Hand preference and performance effects on line bisection.

Right- and left-handed subjects performed a visual line bisection task with each hand. When bisecting horizontal lines, both groups bisected left of true center regardless of hand used. Regardless of hand preference, bisections were significantly left of center only when subjects performed with their left hand. Left-handed subjects using their left hand deviated significantly further left than right-handed subjects using their left hand. Regardless of hand used, right-handers bisected vertical lines significantly above veridical center. Left-handed subjects were not significantly above center with either hand. The results require both hemispheric advantage and lateralized activation effects for a complete explanation.