Visual and motor components in simple line bisection: an investigation in normal adults

Visuomotor bisection and bisection judgement of centrally presented 10-cm horizontal lines were proposed to 43 normal adults, both on paper and on the vertical screen of a computer. Tasks on paper showed slight left-side of the line overestimation and weak link between actual bisection and judgement. Tasks on screen showed, on the contrary, right-side of the line overestimation and stronger link between actual bisection and judgement. Centrally pretransected lines were often judged wrongly. These results suggest an important role of motor factors on classical paper-and-pencil visuomotor line bisection, and the relevance of the distinction between peripersonal and extrapersonal space.