Sex differences in cognition

Sex differences in cognitive abilities: a cross-cultural perspective

Studies in Western cultures have indicated significant sex differences in certain cognitive abilities. To determine whether similar differences occur in a non-Western culture, this study administered a cross-linguistic battery of tests to high school students in Japan and America. In both cultures, girls averaged significantly higher scores on a Story Recall test, the Digit-Symbol test and a Word Fluency test whereas boys achieved significantly higher scores on a Mental Rotation test. The analysis of standardized test scores further indicated that the size of the sex difference was culture-independent in three out of these four cases. These results are discussed in the context of the GESCHWIND and GALABURDA [Cerebral Lateralization, Biological Mechanisms, Associations and Pathology, Bradford Books, Cambridge, Massachusetts] account of the contribution of testosterone to left-right asymmetries in early cerebral development.

Manual asymmetry in weight discrimination: hand preference or hemispheric specialization?

One-handed weight discrimination was investigated as a function of hand, hand preference and hemispheric specialization. Differential thresholds (DLs) were measured for the left and right hands and left- and right-handed male and female subjects. DLs were found to be lower for the hand contralateral to the ear that proved superior in a verbal dichotic listening task. These results establish the existence of a manual asymmetry for the discrimination of lifted weight with the advantage accruing for the hand contralateral to the non-language cerebral hemisphere.

Sex differences in the lateralization of spatial abilities: a spatial component analysis of extreme group scores

Sex differences in the cerebral lateralization of two discrete components of spatial processing were investigated in high and low ability males and females using the dual-task paradigm. In the first phase of the experiment, the results indicated a pattern of right hemispheric control for a spatial visualization component, regardless of sex and ability level. In the processing of the spatial orientation component of spatial ability, high ability males and females showed left hemispheric lateralization, whereas low ability males and females displayed right hemispheric control. In the second phase of this study, it was observed that high ability females and low ability males may use a verbal mediation strategy in processing spatial visualization tasks. No verbal mediation effects were found for the spatial orientation component.

The distribution of hand preference in normal men and women

The distributions of the hand preferences (Geschwind scores) were studied in men and women. The incidences of the right-, mixed-, and left-handers were 66.1, 30.5, and 3.4%, respectively. The left- and right-handers (LHs, RHs) were represented by two bars located at the opposite ends of a J-shaped histogram for the total sample, men, and women. The distributions for the total RHs, and male RHs were not J-shaped, but negatively skewed, the mode being close to the mean. The frequencies for the females increased linearly. The distributions for the LHs did not significantly deviate from normality. Except for the LHs, the percentage distributions of the Geschwind scores were J-shaped. The LHs were evenly distributed by chance to be expected in a random sample from a rectangular population. The incidence of weak right-handedness was significantly higher in men than women. The total RHs were more lateralized than the total LHs who showed a tendency toward weak left-handedness. In males, the incidence for weak left-handedness was significantly higher than that for strong left-handedness. The opposite was established for females. The probability of the consistent right-handedness was significantly higher in women than men. The LHs were less lateralized, and more widely dispersed than the RHs. The statistical analysis of the distributions indicated that females tended to be more lateralized, i.e., more right-handed, and more left-handed, than males.

Neuropsychological development of cognitive abilities: a new research strategy and some preliminary evidence for a sexual orientation model

The organizing action that prenatal sex hormones exert on the brain has been implicated in the aetiology of sex differences in cognitive abilities and cerebral asymmetries. Prenatal sex hormones are known to determine neuroendocrine responses and subsequent adult sexual behaviour in nonhuman animals and these hormones may also influence human sexual orientation. To unify these observations, we elaborate a sexual orientation model of neuropsychological development which predicts that sex differences in neuroendocrine responses, cerebral asymmetries, and cognitive abilities are related to sexual orientation rather than to sex per se. A common problem in the study of sex differences is that biological and sociocultural explanations are confounded. The sexual orientation model suggests a new research strategy, the comparison of homosexual and heterosexual groups, for which explanations in terms of sociocultural factors would be more difficult to sustain. The available evidence supports the model: In terms of a neuroendocrine response, cerebral asymmetry, and cognitive abilities, homosexual males resemble heterosexual females rather than heterosexual males. Our conclusions lead to questions that further research in this area should address, and to a consideration of problems which such research may have to face.

Sex differences and practice effects on two visual-spatial tasks

Sex differences on visual-spatial tasks have been assumed to be present in young children, and performance on visual-spatial tasks has been assumed to be resistant to modification. Third and fifth graders were pretested on embedded and successive figures. Half of the 110 children then received limited feedback after which both groups were posttested. Grade, time of testing, and type of task significantly affected visual-spatial performance. Additional study might indicate whether amount of practice influences final level of performance for girls and boys and the asymptote on visual-spatial tasks is similar.

Sex, handedness and weight discrimination

Manual asymmetries in weight discrimination were investigated by testing 50 subjects with their left hand and 52 with their right hand, the groups being approximately balanced for sex and hand preference. Performance was better for the left-tested group, and for strongly handed males tested with the dominant hand. Female performance was unrelated to handedness. There was no overall superiority due to sex, males being superior with the dominant hand and females with the nondominant hand. The results are interpreted in terms of spatial hemisphere involvement, hand dominance, and the greater hemispheric specialization of males.

Sex differences in categorization of tactile stimuli

This experiment investigated the effect of sex differences in categorization of tactile stimuli. 9 men and 9 women rated the perceived similarity between pairs of stimuli varying in texture and shape. The magnitudes of sex-related differences, using omega 2 and d, were relatively large and indicated that men had better categorical abilities in processing haptic information.

Individual use of judgmental dimensions and hemispheric specificity

The present study investigated the relationship of hemispheric functional specificity to a subject's use of judgmental dimensions when discriminating temporal and spatial visual stimuli using a multidimensional scaling (MDS) paired-comparison paradigm. The major purposes of the study were: To identify the judgmental dimensions used in discriminating unidimensional (temporal or spatial) and multidimensional (combinations of temporal and spatial parameters) stimuli presented to the two visual hemifields; to study the relationship of the use of judgmental dimensions to the visual hemifields; to investigate whether the use of judgmental dimensions in discriminating unidimensional stimuli can be used to predict their use in discriminating multidimensional stimuli. Subjects used two dimensions in discriminating the spatial and temporal unidimensional stimuli: A dimension whose scaling paralleled the physically interval-scaled stimuli; a dimension, in which the extreme values were located on one end of the scale, while the mid-values are located at the other end of the scale. There is significantly greater use of the spatial dimension when spatial stimuli are presented to the left visual field (LVF) then when presented to the right visual field (RVF). Conversely, there is significantly greater use of the temporal dimension when temporal stimuli are presented to the RVF then when they are presented to the LVF. Three perceptual dimensions were used to judge multidimensional stimuli: Spatial-to-temporal; stimulus quality; apparent movement. Two groups of subjects were identified who differed in their relative use of the temporally and spatially scaled unidimensional stimuli presented to the RVF. These two groups differed with respect to their relative use of a spatial-to-temporal dimension when multidimensional stimuli were presented to the RVF.

Cognitive asymmetries after wakings from REM and NONREM sleep in right-handed females

Eleven right-handed females were awakened from REM and NONREM sleep and tested on three tests designed to measure functions attributed to the left hemisphere and on three tests designed to measure right hemisphere function. A significant shift in cognitive profile was found in the direction of right hemisphere dominance after waking from REM sleep, and left hemisphere dominance after waking from NONREM sleep. Comparison of the cognitive shifts in females to that observed in males revealed a significant interaction of gender and awakening condition. Females showed a larger increase in right hemisphere performance following awakening from REM sleep relative to NONREM sleep, and a smaller increase in left hemisphere performance following awakening from NONREM sleep relative to REM sleep. The reverse trend was found for males.

Effect of visual half-field predictability and task strategy on brain laterality in men and women

In a visual half-field study 40 normal, dextral subjects, 20 men aged 18 to 20 yr. and 20 women aged 17 to 23 yr. acquired verbal labels for random shapes. Both men and women selected a verbal task strategy when the shapes were presented in a random half-field order and a spatial strategy when the figures were presented in a more predictable blocked-trials design. Women had slower RTs than men with verbal but not spatial mediation and were more lateralized for spatial function. Women seemed more lateralized for spatial tasks but disadvantaged for verbally mediated lateral-input tasks.

Sex differences and cognitive/motor interference with visual half-field stimulation

This study examines the possible influence of the response on the asymmetry of lexical decision in a visual half-field study and whether sex differences in asymmetry might be determined by response factors. The results support the importance of these factors: when response demands were increased (pressing the button three times instead of once) the reaction time asymmetry was reversed for male subjects.

Sex differences and asymmetry of lexical processing: effects of responding hand, stimulus familiarity and intraexperimental experience

The possibility that language processing functions are more nearly equally represented in the two hemispheres of women than of men was investigated tachistocsopically by means of a lexical decision task in which words and nonwords were controlled for familiarity, and exposed vertically in the left and right visual half-fields. Analysis of both unimanual reaction times and response accuracy revealed differences in asymmetry as well as differences between male and female subjects which tended to decrease as a function of intraexperimental experience. Theoretical and methodological problems associated with reaction time and response accuracy as measures of language lateralization are discussed.

Do laterality measures relate to speed of response in central vision?

This study was aimed at determining whether an efficiency index (speed of response in central vision) related to a laterality index (difference in speed of response between right and left field presentations). In Experiment 1 female subjects were required to discriminate facial emotional expressions shown in either central vision or the periphery. In Experiment 2 male and female subjects had to classify as same or different pairs of letters printed in different typefaces. It was found that the efficiency index related (negatively) to the laterality index only in Experiment 1 so that slower responses indicate larger visual field differences. The results are discussed in terms of current models of hemispheric specialization.

Relationships between speed, accuracy of performance and hemispheric superiorities for visuo-spatial pattern processing in the two sexes

The aim of this study was to investigate the relationship between visual field differences in tachistoscopic recognition of visuo-spatial patterns and overall proficiency in the two sexes. The results demonstrated a left visual field advantage in males but not in females. A female subgroup showed opposite rather than lacking visual field superiorities without affecting speed and accuracy of performance. These data warn against explaining differences in performance in the two sexes in terms of different hemispheric asymmetries.

Functional cerebral lateralisation; dichotomy or plurality?

Cartoon faces were presented tachistoscopically in the right and left visual fields, and required to be matched to a previously memorised target face. The three different stimuli differed from the target either on only one, or on all three features (eyes, nose, mouth). Reaction times varied considerably across the individual different responses in both conditions. In the first condition field differences consistently favoured the right field; in the second, two favoured the left and the third the right. In both conditions same responses were faster than at least one different response class. Several interpretations in terms of the distinction between "analytic" and "holistic" processes were entertained. Such processes themselves remain somewhat obscure, but there is nothing in the data to suggest that the two cerebral hemispheres might not be essentially ambivalent in their predilections for the two kinds of processing. In which case future research might profitably focus on the emerging plurality of experimental factors governing this cognitive ambivalence, rather than on the simple physical dichotomy.

An evaluation of evidence for innate sex differences in linguistic ability

A female superiority in verbal ability is reported on many tests. It has been hypothesized that the female brain is more functionally symmetrical for language then the male, and that this is the cause of the alleged superiority. Recent research has suggested that factors other than sex are involved: handedness, age of maturity, and endocrine influences. It is not yet clear whether, despite its biological correlates, the female superiority is innate.

Hemispheric lateralization and aesthetic judgement

Pairs of slides depicting works of art were presented tachistoscopically to the left or right visual half-fields. Subjects performed an aesthetic judgement task, selecting the better work of art in each pair. Subjects with highly lateralized cerebral organization, as inferred by handedness or sex, performed significantly better in response to slides presented in one visual half-field (VHF) than in response to slides presented in the opposite VHF. Some of these subjects showed a left VHF superiority, while others showed a right RHF superiority. Subjects who were less lateralized showed no significant tendency to perform better in response to slides presented in one VHF or the other. The results are interpreted as an indication that subjects will perform a given task in a lateralized or a non-lateralized manner as a function of the interaction between individual differences in cerebral organization and the cognitive processes used to perform the task.