Comparing the effects of vertical elevation and horizontal position on line bisection biases in peripersonal and extrapersonal space

The line bisection task is a simple measure of visuospatial bias, with the majority of adults bisecting lines to the left of true centre. This leftward bias is referred to as pseudoneglect, and is thought to arise from right hemisphere dominance for spatial processing. In the present study, we examined how line bisection performance was affected by physical elevation (the task was completed at eye level, above the head, and near the knees) and horizontal position (the lines were presented centrally, offset to the left, and offset to the right). We also
compared performance on the pen-and-paper task to performance on a laser line bisection task, to see whether these spatial manipulations affect performance in similar ways in peripersonal and extrapersonal space. Results showed a leftward bias for the peripersonal pen-and-paper task, and a rightward bias for the extrapersonal laser line bisection task. Physical elevation and horizontal position influenced the direction and extent of the biases on these two line bisection tasks, and performance on these tasks was correlated when lines were up and to the left, and down and to the right. These findings are discussed in the context of other known influences on visuospatial attention.