Vertical orienting control: evidence for attentional bias and "neglect" in the intact brain

Unilateral neglect may be due to attentional bias: an exaggerated tendency to orient in an ipsilesional direction. Likewise, cases of vertical neglect suggest the existence of vertical attentional biases. This article reports evidence of upward biases in neurologically intact observers. In 5 experiments, observers performed a visual line-bisection task by judging the location of a gap along a tachistoscopically presented vertical line. The upward bias was influenced by attentional cues and was stronger in the right visual field than in the left visual field. Instructions designed to foster the use of an object-based, categorical encoding strategy were associated with an upward bias, whereas those fostering spatial, between-object comparisons were not. The results are discussed in terms of hemispheric differences in attention and specializations along the dorsal-ventral axis of the brain that influence directional orienting.