Sex differences in cognitive functions

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Abstract

Gender differences in neuropsychological functioning of patients with psychiatric disorders have been studied extensively in the last years. The available studies provide conflicting results, which can be attributed to the complexity of variables influencing cognitive sex differences. In the present study, we tried to evaluate the magnitude of gender differences in verbal and visual–spatial functions and to correlate the results with a self-rating of these abilities in healthy men and women. Ninety-seven college students (51 women and 46 men) were examined with a neuropsychological battery, focusing on verbal and visual–spatial abilities. In general, we found, that women tend to perform at a higher level than men on most verbal tests and men outperfom women on visual–spatial tasks. Nevertheless, it is worth mentioning, that the effect sizes were generally small, which suggests the assumption, that the overlap in the distribution of male and female scores is much greater than the difference between them. Additionally, in a self-rating scale, men rated their spatial abilities significantly superior to those of women, while women did not rate their verbal abilities superior to those of men. In this context, the relevance of socio-cultural factors, educational factors and training on the occurrence of sex differences is highlighted, as these factors add significantly to the overall explanation of neuropsychological task-performance.

Introduction

Over the past decade, the differences between males and females in terms of neuropsychological functioning have been extensively documented (Astor et al., 1998, Bryden, 1979, Buffery and Gray, 1972, Caplan et al., 1997, Collins and Kimura, 1997, Dabs et al., 1998, Delgado and Prieto, 1996, Fairweather, 1976, Halpern, 1996, Harris, 1978, Harshman and Remington, 1974, Hutt, 1979, Maccoby and Jacklin, 1974, McGivern et al., 1997, McGlone, 1977) and highlighted in the media. When sex differences and similarities are considered, discussion often centres on either “nature” (most characteristics are attributed to biological differences) or “nurture” (social factors and learning which lead to the differences). This debate has been intensified after the invention of new imaging technologies like positron emission tomography and functional magnetic resonance. The last years have shown an exponential increase in investigating gender differences in neuropsychological functions, epidemiology and brain morphology of patients with psychiatric disorders such as schizophrenia, depression or Alzheimer's disease providing conflicting results due in part to methodological artifacts (Goldberg et al., 1995, Goldstein et al., 1998, Hoff et al., 1998). Nevertheless a thorough defining of these sex differences is important to understand the behavioural problems of these diseases and to develop a more refined approach to their treatment. However, the research into gender differences needs to be approached with caution, because many variables like culture, gender, self-perception, hormones etc. influence the results. Generally, it is assumed that the differences between the intellectual functions of the sexes seem to lie in patterns of abilities, rather than in overall intellectual functioning (Collins and Kimura, 1997, Halpern, 1992, Kolb & Wishaw, 1990). Reviews of the literature suggest that men, on average, perform better than women on certain spatial tasks, although the concept of spatial ability or spatial cognition is vague. There are several approaches as to how spatial abilities can be defined or classified. Linn and Petersen (1985) suggested a classification of spatial tests into three distinct categories, which they labelled spatial perception, mental rotation and spatial visualisation. Spatial perception was defined as the ability to determine spatial relations despite distracting information. Mental rotation was defined as the ability to rotate, quickly and accurately, two or three dimensional figures in their imagination. Finally, spatial visualisation was defined as the ability to manipulate complex spatial information, when several stages are needed to produce the correct solution. This categorization was tested by Voyer, Voyer, and Bryden (1995) in a meta-analysis of studies published between 1974 and 1993, that showed that sex differences are seen in some categories of spatial ability but not others. In fact, large sex differences in favour of males were found only on different measures of mental rotation. Smaller differences were present on measures of spatial perception (Linn & Petersen, 1985), whereas for tests in the spatial visualisation category, the differences were highly variable and frequently non-significant. Furthermore, men outperfomed women in mathematical reasoning tests and in navigating their way through a route. Men were also more accurate in tests of target-directed motor skills—that is, in guiding or intercepting projectiles.

In contrast, females exhibit greater flexibility in linguistic tasks. Women tend to be better than men in rapidly identifying matching items, a skill called perceptual speed. Common linguistic skills, in which females have been found to be superior, are verbal fluency, speech articulation, grammatical skills, and use of more complex and longer sentences. Moreover, women are faster at certain precision manual tasks, such as placing pegs in designated holes on a board and have a better perceptual speed and accuracy.

In childhood, they usually learn to speak earlier (Morley, 1957), have larger vocabularies (Nelson, 1973), are better at reading and spelling (Gates, 1961), use complex grammatical constructions sooner (Harris, 1978), and perform better on immediate and delayed memory recall tests (Kramer, Delis, Kaplan, O'Donnell, & Prifitesa, 1997). After puberty, when hormonal and psychosocial influences increase, the gap between boys and girls on verbal tasks widens (Maccoby & Jacklin, 1974).

It is important to place the sex differences on verbal tasks described above in context: some are small, some are quite large. The largest female advantage is found in certain executive speech tasks such as speed of articulation, accuracy of speech production and fluency, but this advantage in verbal expression does not extent to other aspects of the use of language such as verbal reasoning (Hutt, 1979), vocabulary and comprehension.

Also in non-verbal abilities, such as memory, some studies have shown an advantage for women (Hampson & Kimura, 1992). More specifically, it has been found that women perform at a higher level than men on episodic memory tasks such as word recall (Berenbaum et al., 1997, Hill et al., 1995, Kramer et al., 1997), word recognition (Herlitz et al., 1997, Temple and Cornish, 1993, Zelinski et al., 1993), story recall (Hultsch et al., 1991, Zelinski et al., 1993), recall of words under conditions of focused and divided attention (Herlitz et al., 1997), face and name recall and recognition (Herlitz et al., 1997, Hill et al., 1995, Larrabee and Crook, 1993). Furthermore, women tend to outperform men on tests of psychomotor speed and accuracy, using verbal or visual stimuli (Hampson and Kimura, 1992, Majeres, 1988, Majeres, 1990).

Several studies have shown, that at least some of the gender differences could be related to socio-cultural or educational factors (Baenninger and Newcombe, 1989, Gittler and Vitouch, 1994, Hamilton, 1995, Lawton, 1994, Sharps et al., 1994). When there are no explicit spatial test instructions (subjects are not told that it is a spatial task, they are just told what to do) there are no sex differences in performing mental image rotation tasks (Sharps et al., 1994). As men constantly rate their spatial abilities as superior to those of women, women are repeatedly subjected to the expectation that they cannot, or may not, excel in spatial behaviours. Thus, the negative perceptions of women toward spatial cognitive activities may be culturally mediated by traditional feminine self-concepts. Good performance on spatial tasks such as mental image rotation would be perceived as a gender inappropriate activity (Sharps et al., 1994). Consitent with these findings, Hamilton (1995) reported results, that self-perceived gender trait possessions add significantly to the overall explanation of performance in a 3D mental rotation task.

To shed more light on the possible sex differences in cognitive functions, the first purpose of the present study was to evaluate the magnitude of gender differences in verbal and visual–spatial functions and to replicate previous findings in the literature. As mentioned above, these sex differences may be due to socio-cultural factors. Therefore, the second objective was to show differences between self-ratings of spatial and verbal abilities in men and women and to correlate these findings to the objective test results.

Section snippets

Subjects

Ninty-seven university students, who studied psychology or medicine (51 women and 46 men) participated in this study. Testing was conducted in small groups of 5–10 probands in a quiet laboratory room. All subjects were examined using a battery of neuropsychological tests in a standardized fashion. In selecting the neuropsychological tests, we focused on the neuropsychological abilities that are regarded as showing gender differences, especially verbal and visual–spatial functions.

Neuropsychological tests

Verbal

Results

Demographic data (age, handedness, verbal and non-verbal Intelligence) were compared using the two-sample t-tests. Neuropsychological data and subjective estimates were compared using a nonparametric test (Mann–Whitney U-Test). In order to reduce the number of neuropsychological variables, a factor analysis was performed and subscores based on this analysis were calculated, as described below.

There were no statistically significant gender differences with regard to handedness and non-verbal

Discussion

The aim of the present study was to investigate gender differences in verbal and visual–spatial abilities. In general, the results showed, that women perform at a higher level than men on most verbal tests and men tend to outperform women on visual–spatial tasks. A significant difference between men and women was found in three of the four verbal measures and one of the three visual–spatial tasks. We will discuss the results in more detail in the following discussion.

In the present study we

Acknowledgments

E.M. Weiss was supported by the Austrian Fonds zur Förderung wissenschaftlicher Forschung (FWF: J2009).

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