Visuospatial neglect is more severe when stimulus density is large

Patients with visuospatial neglect (VSN) suffer from an imbalance in visual attention between their left and right (egocentric or allocentric) hemispace. The view of VSN as an attentional imbalance between two hemispaces ignores the fact that—in our daily life—we are presented with varying levels of stimulus density, within but also across hemispaces. Therefore, we developed a novel experimental paradigm in which stroke patients (n = 207) were presented with a different number of simple objects in the left and right (egocentric) hemispaces and were asked to indicate whether there were more objects in the left or the right hemispace. We systematically varied the density of visual stimuli to investigate whether a high level of stimulus density impairs task performance of patients with VSN to a larger degree than it does for patients without VSN. Error rate increased when more objects were presented in the display, but this effect was most pronounced in patients with VSN, especially when more objects were presented in their contralesional than in their ipsilesional hemispace. Our findings reveal that deficits in early visual processing in patients with VSN become especially apparent when overall stimulus density is high. The degree of stimulus density should therefore be taken into account when considering the impact of attentional deficits on activities in daily life.