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So I have this underwater echolocation using species. I'm wondering if they could have a language partly based on recreating sounds from returning echolocation waves to 'talk' images at each other. (I hope you can understand this. I'm having a bit of difficulty putting it into words).
Just realized the many thin fins I put on this creature's limbs cause it looks cool could be used to pick up vibrations from the sonar based communications.
Perhaps they have different, and more intricate, forms of onomatopoeia than we do.
In English, I could say "the dog barked" and the word bark does not sound the same as a real bark but it is, broadly, reminiscent of a bark.
In Auslan, a sign language, I could say "I have a bowl" and the hand sign for the bowl obviously does not look like a photograph of a bowl but it is indicative of the shape of a bowl, and I could adjust it to indicate the approximate size and shape of the actual bowl I have.
In your fictional dolphin language, perhaps some nouns have different qualities of reverberation and abruptness and harmonics that are reminiscent of how sonar reflects from objects of different texture, density, thickness and hardness. So the word doesn't sound exactly like the object, but it does sound a bit like a one dimensional cross section of the object.
Consider how echolocation works.
The active emitter in the user transmits a relatively uniform pulse. If there is evolutionary pressure towards a "clearer" sonar vision, the emitter has to produce stronger, shorter pulses in a narrow frequency range, while the receivers (i.e. the ears) need the ability to detect subtle differences.
To transmit a "fake" sonar image to another recipient, the user would have to transmit the complex 3D information that would naturally return from the depicted objects. That requires
A completely new set of requirements. It might evolve naturally as the defensive mechanism of a prey species, who transmit "this is a solid rock, nothing to eat," not as a form of echolocation sense.
To give you a comparison, take a flashlight and a TV screen. Yes, a TV screen emits light in the dark, but it isn't really suitable as a flashlight or vice versa. The flashlight has a strong, steady beam from a narrow aperture. The TV screen has many different pixels, which can switch rapidly and cover a large surface.
This is quite an interesting question, because fundamentally what you are describing is the art of holography.
This question is, in fact, completely analogous to asking why species which see using light don't simply project holograms to one another to communicate. Actually, this isn't quite true. It's a lot harder to make something that emits easily controllable light than something that emits easily controllable sound, because soundwaves are generated by motion at a much lower frequency. However, aside from that, the physics of projecting an image into thin air is exactly the same for light as it is for sound.
So, if we're looking at holography, we should look at the question of what we see as a 3D image. Well, when we look at something which is truly 3D, light reflected off of it travels in a straight line towards our eyes. However, our eyes aren't quite points, and so there's a cone-like shape containing all the light reflected off the object which reaches our eyes - this light contains all the information we receive about the image (well, actually, two cones, one for each eye). We get information about distance in two ways. Firstly, if both our eyes have to cross significantly to focus on the point, it's quite close, if they don't, it's further away, this is what gives us a large part of our depth perception, and it's this that 3D movie glasses capitalise on. However, our eyes also have a second method, which is that, in order to see an image, we need to focus that light cone onto the backs of our eyes. If the cone has steeper sides, this corresponds to an object further away, requiring less focusing power, whilst nearer objects require more work to focus, and this also lets use gauge distance. In order to properly see a 3D image, both of these effects must occur.
So, how to make a hologram? Well, we can fake these cones of light. If we take a beam from a torch, and put it through a lens, it will generate its own cone of light, easily enough: there will appear to be a point of light floating in mid air, where the light is focused, as long as you are within that particular cone - if you're outside it, you'll see nothing. However, this only gets us one point, and we want a whole image. In fact, this is one of the reasons most of what I would regard as 'true' forms of holography don't really work: conventional optical methods can only project points at a time, and it takes lots of points to make an image. To trick the human eye, it has to move throughout all points faster than the eye can detect, which is really difficult.
So, projecting even a 2D image - that'd be difficult. However, for a simple form of communication, you don't need to draw a whole 2D image - you only need to draw an outline of the thing, which is only a 1D object, created with multiple lines, and this suddenly becomes feasible, as long as people have reasonable memories to build up the sound patterns in their heads - something which would be required for echo-location anyway.
So, could a species evolve in such a way as to project sound-waves focused into points?
Definitely!
In fact, humans already have evolved the ability to focus light in a way which would achieve the same thing - our eyes! If, rather than receiving images, the back of our eyes contained an emitter of light, our eyes would have the ability to project points like I've described. There's a tradeoff between the size of the pupil, how far from the person a point can be projected, and from what range of angles it can be seen (generally, there's a tradeoff, for any given pupil size, inversely linking the range of angles and the distance of projection - and the larger the pupils, the further away is it possible to project an image, and the more powerful the image can potentially be).
In other words, humans have already evolved the two traits needed for this: the ability to precisely control the movements of a lens, and the ability to produce waves with particular qualities. All that would be needed is for both to have evolved to work with sound, rather than our eyes working only for light, and you could design a race of creatures with the ability to project and receive images by sound and echo-location. It would require a lot of practise with audio mirrors (basically a smooth surface which echos) for a being to get good enough to project an image, but just like any language, if learnt from an early age, it would easily be possible to acquire enough skill to communicate thus.
Such a society would be really amazing, with the spoken word lifted to an entirely new level of artform.
One final interesting point, is that it'd actually be quite easy to talk in relative secrecy with this. Anyone existing outside of the cone of sound you generate would not be able to see/hear the images you project within the cone - similar to those ATMs or some corporate laptops which are made to be invisible from a side-on view.
EDIT:
When I mention a sound-cone, I'm not saying that the sound is inaudible outside of this region, but simply that it doesn't contain the same information (i.e. the image of the point). It might still give away one's position, if not the information one's trying to convey.
In our written languages we have those in which each symbol is a sound, like indoeuropean languages, and those in which each symbol is a concept, like Chinese or Japanese.
Likewise in this language each object could be abstracted into a concept, on the path of Chinese or Japanese.
E.g. the character for "house" in Chinese is 家, made by a pig under a roof. The echo of a pig and the echo of a roof could convey the same concept.
If you think about it, humans were pretty much in the same boat. We started with very sophisticated sound processing organs to identify a huge range of sounds. But we started with limited capacity to make detailed sound which became more sophisticated over time.
Creatures using echolocation have very sophisticated audio processing. Although they need to make precisely controlled sounds, those sounds are very task-specific. At that stage they may make the usual mating calls and sounds of dominance or warning, not using pictures but by distinctive patterns.
Evolution likes to take advantage of things that are already there, so the "calls" would begin to become richer and draw advantages from the echolocation senses.
This probably wouldn't involve faking 2D images, since that is very hard. But there is a much easier option, and evolution also likes to take the path of least resistance. I think it would be possible to very rapidly "send" things that "feel" like a sequence of pointy/flat/approaching/receding/startionary/vibrating/calm/fish/seaweed/rock. Mostly signals that originate from a particular point in space.
There simply wouldn't be enough evolutionary pressure to be able to fake 2D images.
This process is, in a real sense, communicating using images*. It's just doesn't involve communicating using "extensive maps of the environment" that echolocating creatures can construct.
* Typically not images of things being talked about, but rather images strung together to form words with their own meaning.
Doing this is exceedingly difficult. I would not expect any species to evolve that way. There's far easier ways to communicate.
However, it is not impossible. It is possible to create a sound field. Some modern entertainment technologies, can regenerate such a field. However, they rely on a large number of speakers (easily dozens) kept in strict phase alignment based on the room they are in. The real challenge would be maintaining coherence across this many emitters using only organics to do so.
A limitation of these systems is that they can only reproduce far field. Near field effects are very hard to forge. So thus a bomb going off in the distance is very easy to create, but someone whispering in your ear is very difficult.
