Patterns of oculomotor scanning in patients with unilateral posterior parietal or frontal lobe damage.

Eye movements were recorded during the inspection of dot patterns in control subjects and in patients with acquired unilateral brain damage involving posterior parietal or frontal cortical regions. Normal subjects adapted their oculomotor scanning pattern effectively to the stimulus configuration. Patients' oculomotor scanning patterns were characterized by a rather rigid sequence of fixations and saccades, with no evidence for a systematic and flexible spatio-temporal organization. In a stimulus condition where dots were grouped, patients with frontal damage accurately shifted their gaze between the dot groups, but had difficulties with dot sampling. These observations suggest that the posterior parietal damage mainly affected the visuo-spatial guidance of the scanpath, whereas the frontal damage impaired its planning. It is concluded that both, posterior parietal and frontal brain structures, and their reciprocal connections, are part of a distributed neural network subserving visually-guided oculomotor scanning, and that the spatio-temporal organization of the scanpath depends critically on both structures and their close co-operation.