Date of Award


Degree Type


Degree Name

Master of Science (MS)


Medical Sciences (Growth and Development)


S.F. Witelson


The primary focus of this research was to investigate the possible influence of biological sex, specifically the sex chromosomes and hormones, on level of cognitive abilities and pattern of hemisphere specialization in humans. Normal males, and females are known to differ in level of cognitive abilities, with males typically having a higher level of spatial ability than females, and females achieving higher scores on tests of several aspects of linguistic ability. A growing body of research indicates that the sexes may also differ in degree of hemisphere specialization, with males being more lateralized than females. It has been suggested that degree of hemisphere specialization for spatial and linguistic processing may be related to the level of these cognitive abilities. The specific hypothesis of this research was that since the sexes differ in cognitive abilities and perhaps in hemisphere specialization, then perhaps the sex chromosomes and hormones may play a role in determining patterns of neural organization and cognitive abilities.

This hypothesis was explored by comparing a group of eight Turner syndrome subjects to normal control groups of both females and males. Turner syndrome individuals were studied because they do not have a normal second X chromosome as do normal females or the Y chromosome of normal males. Thus they are genetically different from both normal males and females. Nor do Turner syndrome individuals have normal sex hormone production. Thus the possible role of these biological variables could be studied. However, on the basis of this syndrome alone, the relative importance of these factors cannot be disentangled. The study of Turner syndrome also allows one to rule out environmental factors since Turner syndrome individuals phenotypically resemble normal females. Previous research has indicated that TS individuals have a deficit in spatial ability compared to normal females.

Male and female control subjects were matched with the Turner syndrome subjects on aspects of both Verbal and Performance IQ. Each group had a mean age of approximately 17 years.

A battery of tests measuring spatial ability, linguistic ability and hemisphere specialization was administered to the eight subjects in each of the three groups. A trend toward bilateral representation for linguistic processing was observed in the Turner syndrome group. Right hemisphere specialization for the processing of nonverbal stimuli appeared to be normal.

With regard to cognitive abilities, the Turner syndrome subjects were found to perform at a normal level on many tests such as a phonetic reading test, tests of verbal intelligence, and tests of some aspects of spatial ability, compared to normal males and females. However, their performance was found to be deficient on some aspects of a test of three-dimensional perception, a word recognition reading test, a written word fluency test and a coding or digit symbol test. It is suggested that a common element required in the performance of these tests on which Turner syndrome individuals were deficient may be some aspects of visuospatial perception and memory which become particularly deficient when there are time constraints.

Given the cognitive differences and the tendency toward a difference in hemisphere specialization between the Turner syndrome and normal subjects, it is suggested that either the lack of a second X chromosome or the lack of normal sex hormones, or both, play a role in determining the level of cognitive abilities and pattern of hemisphere specialization in normal humans. The evidence from this and previous studies suggests that the absence of a normal second X chromosome alone may underlie the differences between Turner syndrome subjects and normal females.

Some of the methodological problems encountered in this type of research are also discussed.

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