The following photographs show types of tests, used for making mental diagnoses of children at Vineland, the Lincoln Institution in Illinois, the University of Chicago, the Chicago Juvenile Court, Columbia University, University of Pennsylvania, University of Washington, University of Texas, and similar institutions (Figs. 4 to 14).
The foregoing tests and experiments show that mentally defective children offer excellent material for psychological investigation, since they are a more or less isolated group with quite definite boundaries and are dependent on others. They may be observed continuously during their lifetime, they are incapable of being stimulated or enthused by artificial reactions, they are not easily embarrassed or self-conscious; some of their mental processes are slowed down, others almost eliminated and some grossly exaggerated; their motor reactions are usually the direct result of their ideas with little inhibition, decision, choice or judgment, and may therefore be considered fairly safe criteria of the concomitant mental activities. The various stages of mental deficiency frequently parallel the stages of development of the normal mind and since the defective mind may remain for a lifetime at a given level, it may be studied in such a manner as to shed much light on the corresponding stages of the developing mind of the normal child, which is so fleeting in its passage to higher levels.
Finally: 1. Defectives are worthy of careful study for their own sake, for the welfare of society, and for the scientific insight they offer into the mental processes of normal children and the problem of education.
2. They offer, where their ancestry may be traced, the best material at present available for the study of human heredity on account of the pronounced deviations which may be traced.
3. They have so far contributed most to the scientific application of "mental and physical tests" which dominates contemporary tendencies in child psychology and its application to education.
4. Mental defectives present tremendous sociological difficulties in