The Effect of Blindness on Spatial Asymmetries.

Luca Rinaldi,Lotfi B Merabet,Andrea Ciricugno,Zaira Cattaneo,Tomaso Vecchi

doi:10.3390/brainsci10100662

Abstract

The human cerebral cortex is asymmetrically organized with hemispheric lateralization pervading nearly all neural systems of the brain. Whether the lack of normal visual development affects hemispheric specialization subserving the deployment of visuospatial attention asymmetries is controversial. In principle, indeed, the lack of early visual experience may affect the lateralization of spatial functions, and the blind may rely on a different sensory input compared to the sighted. In this review article, we thus present a current state-of-the-art synthesis of empirical evidence concerning the effects of visual deprivation on the lateralization of various spatial processes (i.e., including line bisection, mirror symmetry, and localization tasks). Overall, the evidence reviewed indicates that spatial processes are supported by a right hemispheric network in the blind, hence, analogously to the sighted. Such a right-hemisphere dominance, however, seems more accentuated in the blind as compared to the sighted as indexed by the greater leftward bias shown in different spatial tasks. This is possibly the result of the more pronounced involvement of the right parietal cortex during spatial tasks in blind individuals compared to the sighted, as well as of the additional recruitment of the right occipital cortex, which would reflect the cross-modal plastic phenomena that largely characterize the blind brain.

Highlights

At first glance, the brain appears to be a symmetrical structure; a closer inspection reveals lateralized changes from the subcellular and neurochemical to gross anatomical levels [1].These laterality patterns are not limited to the level of the brain but pervade as well in traits of human overt behavior such as handedness and spatial asymmetries as measured by line bisection tasks
The debate as to what extent visual experience contributes to a different development of functional asymmetries subserving spatial processing has not reached definite conclusions
Available evidence indicates that the hemispheric dominance for spatial processing seems, overall, largely unaffected by visual loss, as in both sighted and blind individuals’ spatial functions would predominantly rely on the right hemisphere

Summary

Introduction

The brain appears to be a symmetrical structure; a closer inspection reveals lateralized changes from the subcellular and neurochemical to gross anatomical levels [1]. Investigating the role of environmental factors [6], recent research has suggested that epigenetic regulation contributes to the development of hemispheric asymmetries subserving spatial processing in line bisection tasks [7]. This may indicate that the bias in the line bisection task is likely influenced by multiple genetic, epigenetic, and environmental factors. Within this theoretical framework, the study of visual deprivation represents a unique model to investigate lateralization phenomena, as experiential factors are clearly different compared to typical. In analogy with the classification adopted by most previous works, congenital (i.e., usually defined as those individuals blind from birth) and early (i.e., usually defined as those individuals who become blind during early postnatal life, generally around 2 or 3 years of age) blind participants will be treated as a single group

Pseudoneglect

Behavioral

Mirror Symmetry

Localization Tasks

The Role of Sensorimotor Experience

Conclusions