number of a certain store or house is 3948, but you may easily remember the sound of the spoken words “thirty-nine forty-eight,” or the form of “3948” as it appeared to your sight on the door of the place. In the latter case, you associate the number with the door and when you visualize the door you visualize the number.
Kay, speaking of visualization, or the reproduction of mental images of things to be remembered, says: “Those who have been distinguished for their power to carry out long and intricate processes of mental calculation owe it to the same cause.” Taine says: “Children accustomed to calculate in their heads write mentally with chalk on an imaginary board the figures in question, then all their partial operations, then the final sum, so that they see internally the different lines of white figures with which they are concerned. Young Colburn, who had never been at school and did not know how to read or write, said that, when making his calculations ‘he saw them clearly before him.’ Another said that he ‘saw the numbers he was working with as if they had been written on a slate.’” Bidder
