I'm surprised that spelling and writing are something that people with aphantasia find difficult, as I would not have thought that there is a strong visualisation component involved in those activities. Maybe that is because for me, who cannot visualise anything, I developed a different way of learning to write and spell. For me I could always "hear" the words in my head and I was able to remember the alphabet by knowing how each letter was constructed, so I did not have any trouble learning to write and spell. In fact I feel that because I cannot visualise anything, I rely much more on words and descriptive phrases to remember things. On the other hand, I cannot draw anything from memory and am still limited to stick figures, so I understand that perfectly. I also feel, having lived in Japan for 10+ years, that had I been born there, where it is necessary to learn approximately 2000 kanji characters in order to read a book, I would have struggled much more. My attempts to learn kanji in adulthood, where most methods rely on visual association of the characters with particular scenes, were a complete failure. You also mention music, but again I don't see why being aphantasic should have any bearing on musical ability, since I don't believe that visualisation is really a necessary skill for learning music. After all music is all about sound, and I can "play" a song in my mind, imagining how it sounds, without requiring any visual element, but maybe I am lucky in that way and some people cannot do that. To be both without sound and without vision must be very tough indeed.

A few years ago I read something about a man who was aphantasic (I'm not sure that was the word that was used then but he was blind in his mind's eye) and he gave the following example: Tell someone to think of a nice big juicy apple and picture it in their mind. Then ask "what color is the apple?".  Almost everyone will say red, green, or possibly golden yellow. I knew at once that I could not say anything about the color of the apple because there was no visual element to the apple I was thinking about - merely an "apple concept" that had no color. The man I read about was the same as me. I have tried this on some people and they all instantly know the color of the apple they are visualizing. This is when I realized I was aphantasic. I was already in my late fifties by then and it came as a shock to me that most people can visualize things in a different way from me. Other evidence came from learning languages. There is a learning method that relies on visual imagery to remember words. For example in Italian picture a cat sitting on a gateau - the Italian for cat is "gatto". This method was zero help to me and the same was true of visual methods to remember Japanese kanji characters, or remember cards in a deck (go through your house in your mind and put particular cards in each room, etc.). 

I'm surprised that spelling and writing are something that people with aphantasia find difficult, as I would not have thought that there is a strong visualisation component involved in those activities. Maybe that is because for me, who cannot visualise anything, I developed a different way of learning to write and spell. For me I could always "hear" the words in my head and I was able to remember the alphabet by knowing how each letter was constructed, so I did not have any trouble learning to write and spell. In fact I feel that because I cannot visualise anything, I rely much more on words and descriptive phrases to remember things. On the other hand, I cannot draw anything from memory and am still limited to stick figures, so I understand that perfectly. I also feel, having lived in Japan for 10+ years, that had I been born there, where it is necessary to learn approximately 2000 kanji characters in order to read a book, I would have struggled much more. My attempts to learn kanji in adulthood, where most methods rely on visual association of the characters with particular scenes, were a complete failure. You also mention music, but again I don't see why being aphantasic should have any bearing on musical ability, since I don't believe that visualisation is really a necessary skill for learning music. After all music is all about sound, and I can "play" a song in my mind, imagining how it sounds, without requiring any visual element, but maybe I am lucky in that way and some people cannot do that. To be both without sound and without vision must be very tough indeed.

A few years ago I read something about a man who was aphantasic (I'm not sure that was the word that was used then but he was blind in his mind's eye) and he gave the following example: Tell someone to think of a nice big juicy apple and picture it in their mind. Then ask "what color is the apple?".  Almost everyone will say red, green, or possibly golden yellow. I knew at once that I could not say anything about the color of the apple because there was no visual element to the apple I was thinking about - merely an "apple concept" that had no color. The man I read about was the same as me. I have tried this on some people and they all instantly know the color of the apple they are visualizing. This is when I realized I was aphantasic. I was already in my late fifties by then and it came as a shock to me that most people can visualize things in a different way from me. Other evidence came from learning languages. There is a learning method that relies on visual imagery to remember words. For example in Italian picture a cat sitting on a gateau - the Italian for cat is "gatto". This method was zero help to me and the same was true of visual methods to remember Japanese kanji characters, or remember cards in a deck (go through your house in your mind and put particular cards in each room, etc.).