Vertical line quadrisection: “What” it represents and who gets the upper hand

Abstract

BackgroundNormal adults demonstrate a slight upward bias (vertical pseudoneglect) when attempting vertical line bisection. The mechanism for this bias is unknown. Activation of the allocentric (object-centered) ventral visual system during attempted bisection may induce this bias. This object-centered ventral stream may also mediate focal attention. As compared to bisection, when normal participants perform a vertical line quadrisection task that requires more focal attention, they may have a greater upward bias. MethodsSixteen participants bisected and quadrisected vertical lines. ResultsThe mean upward bias (deviation error) for the quadrisection tasks was significantly higher than the mean error for the line bisections. ConclusionsThese results are consistent with the hypothesis that activation of the ventral stream by a task that requires focal allocentric attention can induce an upward vertical bias that is greater than the upward bias observed with allocentric line bisection, a task that requires more global attention.