I'm not entirely sure what you mean by your first line "you can't read because you have no memory of what you are reading" - could you clarify that for me please?Tom
You can't read because you have no memory of what you are reading. It's a just a bunch of dots and lines to you. You also have no memory of the patterns the dots and lines are creating thus you are overwhelmed when you look at it.
This is why you must memorize many things to be able to sight-read.
Neither of us has met the OP or seen what he does with music, so we don't actually know this. We do know that he has a degree in music, composes, and plays guitar (whether with or without music, we don't know). The notes may not just be dots. We'd have to find out what the OP can do at present with notation, under which circumstances, and how he goes about it.
You then write about memory, which I think most people would agree on. But what kind of memory? Is this an intellectual memory that sees E on the bottom line of the treble clef and knows it's E? (Which a composer may already have). Does one go about memorizing this?
Is it an intellectual memory that knows that the piano has 2 black keys, and the note in the middle is D, which corresponds to D in notation? Is it a physical memory that gets created by repeating that knowledge? Or do you establish the physical memory in another way? If so, how? What happens when we read piano music?
What kinds of things do you memorize? Supposing that I play classical guitar (which I do), and recognize a melody line, interweaving voices, and chords, all written on the staff in the treble clef (which I do). Does that mean that I'm all set to go for playing notes written in the treble clef on the piano? Or is something else missing?
To be able to play the piano, one must have a thorough kinesthetic topographic knowledge (memory) of the keyboard layout. Sight is helpful, but not necessary (as in the case of blind pianists.) Topographic memory can only be done at the piano. This requires actual playing, including random mashing of the keys, in order to memorize the keyboard layout................As for transferring knowledge from guitar to piano, assuming that the theoretical knowledge of reading is known, the necessary skills involve associating the written notes with which piano keys to depress. The only way to develop this skill is to practice, which is a fancy way of saying "repeat".
One thing that often happens when someone with a musical background starts taking lessons on piano as a new instrument, is that the teacher does not spend enough time on fundamental skills. I believe that we need the same skills as a rank beginner, and this tends to be rushed through. We can do relatively advanced things early on, and then find ourselves perpetually missing the basics. There are so many things that are more interesting to teach than seeing C and pressing C, or finding all the D's on the piano. We're capable of understanding the more interesting things, so the temptation is there. I'm remembering the fact that the OP's teacher is mystified by his weakness in reading. Should he be?
Most people assume that I can sightread simply because I can play very difficult sounding music. The truth is that I was and am a poor sightreader; it was never a necessary skill. Even though I told my teachers my weakness, their best advice was to "practice". I don't know how to do something and they told me to practice what I didn't know how to do.
What's nice about having a musical background is that the theory does not need to be taught. However, it does need to be applied to the new instrument and I think this is where the problem is.
Identifying notes is one problem. But since theory is understood, notes can be combined into chords on the piano. This tackles learning 3 or 4 keys on the piano, and saves a lot of time.