Topographic instability of spatial vision as a cause of dyslectic disorder: a case study.

ABSTRACT

A case of severe disorder of spatial perception with concomitant dyslexia is described. The patient, a 15-yr-old girl, has a systematic tendency to misperceive the spatial order of symbols or objects lying on the same horizontal level and within a few degrees of visual angle. The syndrome includes a spatial extinction phenomenon in which an object in her left visual field disturbs the perception of another object in the corresponding symmetry point of her right visual field. The order reversal symptom was abolished if the letters presented for her were shown for less than 15 msec. The disorder is probably due to a pathological interhemispheric interference in the processing of visual topographic information.