Specific vs. unspecific long-term deficits of intermediate visual perception after stroke C Grimsen1, M Praß2, F Brunner3, S Kehrer4, A Kraft4, S A Brandt4, M Fahle1 |
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1Institute for Human-Neurobiology, University of Bremen, Germany |
| Lesions of human visual association cortex can result in achromatopsia, akinetopsia, or other specific impairments of visual recognition. Patients with unilateral stroke of occipito-temporal cortex and intact visual fields (as proven by standard perimetry) show large inter-individual differences in the pattern of impairment when tested psychophysically in different visual sub-modalities [Grimsen et al., 2011, Perception, 40 ECVP Supplement, 43]. For forty patients with chronic damage of visual cortex we determined perceptual thresholds for each quadrant of the visual field in four different visual modules (luminance, colour, texture, motion). Thresholds were normalised and corrected for age (control group, n = 60). More than 40% of the patients had significantly increased thresholds. The deficits were more pronounced in visual form discrimination than for detection, but unspecific for individual visual sub-modalities. But in both, patients and controls, we found only minor correlations between performance in different modules, indicating little correlation between visual sub-functions. These findings show that 1) intermediate visual perception is disturbed in a sizeable number of our patients in spite of intact visual fields, 2) chronic deficits are relatively unspecific for modality and 3) deficits may be caused by impaired grouping/segmentation mechanisms on a higher processing stage. |
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