Persisting asymmetries of vision after right side lesions

Visual neglect and extinction are well-known effects of lesions in the right hemisphere. This study shows that even with minor or no clinical signs of these deficits, and in the stable phase of recovery, asymmetric visual perception is common after right side lesions. Whole, partial and colour report experiments were used to estimate psychophysical parameters related to visual capacity and attentional weighting in 26 patients with stroke in the right side of the brain. The results were analyzed using Bundesen's Theory of Visual Attention (TVA [Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523-547]) including bootstrap estimation of the measurement error related to each test result [Habekost, T., & Bundesen, C. (2003). Patient assessment based on a theory of visual attention (TVA): Subtle deficits after a right frontal-subcortical lesion. Neuropsychologia, 41, 1171-1188]. Lesions were examined by MR scanning and analyzed statistically. Two main types of deficit were found. The first type was related to perception of unilateral displays, where most patients showed left side reductions of visual processing speed. This visual asymmetry correlated with injury to the putamen and surrounding white matter. The second deficit type occurred with bilateral displays, which increased the visual asymmetry (extinction effect) for most patients with large cortico-subcortical lesions, but rarely for patients with focal lesions. However, in a single case with pulvinar damage, visual asymmetry occurred selectively with bilateral stimulation. Overall, the study provided an overview of the cognitive structure and lesion anatomy of subtle visual asymmetries after right side stroke.