Various factors influence the degree of leftward
error (pseudoneglect) that typifies the performance of
normal individuals in line bisection tasks. This experiment
reveals that the eye through which stimuli are viewed also
exerts a modulating influence on spatial attention, as
indexed by significant alterations in the magnitude of
pseudoneglect. Using a forced-choice tachistoscopic line
bisection protocol, 24 participants (12 male; 12 female)
bisected horizontally oriented lines (22.6° w ×
0.39° h) presented to central vision in 3 conditions:
left uniocular viewing (L), right uniocular viewing (R),
and binocular viewing (B). Perceived line midpoint, a measure
of bisection accuracy, deviated significantly leftward
of veridical ( p < .05) in all viewing conditions,
confirming a tonic asymmetry of visuospatial attention
in normal young observers. In addition, a significant influence
of viewing condition was found (p < .05) where
pseudoneglect was greatest in the L condition, followed
by the B and R conditions, respectively. Analysis of the
slopes of the psychometric functions revealed significantly
greater bisection precision in the binocular versus uniocular
viewing conditions (p < .05). The results are
interpreted to suggest that phasic effects on spatial attention
can be produced by uniocular viewing via asymmetric retinotectal
projections. The results are consistent with activation–orientation
theories of attentional asymmetry. (JINS, 2001,
7, 391–395.)