You have the title wrong, but i see you have acknowledge this.
If what you asking about is 'Proprioception' the bodies senses combined to make the task of what we think and how we react to it and visa vera.
Synesthesia as you are finding out is the crossing of senses to the effect that the brain places a different way to relate to the information they provide.
In learning we learn not only direct information, but in-direct information through association.
So playing bass is physical movement, but it can be physical movement combined with listening, so two senses combined, but the hearing side is 'association' as you cannot really control what you hear.
But you can learn what you hear or what not to hear.... hearing what is wrong but not knowing why it is wrong, you just know it is wrong.
Visual learning comes into it in a few different ways.
A new player will look at the neck for example and use their eyes to find notes or positions on the neck (using fret markers or gauging the position on the hand on the neck) until their ears take over more of the role once they do not depend on needing to look at their hands.
Also if the notes are known then those positions where they are found are learned, as are the relationship to all notes around it.
So in playing a C, your brain will confirm that you are playing a C by, the pitch of the note, the position on the hand, the string being played, the fact that there is a G under it and F above it, it is on the 3rd fret, there is a fret marker on it, it is in between a B and a C# etc etc.
All these things are taking in, sorted and ordered, then the correct reaction iniciated without the player even thinking it.
The player wants a C they just play a C.
This will develop as the ears learn what sounds right and what sounds wrong and move the fingers with more frequency to notes that sound right....ignoring the those that it now recognises as not wrong through a process of trial and error....eliminating what does not work in favour of what does work and remembering it, not as a conscious thought but a subconscious one.
The eyes will make the same development, as will the hands, as will any other senses used in learning, some may develop as habits, some may be just implied rituals to make us feel comfortable by introducing a familer feeling we relate to.
The visual sense may be developed in a different way if a player learns to read and play from the beginning.
Now a player is looking at the notes and associating there position on the staff to a sound and position on the neck.
The eyes can now see the length of notes but not hear them, so the physical skill of playing needs to develop counting what is seen and relate that to the correct position on the neck, with the correct amount of pressure to sustain the note for the correct duration.
The acquired skill of relating the postion of C to the pitch now teaches the player if their instrument is in tune with itself, so intonation develops as the player develops.
And so on it goes with many senses combining to allow us to play and master playing the bass. A player with an under developed part in any of their skill sets may struggle to learn as good or as fast as the person next to them. Also a person with a highly developed part in their skill sets may find playing easy or at least certain parts of it.
As we get older we can loss some skill sets that will impact on our ability to play, loss of hearing, loss of touch, loss of sight etc can inhibit what we do are the brain losses some of the information it has be used to using.
It sort of stalls or hesitates the thinking process, so the reaction to the thought is inhibited, so you see the note C, but hesitate playing it, what is around it, or maybe cannot relate fast enough where it is to be found on the neck or staff.
Now for the scary part, depending on how fast the skills are compromised or lost can have an impact on other seeminly un-related skills. A slow deterioration may see all slow down gradually as they all slow at the same time, but a sudden loss can have more serious results.
I was in a car accident in 2008 in which i broke my neck at C7, the end result was i was paralyed the right upper limb, with secondary nerve damage in the left upper limb, this caused muscle deterioration in mass and form.
So i lost the use of my right arm and could not move my fingers, and lost part of the use of my left arm, but had limited use of my fingers.
In the following months one of the apparant related skills i lost was sight reading, i could not relate to the notes on a staff let alone a score.
As i healed and started to get the use of my hands again, the sight reading came back a bit, but still very much reduced.
It seems the nerve damage that leaves me unable to have a sense of touch is not supporting my brain with the information it is used to receiving.
My next problem was i could not relate to the neck because i could not feel the neck, so i had to look at the neck to place my finger on the note, then look at my plucking hand to make sure i picked the right string to pluck and then play it. I then had to decide if the note was correct, did it sound correct?
This frequently had me checking the reason if a note was wrong, did i fret it wrong or did i pluck the wrong string, did i use the correct pressure/force etc.
Trouble was i cannot look at my left hand and right hand at the same time so i cannot tell instantly what was correct or more importantly what was wrong let alone the amount of pressure i was applying.
In the end a neuro-surgeon explained what i have partly set out above at the beginning of this post, my brain when learning music had all senses working to confirm or deny what i was learning and how that knowledge was developed to be used.
My sight reading is tied to my relationship to my 'minds eye', so not only did i see the note on the page, but i heard it in my head, and more importantly i saw its position on the neck in my mind.
Add to this that my body knows how to position my arm and allow my wrist, hand, and fingers to get in postion to play, the pressure used to fret, the force used to pluck etc..
Further add to this that i was playing not what i was reading, but what i had read, my eyes were reading a few bars ahead to what i was actually playing to allow my brain to work out in time what and where the hands need to be, as well as where the fingers need to be, how they are to be used the notes to be played, how they are played etc etc.
But as all this i done without thinking, because all the information is collated and used.......the lack of any one part will slow down or neutralize the effect of others.
So my sight reading and relation to the neck was suffering because the nerve damage did not allow me to feel my hands and finger tips,so that information was missing and this was causing me to hesitate and question what was doing. So by not having all the information available that it developed over 40 years to make verify my actions as correct.... my brain is questioning it and that impacts on how it processes the final decision it makes as to whether is is correct info or not.
In all i could read, but very limited if i worked it out slowly, i could play, but so long as i used my eyes rather than my ears, but it was impossible to see the note C of a staff and play it on a bass, let alone add a value to it.
These days things are much better as my physical skills return slowly, but the nerve damage is permanant so not all skills will come back the way they were before because my brain has to learn to work things out with less info before it confirms or denies its viability to what i am doing, this shows up in many things i do not just playing.
So for me it is onwards and upwards, take each day and each new playing job as it comes and just keep on working slowly and carefully on playing.
Because of my own skills and understanding of body mechanics and playing, i am the best qualified person to gauge how and what i am doing and what i need to develop and what will develop from what i do but this is my situation, my problem, and for me to deal with......so for me i just started again learning to play the way i did 40 odd years ago and see if the work produces the same results and some of the same skills i had before my accident.
Are skills and senses interchangeable or co-dependant on each other? Well i would have to say yes they are, but we may not recognise it at the time of learning.
I have PP (had it, actually...still have great pitch but it's deteriorating slightly as I get older), and I never once thought of colors in relation to pitch. But it really does help picking songs out, for sure.
