This study originated in research—by Goldstein and Gelb—on patients with irreversible brain lesions. The examination of the patients' behavior led to the distinction between concrete, i.e., realistic, and abstract, i.e., categorical or conceptual attitudes. The characteristic change in patients with brain lesions is a disturbance of attitude towards the abstract. The authors arrived at their results by the use of various sorting tests, a procedure adopted by Vigotsky in his studies on schizophrenia.

An investigation of schizophrenia by use of the various tests showed many similarities between schizophrenic patients and those with brain injuries: 'In a certain group of schizophrenics, there is a characteristic impairment of