Parietal and occipital lobe contributions to perception of straight ahead orientation

Objectives-Several studies have investigated how peripheral stimulation aff ects the perception of body orientation in healthy subjects. The studies sh owed that opposing stimulation of two different input modalities can cancel out, leaving perception of body orientation unchanged. It was ascertained whether a comparable phenomenon could be found in brain damaged patients wi th two distinct-disorders which individually lead to opposing shifts of the perceived midline. Methods-The visual subjective straight ahead was measured in patients with pure neglect, pure hemianopia, or a combination of neglect and hemianopia. Results-As in previous studies, patients with pure neglect displayed an ips ilesional displacement of the perceived straight ahead. Patients with pure hemianopia showed a contralesional shift. By contrast, no significant midli ne shift occurred in the patients with both neglect and hemianopia. Conclusions-Neglect and hemianopia interact so that opposing biases in the perception of body orientation neutralise each other. Both parietal and occ ipital areas seem to contribute to the perception of straight ahead body or ientation and seem to have counteracting effects when lesioned in the same hemisphere.