Popular Science Monthly/Volume 32/February 1888/The Time it Takes to Think
By J. McK. CATTELL.
ALL science is partly descriptive and partly theoretical. Care must, however, be taken lest too much theory be built up without sufficient foundation of fact, or there is danger of erecting pseudo-sciences, such as astrology and alchemy. The theories of the conservation of energy and of the evolution of species are more interesting to us than the separate facts of physics and biology, but facts should be gathered before theories are made. The way of truth is a long way, and short cuts are apt to waste more time than they save. Psychology is the last of the sciences, and its present business seems to be the investigation of the facts of consciousness by means of observation and experiment. Everywhere in science experiment is worth more than observation; it is said that the evidence in pathology is so contradictory that almost anything can be proved by clinical cases. Psychology, owing to its very nature, must always depend largely on observation for its facts, and some progress has been made in spite of the difficulties lying in the way of introspection and the correct interpretation of the actions of others. The application of experimental methods to the study of mind is, however, an important step in advance, and would seem to be a conclusive answer to those who, with Kant, hold that psychology can never become an exact science. I propose explaining here how we can measure the time it takes to think, and hope this example may show that the first fruits of experimental psychology are not altogether insignificant or uninteresting. Just as the astronomer measures the distance to the stars and the chemist finds atomic weights, so the psychologist can determine the time taken up by our mental processes. It seems to me the psychical facts are not less important than the physical; for it must be borne in mind that the faster we think, the more we live in the same number of years.
It is not possible directly to measure the time taken up by mental processes, for we can not record the moment either of their beginning or of their end. We must determine the interval between the production of some external change which excites mental processes, and a movement made after these processes have taken place. Thus, if people join hands in a circle, and one of them. A, presses the hand of his neighbor B, and he as soon as possible afterward the hand of C, and so on round and round, the second pressure will be felt by each of the persons at an interval after the first, the time depending on the number of people in the circle. After the hand of one of the persons has been pressed an interval very nearly constant in length passes before he can press the hand of his neighbor. This interval, which we may call the reaction-time, is made up of a number of factors. A period elapses before the pressure is changed into a nervous message or impulse. This time is very short in the case of touch; but light working on the retina seems to effect chemical changes in it, and these take up some little time, probably about one fiftieth of a second. After a nervous impulse has been generated it moves along the nerve and spinal cord to the brain, not traveling with immense rapidity like light, but at the rate of an express train. In the brain it must move on to a center having to do with sensation, where changes are brought about, through which a further impulse is sent on to a center having to do with motion, and a motor impulse having been prepared there is sent down to the hand. Another pause, one two hundredth to one one hundredth of a second, now occurs, while the muscle is being excited, after which the fingers are contracted and the reaction is complete. The entire time required is usually from one tenth to one fifth of a second. The reaction-time varies in length with different individuals and for the several senses, but as long as the conditions remain the same the times are very constant, only varying a few thousandths of a second from each other. One may wonder how it is possible to measure such short times and with such great accuracy. It would not be easy if we had not the aid of electricity; but when it is called to mind that a movement made in London is almost instantaneously registered in Edinburgh, it will not seem inconceivable that we can record to the thousandth of a second the instant a sense-stimulus is produced and the instant a movement is made. The time passing between these two events can be measured by letting a tuning-fork write on a revolving drum. The tuning-folk can be regulated to vibrate with great exactness, say five hundred times a second; it writes a wavy line on the drum, each undulation long enough to be divided into twenty equal parts, and thus time can be measured to the ten thousandth of a second.
The psychologist is chiefly interested in what goes on in the brain and mind. It seems that about one half of the entire reaction-time is spent while brain changes take place, but we know very little as to these changes, or as to how the time is to be allotted among them. It is probable that in the ease of the simple reaction the movement can be initiated before the nature of the impression has been perceived. We can, however, so arrange the conditions of experiment that the observer must know what he has seen, or heard, or felt, before he makes the movement. He can, for example, be shown one of a number of colors, and not knowing beforehand which to expect, be required to lift his finger only when red is presented. By making certain analyses and subtracting the time of the simple reaction from the time in the more complex case, it is possible to determine with considerable accuracy the time it takes to perceive, that is, the time passing from the moment at which an impression has reached consciousness until the moment at which we know what it is. In ray own case about one twentieth of a second is needed to see a white light, one tenth of a second to see a color or picture, one eighth of a second to see a letter, and one seventh of a second to see a word. It takes longer to see a rare word than to see a common one, or a word in a foreign language than one in our native tongue. It even takes longer to see some letters than others.
The time taken up in choosing a motion, the "will-time," can be measured as well as the time taken up in perceiving. If I do not know which of two colored lights is to be presented, and must lift my right hand if it be red and my left hand if it be blue, I need about one thirteenth of a second to initiate the correct motion. I have also been able to register the sound-waves made in the air by speaking, and thus have determined that in order to call up the name belonging to a printed word I need about one ninth of a second, to a letter one sixth of a second, to a picture one quarter of a second, and to a color one third of a second. A letter can be seen more quickly than a word, but we are so used to reading aloud that the process has become quite automatic, and a word can be read with greater ease and in less time than a letter can be named. The same experiments made on other persons give times differing but little from my own. Mental processes, however, take place more slowly in children, in the aged, and in the uneducated.
It is possible, further, to measure the time taken up in remembering, in forming a judgment, and in the association of ideas. Though familiar with German, I need, on the average, one seventh of a second longer to name an object in that language than in English. I need about one quarter of a second to translate a word from German into English, and one twentieth of a second longer to translate in the reverse direction. This shows that foreign languages take up much time even after they have been learned, and may lead us once more to weigh the gain and loss of a polyglot mental life. It takes about two fifths of a second to call to mind the country in which a well-known town is situated, or the language in which a familiar author wrote. We can think of the name of next month in half the time we need to think of the name of last month. It takes on the average one third of a second to add numbers consisting of one digit, and half a second to multiply them. Such experiments give us considerable insight into the mind. Those used to reckoning can add two to three in less time than others; those familiar with literature can remember more quickly than others that Shakespeare wrote "Hamlet." In the cases which we have just been considering a question was asked admitting of but one answer, the mental process being simply an act of memory. It is also possible to ask a question that allows of several answers, and in this case a little more time is needed; it takes longer to mention a month when a season has been given than to say to what month a season belongs. The mind can also be given still further liberty; for example, a quality of a substantive, of a subject or object for a verb, can be required. It takes about one tenth of a second longer to find a subject than to find an object; in our ordinary thinking and talking we go on from the verb to the object. If a particular example of a class of objects has to be found, as "Thames" when "river" is given, on the average a little more than half a second is needed. In this case one nearly always mentions an object immediately at hand, or one identified with one's early home; this shows that the mind is apt to recur either to very recent or to early associations. Again, I need one second to find a rhyme, one fifth of a second longer to find an alliteration. The time taken up in pronouncing an opinion or judgment proved to be shorter than I had expected; I need only about half a second to estimate the length of a line, or to say which of two eminent men I think is the greater.
Our thoughts do not come and go at random, but one idea suggests another, according to laws which are probably no less fixed than the laws prevailing in the physical world. Conditions somewhat similar to those of our ordinary thinking are obtained, if on seeing or hearing a word we say what it suggests to us. We can note the nature of the association and measure the time it takes up, and thus get results more definite and of greater scientific value than would be possible through mere introspection or observation. By making a large number of experiments, data for laws of association can be collected. Thus, if a thousand persons say what idea is suggested to them by the word "Art," the results may be so classified that both the nature of the association and the time it occupies throw much light on the way people usually think. Such experiments are useful in studying the development of the child's mind; they help us to understand the differences in thought brought about by various methods of education and modes of life, and in many ways they put the facts of mind into the great order which is the world.—Nineteenth Century.
Recognizing that the surface of the earth will in a few years be all explored for ordinary geographical purposes, Professor Boyd Dawkins has called attention to the fact that besides the geography in space, there is a nearly untouched field of geography in time. It concerns the ancient changes by which the earth's surface has come to be what it Is, and the geographical outlines as they appeared at the various geological periods. In working this field geographers would do as good geographical work as in recording any of the facts which are brought from the interior of Africa or from the polar regions.