I was studying up on SLIPA and I'm kind of curious how one would go about performing sound changes (hand position changes?) with a signed language? Do the concepts translate over to SLs similarly? Like, how would you express assimilation or metathesis or umlaut through a SL? Or do they just have their own completely unique set of changes separate from spoken languages?
Remember that when we write things like C[-cont] > [+voice] / V_V that these are shorthands for descriptions, and they're not necessarily consistent across the discipline. There are absolutely changes that occur in sign languages—both synchronically and diachronically—and there are linguists who have studied them. For example, in the history of ASL, signs that were signed in the periphery have moved closer to the center; signs where two hands were doing non-parallel actions have switched to parallel; and two handed signs have shifted to one handed signs. These are long-term, general trends, but there'es plenty of assimilation that's quite explicable.
For example, consider the verb TEACH, signed up at the top of the forehead. In TEACHER, where TEACH is followe dby the two hand PERSON suffix, the hands rarely get so high as the top of the forehead. This makes sense, as the place of the TEACH sign is farther from the usual place where the PERSON suffix happens, and so its shift to be closer to the place of PERSON is a kind of anticipatory assimilation, akin to nasal place assimilation. You could describe this with SLIPA, or you could describe it in words, as I've just done, or you can describe it with video augmented by words, etc. The concepts are the same; only the articulators are different.
A lot of sound changes (synchronic or diachronic) boil down to two major factors:
While it is possible for human beings to be precise in their actions (to say the same word the same way every single time; to sign the same thing the same way every single time), it's not convenient, and so humans take shortcuts, where they can (i.e. where they can get away with it without sacrificing the whole enterprise, i.e. conveying a message).
While it is possible for humans to pay careful attention and decode a message precisely as it was intended—and even to inquire when there is confusion—it's not convenient. We will often make false assumptions about what we see and hear. Furthermore, we will often assume that when what we perceive doesn't square with what we expect, it is our expectations that were incorrect, not the sender of the message. If in replicating the error the message doesn't suffer, the error may propagate, leading to change (i.e. errors in perception that don't interfere with the transmission of a message can be replicated and become largescale language changes).
These two factors account for the majority of sound changes (not ALL of them, of course, but the lion's share). Notice that neither of them require that the language be either spoken or signed, because they deal exclusively with transmission and reception. Only the details are different when the medium changes. For example, there's nothing similar to a velum and how it works in sign languages. It's too specific an organ with too specific a function in spoken language. But that doesn't meant that some of what it's involved with (e.g. various assimilations, blocking, etc.) won't have analogs in manual languages.
To offer a more concrete analogy, I was born with six fingers and no thumbs (two index fingers on each hand). I had surgeries to turn one index finger on each hand into something that approximates a thumb, and it functions fairly well most of the time. When I learned ASL, I discovered there were certain things I simply could not do. In signing numbers, for example, 6 and 7 are very hard to form on my right hand, and impossible on my left. My new thumbs simply don't connect that way, and furthermore, there's some connection to my other fingers when I try to move the thumb, and so I can't raise my other fingers while I'm trying to make that connection. This is what the number 6 is supposed to look like (signed with my right hand):
You can see my thumb is making contact with my pinky with the other three fingers extended upward.
Now this is what happens when I try to make that sign with my left hand:
You can see my hand is basically forming a claw. If I thought about it, I could extend my index and middle fingers, but I cannot continue to stretch my thumb to my pinky while extending my ring finger. Furthermore, that is the very furthest I can stretch my thumb. It simply will not extend anymore. i can use my other hand and push it, but what I'm doing is pushing my pinky closer. That's the furthest my thumb will go.
As a result of this, the way I sign is always noticeably distinct. There are things I simply cannot do that the majority of signers accomplish with ease.
Even so, the way my hands are does not and has never interfered with my ability to speak any oral language. Why would it? It's not relevant to speech.
Having said that, what if instead of hands it were my tongue? Or velum? Or lips? Or teeth? If I'd been born without front teeth, for example, it would impact the way I sounded when I spoke English. Consider that [f], [v], [θ], and [ð] all crucially involve the front teeth.
So back to the original question, there is no direct analog for the way my hands work to speech, in that my hands will affect a sign language in the same way that some change in the mouth will affect an oral language. But the CONCEPT! That is analogous. That is, a change in your physiology can affect your ability to produce an oral language int he same way your physiology can affect your ability to produce a signed language. The concept is the same; the instantations will differ. That means the specifics will crucially differ, as well.
In other words, yes, sign languages do have their own specific sets of changes, but, no, the basic concepts are the same as spoken languages, because both of them are nothing more than human patterns of production and perception.
