Edward L. Thorndike, answered from the texts and cited to the page.
The learning curve is simply the time-record of an animal's — or a person's — progress in forming an association, plotted trial by trial. Put a hungry cat in a puzzle box, note how many seconds it takes to work the latch on each successive trial, and you have the raw material. Cat 12 in box A, for instance, took 160 seconds on the first trial, then 30, then 90, then 60, and so on down — 15, 10, 8, 6, 7 — across 24 trials, with occasional reversals that mean nothing in themselves.1
The general slope downward is what matters, not any single point on it. The curve represents two things at once, and they are really one thing on closer inspection: the disappearance of useless activity, and the perfection of the particular act that brings success.2 A kitten put in a box claws at the bars, squeezes, bites, scratches at everything — and then, by accident, turns the button that opens the door.
Put it back, and the useless clawings grow fewer; the successful claw at the particular spot comes sooner. Repeat the experience, and the animal turns the button without delay whenever placed in the box.3 That gradual descent in the time-curve is the association forming — not a leap of understanding, but a selection, trial by trial, of the response that works.
A steep, abrupt descent means an easy association; a long, slow descent means a hard one.4 Where what looks like insight is involved — a sudden grasp of how a mechanical puzzle works — the curve shows a sharp drop rather than a gradual slope, and if several such insights are needed, there may be several drops in succession.5 But rescale those same curves so that equal units of time rather than equal numbers of trials run along the base, and the picture changes: what appeared as a sudden jump smooths out considerably.6
The curve, in other words, is not merely a record; it is a diagnostic. Its shape tells you what kind of learning is happening and how much of it depends on the frequency and spacing of successful acts.
cat 12 took the following times to perform the act, 160 sec., 30 sec., 90 sec., 60, 15, 28, 20, 30, 22, 11, 15, 20, 22, 10, 14, 10, 8, 8, 5, 10, 8, 6, 6, 7.Animal Intelligence
The time-curve is obviously a fair representation of the progress of the formation of the association, for the two essential factors in the latter are the disappearance of all activity save the particular sort which brings success with it, and perfection of that particular sort of act so that it is done precisely and at will.Animal Intelligence
By repeating the experience again and again, the animal gradually comes to omit all the useless clawings, and the like, and to manifest only the particular impulse… which has resulted successfully. It turns the button around without delay whenever put in the box.Educational Psychology Vol 2 The Psychology of Learning
a gradual descent—say, from initial times of 300 sec. to a constant time of 6 or 8 sec. in the course of 20 to 30 trials—represents a difficult association, while an abrupt descent, say in 5 trials, from a similar initial height, represents a very easy association.Animal Intelligence
The sudden drops represent happy variations preserved by their success alone or, and far more often, by being comprehended and fixed in thought so as to be deliberately defined and sought after in the next trial. Where solution depends on a single insight, there is one main drop as in FIG. 133. If it requires several insights for separate features of it, there may be several drops as in FIGS. 134 and 135.Educational Psychology Vol 2 The Psychology of Learning
This method of presenting progress in analytical and selective learning rather conceals some of the facts which appear when we consider the learning in the same way as has been done hitherto in this volume, namely, with the abscissa scaled for equal units of time spent and the heights above it representing the amount of product of a given quality produced per unit of time.Educational Psychology Vol 2 The Psychology of Learning