It's actually easier to play by memory than with music when much of the concentration is taken by looking at the notes and translating them onto the piano keyboard. If you play by memory, this now spare brain power is free to concentrate on the real job at hand - that of playing and interpreting the music as well as looking ar your hand for those big jumps.
You have many types of memory to help you learn music
It'st's useful to know about memory types before setting about devising a system of memorising a piece of piano music. They are: muscular memory; aural memory; visual memory relating to the music page; visual memory relating to the geography of the keyboard and lastly but most importantly, intellectual memory - that type of memory which is based on analysing the piano music in detail. Different people have varying degrees of ability in these skills.
Muscular memory ... consists of the movements of the hands arms and fingers which the brain recalls easily if there has been a lot of repetition in the learning process. In order to develop this memory efficiently it's essential to learn the piece of music using the correct finger on each note every time you play or rehearse the music. Repetition of short overlapping phrases improves muscular memory.
Aural memory ... consists basically of remembering the tune in your head. This can be developed to include the chords accompanying the tune as well as any other detail, assuming that you can recognise and remember the different sounds. Most of us have some natural aural memory because we can sing a tune without access to the music, but highly developed aural memory requires much training even if you are a naturally gifted musician.
Visual memory of the music ... page is about recognising patterns and shapes on the page and could be called photographic memory. You can remember the way the piano music is set out on the page and actually what the notation looks like in the form of a graphic in your mind.
Visual memory of the keyboard ... is about recognising the geographic patterns and shapes on the keyboard itself, begins by noticing that there are black and white notes - the black notes in groups of twos and threes. This can then be developed into recognising the complex keyboard patterns created by the piano music and starts by noticing where the semitones and tones come in addition to the distances between one note and the next (called intervals). Chords are also a great aid to visual keyboard memory.
Intellectual memory Although the types of memory explained so far, are useful in their own way, none of them are completely reliable if you want to remember the music with confidence so that you can play to others in private or especially in public. As soon as you play to others, you will feel "watched" and under pressure, and the most reliable way to combat nerves - which can lead to mind wandering, lack of focus and resulting mistakes - is intellectual memory, which consists of mentally being aware, knowing and analysing how the piano music is constructed in every detail. Intellectual memory includes knowing all the scales, arpeggios and chords, recognising and remembering them as they appear in the music.
Chords help you memorise piano music
as they show how most of the notes relate to each other and if you learn about chords progressions, this helps to understand how the piano music unfolds. Many of these patterns are repeated thousands of times if you look at many different sorts of music and it is these reoccurring patterns which enable musicians to remember securely, two hours of piano music under pressure in a piano recital, for example. Secure memory results in being free to concentrate and focus on the interpretation and performance of the music - on other words, the better you have studied the music, the more easily you can relax and enjoy it - even under pressure.
Memory testing methods Even professionals make mistakes and the human element cannot be ignored but there are quite a few methods one can use to test and improve memory. They include playing the piano music in different keys - a good test of intellectual memory. Playing in the dark or blindfolded deprives one of visual memory and forces one to use the aural memory and listen very carefully. It also tests the reliability of any jumps in the piano music. Another method is to deprive one of muscular memory by playing the left hand notes with the right hand and vice versa - usually one hand at a time. It's even useful to test your memory of a melody by playing the tune with one finger instead of the rehearsed chosen fingering.