Measure Your Mind: The Mentimeter and How to Use It

by Marion Rex Trabue; Frank Parker Stockbridge

“What, precisely, do psychological tests measure?”

It is a question that is easier to ask than to answer.

It is simple enough to say that mental tests are designed to measure the natural or inherent mental capacity of the individual, but in order to approach a clear understanding of just what this means we must first define what is meant by the term “mental capacity.”

As a matter of scientific fact, the term “mental capacity” can hardly be regarded as accurate, although it is the best term we have to describe the qualities which determine the individual’s ability to perform acts requiring conscious thought. Psychological and biological science no longer regard the human mind as something different from or in any way apart from the human body. The idea that there is such an entity as a mind that operates even in the slightest degree without reference to and independent of the physical body must be dismissed, if we are to grasp clearly the principles and methods of mental tests.

To the psychologist the mind is merely a specialized organ of the physical body. The intangible something, which is what is usually meant when persons speak of the human mind, is merely the sum of all the sensations, feelings, and judgments resulting from the delicate adjustment of an almost infinite number of nerve fibres which in themselves are a part of the physical body. One may have at birth a plentiful supply or a poor supply of potential nerve endings which are ready to be organized and coördinated by experience and training, but unless one has the opportunity to learn from study and experience, the desirable connections may never be developed.

The maximum capacity of the mind in any particular field is, therefore, practically determined by physical inheritance of an abundant supply of nerve endings. Thus, it may be that one individual is born with two or three times as many nerve terminals connecting at the point at the back of the eyeball where the optic nerve—which is simply a bundle or rope of nerve fibres—is attached to the mechanical apparatus upon which the reflection of objects passing before the field of vision is registered. Such an individual’s powers of observation are normally greater than those of the person of less fortunate heredity in this respect, whose lesser number of terminals of the optic nerve fibres limit his powers of optical perception and observation. Thus, one person may see at a glance a hundred details, all of which register sharply upon his consciousness, while another sees only the gross outlines and shadows, and in between is the average person who sees some details but not all.

It is well known to psychologists and biologists, although not generally understood by those who have not made a special study of these sciences, that mental capacity does not change or increase materially after the individual has reached maturity. It may be diminished through accident or disease, but the chief increase in adult life is in the volume and variety of stored-up impressions. The average girl of eighteen or boy of twenty has reached the approximate limit of his or her mental capacity. The mental tank will never grow much larger. It may be half empty or almost entirely vacant, but unless at the average age of university sophomores scientific mental tests prove the individual to be possessed of average or better than average mental capacity, it is futile to expect any great intellectual development to take place in later life.

But while the maximum capacity of the mind depends upon physical inheritance, the actual ability which is necessarily reflected in the scores made by a person subjected to mental tests is determined by the number and variety of nerve connections that have actually been made by environment or training. Inheritance sets the maximum limit, but as a matter of practice this maximum is never reached, or at least is so seldom reached by any individual that it can hardly be said of any human being that he has developed his mind in any direction to the utmost limit of its capacity. What we actually measure in scientific mental tests is a complex of natural or inherent abilities plus the results of education and training; because, while it is possible to a considerable extent to eliminate by properly devised tests a record of the individual’s acquired knowledge, it is practically impossible to distinguish between acquired and inherent mental ability.

Note carefully the distinction between mental ability and mental capacity. Mental ability in any individual is always less than his mental capacity. If, therefore, the mental ability as determined by scientific tests reaches the highest point on the scale of measurement, whatever that may be, it follows that the mental capacity of the individual making a perfect score is even greater than the scale is designed to measure, and how much greater can only be determined by setting up new tests based upon higher standards.

The result of any scientific test simply indicates the wealth of nerve connections that are ready to be made when the stimulus necessary to their establishment is applied. It must be understood that no one having a sound claim to the possession of scientific knowledge can contend that there are tests in existence that actually measure with complete precision the inherited as distinguished from the acquired mental characteristics. It is not conceded, however, that such precise measurements cannot be made if at any time it becomes necessary or desirable to do so. For all practical present-day purposes it is sufficient that psychological tests shall measure mental qualities which are manifested by the individual’s ability to express them by action or speech. The classification of individuals relative to one another and with reference to the possession of a particular mental ability or group of abilities is, therefore, necessarily based upon their relative ability to express in some intelligible and unmistakable fashion their mental power and qualities.