attached to the timbals causes the ribs to pop, and the rest of the structure to vibrate. It's essentially the same mechanism that makes sound when you stretch or compress a bendy straw (or, as Wikipedia calls them, straws with "an adjustable-angle bellows segment"). This sound is amplified and adjusted by passage through resonant chambers in the insects' abdomens. Some animals use percussion on the ground to produce sounds for communication. Any of these mechanisms could be recruited by a highly intelligent species as a means of producing language, without demanding any deviation from an essentially-humanoid body plan.

There is, of course, one significant exception: birds have a much more flexible sound-production apparatus than mammals, and some of them are capable of reproducing human-like sounds, even though they do it by a completely different mechanism (but it does still involve expelling air from the lungs through the mouth and nose!) Lyrebirds in particular seem to have the physiological capacity to mimic just about anything... but they extent to which they choose to imitate unnatural or human sounds is limited. Parrots and corvids are known to specifically imitate human speech, but they do so with a distinct accent; their words are recognizable, but they do not sound like humans. And amongst themselves, they do not make use of those sounds. Conversely, intraspecific communication among birds tends to make use of much simpler sound patterns, many of which humans can imitate, about as well as birds can imitate us, by whistling. So, sure, some aliens may be able to replicate human speech--but they should have an accent, and if their sound production systems are sufficiently flexible to produce our sounds by different means, there is no reason they should choose to restrict themselves to human-usable sounds in their own languages. Similarly, humans may be able to reproduce some alien languages, but they will not sound like human languages--and when's the last time you heard a human actor in alien makeup whistling? (Despite the fact that this is a legitmate form of human communication as well!)

The most flexible vocal apparatus at all would be something that mimics the action of an electronic speaker: directly moving a membrane through muscular action to reproduce any arbitrary waveform. As just discussed, birds come pretty close to capturing this ability, but they aren't quite there. There are a few animals that produce noise whose waveform is directly controlled by muscular oscillation which controls a membrane, but they are very small: consider bees and mosquitoes, whose buzzing is the result of their rapid wing motions (or, in the case of bumblebees, muscular vibrations of the thorax). Hummingbirds are much bigger than those insects, and they can actually beat their wings fast enough to create audible buzzing sounds (hence, I assume, the name "humming"bird), but they are still prety small animals. And despite these examples of muscule-driven buzzing, it seems rather unlikely that a biological entity--or at least, one which works at all similarly to us--could have the muscular response speed and neurological control capabilities to replicate the complex waveforms of human speech through that kind of mechanism. But if they did (say, like the Tines from Vernor Vinge's A Fire Upon the Deep), just like parrots and crows, why would their native communication systems happen to use any sounds that were natural for humans?

Now, some people might argue with my assertion that "any of these mechanisms could be recruited... as a means of producing language". That doesn't really impinge on my more basic point that an alien language should not reasonably be expected to be compatible with the human vocal apparatus, but let's go ahead and back up the assertion anyway. Suppose a certain creature's sound-production apparatus isn't even flexible enough to reproduce the kinds of distinctions humans use in whistled speech, based on modulating pitch and amplitude (which cicadas certainly can). Suppose, in fact, that it can produce only four distinct sounds. That should be doable by anybody that can produce sound ata ll--heck, there are more than 4 ways of clapping your hands. With 2 consecutive sounds, you can produce 16 distinct words. If you allow 3, it goes up to 80 words. At a word length of 4 or less, you've got 336 possible words. So far, that doesn't sound like very much. But then, there are 1360 possible words of length 5 or less, and 5456 of length 6 or less. At a length of 7, you get 21,840 possible words--comparable to the average vocabulary of an adult English speaker. The average length of English words is a little less than 5 letters, and we frequently (9 letters) use words that are longer than 7 letters, so needing to go up to 7 to fit your entire adult vocabulary isn't too bad. And that's before we even consider the ability to us homophones to compress the number of distinct words needed! So: we might argue about exactly how many words are needed for a fully-functional language with equivalent expressive power to anything humans use, but through the power of combinatorics, even small numbers of basic phonetic segments can produce huge numbers of possible words--indisputably more than any number we might come up with as a minimum requirement. A language with only four sounds might be difficult for humans to use, as it would seem repetitive and difficult to segment... but we're talking about aliens here. If 4 sounds is all their bodies have to work with, their brains would simply specialize to efficiently process those specific types of speech sounds, just as our brains specialize for our speech sounds.

Now, to be clear, this is not intended to disparage any conlanger who's making a language for aliens and using human-compatible IPA sounds to do so. It's an established trope! And even if it's not ever used in a film or audio drama, it can be fun. There are plenty of awesome, beautiful examples of conlangs of this type, and there's no inherent problem with making more if that's what you want to do. Y'all do what you want. But we should not mistake adherence to the trope for real-world plausibility! And it would be great to see more Truly Alien Languages out there.

On Mantis Shrimp, Butterflies, & Frogs

Previously, I discussed how to conceptualize the experience of organisms with different dimensionalities of their color spaces, along with a few other effects like the varying color sensitivy across different parts of the retina as seen in rabbits. But, as hinted out by the mention of Mantis shrimp at the end, multichromatic visual systems can actually get a lot weirder than that.

Even humans, and in fact most vertebrate animals you are likely to be familiar with, actually have a more complex visual system than our 3-dimensional color space implies. After all, we have four different types of light sensing cells in our retinas, and yet we do not have tetrachromatic vision! What is that fourth type--the rods--doing? Most readers will probably already know that rod cells are what give us low-light vision. Most of the time there is very little, if any, interaction between rod cells and our three types of cones: either it is too bright, rods are completely bleached, and we only get visual information from cones (known as photopic vision); or, it's too dark for cones to respond at all, and we only get visual information from rods (known as scotopic vision). In those sorts of low-light situations, humans become monochromats--we physiologically cannot see color in dim light! Our brains, however, are very good at lying to us, and filling in the colors that we know things should be. Unless, perhaps, you are small child who does not have a whole lot of experience with what colors things should be yet--a situation which once led to an adorable experience with my oldest child when he was very small. Once, when he had woken up early in the morning, I found him playing in his bedroom with a pile of balls, sorting them into "black ball!" and "grey ball!"; and then, when I turned on the light in the bedroom he gasped and said "Oh! Color!"

Incidentally, it is possible for each of these parallel visual systems to fail independently, mostly due to genetic conditions that inactivate either rods or cones. Humans lacking cone cells are rod monochromats and experience day blindness; humans lacking functional rod cells are nyctalopic and experience night blindness. And while most mammals are at least dichromats, armadillos, anteaters, and tree sloths are all rod monochromats, as are 90% of deep-sea fish species.

In between these extremes, there is range of mesopic vision, where both rods and cones have significant activity, and color perception gradually shifts as light levels get progressively darker or lighter. At no point do we incorporate rod cell data into the opponent process to get tetrachromatic vision, though; it's essentially used to augment luminosity information when cone cells start to struggle, causing a shift in the spectral sensitivity peak and altering apparent saturations.

Not all vertebrates handle dark vision in the same way, though, or have the same rod or cone sensitivity limits. Birds transition into scotopic vision at much brighter illumination levels than we do, as their color vision is sharpened by oil droplets that cut out noise at the tails of cone cell receptivity--but that also means that they waste more light, and so need more light to see color. Meanwhile, although most nocturnal vertebrates rely heavily on rods and tend to reduce their color perception or lose it entirely (which is why so many mammals are dichromats, and as mentioned above some are even rod monochromats--we lost tetrachromacy when our ancestors were nocturnal, and occasionally re-evolved trichromacy in more recent eons) nocturnal geckos don't have rods at all--they rely entirely on cone cells, which have simply evolved to be more sensitive than ours, and so retain a constant sense of color perception across their entire perceptive range of luminosity. (This is probably because they evolved from diurnal ancestors who had already lost their rods, as most diurnal lizards and some snakes have). In fancy terms, they have simplex retinas (containing receptors for a sngle integrated visual system), while we have duplex retinas (containing receptors for two parallel visual systems). Hawkmoths and nocturnal bees have parallel adaptions, with altered ommatidium geometry that improves light concentration onto individual receptors, for monoplex trichromatic low-light vision. But that's less weird and complicated than humans--what about more weird?

Toads and frogs, it turns out, have multiple types of rod cells, which are sensitive to even lower levels of light than human rods are. Which means they have genuine dichromatic vision in situations that would seem to us pitch black! In theory, there could be creatures that integrate their visual experiences across different light levels, using multiple rod types so that the brain has to lie less about what colors things should be in the daylight--but amphibians don't do that! Neither do they have a single 5-dimensional color space--rather, they have two completely independent color spaces, one dichromatic and one trichromatic, overlapping the same frequency range, which could in the correct conditions be perceived at the same time, but generally show up in different environments and are used for different purposes. Frogs and toads use their cone-based vision to identify food and mates, but they use their rod-based vision exclusively for navigation, with dichromacy allowing them to better distinguish directions based on different colors of light sources (incidentally, they prefer to jump towards high-frequency sources in light conditions, and towards lower-frequency sources in dark conditions).

Now Mantis shrimp provide the most famous example of optical complexity, but plenty of arthropods have large numbers of opsin types. Even daphnia, or water fleas, which don't even have image-forming eyes, are tetrachromatic in their ability to respond to the colors of light sources! Does this mean that butterflies with 8 receptor types are octochromats, with a 6-dimensional hue space? Well, no, for the same reason that frogs aren't pentachromats. Like dichromatic rabbits, creatures with large numbers of photorecptor types tend to have them localized in different parts of the visual field, to serve different purposes, and the signals are not neurologically combined to form a single coherent color space. Papilio butterflies, for example, which do have 8 different photoreceptor types, behave like tetrachromats when identifying flowers as food sources, but behave like dichromats (despite using 3 receptor types to form the relevant dichromatic retinal signals!) when selecting leaves for egg-laying. This kind of behavior-specific segmentation of visual systems means that in some species, different sexes actually have completely different visual systems, because they need them for different reproductive tasks! Which suggests some interesting sci-fi possibilities. And while daphnia are individually tetrachromatic, they have genes for many more than just 4 opsin types. If different sets of opsin genes were expressed in different individuals, the philosophical question "is what I call red really the same as what you call red?" would have an objectively-verifiable answer, as every different morph of the species (whether segmented by sex or caste or random variation) would have different color perceptions.

That brings us to the Mantis shrimp. With 12 different spectral receptor types, they could be doing a multiple-parallel-colorspace thing, like frogs and butterflies do. But... they aren't. As mentioned in that previous post, Mantis shrimp don't actually have particularly high spectral resolution, and they don't have the neural architecture to construct decorrelated opponent channels to produce a single perceptual color space. Instead, their large number of receptor types seems to exist to avoid the need for that kind of complex neural architecture! Instead, the Mantis shrimp visual system is built for speed and efficiency. Because of the spatial distribution of different receptor types into bands across their compound eyes, getting a full spectral profile on any given object requires mechanical scanning, which is relativey slow, but metabolically cheap; and wherever a given object falls in the visual field, determining whether or not it matches the spectral sensitivity of that region is instantaneous.

If Mantis shrimp were conscious, we might imagine their experience of color as being more analogous to our own perceptions of sound or taste. Mantis shrimp don't recognize abstract colors--they recognize specific fuzzy spectral patterns. Similarly, we have thousands of auditory hair cells that each respond to a specific frequency, but we don't uniformly group them into a kilodimensional "sonic color" space--we can selectively identify individual frequencies overlayed, or recognize particular spectral patterns of timbres and specific known source types. Taste and smell are similar; we have more than 400 types of olfactory receptors and at least 5 taste receptors, but we don't have a 405-dimensional experience of taste and smell (in fact, we don't know what the neurological dimensionality of human chemoreception is; to date, there is no model that can predict olfactory sensation from receptor activations). Instead, we can pick out individual receptor channels that are useful for specific purposes (sour helps us identify acids; bitter helps us identify poisons; salty helps us identify, well... salt; sweet helps us identify carbohydrates; and umami helps us identify proteins), and we can recognize specific fuzzy patterns that form the chemical signature of specific source types. For a good long time, western philosophy held that smell was "ineffable", and impossible to describe in language through any means other than "smells like a specific thing"; that turns out to be a symptom of western philosophers just not being bothered to try, though, and in fact there are many languages around the world which have generic olfactory terms disconnected from a specific source just as we have generic color terms. Statistical analysis of those language's vocabularies suggests that humans actually conceive of smells arranged in a two-or-maybe-three-dimensional space, where the major axes are "edible vs. non-edible" and "pleasant vs. unpleasant" (or "dangerous vs. safe"). Thus, durian is unpleasant but edible, ammonia is unpleasant and inedible (and dangerous), flowers are (generally) pleasant but inedible, and fruits are pleasant and edible. Languages which have generic olfactory terms generally have 12-16 of them--similar to the maximum number of basic color terms found in human languages.

So, a conscious alien species with Mantis-shrimp-like vision, or even a large number of parallel multidimensional color systems like butterflies have, might experience their spectral perceptions not in an analogous manner to our experience of color, but collapsed down into a small number of behaviorally-relevant dimensions. Is this the spectral pattern of something I can eat? Is this the spectral pattern of something dangerous? Is this the spectral pattern of something useful to me? Is this the spectral pattern of a potential mate? Etc. And depending on how important vision is to their culture (vision doesn't have to be an alien's primary sense just because it's ours!), they may consider the categorization and naming of generic colors to be completely ineffable, or totally normal--just disconnected from the raw physiological inputs which exist below the level of conscious awareness. 

But could there be creatures with extremely high dimensional color vision? Aside from the lack of evidence that they exist on Earth implying that high-dimensional vision probably wouldn't evolve elsewhere either, there are some practical arguments for why they shouldn't exist. Dichromatic vision permits distinguishing between objects and areas exhibiting predominantly higher-frequency vs. predominantly lower-frequency light, which is useful for picking out objects and against a background and general navigation, as seen in amphibians; however, because dichromatic vision conflates hue and saturation, it is not reliable for picking out specific wavelengths. While trichromatic vision can still be fooled by pairs of inputs that are indistinguishable from monochromatic light, it at least provides the possibility of identifying a unique spectral peak, giving us perception of the spectral colors. A lot of animal behaviors rely on this ability, such as the aforementioned Papilio butterflies which use a g-(r+b) opponent color signal to identify green leaves for egg laying, excluding objects which are too red or too blue; or apes and humans, whose trichromatic vision allows us to distinguish ripe, unripe, and overripe fruit (among other things!) as the peak reflectance shifts across the spectrum. Separating out the hue and saturation dimensions also gives us more information about the material properties of reflecting objects. So if trichromacy is alreadys so much better, why are there so many tetrachromats in the world? Well... we don't know. There are probably multiple contributing factors; trichromacy is mostly-adequate for disinguishing most ecologically-significant variation in most natural spectra, but tetratchromacy does reduce further reduce the possibility of spectral confusion. It may assist with color constancy--the ability to calculate what the color of a reflecting object "should" be under varying light conditions (although even dichromats can do that to some extent). Having more receptor types may provide better spectral resolution when covering a wider visual range--note that most tetrachromats can see further into the infrared and ultraviolet than we can. So perhaps pentachromacy or hexachromacy would be more useful to creatures that evolved in an environment with a different atmosphere that transmitted a wider band of potentially-visible light!

References:

Thresholds and noise limitations of colour vision in dim light
From spectral information to animal colour vision: experiments and concepts

Unconventional colour vision

Describing Non-human Vision

Thanks to LangTime Studio creating languages for a lot of mammals with dichromatic vision, I few years ago I did a good bit of research into how visual perception varies between different species. The issue of non-human vision came up again yesterday in George Corley's (of Conlangery fame) latest Draconic language stream, so I dug up some old notes on how to describe colors that you can't see. And in fact, this isn't just useful for conlangers trying to come up with vocabulary for a non-human language; this is good information for fantasy and sci-fi writers, too!

Since I started out with researching rabbits... let's talk about rabbits. It turns out that rabbit vision differs from human vision in just about every way that tetrapod vision can, so it makes an excellent case study. Rabbits have 2 types of color-receptive cone cells, corresponding to peak sensitivities in the green and blue ranges, and one rod cell type. I.e., they are dichromats, like most mammals. Rods don't contribute to color differentiation, so we can ignore those. At first glance, this seems similar to human red-green color blindness, except the peak sensitivities of the rabbit green cone and the red/green cones of a deuteranopic human are not in the same place! This is the first are in which human and non-human visual perception can differ--even other trichromats (e.g., penguins, honeybees) may not have the same spectral sensitivities as humans, and so see completely different color distinctions than we do. The rabbit cone sensitivities are shifted downward to a 509nm peak, compared to the human green cones with peak at 530nm, and red cones which peak at 560nm. Thus, not only can rabbits not distinguish red from green, but everything on the red end of the spectrum appears much dimmer than it would to a human, due to weaker response of the Long-Wavelength Cones to those spectral colors. Note, however, that not having separate cones for red and green does not mean that rabbits (or dogs, for that matter) would always see things-we-perceive-as-red and things-we-perceive-as-green as indistinguishable--it depends on the actual spectral signature of each object. For example, where we perceive two objects as having equal perceptual brightness but different hue, rabbits might perceive identical hue but lower perceptual brightness for the red object compared to the green.

Much like humans have an anomalous blue response in our red cones, which causes us to conflate purple (red+blue) and violet (a spectral color, extreme blue),  rabbit and rat green cones also have a
sensitivity peak in the ultraviolet. Initially, I assumed that, unlike the human anomalous blue response, UV light would be blocked by the structures of the eye, as it is for humans; however, while talking with a sci-fi writer friend of mine about non-human vision last night (as ya do, y'know), when I mentioned that rabbit and rat green-cone pigments have a weird bi-stable response to UV light, but UV is absorbed by mammalian eye tissue, so it's probably just a random non-conserved evolutionary quirk... he noted that UV is absorbed by primate eye tissue, but had I actually explicitly checked on rabbits? And I had not. So I did. And it turns out that that lapine corneal, lens, and vitreous humor tissues are considerably more transparent to near-UV light than human eye tissues are. Now, nobody (that I have been able to find) is actually saying outright that rabbits (or rats) can see UV... but rabbits might actually be able to see UV. If they can, it would be indistinguishable to them from green (not blue!) If it was not already clear from the shifted sensitivity peaks, I think that should highlight the impossibility of just taking, e.g., a JPEG image captured with equipment built for humans and transforming it into an accurate representation of what some other animal would see--if nothing else, the UV information would be completely missing!

Incidentally, if rabbits are UV-sensitive, the bistable nature of the UV response in their green cones means that they would actually be more strongly sensitive to UV in the dark than they are during daytime illumination. I have no idea what to make of that, as there isn't really a whole lot of
environmental UV going around at night or in tunnels... but that's a quirk you can keep in mind as a possibility for fictional creatures. In general, just note that spectral response can vary in different environmental conditions; in humans, we lose the ability to distinguish color entirely in low-light conditions (and your brain lies to you to fill in the colors that you believe things should be), but things can be more complicated than that.

Another interesting feature of rabbit eyesight is that they have a much less dense foveal region than humans (so less effective resolution), and their color-sensitive cells are not evenly distributed--there is a thin band with a mixture of both green and blue cones, with blue cones concentrated at the bottom of the retina (corresponding to the top of the visual field) and green cones concentrated at the top (corresponding to the bottom of the visual field). I.e., their vision along the horizon is in color, but the top and bottom extents of their visual fields are black and white, and specialized for better spectral response to the most common wavelengths of light coming from those directions--blue from the sky, green from the ground. This isn't too different from human peripheral vision (where color information is inferred by the brain, not actually present in the raw retinal output), except that in rabbits different parts of the peripheral fields actually have a different peak spectral response! In wild rabbits, this is probably just an adaptation to getting the maximum information out of a predominantly-blue-background sky and a predominantly-green(/red)-background ground, but intelligent rabbits could theoretically learn to extract additional color information (e.g., distinguishing monochromatic white from dichromatic white) from an object by wiggling their eyes up and down or tilting their heads to put it in different parts of the visual field. Or not, if their brains just fill in missing color information automatically like ours do.... But if you want to write about creature that can do that, by authorial fiat, they could have a whole auxiliary class of color words, analogous to pattern words like "speckled" or "sparkly", to describe objects that have different appearances in different parts of the visual field.

But, if we abstract away from physiological perceptual abilities, what would their experience of color space be like? Tetrapod retinas pre-process raw cone cells signals into antagonistic opponent channels before color information gets sent to the brain; i.e., what your visual cortex has access to is not the original cone cell activations, but sums and differences of the activations of multiple types of cone cells. In human eyes, that means our brains see color coming down the optic nerves as a combination of red vs. green and blue vs. yellow signals--even though yellow isn't actually a physiological primary color! In dichromats like rabbits, the two raw spectral signals (green and blue) are still
processed by an antagonistic opponent system in the retinal ganglia; thus, just like we can't perceive the impossible colors "reddish green" or "yellowish blue", they cannot have any perception of a distinct blue-green mixture--dim dichromatic light at both spectral peaks will look exactly the same as bright monochromatic light exactly in between, which will be indistinguishable from white. In effect, the loss of one cone type compared to humans reduces the color space from 3 dimensions to 2, and the perceptual dimension that is lost after ganglial processing is that of saturation.

The lapine color space is thus defined by a 2D, triangular range with black at one vertex, white (or whatever you want to call it) at the center of the opposite edge, and pure green and pure blue at the
remaining vertices. The hue and saturation axes are the same, with green fading into white and then white fading into blue.

If the most basic colors are defined by the extrema of the opponent-process space, as they are for humans, there should be 3 basic colors, corresponding to black, blue, and green. White would be
the natural next step, followed perhaps by light and dark shades of blue and green. Or you could call the green extremum "yellow" instead, as the Long Wavelength Cone still has sensitivity into the yellow and red ranges of the spectrum, even though its peak is in green, as I have done in the image above. Fundamentally, the 3D human color space and 2D dichromat color spaces are mathematically incommensurate, so all human-perceptible representations involve some arbitrary choices anyway. Treating the long-wavelength end as "yellow" rather than "red" makes is convenient if you want to do something like copying the Old Norse poetic convention of treating blood and gold as being the same color. :)

We can squish and stretch that gamut to get a representation of the dichromat color wheel, with a radial saturation axis and polar hue and brightness:

And the sort of Cartesian representation that an intelligent dichromat graphic designer would use to pick out colors in a computer graphics program:

Keep in mind that the actual colors used in these illustrations are completely arbitrary, aside from being "towards the long-wavelength end" vs. "towards the short-wavelength end". What matters is just the set of possible distinctions. Figuring out exactly what lapine colors any particular object would correspond to would require recording the actual emission spectrum of that object, and then mapping it into the rabbit color space--and being dichromatic does not merely mean that they see a subset of the colors that we can see; the available distinctions are different. E.g., two objects which look identically purple to a human may be monochromatic in the violet spectral range, or they may be dichromatic with light in the
blue and red ranges, but those two objects will look distinct to a rabbit--the first one being obviously pure blue, the second being light blue or white.

So, that's dichromatism... what about tetrachromatism, or higher? My best reference on this subject is this absolutely lovely article: Ways of Coloring: Comparative Color Vision as a Case Study for Cognitive Science, which contains descriptions of comparative color spaces for humans, bees (also trichromats, but with different frequency response), goldfish, turtles (both of which are tetrachromats), and pigeons (suspected pentachromats). And it has an excellent statement of what the problem actually is:

It is important to realize that such an increase in chromatic dimensionality does not mean that pigeons exhibit greater sensitivity to the monochromatic hues that we see. For example, we should not suppose that since the hue discrimination of the pigeon is best around 600nm, and since we see a 600nm stimulus as orange, pigeons are better at discriminating spectral hues of orange than we are. Indeed, we have reason to believe that such a mapping of our hue terms onto the pigeon would be an error: [...] 

Among other things, this result strongly emphasizes how misleading it may be to use human hue designations to describe color vision in non-human species. This point can be made even more forcefully, however, when it is a difference in the dimensionality of color vision that we are considering. An increase in the dimensionality of color vision indicates a fundamentally different kind of color space. We are familiar with trichromatic color spaces such as our own, which require three independent axes for their specification, given either as receptor activation or as color channels. A tetrachromatic color space obviously requires four dimensions for its specification. It is thus an example of what can be called a color hyperspace. The difference between a tetrachromatic and a trichromatic color space is therefore not like the difference between two trichromatic color spaces: The former two color spaces are incommensurable in a precise mathematical sense, for there is no way to map the kinds of distinctions available in four dimensions into the kinds of distinctions available in three dimensions without remainder. One might object that such incommensurability does not prevent one from “projecting” the higher-dimensional space onto the lower; hence the difference in dimensionality simply means that the higher space contains more perceptual content than the lower. Such an interpretation, however, begs the fundamental question of how one is to choose to “project” the higher space onto the lower. Because the spaces are not isomorphic, there is no unique projection relation.

It is also the case that lower-dimensional color spaces, such as those of dogs or rabbits (both dichromats, but in slightly different ways) are incommensurate with our 3D color space, in exactly the same way that our 3D color space is incommensurate with the higher-dimensional perceptions of a pigeon, turtle, or goldfish, and have no unique projections. Thus, visualizations of how your dog or cat sees things are always only approximations--we can try to recreate the kinds of distinctions relevant to a dichromatic animal in our own color space, but we will always experience it differently.

A common feature of all of the systems described is the production of a combined luminance channel from the raw n-dimensional cone cell inputs, and n-1 oppositional chroma channels--in humans, these are the red-green and blue-yellow oppositions, which produce a two-dimensional neurological color space othogonal to the luminosity axis. The YCbCr color space (used for analog color TV transmission) arises from representing the two chromatic dimensions directly in Cartesion coordinates. Saturation arises as the radial dimension--distance from the white-black axis--in a polar transformation of this oppositional color space to produce the trichromat color wheel, with hue arising as the radial coordinate. Trichromat color spaces for different species can vary both in their precise spectral sensitivities, and in how the oppositional chroma channels are generated in the retina; i.e., instead of an RG-B apposition, where R and G physical channels combine to produce Y, there can also be an R-GB opposition: red-cyan vs green-blue. For us, there's no such thing as reddish-green (nor blueish-yellow), because yellow comes in between, but we do have blueish-green. For that other sort of trichromat, reddish-green would make perfect sense, but blueish-green and reddish-cyan would be impossible to perceive instead.

Monochromatic vision is pretty easy to understand--it's just black-and-white / greyscale--luminosity is the only dimension, and leaves zero additional channels for chroma information. As illustrated above, in dichromat vision, the equivalent of the trichromatic color "wheel" is just a line--the radial dimension is not meaningfully distinct from the single linear chromatic dimension, and while we require an additional axis to represent brightness, the dichromat color wheel really does represent every color they can possibly see. As a result, "saturation" and "hue" (or, alternatively, brightness and hue) are indistinguishable to dichromats, and grey (or white, depending on whether you represent the space as a triangular gamut or a Cartesian diamond) is a spectral color. There are only two primary colors (or 4, if you count white and black), and no secondary colors.

In higher-dimensional color spaces, as determined by discrimination experiments on tetrachromatic and pentachromatic organisms, we still see the generation of oppositional color channels from retinal processing. How to generate these oppositional channels, however, is not obvious a-priori; for example, in humans one opposition is between red and green, both of which are primary colors, but the other is between blue, a primary color, and yellow, a composite--and, as mentioned above, that could be reversed in a different species with different specific spectral sensitivities. But why that particular combination for us?

It turns out, across different species, opponent channels are constructed to maximize decorrelation--in other words, to remove redundant information caused by the overlapping response curves of different receptor types. Thus, the precise method of calculating color channels will be slightly different for each species, dependent on physical characteristics of the retinal cells, but they are all qualitatively the same kind of signal, and end up producing a a higher-dimensional chroma-space orthogonal to the white-black luminosity axis. However, there's pretty good reason to believe that this would be a convergently-evolved process to maximize visual acuity (except in some specific circumstances like Mantis shrimp), so this analysis of color perception plausibly applies universally, to most kinds of weird aliens you might come up with, so long as they have eyes at all. Effectively, the retinal ganglia are performing Principle Component Analysis to turn "list of specific frequency activations" information into "total luminosity vs. list of chroma components" information.

Meanwhile, in any such neurological color space, there is only ever a single radial coordinate. Trichromatic vision is kind of special in that it is the first dimensionality at which chroma can be split into saturation and hue components. At higher dimensionalities, the hue space gets more complex, but we can say with some confidence that the extra dimensions introduced in higher-dimensional perceptual color spaces are not some extra sort of radial-coordinate saturation or any kind of weird third thing, but are in fact additional dimensions of hue--and along with extra dimensions of hue, qualitatively different kinds of composite colors!

Monochromats don't have any color. Dichromats don't have any secondary colors--just the spectral colors which, strangely to us, include white/grey. Our three dimensional human color space allows us to perceive two opponent channels, corresponding to 4 pure hues--red, yellow, green, and blue--and weighted binary combinations thereof that give rise to the secondary colors--r+y (orange), y+g (chartreuse?), g+b (cyan), and b+r (magenta), with one non-spectral hue (magenta). Non-spectral colors derive from simulataneous activation of cones with non-adjacent response peaks, and with three cones, there's only one such possibility. Meanwhile, a tetrachromatic system would have 3 opponent axes with 6 basic hues (r-g, y-b, and the new p-q), binary combinations of those hues with their non-opponents producing 12 secondary colors (r+y, r+b, r+p, r+q, g+y, g+b, g+p, g+q, y+p, y+q, b+p and b+q), and ternary combinations producing 8 extremal instances of an entirely new kind of hue--tertiary colors--not found in the perceptual structure of trichromatic color space (r+y+p, r+y+q, r+b+p, r+b+q, g+y+p, g+y+q, g+b+p, g+b+q), just as our secondary colors are not found in the dichromatic space. Additionally, there is not merely one non-spectral secondary color (magenta) in the fully-saturated hue space, but 3--and in general, that number will correspond to however many pairs of non-spectrally-adjacent sensor types there are (which actually works out to the sequence of triangular numbers!) If we assume that r, g, b, and q are the physiological primaries (note that the spectral locations of y and p depend on the decorrelation output for a specific set of 4 receptors with species-specific sensitivities), then the non-spectral secondaries are r+b, r+q, and g+q. All of the tertiary colors are non-spectral.

Ultimate writer takeaway: you may not be able to intuitively understand what non-human color experiences are like, but you can make some arbitrary implicit decisions about retinal physiology (i.e., just decide where you want to the opponent colors to appear along the spectrm), do some basic combinatory math, and then you have a list of descriptions of basic focal colors that you can assign words to--or, if you want to be a little more realistic, assign words to ranges of those focal colors, which you can precisely mathematically describe. This gets more complicated at higher dimensionalities (like pigeons' pentachromatic color space), but tetrachromacy is kind of convenient because you still have only 2 dimensions of hue, so you can actually diagram out what the color regions are, and just tell people "y'all already know how brightness and saturation work, so I don't need to put those on the chart".

Someday, I aspire to have a program where you can input the physiological frequency response curves for an arbitrary organism, and a spectrum, and it'll give you the mathematical description of the perceptual color that that would produce. But till then, you'll just have to do your best at guessing what the aliens and monsters and anthropomorphic animals see whenever a human thinks something is a particular color--but guess informedly, knowing what the structure of their color spaces is like!

P.S. What was that about Mantis shrimp? Well, Mantis shrimp have 16 different light receptor types, with 12 different color receptors, which kinda suggests that they should have a 12-dimensional color space with 10 dimensions of chroma. But... empirically, that's not what happens. Experimentally, they don't actually have all of those different color categories, or a particularly fine capacity for spectral distinction. Rather, they have a large number of different receptor types so that they can identify spectral colors at high speed, without doing any retinal pre-processing--chartreuse cone fires? Cool, that's a chartreuse thing! No need to bother with oponent processing! These kinds of extreme high dimensional visual systems might end up working more like our senses of smell or taste than like our perception of color. However, there's also another aspect of Mantis shrimp vision that's outside of color perception (and not entirely unique to Mantis shrimp, either): they can see polarization (hence the 4 visual receptor types that aren't for color, rather than just 1). This ability is comparatively easy to imagine and describe--it's an overlay of geometric information, that tells you "not only does this light have a particular color, it is also oriented in a particular way". Mantis shrimp are, however, unique in being able to distinguish circularly polarized light; other creatures with polarization sensitivity would be unable to tell circularly polarized from unpolarized light.

Stridulation in Landscape with Invisible Hand

Landscape with Invisible Hand is a 2023 sci-fi film based on a book of the same name from 2017, taking its title from a work of art created by the protoganist in the story. It is set in a world that has been economically colonized by aliens known as the Vuvv--though it is unclear where that name comes from, as their language is unpronounceable by humans. And, that's why we're doing this review!

The sounds of the Vuvv language are produced by stridulation--rubbing together pads on the ends of their appendages.

A Vuvv, seen rubbing pads together mid-sentence.

The Vuvv in the film are seen making a wide variety of articulatory gestures, which suggests the possibility of a range of distinguishable stridulation sounds which could form the basis of a phonemic inventory. However, this variety is not reflected in the accompanying audio. According to IMDB,

The unique sound of the alien Vuvv language was created using dried out coconuts with nails in them, rubbed against mossy rocks.

The inspiration for the sound of the alien Vuvv language came from a line in the book that the film is based on that describes the Vuvv language as "someone walking forcefully in corduroys."

Now, there is no inherent reason why a fully fleshed-out language could not be articulated by rubbing coconuts with nails in against rocks... but between the experience of actually listening to the film, and the fact that IMDB doesn't list any language creator or consultant in the credits, I'm pretty sure they didn't bother. Also note that Vuvv language lessons for humans are a thing in the film, so we know that the relevant acoustic patterns are audible to humans, and it's not a matter of just not bothering to represent stuff that is theoretically there but not perceivable by the human characters or audience, as would be the case in, for example, a film adaptation of Little Fuzzy. (It's possible that the glyphs for Vuvv writing actually mean something, but I don't have high hopes for that.) Awesome idea for an alien language, and the presentation of the fictional language works for the film, but it's a little disappointing that there isn't more there. On the other hand, if Phil Lord and/or Chris Miller are reading--hey, you still have a chance to make Project Hail Mary the first major film to feature a fully fleshed-out alien language not pronounceable by human actors! And it would really be a shame to deprive audience of the opportunity to learn to recognize Eridian words right alongside Ryland Grace...

But anyway, back to Landscape--there's really just one consistent choice of integration techniques to make the Vuvv dialog comprehensible to the audience. It's 100% diegetic translation, which is carried out automatically by translator boxes that allow the characters in the scene to understand the Vuvvs talking to them. Meanwhile, all of the Vuvvs we see on-screen seem to be receptively bilingual--they can't pronounce human languages, just we can't pronounce theirs, but they can comprehend English when spoken to. This arrangement actually works out really well--since translation is necessary for the characters, this nicely avoids the need for any additional integration mechanisms just for the sake of the audience. I.e., we don't need to worry about the possible need for subtitles. And that's a darn good thing, because a few possible integration techniques are taken off the table by the simple fact that this is a fully fictional language, rather than an artificial-but-real conlang--there is no meaning actually encoded in the Vuvv speech, so there's no way to expect the audience to extract what isn't there!

So, while I am disappointed at the lack of depth, we can take at least two good lessons from this film:

1. Certain settings and stories lend themselves naturally to specific secondary-language integration techniques, and theoretically you could consciously choose to structure your story to take advantage of a particular technique. (I don't know if this is the case, but I would not be surprised if that was the case here--maybe they gave everybody translator boxes specifically to avoid having to do subtitles?)
   
2. Stridulation! Man, I'd love to see someone tackle this as a modality for a real alien conlang.

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The Linguistically Interesting Media Index

A Loudspeaker-Compatible Photo-Phonology

Last weekend, I gave a talk at the 10th Language Creation Conference on creating languages that do not use the human voice, in which I went over four case studies of successively more-alien phonologies. (One of which I have previously blogged about here.) Israel Noletto called it a "must-watch" for any speculative fiction writers putting created languages in their stories! Turns out, I had extra time, and could've talked about a fifth... but when I put together my abstract, I thought I'd be hard-pressed to fit 4 case studies in half an hour, so I cut it out. And so, I shall now present case study #5 here, in blog form!

After noodling over the cephalopod-inspired phonology for a while (for context, go watch my talk), it occurred to me that human sign languages and cephalopod communication have in common the feature that you can't flood an area with a linguistic signal the way that you can with a disembodied voice from a speaker system--they have to be displayed on a screen with a certain defined spatial extent, and even if it's a very big screen, the components of the signal are still not evenly distributed throughout space.

So, could we create a light-based language that is broadcastable in the way that audio-encoded languages are? And what sort of creature could evolve to use such a system? Well, trivially, yes, we can--just encode the existing language of your choice in Morse code (or something equivalent), and pulse the lights in a room in the appropriate pattern. Heck, people actually do this sometimes (although more often in thriller movies than in real life). But designing a language whose native phonology is Morse code is just... not that interesting. It doesn't feel materially different from designing a language to use the Latin alphabet, for example. We need more constraints to spark creativity here! So, what else could we do to more directly exploit the medium of non-localized light? In Sai's terms, how could we design something that is natural to the medium?

A first thought is that light and sound are both wave phenomena, and one could just transpose sound waves directly into light waves, and use all the same kinds of tricks that audio languages do... except, it turns out that continuously modulating the frequency of light is considerably harder than modulating the frequency of sound. We can do it with frequency-modulated radio, but that's still not how we actually encode audio signals in radio, and similar technology just doesn't exist in the visible range. And if we look at how bioluminescence actually works in nature, no known organism has the ability to continuously modulate the frequency of their light output; they have a small number (usually just one) of biochemical reactions that produce a specific spectrum, and that's it.

But, a bioluminescent creature could do essentially the same thing we do with AM radio: ignore the inherent wave properties of the carrier signal entirely, and vary the amplitude over time to impose a secondary information-carrying waveform, which can be considerably more complex than the binary on/off of Morse signals, and can in fact have its own frequency and amplitude components. That doesn't mean high-contrast flashes couldn't still be involved--going back to nature again, the intraspecific visual signalling of fireflies, for example, is very Morse-like. But it can have more complex components, resulting in a higher bitrate that feels more suitable for a language that's on par with human languages in utility and convenience. Biological signal modulation can be done by controlling the rate of release of certain chemicals (e.g., the rate at which oxygen is introduced into a firefly's light organ to react with luciferin), or by physical motion of shutters to occlude the light to varying degrees (a common mechanism among, e.g., bioluminescent fish whose light is produced by symbiotic bacteria).

So, now we have a single-channel frequency-and-amplitude-modulable signal; the next obvious analogy to explore (at least obvious to me) is whistling registers (again, for context, go watch my talk, or listen to the Conlangery episode on Whistle Registers in which I talk about my conlang Tjugem). However, we can't directly copy whistling phonology into this new medium, precisely because we are ignoring the wave nature of the carrier signal; for a creature with a high visual flicker-fusion rate, perceivable modulation frequencies could be fairly high, but still nowhere near the rate of audio signals; rather, frequency information would have to occupy about the same timescale as amplitude information. In other words, varying "frequency" would give you a distinction between amplitude changes that are fast vs. slow, but it would be much harder to do things like a simultaneous frequency-and-amplitude sweep and keep each component distinguishable, the way you can with whistling. You could do it with flickering "eyelids" or chemical mixing sphincters (or, as Bioluminescent backlighting illuminates the complex visual signals of a social squid in the deep sea puts it, "by altering conditions within the photophores (41) or by manipulating the emitted light using other anatomical features")--trills in human languages introduce low-frequency components of about the right scale--but just as the majority of phonemic tokens in spoken languages are not trills, I would expect that kind of thing in a light-based language to be relatively rare. (Side note: perhaps audio trills and rapid light modulation could both be considered analogous to cephalopod chromatic shimmer patterns.)

So, the possibilities for a single-channel light-based phonology are not quite as rich as those for a whistling phonology, although the possibility of trilling/shimmering does help a bit (even though, AFAIK, no natural whistle register makes use of trilling). But, while the number of channels available to a given bioluminescent species will be fixed, the number of channels that we choose to provide when constructing a fictional intelligent bioluminescent creature is not! And if they have multiple light organs that allow transmitting on multiple different color channels simultaneously, then just two channels would allow them to exceed the combinatorial possibilities of human whistle registers.

Using this sort of medium for communication would have some interesting technological implications. Recording light over time is in some ways much more difficult than mechanically recording sound, but reproducing it is trivial. Light-based semaphore code systems for long-range communication with shuttered lanterns might be a blatantly obvious technology very early in history; and even if it cannot be mechanically recorded, if someone is willing to sit down for a while and manually cut out the right sequence of windows in a paper tape, mechanical reproduction of natural-looking speech could also occur at a very low tech level (especially if the language is monochromatic). Analog optical sound is in fact a technology that was really used in recent human history, and the reproduction step for a species using optical communication natively would be much simpler than it was for us, as there's no need for them to do the translation step from optical signal back into sound.

Now, there's a lot of literature on animal bioluminescence, but not a ton on specific signalling patterns used by different species... except for fireflies. So, if we want to move away from abstract theorizing and look at real-world analogs to extract a set of constraints for what a light-based language might look like, borrowing from firefly patterns is probably our best bet. Additionally, and in line with modelling off of fireflies, I am going to avoid using polychromatic signals, and see just see how far we can get with a single-channel design. After all, I already looked at a multi-channel / multi-formant signal system in the electroceptive phonology of Fysh A. I won't be sticking strictly to firefly patterns, because fireflies pretty much only use flashes, without significant variation in amplitudes, and that would end up being very Morse-like. However, per the US National Park Service, there are some interesting variations in the flashing patterns seen in various species; for example:

• Long, low-amplitude glows (not really a flash at all).
• Single, medium-amplitude flashes with long gaps.
• Pairs of medium-amplitude flashes.
• Trains of medium-amplitude flashes.
• Single high-amplitude flashes ("flashbulbs").

I see a pattern going on here that may just be a coincidence, but seems like a plausible restriction on a bioluminescent alien: for a creature like a firefly which is using its own metabolic resources to produce light, rather than relying on symbiotic bacteria, there may be a maximum average rate at which power can be delivered to photophores, thus implying that, while you can glow at a low level indefinitely, brighter flashes, using more power all at once, entail a longer recovery period between flashes to "recharge". So, IF. YOU. ARE. SHOUTING. YOU. MUST. SPEAK. SLOWER. This is analogous to the amplitude-frequency dependence seen in the Fysh A electroceptive phonology.

So, let's go ahead and define three amplitude bands that phonemic segments might occupy, analogous to the frequency bands that organize whistling phonologies:

1. A low band, which allows continuous glows and smooth waves.
2. A middle band, where we have to pause between blinks, but we can blink fast enough for multiple blinks to constitute a single segment.
3. A high band, where recharge pauses are too long for sequential blinks to be interpreted as a single segment.

These are sort of analogous to "places of articulation". Then, we can also define attack/decay characteristics for each blink--something like "manners of articulation":

1. Slow attack vs. hard attack
2. Slow decay vs. hard decay--only available in the low band; the upper bands only allow hard decay, since they use up all the luciferin!

And, furthermore, we can have a distinction between:

1. "Tapped" -- a single amplitude peak.
   
2. "Trilled" -- two or more close-spaced amplitude peaks (not available in the high band)

And, in the low band only, a unique distinction between short peaks and long peaks.

So, now we can map out the complete set of distinctive segments that might exist--the alien IPA!

1. Low
1. slow, short, slow, tapped
2. slow, short, slow, trilled
3. slow, short, hard, tapped
4. slow, short, hard, trilled
5. slow, long, slow, tapped
6. slow, long, slow, trilled
7. slow, long, hard, tapped
8. slow, long, hard, trilled
9. hard, short, slow, tapped
10. hard, short, slow, trilled
11. hard, short, hard, tapped
12. hard, short, hard, trilled
13. hard, long, slow, tapped
14. hard, long, slow, trilled
15. hard, long, hard, tapped
16. hard, long, hard, trilled
2. Mid
1. slow, tapped
2. slow, trilled
3. hard, tapped
4. hard, trilled
3. High
1. slow attack
2. hard attack

And we could also have phonemic lengthening of the darkness following a hard decay for the tapped segments in the lower bands, which would give us an additional 10 possible segments, for a total of 32. Note that there's not really anything here that corresponds to "vowels". You might try to think of the low+long or low+slow-decay+trilled segments as vowels, or at least continuants, but they don't have the amplitude peaks that we would typically associate with human vowels as syllable nucleii. In fact, the whole basis of human syllable structure is missing! Instead, we might organize segments into larger units based on what kinds of segments can start or end those units--kind of like I did in Fysh A with initial and non-initial segments. The higher amplitude bands make it harder to follow up quickly with additional segments, so it would make sense if those are finals in larger, syllable-analogous units, and we end up with alien syllables that terminate in amplitude peaks rather than having them in the middle--kinda like all of their syllables are "CV" (but recall that we don't actually have a good analogy for vowels here!)

Now, with 32 different possible segments to choose from, with varying degrees of distinctiveness, not all languages in this phonetic space will use all of them, or choose exactly the same subset--just like human languages don't all use every possible human spoken phone! In particular, the low-band segments will be the most difficult to distinguish on average, due to being the "quiet"-est, so I would expect languages to vary significantly in exactly which low-band segments they utilize.

For purposes of this sketch, I'll select the following phonemes for maximal distinction:

1. Low
1. slow, short, slow, trilled - <w>
2. slow, long, slow, tapped - <r>
3. hard, long, slow, tapped - <t>
2. Mid
1. slow, tapped - <d>
2. slow, trilled - <rr>
3. hard, tapped - <k>
3. High
1. slow attack - <b>
2. hard attack - <p>

Plus long <tt> and <dd>, exploiting the geminated-darkness feature, giving us a total of 10 distinct phonemes. As in the canine phonology sketch, that's not a ton (actually less than occur even in Rotokas, with its famously small phonemic inventory), but if we look at organizing the language in terms of possible syllables rather than possible segments, things look better. If we specify that every syllable must have a rise from a dark segment to a bright segment, and terminates with the brightest segment, as soon as we see a drop, then we get the following possible syllable types:

L>M: 16 possible syllables
L>H: 8 possible syllables
L>M>H: 32 possible syllables
M>H: 8 possible syllables

For a total of 64--and that's without allowing multiple segments of a single type per syllable! If we allow clusters of low or mid segments, we get multiplicative gains. Again, different languages of this same theoretical species could vary in what kinds of clusters they allow, just as, e.g., Russian differs from Hawai'ian, so perhaps there are small-phonology languages that allow no clusters, but for convenience let's say that in this sketch we'll allow either two low segments or two mid segments per syllable; then we get:

LL>M: 64 possible syllables
L>MM: 64 possible syllables
MM>H: 32 possible syllables
LL>M>H: 128 possible syllables
L>MM>H: 128 possible syllables

And suddenly, it has become impractical to write with a syllabary!

After my LCC presentation, I had a conversation with Biblaridion in which he pointed out an aspect of all of these non-IPA-codable languages that's directly relevant to writing stories with them: who can perceive them, and who can produce them? Audio and visually-coded languages like the canine sketch, the cephalopod sketch, and Tjugem can all be perceived by humans, so we could in principle develop receptive multilingualism in them, even if we couldn't produce them (and in the case of languages like Tjugem, we can even learn to produce them, even though they don't use typicaly human phonemes). This "firefly" phonology falls into that class as well--if humans can learn to decode morse code, surely we could learn to understand a firefly phonology, but we couldn't reply in the same language, or at least not in the same modality, without technological assistance. Fysh A presents a more extreme case--if there were, say, some intelligent star-nosed moles with electroceptive noses inhabiting the Fysh's world, they could gain receptive competence while being mute, but humans can neither produce nor even perceive the language without technological assistance. This suggests a new pathway for developing alien creatures: decide what communicative barriers you need in place to drive the plot, pick a modality that makes that work, and design your creatures to make it plausible for them to communicate in that modality. In fact, on further reflection, this seems to be exactly what H. Beam Piper did for Little Fuzzy (and you thought I would get through this whole post without an affiliate link! ha!)--the Fuzzies do communicate with sound, but in a frequency range that humans can neither hear nor replicate!

Weird Worlds: Cronus

 < Fornax | Introduction to Xenobiology

Cronus is a cold world only slightly larger than Earth. The average surface temperature is approximately -150C, similar to Blue Crystal, with an atmosphere composed of 4 bars nitrogen, 2 bars of methane, 0.5 bars helium, 0.3 bars hydrogen, 0.1 bars of argon, 0.1 bars of neon, and traces of more complex hydrocarbons. At these pressures, methane and ethane are liquid on the surface, and methane powers a weather cycle just like water on Earth. Like our own solar system's Titan, Cronus features an orange blanket of high-altitude tholin smog produced by photochemistry. Unlike Blue Crystal, the surface pressure is not high enough to liquify nitrogen.

Also like Titan, the solid surface of Cronus is composed primarily of water ice, with about 10% admixture of ammonia ice (precise ratios varying by region). Surface geology is complex, with rocks composed of a wide variety of hydrated minerals. Unlike Titan, the ice crust is relatively thin, and underlain by a silicate crust and mantle. It is not known if a continuous water/ammonia ocean is present between the water and silicate layers, but silicate volcanism produces hot water/ammonia pockets with large loads of dissolved minerals, driving cryovolcanism on the surface which builds mountains and replenishes surface supplies of heavier elements.

Life on Cronus is based on a mixed methane/ethane solvent, with cells based on azotosomes--bilayer membranes composed of relatively small molecules with polar nitrile heads in the interior and short hydrocarbon tails interacting with the methane/ethane mixture. Unlike Earthling lipid-based vesicles, Cronus's azotosomes fundamentally depend on a mixture of different nitrile molecules for their stability; the largest single component in acrylonitrile, but while flexible pure acrylonitrile vesicles can be constructed, the lowest-energy state is a crystalline solid. Much like water and ammonia in combination form a eutectic mixture with a freezing point far below that of either pure substance, inclusion of additional nitrile molecules produces a "eutectic" membrane structure which strongly resists crystallization.

Due to the thinness of azotosome membranes, they do not contain complex membrane-embedded structures. Instead, equivalent macromolecules are attached to the inner and out surfaces of the membranes, giving Cronian cells a nearly-universal extremely rough texture. This also helps to account for the low solubilities of most materials in cryogenic methane, as the rough surfaces improve capture and adsorption of any rare solutes that a cell may encounter, and a large amount of chemistry in fact occurs in the exterior cellular environment. It is theorized that Cronian protolife may have originated as autocatalytic patterns on rough crystalline sheets, which later evolved to produce mixed-species eutectic sheets that could fold into independent vesicles. In its modern state, however, having developed cellular interiors, Cronian life does rely on the compartmentalization of membrane-bound vesicles to retain useful molecules at much higher concentrations than would be available otherwise, thus vastly improving control and reaction efficiencies, and to store genetic material. As on Blue Crystal and other worlds with aprotic solvents, electrochemistry is accomplished through electron conduction and intramolecular charge separation.

Cronian biochemistry is unusually sparse in its elemental repertoire. While trace heavier elements are available from weathering of aqueous rocks, none are strongly soluble. Thus, Cronian life relies almost exclusively on carbon, hydrogen, and nitrogen to build itself, with occasional inclusions of oxygen. Silicon is virtually unknown; although silanes would be useful functional molecules, the lack of surface-exposed silicate features means that, unlike on Blue Crystal (an even colder world), any silanes that might be geologically produced are hydrolyzed water-magmas long before they would be available to the surface biosphere--and silica grains are completely inaccessible, except as inert grains upon which microorganisms might grow. The limited elemental repertoire has the consequence that Cronian functional molecules are, on average, much larger than their Earthling equivalents. Conveniently, this serves to increase cellular surface roughness! Even so, life is sparse in the fluid column of Cronus's seas, with even photosynthetic life concentrating heavily on the seafloors, where rare low-solubility materials settle out. As on Blue Crystal, water is used for structural purposes by Cronian life, serving equivalent functions to silica, calcium carbonate, and hydroxyapatite for building cell walls and skeletons.

Photosynthesis is predictably hydrogenic, based on consumption of liquid methane and ethane and atmospheric nitrogen to produce complex nitro-organic molecules. Respiration is, conversely, hydrogen-breathing, consuming complex hydrocarbons and atmospheric hydrogen to regenerate methane and ethane. Large amounts of energy, however, can be stored in azides and polyazoles; large, nitrogen-rich molecules, which are much more stable in the cryogenic conditions of Cronus than they are in Earth standard conditions, serve functions very roughly equivalent to fats as compact energy stores, though the high reactivity of azide groups is also very useful in a wide variety of common metabolic cycles. As a result, Cronian biomass usually poses a serious detonation risk if warmed to Earth-standard temperatures, and conventional laboratory study of that subset of Cronian biomolecules which remain stable in human-compatible conditions should be done only after isolation and purification is accomplished in cryogenic conditions.

Free oxygen is poisonous to Cronian lifeforms, but, due to the low temperatures, not acutely so. Similarly, the low temperatures are the only serious risk to human life. Surface exploration is thus possible with suitably insulated and heated suits. Offworld transport of Cronian lifeforms requires maintenance of at least 3 bars of pressure, and temperatures between -140 and -180 C. Below 180C, most Cronian life will be killed by methane crystal formation; above -140, most lifeforms will have died, and there is attendant risk of gas explosion.

Weird Worlds: Fornax

< Brimstone | Introduction to Xenobiology | Cronus >

It has been said that "carbon chemistry is the chemistry of life, silicon chemistry is the chemistry of rocks". Of course, this is a severely oversimplified point of view, based on the limitations imposed on stable carbon chemistry by the high temperatures and ubiquity of water on Earth; many other biospheres incorporate silicon in a variety of ways. However, Fornax challenges this statement in another way: the chemistry of life and the chemistry of rocks are not necessarily entirely disjoint!

Fornax bears the highest-temperature biosphere currently known, and is likely near, if not at, the limits of what chemical biosystems can support. Fornax is in some ways a hybrid of our own solar system's Venus and Mercury--closer in size to Venus, and with a non-negligible atmosphere, but with an elliptical orbit even closer than Mercury's, with a 3:2 spin-orbit synchronization. Daytime surface temperatures reach 900C, but can drop as low as 400C at night. Due to these temperature variations, which would be exacerbated by a 1:1 tidal lock, the orbital eccentricity and consequent lack of 1:1 tidal locking are critical for the survival of the Fornaxian biosphere. While photosynthetic biospheres can exist on water-based "eyeball" worlds, so long as there is sufficient water for atmospheric or glacial processes to continually replenish the dayside supply, the much lower-abundance materials which serve as Fornax's biosolvents would be expected to entirely freeze out on any similar worlds which have a permanent dark side.

Fornaxian life is based on an ionic liquid solvent system consisting of a mixture of metal chlorides and fluorides. The major metallic species are iron, calcium, sodium, magnesium, potassium, and copper. The surface atmospheric pressure is 0.52 bars, consisting of 0.3 bars of sulfur dioxide, 0.2 bars of nitrogen, 0.01 bars of carbon dioxide, and less than 0.01 bars each of sulfur, argon, aluminum trichloride, iron dichloride, zinc dichloride, copper (I) chloride, and silicon tetrafluoride.

Biochemistry in this environment is based on halogenated aluminosilicate polymers with additional metal ion and metal oxide functional groups. With carbon integrated only as a relatively rare heteroatom, this constitutes the most thoroughly silicon-based, as well as hottest, biosphere yet known. While tetravalent silica is roughly equivalent to carbon in Earthling biochemistry, aluminum serves a role similar to nitrogen, with regular aluminum substitutions in silicate polymers introducing local negative charge concentrations and trivalent structures. Such aluminum substitutions, creating replicable surface charge patterns, are a key feature of the clay-substrate hypothesis for the origin of prebiotic chemistry on Earth; it is an intriguing possibility that Fornax may be an example of a world where autocatalytic aluminosilicates were able to make the jump to full independently-evolving genetic and autocatalytic biosystem directly, rather than simply providing a prebiotic template for the development of more typical replicator systems. Oxygen functions similarly to hydrogen in colder biosystems, saturating excess silicon and aluminum valences and forming weak intermolecular bonds.

Like carbon, nitrogen and phosphorus are also occasional heteroatoms in Fornaxian biochemistry. As on Earth, phosphorus circulates almost entirely in the form of phosphate ions and nitrogen is regularly fixed from the atmosphere and returned to gaseous form when biological materials decay. The fixing of nitrogen is, however, simpler than the equivalent process in Earthling biology, as they high ambient temperatures significantly reduce the activation energy hill that must be overcome to split N2 molecules.

The dominant cycle for producer-consumer energy metabolism on Fornax is still based fundamentally on oxygen; autotrophs split oxygen from silicate and alumina groups to form aluminate anions, halogen-substituted silicates, and desaturated siloxanes. However, free oxygen at Fornaxian temperatures would rapidly recombine with any newly created reduced biomolecules. Thus, as on Oxio and Brimstone, autotrophic organisms consume sulfur (in this case, purely in gaseous form) to bind oxygen and reduce its chemical activity. Biogenic production of sulfur dioxide on Fornax is similar to biogenic production of oxygen on Earth, resulting in the high proportion of SO2 in the atmosphere. Heterotrophs inhale sulfur dioxide to oxidize silicon and aluminum(and occasionally other metals), and exhale waste sulfur, while also regenerating soluble halogen ions in the process. Substituting oxygen bonds for fluorine bonds, however, is not energetically favorable, as the silicon-fluorine bond is among the strongest chemical single bonds known; this leads to Si-F bonds being preserved in catabolic metabolism, eventually resulting in the release of waste silicon tetrafluoride gas and the depletion of soluble fluoride ions. Autotrophic organisms must therefore periodically expend energy to capture atmospheric SiF4, partially incorporating the bound fluorines into new biomolecules and returning the rest to solution.

Fornaxian conditions are immediately lethal to humans, and no practical mechanisms for supporting long-term habitation are available. All close-range exploration must be done by robotic remotes. However, the lowered temperatures of the Fornaxian night have resulted in most organisms developing resistance to freezing. This makes offworld transport of biological specimens for laboratory study surprisingly straightforward.

Commentary

This world was inspired by Feinberg & Shapiro's highly underspecified "Thermia" proposal (Life Beyond Earth, 1980), in which they suggest that silicates could form biomolecules above 1000C. However, Petkowski, Bains (of "Many Chemistries Could Be Used to Build Living Systems" fame), & Seager (in "On the Potential of Silicon as a Building Block for Life") point out that silica doesn't look so good for forming biological structures when all of the oxygen-network bonds are as labile as hydrogen bonds in a 1000-degree melt, and Feinberg & Shapiro didn't really explain what kind of distinction (if any) they had in mind between solvent and partially-solvated structures.

However, many salts, which can form ionic solvents, and silica-containing minerals, melt into solution at well below 1000 degrees, and others are solid up to much higher temperatures. Since I have been doing rather a lot of thinking about Hal Clement's Sarrians (who live at a mere 500 degrees), slightly lowering the operating temperature, introducing an ionic solvent, and throwing in sulfur to modulate oxygen metabolism seemed like obvious compromises to bring Thermia to "life".

Weird Worlds: Brimstone

< Oxio | Introduction to Xenobiology | Fornax >

Brimstone is a small sulfur-rich world, similar to a slightly larger and warmer version of Oxio, or a much larger and hotter version of our solar system's Io. Like both Oxio and Io, Brimstone is a moon of a gas giant, which allows tidal heating to compensate for the lack of primordial internal heat to maintain tectonic activity and transport sulfur from the core to the surface despite being small enough to have lost most of its low-mass volatiles. Having formed in a hotter environment, Brimstone had a lower primordial water fraction than Oxio, leading to a less oxidized modern environment more chemically similar to Io, with large quantities of elemental sulfur and a 0.66-bar atmosphere composed primarily of sulfur dioxide (0.3 bars), carbon dioxide (0.25 bars), and nitrogen (0.1 bars), with traces of carbon disulfide, carbonyl sulfide, a variety of carbon tetrahalides, argon, xenon, and sulfur vapor. The average surface temperature is 132 degrees Celsius. Sulfur is a close analog on Brimstone for the function of water on Earth, as it is both the primary biosolvent and the driver of weather systems, with clouds and rain of liquid sulfur. Weather systems are generally less violent on Brimstone than on Earth due to the lower heat of vaporization (approximately one quarter that of water) and lower vapor pressures of sulfur, resulting in less potential rainfall and enlarged desert regions. However, sulfur vapor also undergoes much more significant, non-ideal alterations in density with changes in pressure, as the equilibrium of molecular structures shifts between heavier and lighter sulfur ring structures.

The liquid phase consists almost entirely S8 rings, with just under 7% concentration of lighter species. The small concentration of S2 and S4 structures is, however, critical to Brimstone biology, as they are much more easily transported across membranes than the large S8 rings, and provide much more convenient feedstocks for sulfur-involved reactions. On long time scales (compared to typical reaction speeds), S2 concentrations will naturally re-equilibrate as S2 molecules are removed from solution by pumping or consumption in anabolic reactions, but several highly conserved enzyme complexes exist specifically to cleave S8 rings into S4 and S2 groups to feed into other reactions. Large S8 rings are, however, sometimes used directly in the synthesis of large polysulfides. While sulfur-sulfur bonds lend rigidity and insolubility to many Earthling protein complexes, sulfur chains induce improved solubility in the Brimstone biosystem, and carbon-carbon double bonds serve an analogous structural purpose at Brimstone's higher temperatures (similar to Vitrium biology).

Sulfur is a nonpolar solvent, and as such dissolves several small hydrocarbon species. However, it is also a weak Lewis acid (electron acceptor), and so preferentially dissolves Lewis bases (electron donors), and is not a lipophile. Additionally, while some bioavaiilable hydrogen is retained in the form sulfuric acid and hydrogen halides, hydrocarbons are also quite rare, as on Oxio, being substituted with halogen-rich equivalents. Fluorine, chlorine, bromine, and iodine are all highly active in Brimstone biology, as organohalogen groups exhibit higher solubilities with increasing halogen atomic number; functional groups with different halogen terminations are thus selected to precisely control the solvent activity of different macromolecules. Bilayer membranes are composed of long-tail fluorocarbons (essentially, teflon) with solvent-facing nucleophillic thiol heads. With sulfur being both aprotic and non-polar, Brimstone biology cannot rely on ion pumping for energy management purposes, and so relies exclusively on intramolecular electron transport, as on Blue Crystal (a world which is otherwise quite different in nearly every way!)

As on Oxio, energy metabolism is primarily oxygen-based, though mediated by sulfur oxide molecules. Photosynthesis is weakly oxygenic, as there are several non-oxygenated atmospheric carbon sources available (namely, carbon disulfide and the carbon halides), with all oxygen liberated from CO2 being re-bound in sulfur dioxide. As the formation of both carbon disulfide and carbonyl sulfide are endothermic (being produced as as hormone molecules and by lighting and UV-light activated atmospheric reactions), sulfur is a complete bystander to the respiration process, serving only as a vehicle for oxygen. Catabolic reactions of SO2 with typical energy-rich biomolecules (such as fluorolipids) produces CO2, carbon tetrahalides, and elemental sulfur as byproducts. In fact, all atmospheric halides are biogenic in origin, resulting from the breakdown of organohalogen molecules whose halogen content was originally organically fixed from geological sources.

Unlike water, ammonia, nitrogen, and sulfuric acid, but like the iron carbonyl used on Cannonball, molten sulfur is not a transparent fluid. Thus, photo-active structures, such as retinas and photosynthetic pigments, cannot be deeply embedded inside the fluid. Eye and leaf structures thus mirror those on Cannonball and Rust, and the photopic zone of oceans, lakes, and rivers is limited to the upper few millimeters, and most marine creatures completely lack eyes (similar to the situation on Vitrium, though for different underlying reasons). Unlike Cannonball's iron carbonyl and Rust's hydrogen peroxide, however, elemental sulfur is not subject to photodegradation, so protective pigments are not required. The default color of most organisms is therefore a orange-yellow to red, based on the color of the molten sulfur solvent itself.

In low concentrations, water vapor and elemental oxygen are minor irritants to Brimstone life. Exposures to oxygen levels suitable for human life, however, generally results in spontaneous combustion. The Brimstone atmosphere is highly toxic to humans, and temperatures are rapidly lethal. In-person exploration of the planetary surface is possible in a positive-pressure refrigerated environment suit, but is generally considered impractical and discouraged due to the potential damage to the native lifeforms. Refrigerated habitats may be built on the surface, but most exploration must be conducted via robotic remotes. However, the relatively low temperatures and pressures required to support Brimstone life make offworld transport of biological specimens relatively straightforward. Frozen specimens (below 112C) may be safely transported in human-compatible environments, as long as they are contained to prevent contamination from toxic off-gassing.