The Story of the Mind

by James Mark Baldwin

IV. The Accuracy of Memory.—Another investigation may be cited to illustrate quite a different department. It aimed to find out something about the rate at which memory fades with the lapse of time. Messrs. W., S., and B.[7] began by formulating the different ways in which tests may be made on individuals to see how accurate their memories are after different periods of time. They found that three different tests might be employed, and called them "methods" of investigating memory. These are, first, the method of Reproduction. The individual is asked to reproduce, as in an oral or written examination, what he remembers of something told him a certain time before. This is the ordinary method of the schools and colleges, of civil-service examinations, etc. Second, the method of Identification, which calls upon the person to identify a thing, sentence, report, etc., a second or third time, as being the same in all respects as that which he experienced the first time it appeared. Third, the method of Selection, in which we show to the person a number of things, sentences, reports, descriptions of objects, etc., and require him to select from them the ones which are exactly the same as those he has had before. These methods will be better understood from the account now to be given of the way they were carried out on a large number of students.

[7] Prof. H. C. Warren, Mr. W. J. Shaw, and the writer.

The first experiments were made by Messrs. S. and B. in the University of Toronto on a class of students numbering nearly three hundred, of whom about one third were women. The instructors showed to the class certain squares of cardboard of suitable size, and asked them to do the following three things on different days: First, to reproduce from memory, with pencil on paper, squares of the same size as those shown, after intervals of one, ten, twenty, and forty minutes (this gives results by the method of Reproduction); second, to say whether a new set of squares, which were shown to them after the same intervals, were the same in size as those which they had originally seen, smaller, or larger (illustrating the method of Identification); third, they were shown a number of squares of slightly different sizes, again at the same intervals, and asked to select from them the ones which they found to be the same size as those originally seen (method of Selection).

The results from all these experiments were combined with those of another series, secured from a large class of Princeton students; and the figure (Fig. 8) shows by curves something of the result. The figure is given in order that the reader may understand by its explanation the "graphic method" of plotting statistical results, which, with various complications, is now employed in psychology as well as in the other positive sciences.

Fig. 8.—Memory curves: I. Method of Selection. II. Method of Identification.

Briefly described in words, it was found that the three methods agreed (the curves are parallel)[8] in showing that during the first ten minutes there was a great falling off in the accuracy of memory (slant in the curves from 0 to 10); that then, between ten and twenty minutes, memory remained relatively faithful (the curves are nearly level from 10 to 20), and that a rapid falling off in accuracy occurred after twenty minutes (shown by the slant in the lines from 20 to 40).

[8] This figure shows curves for two of the methods only, Selection and Identification.

Further, the different positions of the curves show certain things when properly understood. The curve secured by the method of Reproduction (not given in the figure) shows results which are least accurate, because most variable. The reason of this is that in drawing the squares to reproduce the one remembered, the student is influenced by the size of the paper he uses, by the varying accuracy of his control over his hand and arm (the results vary, for example, according as he uses his right or left hand), and by all sorts of associations with square objects which may at the time be in his mind. In short, this method gives his memory of the square a chance to be fully assimilated to his current mental state during the interval, and there is no corrective outside of him to keep him true.