Pseudoneglect: A review and meta-analysis of performance factors in line bisection tasks

An exhaustive qualitative (vote-counting) review is conducted of the litera ture concerning visual and non-visual line bisection in neurologically norm al subject populations. Although most of these studies report a leftward bi section error (i.e., pseudoneglect), considerable between-study variability and inconsistency characterize this literature. A meta-analysis of this sa me literature is performed in which the total quantitative data set, compri sing 73 Studies (or sub-studies) and 2191 subjects, is analyzed with respec t to 26 performance factors. The meta-analytic results indicate a significa nt leftward bisection error in neurologically normal subjects, with an over all effect size of between -0.37 and -0.44 (depending on integration method ), which is significantly modulated to varying degrees by a number of addit ional task or subject variables. For example, visual bisection tasks, midsa gittal-pointing tasks and tactile bisection tasks all lead to leftward erro rs, while kinesthetic tasks result in rightward errors. Tachistoscopic forc ed-choice testing methods reveal much greater estimates of bisection error (effect size = -1.32) than do manual method-of-adjustment procedures (effec t size = -0.40). Subject age significantly modulates line bisection perform ance such that older subjects err significantly rightward compared to young er subjects, and to veridical line midpoint. Male subjects make slightly la rger leftward errors than do female subjects. Handedness has a small effect on bisection errors, with dextrals erring slightly further to the left tha n sinistral subjects. The hand used to perform manual bisection tasks modul ated performance, where use of the left hand lead to greater leftward error s than those obtained using the right hand. One of the most significant fac tors modulating bisection error is the direction in which subjects initiate motor scanning (with either eye or hand), where a left-to-right scan patte rn leads to large leftward errors while a right-to-left scan pattern leads to rightward errors. (C) 1999 Elsevier Science Ltd. All rights reserved.