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Pioneering work in the study of thinking in schizophrenia has been done by Vigotsky. In this book the authors subject Vigotsky's methods and conclusions to more thorough examination. An experiment was done on a large group of schizophrenics of different clinical types. A group of healthy subjects of comparable age and educational level was used as a control group and the test was also applied to a small group with irreversible organic brain disease. The authors sought to find what variations of performance occurred and what meaning these variations have; to what degree the educational level of the subject influences the result, whether schizophrenics actually show a reduction of conceptual thinking as compared with healthy persons; if there is a reduction, does it apply to all kinds of schizophrenia; and is the disturbance comparable to that found in organic brain disease.
The test performance used is fully and clearly described and the formulation of the results is presented in a well-organized and simple manner.
It was found that there are variations in performance of the test. These can be grouped on three levels which suggest three corresponding levels of thinking—the primitive intermediate and conceptual levels. On the primitive level the correct solution of the test is either not found at all or is found accidentally without insight. On the intermediate level the subject understands he must follow some rule but the nature of this rule does not become clear to him. On the conceptual level the task is clearly understood from the start as that of finding a classification. He goes about the work systematically and discards his erroneous hypotheses as soon as he sees their inconsistency. It was found that this test performance was strongly dependent on the educational level of the subject. Even among the normals only the college educated group performs on the highest conceptual level. The schizophrenic group performs as a whole on a lower level than the normal group