Normal and abnormal early development of handedness: Introduction

Manual asymmetries in bimanual isochronous tapping tasks in children

Tapping tasks have been investigated throughout the years, with variations in features such as the complexity of the task, the use of one or both hands, the employ of auditory or visual stimuli, and the characteristics of the subjects. The evaluation of lateral asymmetries in tapping tasks in children offers an insight into the structure of rhythmic movements and handedness at early stages of development. The current study aims to investigate the ability of children (aged six and seven years-old) to maintain a rhythm, in a bimanual tapping task at two different target frequencies, as well as the manual asymmetries displayed while doing so. The analyzed data in this work are the series of the time intervals between successive taps. We suggest several profiles of behavior, regarding the overall performance of children in both tempo conditions. We also propose a new method of quantifying the variability of the performance and the asymmetry of the hands, based on ellipses placed on scatter plots of the non-dominant-dominant series versus the dominant-non-dominant series. We then use running correlations to identify changes of coordination tendencies over time. The main results show that variability is larger in the task with the longer target interval. Furthermore, most children evidence lateral asymmetries, but in general they show the capacity to maintain the mean of consecutive intertap intervals of both hands close to the target interval. Finally, we try to interpret our findings in the light of existing models and timing modes.

Laterality of acquired cholesteatoma and handedness

OBJECTIVE

To investigate a possible contribution of handedness to the development of unilateral acquired cholesteatoma.

PATIENTS

All patients with unilateral acquired cholesteatoma attending otorhinolaryngology clinic between August 2009 and February 2012 were asked about their handedness.

RESULTS

The study group consisted of 237 right-handed and 31 left-handed (11.8%) patients who included 158 male (59%) and 79 female subjects with an age range of 6 to 81 years (mean, 38.6 yr). There were no ambidexters in the present cohort. Overall, unilateral cholesteatoma involved 146 right (54.5%) and 122 left ears (45.5%). Ten of 31 patients (32.3%) with left hand predominance were female subjects. In the unilateral disease, the right ears were affected more frequently in patients with right-hand dominance (59.5%), and the left ears were more frequently affected in the left-handed patients (83.9%); this difference was statistically significant (p < 0.0001). The sex differences in the distribution of cholesteatoma side and handedness were not statistically significant (p = 0.098).

CONCLUSION

The strong relationship has been observed between the patient's handedness, and laterality of the unilateral acquired cholesteatoma may have contribution in the multifactorial process of cholesteatoma formation.

From the reaching behavior at 5 months of age to hand preference at preschool age

The aim of the study was to examine the reaching behavior at the age of 5 months, and to determine whether and to what extent there is a relationship between hand use at this age and manual laterality at preschool age. 20 participants (13 girls and 7 boys) were investigated on two occasions: At the age of 5 months we assessed the hand use for reaching for four different objects placed at the infant's body midline or in their right or left hemispaces, respectively. At the age of 5 years and 7 months, we assessed the hand use for 22 motor tasks. The handedness status was calculated in order to reflect the sinistrality-dextrality continuum. All but one infant were unimanual reachers at 5 months of age. Preferential reaching was space dependent rather than object dependent at this stage. Children reaching for objects in the right hemispace predominantly with their right hand showed a significantly greater right hand laterality at late preschool age than children who at the age of 5 months had shown inconsistent hand use (p < .05). Children who at the age of 5 months had reached for objects in the left hemispace with their left hand proved to be less lateralized in their right hand use approximately 5 years later (p < .05).