IV. THE PROBLEMS AND POSSIBILITIES OF COMPARATIVE REACTION-TIME STUDIES.
Animal reaction time is at present a new field of research of evident importance and full of promise. A great deal of time and energy has been devoted to the investigation of various aspects of the time relations of human neural processes; a multitude of interesting facts have been discovered and a few laws established, but the results seem disproportionate to the amount of patient labor expended. Physiologists have determined the rate of transmission of the neural impulse for a few animals, and rough estimates of the time required for certain changes in the nervous system have been made, but this is all we have to represent comparative study. Just the path of approach which would seem most direct, in case of the time of neural changes, has been avoided. Something is known of the ontogenetic aspect of the subject, practically nothing of the phylogenetic; yet, in the study of function the comparative point of view is certainly as important as it is in the study of structure. In calling attention to the importance of the study of animal reaction time I would not detract from or minimize the significance of human investigations. They are all of value, but they need to be supplemented by comparative studies.
It is almost impossible to take up a discussion of the time relations of neural processes without having to read of physiological and psychological time. The time of nerve transmission, we are told, is pure physiological time and has nothing whatever to do with psychic processes; the time occupied by the changes in brain centers is, on the contrary, psychological time. At the very beginning of my discussion of this subject I wish to have it clearly understood that I make no such distinction. If one phase of the neural process be called physiological time, with as good reason may all be so named. I prefer, therefore, to speak of the time relations of the neural process.
Of the value of reaction-time studies, one may well believe that it lies chiefly in the way of approach which they open to the understanding of the biological significance of the nervous system. Certainly they are not important as giving us knowledge of the time of perception, cognition, or association, except in so far as we discover the relations of these various processes and the conditions under which they occur most satisfactorily. To determine how this or that factor in the environment influences the activities of the nervous system, and in what way system may be adjusted to system or part-process to whole, is the task of the reaction-time investigator.
The problems of reaction time naturally fall within three classes: Those which deal with (1) nerve transmission rates; (2) the time relations of the spinal center activities, and (3) brain processes. Within each of these groups there are innumerable special problems for the comparative physiologist or psychologist. Under class 1, for instance, there is the determining of the rates of impulse transmission in the sensory and the motor nerves, (a) for a variety of stimuli, (b) for different strengths of each stimulus, (c) for different conditions of temperature, moisture, nourishment, fatigue, etc., in case of each stimulus, (d) and all this for hundreds of representative animals. From this it is clear that lines of work are not lacking.
Closely related to these problems of rate of transmission are certain fundamental problems concerning the nature of the nerve impulse or wave. Whether there is a nerve wave, the reaction-time worker has as favorable an opportunity to determine as anyone, and we have a right to expect him to do something along this line. The relations of the form of the nerve impulse to the rhythm of vital action, to fatigue and to inhibition are awaiting investigation. Some of the most important unsettled points of psychology depend upon those aspects of neural activities which we ordinarily refer to as phenomena of inhibition, and which the psychologist is helpless to explain so long as the physiological basis and conditions are not known.
Then, too, in the study of animals the relation of reaction time to instincts, habits, and the surroundings of the subject are to be noted. Variability and adaptability offer chances for extended biological inquiries; and it is from just such investigations as these that biology has reason to expect much. The development of activity, the relation of reflex action to instinctive, of impulsive to volitional, and the value of all to the organism, should be made clear by reaction-time study. Such are a few of the broad lines of inquiry which are before the comparative student of animal reaction time. It is useless to dwell upon the possibilities and difficulties of the work, they will be recognized by all who are familiar with the results of human studies.
In the study of the time relations of neural processes Helmholtz was the pioneer. By him, in 1850, the rate of transmission of the nerve impulse in the sciatic nerve of the frog was found to be about 27 meters per second[4]. Later Exner[5] studied the time occupied by various processes in the nervous system of the frog by stimulating the exposed brain in different regions and noting the time which intervened before a contraction of the gastrocnemius in each case. Further investigation of the frog's reflex reaction time has been made by Wundt[6], Krawzoff and Langendorff[7], Wilson[8] and others, but in no case has the method of study been that of the psychologist. Most of the work has been done by physiologists who relied upon vivisectional methods. The general physiology of the nervous system of the frog has been very thoroughly worked up and the papers of Sanders-Ezn[9], Goltz[10], Steiner[11], Schrader[12] and Merzbacher[13], [14] furnish an excellent basis for the interpretation of the results of the reaction-time studies.
In the present investigation it has been my purpose to study the reactions of the normal frog by the reaction-time methods of the psychologist. Hitherto the amount of work done, the extent of movements or some other change has been taken as a measure of the influence of a stimulus. My problem is, What are the time relations of all these reactions? With this problem in mind I enter upon the following program: (1) Determination of reaction time to electrical stimuli: (a) qualitative, (b) quantitative, (c) for different strengths of current; (2) Determination of reaction time to tactual stimuli (with the same variations); (3) Auditory: (a) qualitative, (b) quantitative, with studies on the sense of hearing; (4) Visual: (a) qualitative, (b) quantitative, with observations concerning the importance of this sense in the life of the frog, and (5) Olfactory: (a) qualitative, (b) quantitative.
The present paper presents in rather bare form the results thus far obtained on electrical, tactual, and auditory reaction time; discussion of them will be deferred until a comparison of the results for the five kinds of stimuli can be given.