Line bisection: Does introspection inform cognitive strategy?

Line bisection is widely used to diagnose and quantify hemispatial neglect, yet there is little consensus as to the cognitive mechanisms used to perform this simple task. Current cognitive accounts have been deduced solely from behavioural measures. The aim of this study was to discover if subject's own knowledge of the mental strategies used to perform the task actually informs behavioural performance. One hundred and forty healthy volunteers bisected a set of lines and were asked to describe the mental strategies used. Three distinct strategies were identified. These were (1) comparing two segments, (2) computing the centre of mass, and (3) externally centred strategies. Strategies 1 and 2 have previously been described but externally centred strategies have not been reported as a distinct strategy in bisection. Although none of the three strategies predicted performance this may have been due to the fact that 44% of subjects failed to describe any strategy. Men and women bisected lines equally well, however more men than women reported use of externally centred strategies.