Abstract
Language and spatial processing are cognitive functions that are asymmetrically distributed across both cerebral hemispheres. In the present study, we compare left- and right-handers on word comprehension using a divided visual field paradigm and spatial attention using a landmark task. We investigate hemispheric asymmetries by assessing the participants’ behavioral metrics; response accuracy, reaction time and their laterality index. The data showed that right-handers benefitted more from left-hemispheric lateralization for language comprehension and right-hemispheric lateralization for spatial attention than left-handers. Furthermore, left-handers demonstrated a more variable distribution across both hemispheres, supporting a less focal profile of functional brain organization. Taken together, the results underline that handedness distinctively modulates hemispheric processing and behavioral performance during verbal and nonverbal tasks. In particular, typical lateralization is most prevalent for right-handers whereas atypical lateralization is more evident for left-handers. These insights contribute to the understanding of individual variation of brain asymmetries and the mechanisms related to changes in cerebral dominance.
Highlights
The cerebral hemispheres of the human brain have unique properties of information processing; an asymmetry labeled as hemispheric lateralization that implies that cognitive functions are differentially represented in the brain (Josse and Tzourio-Mazoyer, 2004; Vallortigara and Rogers, 2005)
On the basis of the laterality index for reaction time (LITIM) and laterality index for response accuracy (LIACC) scatter plots, we evaluated the number of participants with typical lateralization and atypical lateralization
We studied hemispheric lateralization that captures the dominance of one cerebral hemisphere over the other for information processing and that implies that certain functions are differentially represented in the two sides of the brain (Josse and Tzourio-Mazoyer, 2004; Vallortigara and Rogers, 2005)
Summary
The cerebral hemispheres of the human brain have unique properties of information processing; an asymmetry labeled as hemispheric lateralization that implies that cognitive functions are differentially represented in the brain (Josse and Tzourio-Mazoyer, 2004; Vallortigara and Rogers, 2005). The most commonly studied lateralized functions are language and spatial functions, which display respectively left-hemispheric and right-hemispheric superiority. Initial evidence for dominant language processing within the left hemisphere was provided by Broca (1861) and Wernicke (1874), followed by experimental and clinical research that confirmed that language production and comprehension generally rely more heavily on the left than right hemisphere (Springer et al, 1999; Szaflarski et al, 2002). Language production and aspects of semantic processing are processed within the anterior left hemisphere, including the inferior frontal gyrus, whereas language comprehension is regulated within the posterior temporo-parietal region of the left hemisphere (Price, 2000). In contrast to language functions, spatial processing as required for attention or orientation predominantly activates the fronto-parietal areas of the right hemisphere (Marshall and Fink, 2001). Right-sided lateralization of spatial abilities has been observed to be less consistent than left-sided lateralization of language processing, which may be due to differences in the intrinsic organization of both systems (Seydell-Greenwald et al, 2014)
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