It's important to learn the piece correctly from the outset. It's much easier to study the music carefully than to correct reading errors - you'll first have to unlearn the old note or rhythm and then learn the new one. Old mistakes also have a habit of resurfacing when you're under pressure.
Conjuring up a mental image whilst playing is called visualisation. However, the term is misleading, as the word itself refers only to a visual image. A musician's mental image naturally also includes an aural image of the piece being played, as well as a kinaesthetic aspect - a feeling of what is happening in your body as you play.
Many musicians are afraid of misremembering a piece. The motor memory may fail and, if there's have no support coming on a conscious level, it will be difficult to keep going. Reading music and then visualising one's own playing is an effective way of learning a piece by heart. The idea isn't to get a photocopy of the notes in one's mind, but rather to remember the intonation, chords, fingering, movements, excerpts and feelings, etc. Each person will create a distinctive personal image, and so everyone should try to find his or her own ideal methods for visualisation.
Technique is a question of practising cooperation between the mind and the muscles. One must first form a clear mental image of the movements to be performed. Only then it is possible to begin correctly commanding the muscles. Outlining movements in the mind promotes the formation of nerve connections and clarifies technique.
Most people practice by singing a piece of music in their mind and thinking about the phrasing rather than searching for a musical solution solely through playing. One can build a good foundation for perceiving musical ideas by carefully familiarising oneself with notes and musical symbols, taking an appropriately analytical attitude, singing in the mind, listening, and seeking solutions through movements, playing and feelings.
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