The single most important way to reinforce memory is slow play, VERY slow play, less than half speed. Slow speed is also used to reduce the dependence on hand memory and supplant it with “real memory” (we shall discuss true memory below) because when you play slowly, the stimulus for hand memory recall is changed and reduced. The stimulation from the piano sound is also materially altered. The biggest disadvantage of slow play is that it takes a lot of your practice time; if you can play twice as fast, you practice the piece twice as often in the same time, so why play slowly? Besides, it can get awfully boring. Why practice something you don't need when playing full speed? You really have to have good reasons to justify practicing very slowly. In order to make slow play pay off, try to combine as many things as possible into your slow play so that it does not waste time. Just playing slowly, without well defined objectives, is a waste of time; you must simultaneously seek numerous benefits by knowing what they are. So let's list some of them.
(1) Slow play is surprisingly beneficial to good technique, especially for practicing relaxation.
(2) Slow play reinforces your memory because there is time for the playing signals to travel from your fingers to the brain and back several times before succeeding notes are played. If you only practiced at speed, you could be reinforcing hand memory and losing true memory.
(3) Slow play allows you to practice getting mentally ahead of the music you are playing (next section), which gives you more control over the piece and can even allow you to anticipate impending flubs. This is the time to work on your jumps and chords (sections III.7e, f). Always be at least a split second ahead and practice feeling the keys before playing to guarantee 100% accuracy. As a general rule, stay about one bar ahead -- more on this below.
(4) Slow play is one of the best ways to purge your hands of bad habits, especially those that you might have unconsciously picked up during fast practice (FPD). FPD is mostly reflex hand memory which bypasses the brain; this is why you are usually unaware of them.
(5) You now have time to analyze the details of the structure of the music as you play, and pay attention to all the expression markings. Above all, concentrate on making music.
(6) One of the primary causes of blackouts and flubs during a performance is that the brain is racing much faster than usual, and you can "think" many more thoughts in the same amount of time between notes during a performance than during practice. This extra thinking introduces new variables that confuse the brain, leading you into unfamiliar territory, and can disrupt your rhythm -- which is especially troublesome during a performance. Therefore you can practice inserting extra thoughts between notes during slow practice. What are the preceding and following notes? Are they just right, or can I improve them? What do I do here if I make a mistake? etc., etc. Think of typical thoughts you might encounter during a performance. You can cultivate the ability to detach yourself from those particular notes you are playing, and be able to mentally wander around elsewhere in the music, as you play a given section.
If you combine all the above objectives, the time spent playing slowly will be truly rewarding, and keeping all these objectives going at once will be a challenge that will leave no room for boredom.