Abstract
This study attempted a test of the short-term memory hypothesis by the factor analysis on the results of WISC. The scores on ten subtests of the WISC (Digit span and Mazes excluded) were obtained from three retarded groups. Intercorrelations between the subtests were factor analyzed by the Thurstone's centroid method, and rotations were made with oblique rotation by radial method. Four factors were extracted and identified as General, Verbal. Performance and M factor. The M factor loaded commonly on Coding in all groups, and the other subtest configuration of M factor of the subnormal groups was different from that of normals. In mentally retarded groups, the M factor loaded mainly on Coding and Picture arrangement. The Verbal and the Performance factors were highly and positively associated in the normal groups, but negatively associated in the subnormal groups. On the basis of these results, it was generaly concluded that (A) The intellectural structure of the mentally etarded differs qualitatively from that of normals. (B) The M factor structure in mentally retarded groups was similar at many respects to the results of previous factor analystic studies of the WISC performance of intellectually subnormal. (C) The M factor in mentally retarded may be interpreted as supporting the trace theory of Ellis which suggests that the mental retardates have a short-term memory deficit, however, there should be needed further studies on the validity of M factor.
