A student of telegraphy was tested once a week to see how rapidly he could send a message, and also how rapidly he could "receive a message off the wire", by listening to the clicking of the sounder. The number of letters sent or received per minute was taken as the measure of his proficiency. This number increased rapidly in the first few weeks, and then more and more slowly, giving a typical learning curve, or "practice curve", as it is also called.
Fig. 51.--(From Bryan and Harter.) Practice curve of student W. J. R. in learning telegraphy. The height of the curve indicates the number of letters sent or received per minute. Therefore a rise of the curve here indicates improvement.
The curve for sending, aside from minor irregularities, rose with a fairly smooth sweep, tapering off finally towards the "physiological limit", the limit of what the nerves and muscles of this individual could perform.
[Footnote: A good example of the physiological limit is seen in the hundred yard dash, since apparently no one, with the best of training, can lower the record much below ten seconds; and any given individual's limit may be considerably worse than this, according to his build, muscular strength and quickness of nerve centers. The simple reaction gives another good example; every one has his limit, beyond which no amount of training will lower his reaction time; the neuromuscular system simply will not work any faster.]
The receiving [{322}] curve rose more slowly than the sending curve, and flattened out after about four months of practice, showing little further improvement for the next two months. This was a discouraging time for the student, for it seemed as if he could never come up to the commercial standard. In fact, many learners drop out at this stage. But this student persisted, and, after the long period of little improvement, was gratified to find his curve going up rapidly again. It went up rapidly for several months, and when it once more tapered off into a level, he was well above the minimum standard for regular employment.
Such a flat stretch in a practice curve, followed by a second rise--such a period of little or no improvement, followed by rapid improvement--is called a "plateau". Sometimes due to mere discouragement, or to the inattention that naturally supervenes when an act becomes easy to perform, it often has a different cause. It may, in fact, represent a true physiological limit for the act as it is being performed, and the subsequent rise to a higher level may result from improved methods of work. That was probably the case with the telegrapher.
[Footnote: A plateau of this sort is present in the learning curve for mastery of a puzzle, given on p. 316.]
The telegrapher acquires skill by improving his methods, rather than by simply speeding up. He acquires methods that he didn't dream of at first. At the start, he must learn the alphabet of dots and dashes. This means, for purposes of sending, that he must learn the little rhythmical pattern of finger movements that stands for each letter; and, for purposes of receiving, that he must learn the rhythmical [{323}] pattern of clicks from the sounder that stands for a letter. When he has learned the alphabet, he is able to send and receive slowly. In sending, he spells out the words, writing each letter as a separate act. In receiving, at this early stage, he must pick out each separate letter from the continuous series of clicks that he hears from the sounder. By degrees, the letters become so familiar that he goes through this spelling process easily; and, doing now so much better than at the outset, he supposes he has learned the trade, in its elements, and needs only to put on more speed.