Cerebral hemispheric specialization for spatial attention: spatial distribution of search-related eye fixations in the absence of neglect.

The "specialization" of the right hemisphere for spatial attention is widely accepted but poorly understood. While several theories have been supported by studies of patients with acute hemispatial neglect, generalizability beyond this population remains unclear. In this study, we compared the predictions of two attention models [Brain 119 (1996) 841; Trans. Am. Neurol. Assoc. 95 (1970) 143] when applied to data obtained from subjects with unilateral right- or left-cerebral lesions, but without clinical evidence of neglect during a visual search task. Both Left Lesion and Right Lesion subjects detected fewer targets in the contralesional hemispace. However, the Right Lesion subjects also made fewer visual fixations and longer saccades in the contralesional hemispace, suggesting a fundamental alteration in the architecture of visual search. The spatial distribution of fixations made by Right Lesion subjects more closely fits the prediction of a "salience" model than of the strict interpretation of a linear "gradient" model. These data support the long-standing notion of right hemisphere dominance for spatial attention, especially for the top-down processes entailed in self-directed visual search, and extend this to lesion patients without clinically evident neglect. A theoretical model based on the salience of extrapersonal space appears useful for understanding alterations of attentional allocation, particularly after recovery from stroke.