Line bisection performance of normal adults: two subgroups with opposite biases

Unilateral neglect patients may have either attentional or intentional neglect or both. Determining whether normal individuals are influenced by attentional or intentional biases will lead to a better understanding of the two types of neglect. Normal individuals may not be a homogeneous group.

To determine whether normal individuals show attentional/sensory or intentional/premotor biases when completing line bisections.

Thirty-two normal right-handed individuals participated. On each trial, participants were asked to move a cursor using a computer mouse to the midpoint of a line presented on a computer screen. The line could appear centered on or toward either side of the screen. Participants completed the task under two conditions: either the cursor moved in the same direction as the mouse (direct condition) or the cursor moved in the opposite direction as the mouse (indirect condition).

Twenty-five participants showed an attentional bias, 3 showed an intentional bias, and 4 showed no bias. Of those with an attentional bias, 13 were biased to the left, and 12 were biased to the right. Those with a right-attentional bias made larger errors when the line was presented to the left, whereas those with a left-attentional bias made larger errors when the line was presented to the right.

Our finding that the two attentional-biased groups produced the opposite pattern of results across the three line positions suggests the processes underlying performance in the two groups may in fact differ. Further study of these two groups may lead to a better understanding of unilateral neglect.