The history of animal psychol ogy and its present status alike indicate the prevalence of two methods and resulting kinds of psychological description,— the naturalistic and the experimental. By naturalistic observa tion is meant the study of animals under nat ural and uncontrolled conditions, usually, in a free state; by experimental observation, the study of animals under definitely controlled conditions for the solution of specific problems. Experimental work is usually done in the pre arranged conditions of a laboratory.
Prior to 1900, almost all of the materials of animal psychology were naturalistic or anec dotal. They were gathered without systematic or thorough effort to control or even to describe the conditions. Such, for the most part, are the contributions of Aristotle, Pliny, Buffon, Huber, Hudson, Wallace, Brehm, Fabre, Burroughs, Seton. These writers have presented valuable accounts, as a result of field observations,, of what animals do. The daily life activities of animals, their habits, instincts, education, free play, are the natural objects of interest. Specific problems are not necessarily in the mind of the naturalist. He seeks a kind of natural history of behavior and mind, and this he more or less satisfactorily attains.
Modern experimental work is directed toward definite problems for the solution of which animal and environment are alike com manded and controlled. Whereas the naturalist seeks wood and field and by patient, persistent watching satisfies himself that the young of the cat tribe instinctively captures and kills its prey, the experimentalist places his animal sub ject in an environment which calls forth what ever capacity it may have to respond to prey. The one observer gains intimate and valuable acquaintance with the nature of his animal and becomes sympathetically familiar with it; the other proceeds directly to the solution of hi problem, often ignoring materials of extrenn interest and value.
Naturalist and experimentalist are Alice necessary to the progress of animal But most to be desired, perhaps, is the combinn, !ion of qualifications and interest in a single individual.
Originally, so far as bums records go, the instinctive and habitual mo& of adjustment to environment fascinated ob servers. Thus we find the ancient literature
filled with descriptions of individual and race preservative activities. With the birth of a more truly scientific animal psychology, evols tionary problems came to the fore. the de velopment of various functions now command, attention. To-day several fairly well-defined lines of research are conspicuously furthered in important centres. Of these, six seem worthy of special mention and brief consideration as indicating characteristics of the animal psychol ogises interest. (1) Sensory functions; (2) the role of the senses, as in orientation; (3) in stinctive or hereditary modes of response; (4) emotional experience'and expression ; (5) modi fications of behavior, as in habit formation; (6) ideation and thought processes, together with modes of expression thereof.
Naturally, with these are bound up many problems concerning the functions of the nerv ous system, on the one hand, and the charac teristics of consciousness on the other. But in the main, the present-day student of animal psychology is concerned with behavior and its conditions. If he is deeply interested in mind as a factor, he may be called a psychologist; ii not, he should be called a physiologist.
. Each of the six varieties of problem men tioned above may now be commented upon in order that the achievements of the science of animal psychology may be indicated.
Sensory Functions.— In no field of inquiry has more notable progress been made than in the study of the senses and their role in be havior. The few and crude methods of research employed by the pioneers of the last century have been replaced by varied and refined methods. Nowhere is the contrast and the extent of progress more evident than in the study of color vision.
For several decades, and up to about 10 years ago, it had been customary to test the color sense of animals by noting their responses to colored objects in nature or by arranging colored surfaces so that one color should be sought, another avoided. Food was usually associated with the color to be chosen. The older naturalists and experimentalists unhesitat ingly -attributed color vision of some sort to many insects and to all vertebrates.