Dichotic listening and tactual mental rotation in females as a function of familial sinistrality and strength of handedness

Mental rotation of tactile stimuli

When subjects decide whether two visual stimuli presented in various orientations are identical or mirror-images, reaction time increases with the angular disparity between the stimuli. The interpretation of this well-known observation is that subjects mentally rotate images of the stimuli until they are in congruence, in order to solve the task. Here we review studies involving mental rotation of tactile stimuli. Mental rotation in tactile tasks is specifically associated with the requirement for mirror-image discrimination, as opposed to identity judgments. The key brain region mediating mental rotation of tactile stimuli seems to be the parietal cortex. Visual processing appears to facilitate task performance. We report an experiment from our laboratory addressing the nature of the reference frame for mental rotation of tactile stimuli. Our observations indicate that when the hand is directly in front of the body, with the head facing forward, the shortest reaction times for mirror-image discrimination of stimuli applied to the fingerpad are obtained when the longitudinal axis of the stimulus is in or parallel to the sagittal plane, even when this is perpendicular to the long axis of the finger. Thus, the reference frame for mental rotation of tactile stimuli is not purely hand-centered. This is consistent with other findings indicating variable assignment of reference frames for tactile perception.

Twenty-year follow-up of antenatal corticosteroid treatment

OBJECTIVE

To study late side effects of antenatal corticosteroid treatment on health and sexual development in subjects 20 to 22 years old.

METHODS

A follow-up study among young adults whose mothers had, because of a threatening delivery, participated in a randomized, double-blind, placebo- controlled trial of betamethasone to prevent neonatal respiratory distress syndrome. Measurements were taken on general health, growth, development in puberty, reproductivity, genital or gynecological complaints, gender development, sexual orientation, sex-specific cognitive functioning, and psychoneuroticism. In addition, some measurements were performed on family diseases, socioeconomic status, and education.

RESULTS

No differences were found between the corticosteroid-treated and placebo groups as to medical or psychological variables. In general, the subjects were healthy and had normal intellectual capacities. Groups did not differ on gender development, sexual orientation, sex-specific cognitive functioning, and psychoneuroticism. Systolic blood pressure was significantly lower in the corticosteroid group, but the groups did not differ as to diastolic blood pressure.

CONCLUSIONS

Our 20-year follow-up study indicates that 1 course of antenatally administered corticosteroid to prevent respiratory distress syndrome does not have adverse effects up to adulthood.

Cognitive ability and cerebral lateralisation in transsexuals

It is still unclear to what extent cross-gender identity is due to pre- and perinatal organising effects of sex hormones on the brain. Empirical evidence for a relationship between prenatal hormonal influences and certain aspects of gender typical (cognitive) functioning comes from pre- and postpubertal clinical samples, such as women suffering from congenital adrenal hyperplasia and studies in normal children. In order to further investigate the hypothesis that cross-gender identity is influenced by prenatal exposure to (atypical) sex steroid levels we conducted a study with early onset, adult male-to-female and female-to-male transsexuals, who were not yet hormonally treated, and nontranssexual adult female and male controls. The aim of the study was to find out whether early onset transsexuals performed in congruence with their biological sex or their gender identity. The results on different tests show that gender differences were pronounced, and that the two transsexual groups occupied a position in between these two groups, thus showing a pattern of performance away from their biological sex. The findings provide evidence that organisational hormonal influences may have an effect on the development of cross-gender identity.

Cerebral organization of verbal and motor functions in left-handed and right-handed adults: effects of concurrent verbal tasks on unimanual tapping performance

Two experiments were conducted to study the interference effects of different concurrent verbal tasks on unimanual single-finger tapping and unimanual sequential finger tapping. Experiment 1 involved 24 right-handed university students. In the dual-task conditions, right-handers showed a greater right-hand than left-hand performance reduction for single-finger tapping, and an equal right-hand and left-hand reduction for sequential tapping. Experiment 2 involved 60 left-handed university students, divided into four groups according to familial sinistrality and writing hand posture. In the dual-task conditions, left-handers showed a greater left-hand than right-hand performance reduction for single-finger tapping, and an equal left-hand and right-hand reduction for sequential finger tapping. A dichotic listening task revealed a left hemispheric dominance for auditory linguistic functioning in most of the left-handers. Familial sinistrality and hand posture, on the whole, did not influence tapping performances. However, these factors influenced the ear asymmetries on the dichotic listening task. It is speculated that, with single-finger tapping, interference only takes place beyond the point of language motor programming, that is to say, at the motor areas and the supplementary motor areas of the cortex.