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Background: Right-hand preference is related to stronger right-directional asymmetry in the length of proximal upper-limb bones, although the relationships of hand preference with directional asymmetry in phalangeal bone lengths are not known. Furthermore, dorsal digit length is an easy-to-measure, faithful proxy of X-rayed phalangeal bone length (which is costly and difficult to measure).Aim: To study the effects of hand preference, sex, and age on right-left (R-L) asymmetry in dorsal digit lengths.Methods: We measured all dorsal digit lengths (except the thumb) in comparable numbers of left-handers and right-handers in samples of adults (N = 151, age: M = 22.6 years, SD = 3.3) and children (N = 65, age: M = 5.0 years, SD = 1.0).Results: Right-handers and adults had stronger right-directional asymmetry in digit lengths than left-handers and children. A Bayesian analysis yielded an 'extremely strong likelihood' of no sex differences in the R-L asymmetry of dorsal digit lengths 2 and 4.Conclusions: The effects of hand preference, sex, and age on R-L asymmetry appear to be similar for phalangeal bone length and other (proximal) upper-limb bone lengths. Two distinct biologic mechanisms (i.e., a general right-directional asymmetry mechanism and a handedness-related directional asymmetry mechanism) may contribute to observed R-L asymmetry in limbs. Fingertip fat and bone digit length do not seem to contribute to sex differences in the R-L asymmetry (Dr-l) of the widely studied second-to-fourth digit ratio (2D:4D). [ABSTRACT FROM AUTHOR]

Mixed-handedness was reported indicative of schizotypy, relevant to psychosis and schizophrenia. However, studies suffered from validity threats and did not systematically investigate associations with footedness. Moreover, there is a dearth of studies in the general population and it is currently untested whether widely used self-report scales measure schizotypy in a comparable way in student and community samples. The present study used two large and independent community and student samples (total N >2800) and utilized latent class analysis (LCA) for the classification of handedness and footedness. Psychometric properties and measurement equivalence of the Schizotypal Personality Questionnaire–Brief form (SPQ-B) in the two samples were also examined. We found that mixed-handedness (<6% prevalence), but also much more common mixed-footedness (25% prevalence), was specifically and similarly associated with higher schizotypy in both samples, Cohen d =0.15–0.18. Findings indicate that schizotypal traits in conjunction with mixed lateral preferences are thus more prevalent in the overall population than previously assumed, and that footedness may be the more relevant predictor of schizotypy than handedness. Findings are further consistent with evidence on neurodevelopmental instability, but also epigenetic mechanisms involving the sex chromosomes, regarding possible common causes of both mixed-handedness and psychosis-relevant traits. [ABSTRACT FROM AUTHOR]

Lateral preferences are important for the study of cerebral lateralization and may be indicative of neurobehavioral disorders, neurodevelopmental instability, and deficits in lateralization. Previous studies showed that self-reported preferences are also concordantly interrelated, suggesting a common genetic or biological origin, sidedness. However, with regard to the assessment and classification of lateral preferences, there is a dearth of psychometric studies, but a need for psychometrically validated instruments that can be reliably used in applied research. Based on three independent large samples (total N >15,100), this study investigated the psychometric properties of widely-used lateral preference scales of handedness, footedness, eyedness, and earedness. Preferences were consistently and replicably categorical, consisting of right, mixed, and left preferences each, underlining that primarily qualitative, rather than quantitative, differences differentiate lateral preferences. Right-, mixed-, and left-sidedness underlay the individual preferences, but sidedness alone could not fully explain the observed inter-relations. Footedness was the single most important indicator of sidedness. Our data were further consistent with predictions of right shift theory and corroborated a ‘pull-to-concordance’ in hand–foot preferences. We recommend the use of psychometrically validated scales and of a trichotomous classification of lateral preferences in future research, but conclude that handedness may be a biased indicator of underlying sidedness. Footedness needs to be examined more closely with regard to cerebral lateralization, neurodevelopmental disorders, and neurodevelopmental instability. [ABSTRACT FROM AUTHOR]

Highlights: [•] Left-handed women are assumedly more masculine, left-handed men more feminine. [•] Previous research did not distinguish between mixed- and left-handedness. [•] Mixed-handers, but not left-handers, are less sex-congruent stereotyped. [ABSTRACT FROM AUTHOR]

Background: Prenatal sex hormones may not exclusively determine effects of hand preference on digit ratios. Genetic determination is an alternative possibility.Aim: To study the likelihood of similar effects of hand preference on digit lengths and digit ratios.Methods: We selected similar numbers of left-handers and right-handers in samples of kindergarten children (N = 101, age range: 3.5-7 years) and adults (N = 189, age range: 17-28 years) and measured digit lengths (excluding the thumb) directly on the palmar hand.Results: Compared to right-handers, left-handers had longer digits and lower third-to-fourth (3D:4D) digit ratios among children, whereas an opposite pattern of handedness differences occurred among adults.Conclusions: Effects of hand preference on digit lengths and ratios might be genetically/ontogenetically determined. Also discussed are implications of this set of findings for digit ratio research. [ABSTRACT FROM AUTHOR]