Patients with Alzheimer's disease (AD) might have bilateral attentional disorders, such as a reduced spatial attentional window, due to pathological changes in regions important for mediating spatial attention. AD patients may also be highly distractible with the presentation of unilateral novel stimuli or be impaired at disengaging and reallocating their attention with imperative stimuli. This study sought to test these hypotheses by asking AD patients and normal control subjects to bisect 72 horizontal lines of 3 different lengths in three conditions: no lateral stimuli, novel right or left lateral stimuli ('bottom-up'), and imperative left or right lateral stimuli ('top-down'). Regarding the bottom-up condition, no group differences emerged, but the AD patients had a greater rightward bias with short lines and a leftward bias with long lines, independent of distracting stimuli. In the top-down condition, when the patients with AD, versus controls, were presented with imperative stimuli on their left side, they demonstrated a greater attentional bias than when presented with right-sided stimuli. Thus AD patients have a reduced spatial attentional window and while they are not highly distracted by novel stimuli, after allocating their attention to left sided stimuli, they have a reduced capacity to spatially re-allocate their attention.