I believe the technique you're referring to is called the Farnsworth method where the letters are keyed at a faster speed than the overall transmission speed (e

I believe the technique you're referring to is called the Farnsworth method where the letters are keyed at a faster speed than the overall transmission speed (eg: at 5 words per minute the letters are sent at 13; when learning at 13 the letters are sent at 20). Another thing about learning Morse code is to NEVER try to learn it visually if plan to send/receive aurally. Before I joined the Navy I had been proficient with Morse code at around 15WPM; I was able to read the flashing light codes being sent between ships but I had to "hear the light." The Signalmen had the opposite phenomenon: since they had learned Morse code visually in order to copy Morse code by ear they had to "see the sound." I'm sure between the fields of neuroscience and psychology there could be an interesting discussion as to how that cross-sensory translation takes place but it certainly does.