Physiotherapists and the Hands in Musicians

As your hands develop you can more reliably start to feel these things. Niroko Ishi in Japan has tested this and her PhD is published in Japanese so I can only tell you what she tells me. There's many reasons why and a lot of the answers come from robotics research when they're building prosthesis with hands. The thumb is a spatial orientator it doesn't have the same receptors in it as the palm as the index and the middle finger, for example.