Walter F. McKeever

ANDROGENS AND SPATIAL ABILITY: FAILURE TO FIND A RELATIONSHIP BETWEEN TESTOSTERONE AND ABILITY MEASURES

Shute, Pellegrino, Hubert, and Reynolds (1983) found spatial ability to be positively related to androgen levels in females and negatively related to androgen levels in males. Although they intended to study the relationship of a specific steroid, testosterone (T), to spatial ability, their antibody was not specific for T. The present study assessed the relationship of T, specifically, to spatial and verbal abilities. Additionally, possible T-level differences between left- and right-handed subjects were assessed. Results showed females and left-handers to be inferior in spatial ability to males and right-handers, respectively, on the Stafford Identical Blocks Test. This replicates previous findings (McKeever, 1986). No other sex or handedness effects were obtained on ability measures. No handedness effect was found for T levels. No relationship of T to either spatial or verbal measures was found. We concluded that T is not the critical androgen implicated in spatial ability by studies employing nonspecific steroid measures.

Testosterone, dihydrotestosterone, and spatial task performances of males

Fifty-eight male college students were administered two spatial tests—the Minnesota Paper Form Board (MPFB) and the Stafford Identical Blocks Test (SIBT). Testosterone (T) and dihydrotestosterone (DHT) levels extant during testing were determined from four blood samples collected over the course of testing. Neither T nor DHT showed significant relationships to spatial ability, but the ratio DHT/T was significantly correlated with the MPFB scores. Subjects whose T and DHT values deviated most from the group means had significantly higher mean spatial test scores. The DHT/T deviation scores and T deviation scores were uncorrelated and together accounted for about 15% of the variance in the composite spatial ability scores. Given the inconsistency of previous findings regarding a relationship of T to spatial ability, the present results suggest that future studies should assess DHT as well as T, and that data should be carefully examined for possible curvilinear relationships as well.

Left Handedness and Immune Disorders

The Geschwind-Behan hypothesis that immune disorder (IMD) is more common among left than among right handed persons was tested in a sample of 3080 college students. Subjects indicated, for each of a list of IMDs, whether they: (1) had no reason to believe they had the disorder; (2) thought they might have the disorder; (3) had the disorder diagnosed by a physician; or (4) had had a disorder diagnosed and treated by a physician. Females reported significantly more IMDs than did males. Among females, the distribution of responses across the four response categories was not different for left and right handers, but IMD was significantly higher among left handed females when only the extreme categories were considered. Among males, no handedness effect was seen across the four categories, nor when only the extreme categories were considered. Laterality quotients, from the Edinburgh Handedness Inventory, were unrelated to IMD reports in both sexes. Results provide no real support for the Geschwind-Behan hypothesis. Even in the case of the extreme categories of IMD reports of females, the association of left handedness (for writing) and IMD accounts for only three-tenths of one percent of the variance.

Spatial processing laterality and spatial visualization ability: Relations to sex and familial sinistrality variables

Seventy-four right-handed college students were administered the Clockface Reading Latency Task (CRLT) and the Stafford Identical Blocks Test (SEBT). The lateralized tachistoscopic CRLT yielded a significant left visual field superiority, supporting previous research that had suggested it was a sensitive test of right hemisphere superiority for spatial processing. On the SIBT, males scored significantly higher than females, and there was a sex × familial sinistrality (FS) interaction, like that previously reported by McKeever, Seitz, Hoff, Marino, and Diehl (1983). FS also influenced visual field asymmetries on the CRLT; subjects with left-handedness in their families showed smaller asymmetries. No correlation between spatial laterality and spatial ability was found.

Cross-modal correlation of dichotic and tachistoscopic language laterality tasks: The importance of familial sinistrality

Previous studies have found little if any correlation between dichotic and tachistoscopic language laterality task performance asymmetries. Problems with these studies have been that quite dissimilar auditory and visual tasks have often been used, and the reliability of the asymmetry measures has generally been unknown or, when known, relatively poor. We assessed the cross-modal correlation for two tasks, the Bilateral Object Naming Latency Task (BONLT) and the Dichotic Object Naming Latency Task (DONLT). These tasks are highly similar and have demonstrated high reliabilities. A significant, though rather small, cross-modal correlation was found (r = +.28). When cross-modal correlations were computed for FS- and FS+ subjects separately, no correlation was found for FS+ subjects (r = +.02), but the correlation for FS- subjects was highly significant (r = +.54, p less than .004). This led us to reexamine some previously collected data (P.L. Van Eys and W. F. McKeever, 1988, Brain and Cognition, 4, 413-429) which had administered two highly reliable language laterality tasks (the BONLT and the Dichotic Consonant Vowel Task), but had not assessed cross-modal correlation. A significant cross-modal correlation was found for FS- but not for FS+ subjects. The results are consistent with the hypothesis of H. Hecaen, M. De Agnostini, and A. Monzon-Montes (1981, Brain and Language, 12, 261-284) which suggests that one effect of FS+ is to induce a greater heterogeneity of localizations of different language processes.

Chapter 13 Familial Sinistrality and Cerebral Organization

Publisher Summary Familial sinistrality (FS) is an important variable for understanding cerebral organization. The dichotic language task studies fail to suggest clear differences between FS - and FS + persons, regardless of their handedness. The tachistoscopic studies suggest lesser left hemisphere dominance for language function in both right-handed with FS (RHFS +) and left-hander without FS (LHFS -) persons. Recent studies suggest that different aspects of language function may be more laterally dissociated in the FS + than in the FS -, but further study of this is needed. Tachistoscopic studies also suggest that FS + acts to reduce right hemisphere specialization for visuospatial functions in right-handed persons, and may do so in lefthanders as well. FS has been found to be poorly related to hand preference, hand skill, or eyedness, thereby suggesting that motor laterality characteristics are largely independent of FS. FS is related to handwriting posture in left-handed persons, with the inverted writers having significantly more lefthanders among their first plus second-degree relatives. This greater incidence of left-handedness occurs mainly within the maternal family line. The incidence of FS, when FS status (FS + or FS -) is defined by the presence of at least one first degree relative, is significantly, but very slightly, greater in right-handed females than males (about 37% versus 33%) and in left-handed females than males (about 52% to 47%). A tentative general inference that FS + may influence visually mediated processes more than auditory and motor processes may be advanced in view of this set of conclusions.

Inverted handwriting posture in left handers is related to familial sinistrality incidence.

McKeever (1979) reported that left handers who wrote with an inverted handwriting posture (IHP) had a higher incidence of left handedness in their families than did left handers who wrote with a non-inverted handwriting posture (NHP). Parlow and Kinsbourne (1981), however, failed to find a relationship between handwriting posture (HWP) and positive familial sinistrality (FS+). McKeever had classified his left handed subjects according to whether they had several, one, or no left handers among their first degree relatives and biologically-related second degree relatives. Parlow and Kinsbourne classified subjects as FS- or FS+ on the basis of first degree relatives and did not inquire about the handedness of second degree relatives. In the present study, handedness for writing of all first and second degree relatives was recorded for 216 NIP and 255 IHP left handers. Results showed a significant association of HWP and FS factors when second degree relatives were considered, but not when second degree relative handedness was ignored. The relationship was strongest within the maternal family line, where the proportion of left handers was more than twice as high for the IHP as for the NHP group. These findings suggest that HWP may well be of some importance for a complete understanding of the cerebral organization of left handers.