Asymmetries of visuospatial attention are modulated by viewing distance and visual field elevation: pseudoneglect in peripersonal and extrapersonal space.

Many factors influence the degree of leftward error (pseudoneglect) that typifies the line bisection performance of normal subjects. We find that viewing distance also exerts a modulating influence on spatial attention in normal subjects, as it appears to do in neglect syndrome. Using forced-choice tachistoscopic line bisection, 38 right-handed subjects (15 male, 23 female) bisected horizontal lines (13.7 degrees w x 0.24 degrees h) presented in the midsagittal plane as a function of line elevation (- 3.6 degrees, 0 degrees, and 3.6 degrees relative to horizontal midline) and viewing distance (45 and 90 cm). We find a significant main effect of viewing distance, F (1, 37) = 10.04, p = .003, where pseudoneglect is larger in peripersonal (45 cm) than in extrapersonal (90 cm) space. We replicate an effect of line elevation, F (2, 74) = 4.40, p = .016, where pseudoneglect is greatest in the superior visual field (McCourt and Jewell, 1999). The interaction was not significant, p > .05. Thus, we find evidence for independent spatiotopic (viewing distance) and retinotopic (line elevation) effects on line bisection performance in normal observers, suggesting that the allocation of visuospatial attention is modulated within multiple frameworks.