The length of the index finger relative to that of the ring finger, the 2D:4D ratio, has been taken to be a marker of the amount of testosterone (T) that was present in the foetal environment (Manning, Scutt, Wilson, & Lewis-Jones, 1998). It has also been suggested (Geschwind & Galaburda, 1987) that elevated levels of foetal T are associated with left-handedness and that adult levels of circulating T might relate to foetal levels (Jamison, Meier, & Campbell, 1993). We used multiple regression analyses to investigate whether there is any relationship between either left or right hand 2D:4D ratio and handedness. We also examined whether adult levels of salivary T (or cortisol, used as a control hormone) predict digit ratio and/or handedness. Although the 2D:4D ratio of neither the left nor the right hand was related to handedness, the difference between the digit ratios of the right and left hands, DR–L, was a significant predictor of handedness and of the performance difference between the hands on a peg-moving task, supporting previous findings (Manning & Peters, 2009; Manning et al., 1998; Manning, Trivers, Thornhill, & Singh, 2000; Stoyanov, Marinov, & Pashalieva, 2009). Adult circulating T levels did not predict the digit ratio of the left or right hand; nor was there a significant relationship between concentrations of salivary T (or cortisol) and either hand preference or asymmetry in manual skill. We suggest that the association between DR–L and hand preference arises because DR–L is a correlate of sensitivity to T in the developing foetus.

For parents anxious “lest their children should be left-handed”, the American author Mary Palmer Tyler offered advice and reassurance in her 1811 child-care manual The Maternal Physician. This article provides a brief biography of Tyler and the text of her remarks, along with notes on the text and the author's sources.

Two experiments examined imitation of lateralised body movement sequences presented at six viewing angles (0°, 60°, 120°, 180°, 240°, and 300° rotation relative to the participant's body). Experiment 1 found that, when participants were instructed simply to “do what the model does”, at all viewing angles they produced more actions using the same side of the body as the model (anatomical matches), than actions using the opposite side (anatomical non-matches). In Experiment 2 participants were instructed to produce either anatomical matches or anatomical non-matches of observed actions. When the model was viewed from behind (0°), the anatomically matching group were more accurate than the anatomically non-matching group, but the non-matching group was superior when the model faced the participant (180° and 240°). No reliable differences were observed between groups at 60°, 120°, and 300°. In combination, the results of Experiments 1 and 2 suggest that, when they are confronting a model, people choose to imitate the hard way; they attempt to match observed actions anatomically, in spite of the fact that anatomical matching is more subject to error than anatomical non-matching.

In most teleost fishes, the optic nerves decussate completely as they project to the mesencephalic region. Examination of the decussation pattern of 25 species from 11 different orders in Pisces revealed that each species shows a specific chiasmic type. In 11 species out of the 25, laterality of the chiasmic pattern was not determined; in half of the individuals examined, the left optic nerve ran dorsally to the right optic nerve, while in the other half, the right optic nerve was dorsal. In eight other species the optic nerves from both eyes branched into several bundles at the chiasmic point, and intercalated to form a complicated decussation pattern. In the present study we report our findings that Spratelloides gracilis, of the order Clupeiformes, family Clupeidae, shows a particular laterality of decussation: the left optic nerve ran dorsally to the right (n=200/202). In contrast, Etrumeus teres, of the same order and family, had a strong preference of the opposite (complementary) chiasmic pattern to that of S. gracilis (n=59/59), revealing that these two species display opposite left–right optic chiasm patterning. As far as we investigated, other species of Clupeiformes have not shown left–right preference in the decussation pattern. We conclude that the opposite laterality of the optic chiasms of these two closely related species, S. gracilis and E. teres, enables investigation of species-specific laterality in fishes of symmetric shapes.

A much wider variation in many physical and cognitive behaviours exists among left-handers than among right-handers, which is evidence for more than one aetiology of left-handedness. Despite these findings some researchers are still attempting to link left-handedness to a single cause, most recently genetic determination, by pairing left-handedness with a presumed genetically based characteristic. One of these characteristics is scalp hair whorl, which may be clockwise, counter-clockwise (purportedly associated with left-handedness), or a reversal whorl (rare). Results of recent research in this topic are reviewed, our own findings are presented, and we conclude that there is no logical reason for, nor evidence of, a common aetiology of both hair whorl direction and handedness.

The differences between left and right hemispheric magnitude representations were investigated in two lateralised priming experiments using single-digit (Experiment 1) and two-digit numbers (Experiment 2). Based on recent brain-imaging and TMS studies, some authors have argued that the magnitude representation in the left hemisphere (LH) is more precise than the one in the right hemisphere (RH). In two experiments a prime number preceded a target number that had to be classified as smaller or larger than a fixed standard. In order to reveal hemispheric differences in magnitude representation, the priming distance effect, i.e., faster responses to targets preceded by numerically closer primes, was analysed in both visual half fields (VHF). Using single-digit numbers no hemispheric differences were found for the priming distance effect, supporting an equally precise magnitude representation in both hemispheres. However, the experiment using two-digit numbers revealed a significantly steeper priming curve when targets were presented in the left visual field (LVF) compared to targets presented in the RVF. These results suggest a less precise magnitude representation in the RH, due to a larger overlap of magnitude representations.

Asymmetries of the sylvian fissure (SF) are believed to reflect an enlargement of the posterior temporal lobe, particularly a region that corresponds to part of Wernicke's area in humans. In nonhuman primates the homologue to the region may be involved in the discrimination and processing of species-specific vocalisations. As capuchin monkeys are large brained, socially complex primates with a rich vocal repertoire, it was hypothesised that they would display asymmetry of the SF. We used high-resolution 3T MRI scans to investigate this asymmetry in 17 brown capuchin monkeys (Cebus apella; 9 males, 8 females). Results indicated a trend towards population-level leftward asymmetry in the lateral region of the SF. Post hoc analyses revealed significant sex differences in SF asymmetry, with females displaying a population-level leftward asymmetry of the lateral region of the SF. Age was a significant mediator of the effects of sex on asymmetry of the lateral region of the SF. These results provide evidence that capuchin monkeys display sex differences in the asymmetry of the SF and show developmental changes in hemispheric lateralisation.

Research has shown that persons with mixed hand preference (i.e., who report using their non-dominant hand for at least some manual activities) display an increased tendency to update beliefs in response to information inconsistent with those beliefs. This has been interpreted as reflecting the fact that the left hemisphere maintains our current beliefs while the right hemisphere evaluates and updates those beliefs when appropriate. Belief evaluation is thus dependent on interhemispheric interaction, and mixed-handedness is associated with increased interhemispheric interaction. In Experiment 1 mixed-handers exhibited higher levels of persuasion in a standard attitude-change paradigm, while in Experiment 2 mixed-handers exhibited higher levels of gullibility as measured by the Barnum Effect.

A rightward turning bias has been more frequently noted during adult classical dance practice than during spontaneous rotations. Training could play a role in inducing a preferred direction. We observed the preferred direction for executing four spontaneous whole-body full turns (pirouettes), with eyes open or closed, in pre-pubertal untrained girls and classical dance students. Of untrained girls, 58% showed a leftward turning bias (LTB) and 42% a rightward turning bias (RTB), independently of vision, lateral preferences, and supporting leg. Only one dancer showed a consistent LTB while the majority showed a RTB, with a tendency to use the left leg to turn towards the right. These results suggest that the role of the vestibular and visual systems is minimal for untrained girls, and suggest a training influence for dancers. The dance students’ choice of a supporting leg for turning may exploit some biomechanical properties facilitating the pirouette.

People tend to display the left cheek when posing for a portrait; however, this effect does not appear to generalise to advertising. The amount of body visible in the image and the sex of the poser might also contribute to the posing bias. Portraits also exhibit lateral lighting biases, with most images being lit from the left. This effect might also be present in advertisements. A total of 2801 full-page advertisements were sampled and coded for posing direction, lighting direction, sex of model, and amount of body showing. Images of females showed an overall leftward posing bias, but the biases in males depended on the amount of body visible. Males demonstrated rightward posing biases for head-only images. Overall, images tended to be lit from the top left corner. The two factors of posing and lighting biases appear to influence one another. Leftward-lit images had more leftward poses than rightward, while the opposite occurred for rightward-lit images. Collectively, these results demonstrate that the posing biases in advertisements are dependent on the amount of body showing in the image, and that biases in lighting direction interact with these posing biases.