ABSTRACT
In a study of patterns of language laterality in left- and right-handers, Woodhead et al. (Woodhead ZVJ, Thompson PA, Karlsson EM, Bishop DVM. 2021 R. Soc. Open Sci. 8, 200696. (doi:10.1098/rsos.200696)) noted that several tasks showed no bias to the left hemisphere in left-handed individuals. This might appear to suggest that these functions were mediated by the two hemispheres working together equally-what can be termed 'hemispheric equipoise'. Here, I consider an alternative possibility that individuals show lateral bias on these tasks, but the bias can occur to either the left or right-a form of fluctuating asymmetry. Further analysis of the distributions of data from individuals in Woodhead et al. is compared with simulated data. The pattern of results suggests that the impression of hemispheric equipoise may be an artefact of reliance on group data: even though the group mean does not differ from zero, a high proportion of individuals are biased to the left or right.
ABSTRACT
In this exploratory study we compare and contrast two methods for deriving a laterality index (LI) from functional magnetic resonance imaging (fMRI) data: the weighted bootstrapped mean from the LI Toolbox (toolbox method), and a novel method that uses subtraction of activations from homologous regions in left and right hemispheres to give an array of difference scores (mirror method). Data came from 31 individuals who had been selected to include a high proportion of people with atypical laterality when tested with functional transcranial Doppler ultrasound (fTCD). On two tasks, word generation and semantic matching, the mirror method generally gave better agreement with fTCD laterality than the toolbox method, both for individual regions of interest, and for a large region corresponding to the middle cerebral artery. LI estimates from this method had much smaller confidence intervals (CIs) than those from the toolbox method; with the mirror method, most participants were reliably lateralised to left or right, whereas with the toolbox method, a higher proportion were categorised as bilateral (i.e., the CI for the LI spanned zero). Reasons for discrepancies between fMRI methods are discussed: one issue is that the toolbox method averages the LI across a wide range of thresholds. Furthermore, examination of task-related t-statistic maps from the two hemispheres showed that language lateralisation is evident in regions characterised by deactivation, and so key information may be lost by ignoring voxel activations below zero, as is done with conventional estimates of the LI.
ABSTRACT
En este editorial discutimos qué son los trastornos específicos del lenguaje (TEL) y por qué es una discapacidad escondida, invisible. ¿Por qué tan pocas personas saben lo que es el TEL? Describimos el impacto que tiene esta falta de reconocimiento del TEL no solamente en la investigación, en la cantidad de estudios que hay sobre el TEL, sino también en poder influir en la política de los gobiernos y en las decisiones sobre recursos para apoyar a personas con esta discapacidad. Compartimos información sobre una campaña de toma de conciencia que hemos empezado en Internet mediante un canal de YouTube, RALLI (www.youtube.com/rallicampaign), para poder difundir información y conocimientos sobre el TEL y aumentar así su reconocimiento global. Este canal de YouTube contiene videoclips e información sobre el TEL en español (AU)
In this editorial, we discuss what is specific language impairment (SLI) and why it is a hidden disability that few people have heard about. We describe the impact on research, policy and practice of SLI being a neglected condition. We end by providing the background and rationale of a new Internet campaign, RALLI (www.youtube.com/rallicampaign), aimed at changing this state of affairs and raising awareness of SLI. This YouTube channel has videoclips and information about SLI in Spanish (AU)