Psychology

by Robert Sessions Woodworth

But is anything once learned ever completely forgotten and lost? Some say no, being strongly impressed by cases of recovery of memories that were thought to be altogether gone. Childhood experiences that were supposed to be completely forgotten, and that could not at first be recalled at all, have sometimes been recovered after a long and devious search. Sometimes a hypnotized person remembers facts that he could not get at in the waking state. Persons in a fever have been known to speak a language heard in childhood, but so long disused as to be completely inaccessible in the normal state. Such facts have been generalized into the extravagant statement that nothing once known is ever forgotten. For it is an extravagant statement. It would mean that all the lessons you had ever learned could still be recited, if only the right stimulus could be found to arouse them; it would mean that all the lectures you ever heard (and attended to) are still retained, that all the stories you ever read are still retained, that all the faces you ever noticed are still retained, that all the scenes and happenings that ever got your attention could still be revived if only the right means were taken to revive them. There is no evidence for any such extreme view.

The modern, scientific study of this matter began with [{350}] recognizing the fact that there are degrees of retention, ranging all the way from one hundred per cent, to zero, and with the invention of methods of measuring retention. Suppose you have memorized a list of twenty numbers some time ago, and kept a record of the time you then took to learn it; since when you have not thought of it again.

Fig. 53.--(From Ebbinghaus.) The curve of forgetting. The curve sinks at first rapidly, and then slowly, from the 100 per cent line towards the zero line, 100 per cent. here meaning perfect retention, and 0 no retention.

On attempting now to recite it, you make no headway and are inclined to think you have entirely forgotten it. But, finding the list again, you relearn it, and probably find that your time for relearning is less than the original learning time--unless the lapse of time has run into months. Now consider--if no time at all were needed for relearning, because the list could be recited easily without, your retention would be one hundred per cent. If, on the contrary, it took you just as long now to relearn as it did originally to learn, the retention would be zero. If it takes you now two-thirds as long to relearn as it originally took to learn, then [{351}] one-third of the work originally done on the list does not have to be done over, and this saving is the measure of retention.

By the use of this method, the curve of retention, or curve of forgetting, as it is also called, has been determined. It is a curve that first goes down steeply, and then more and more gradually, till it approximates to zero; which means that the loss of what has been learned proceeds rapidly at first and then more and more slowly.

The curve of forgetting can be determined by other methods besides the saving method--by the recall method or by the recognition method; and data obtained by these methods are given in the adjoining tables. It will be seen that the different methods agree in showing a curve that falls off more rapidly at first than later. More is lost in the first hour than in the second hour, and more in the first week than in the second week. Few of the experiments have been continued long enough to bring the curve actually to the zero line, but it has come very close to that line in tests conducted after an interval of two to four months.

PER CENT. OF WORDS RECOGNIZED AT DIFFERENT INTERVALS
AFTER BEING SEEN (From Strong)
Interval between Per cent. recognized with
exposure and test certainty and correctness
15 secs. 84
5 min. 73
15 min. 62
30 min. 58
1 hour 56
2 hours 50
4 hours 47
8 hours 40
12 hours 38
1 day 29
2 days 24
4 days 19
7 days 10
The subject read a list of 20 disconnected words once
through, giving careful attention to each word.
Immediately at the close of the reading he performed an
example in mental arithmetic, to prevent his reviewing the
list of words mentally. After an interval, he was shown
these [{352}] twenty words mixed with twenty others, and had
to pick out those he surely recognized as having been
shown before. Many lists were used, for testing after the
different intervals. Five adult subjects took part in the
experiment, and in all 15 lists were used with each
interval; the per cents. given in the table are the
averages for the 15 lists.
THE PER CENT. OF ERROR IN RECALLING DETAILS OF A
PICTURE AFTER DIFFERENT INTERVALS OF TIME
(From Dallenbach)
Time of test Per cent, of error Per cent of error
in spontaneous in answering
recall questions regarding
the picture
Immediately
after exposure 10 14
After 5 days 14 18
After 15 days 18 20
After 46 days 22 22
The picture was placed in the subject's hands, and he
examined it for one minute, at the end of which time he
wrote down as complete a description of the picture as
possible, and then answered a set of sixty questions
covering all the features of the picture. After five days
he was retested in the same way, and again after fifteen
days, etc. In one respect this is not a typical memory
experiment, since the test after five days would revive
the subject's memory of the picture and slacken the
progress of forgetting. The experiment corresponds more
closely to the conditions of ordinary life, when we do
recall a scene at intervals; or it corresponds to the
conditions surrounding the eye-witness of a crime, who
must testify regarding it, time after time, before police,
lawyers and juries. However, the subjects in this
experiment realized at the time that they were to be
examined later, and studied the picture more carefully
than the eye-witness of a crime would study the event
occurring before his eyes; so that the per cent. of error
was smaller here than can be expected in the courtroom.

It must be understood that this classical curve of forgetting only holds good, strictly, for material that has barely been learned. Reactions that have been drilled in thoroughly and repeatedly fall off very slowly at first, and the further course of the curve of forgetting has not been accurately followed in their case. A typist who had spent perhaps two hundred hours in drill, and then dropped typewriting for a year, recovered the lost ground in less than an hour of fresh practice, so that the retention, as measured by the saving method, was over ninety-nine per cent.