Line Bisection and Trisection, Age and Accuracy

Congratulations to Drs. Zared SchwartzJohn Williamson, and Kenneth Heilman, on the publication of “Line Bisection and Trisection, Age and Accuracy.”  This article was published in the April 2018 issue of Neurology.



Objective: To assess spatial bias changes with aging.

Background: On the horizontal line bisection test, adult healthy people have a leftward bias called ‘pseudoneglect.’ There have been reports that this bias diminishes with age. Because there is convergent evidence of right hemisphere dominance in controlling aspects of spatial attention, one hypothesis for this decrease of pseudoneglect is right hemi-aging, but another may be a decrease in asymmetrical hemispheric activation when performing spatial judgments. If, with aging there is a decrease in specialized asymmetrical hemispheric activation; older participants may show a reduced bias in all spatial tasks, regardless of leftward or rightward biasing.

Design/Methods: 70 right handed healthy participants, 33 younger and 37 older, were asked to bisect solid and character-letter lines presented at their egocentric midline as well as to perform left and right trisections.

Results: In all bisection and trisection conditions, the direction of deviation was the same in both age groups.

In solid line bisections and left trisections both groups deviated toward the left of midline. In right trisections and character line bisections, both groups deviated toward the right side of the line. However, in all tasks the older participants deviated less from the target than did the younger participants.

Conclusions: The finding that older participants were more accurate than younger participants across all bisection and trisection conditions suggests that the right hemi-aging hypothesis might be inadequate in explaining the changes in spatial attention with aging. Trisections, character line bisections and solid line bisections recruit different areas of the brain when performed and, in young people, this specialization results in different biases. The older participants’ increased accuracy might be induced by a decrease in the asymmetrical hemispheric activation of these specialized networks important in the allocation of contralateral spatial attention or spatial action intention.