Distribution of attention in normal people as a function of spatial location: right-left, up-down

The spatial allocation of attention influences estimates of stimulus magnitude, including line length and the line bisection task has been used to assess the asymmetrical allocation of spatial attention. The purpose of this study is to learn if normal subjects' allocation of attention changes as a function of the trunk-head centered spatial position of the line stimuli. Normal subjects were asked to bisect lines placed in five different head-trunk centered special positions (central, right up-distal, left up-distal, right down-proximal, left down-proximal). When compared with the central condition, deviations in the right or left lateral conditions were only significant in the down-proximal conditions, such that the bisection bias significantly shifted direction to the left of the objective midline in left hemispace and to the right of the objective midline in right hemispace, suggesting that stimuli presented in lateral hemispace primarily activate the contralateral hemisphere's attentional systems. The finding that the lines presented in down-proximal lateral hemispace induce a greater spatial bias than lines in up-distal lateral space suggests that the portion of the brain's dorsal visual system, which processes stimuli in down-proximal space, influences the horizontal (right-left) spatial allocation of attention more than does the brain's ventral visual system.