Schoepf D, Zangemeister WH: In: Facets of Dyslexia and its Remidiation, ed. by R Groner & SFWright, Elsevier, Amsterdam NewYork, 1993; pp. 267 287
In hemianopic patients visual information is available only in one hemifield: Patients are blind on left or right half field i.e. zero to 100 degree to left or right. To compensate for hemianopia it is necessary to have appropriate ocular motor strategies for efficient use of the remaining half of the visual field. To some extent, it is possible to learn to compensate for this visual handicap. Zangemeister et al. (1981, 1982, 1983) found distinct adaptive ocular motor strategies in hemianopic patients to search for objects in their blind hemifield. They used a horizontal target, a small green light spot, the appearance of which was predictable or randomized in amplitude and time. In this artificial experimental situation the subjects employed a consistent set of presumably unconscious compensatory eye movement strategies. With respect to a possible positive effect of head movements Zangemeister et al. (1982) pointed out that hemianopic patients often simplify search and fixation strategies by eliminating head movements. The purpose of the present study was to analyse the qualitative and quantitative changes of the ocular motor scanning behaviour during reading i.e. the reading path. Our hemianopic patients had to read aloud four different short texts as accurately and quickly as possible. First, in an experiment where the head was fixed and second, in a more natural head-free-to-move condition. In one of the four texts presented the distances between the letters and words were decreased. The question was whether this would have a positive or a negative effect on reading behaviour and comprehension. We analysed the reading path for different strategies with respect to the efficiency of reading time and accuracy. To compensate for hemianopia it is necessary to have appropriate ocular motor strategies for efficient use of the remaining half of the visual field. Our studies indicate that patients with pure hemianopia and foveal sparing – fovea, the retinal point of highest resolution (2 degree) – optimally learn to compensate their visual handicap by active and motivated visual training. Characteristically, the two of our four hemianopic subjects that did not produce any acoustical reading errors were the best adapted ones. In daily life they had developed a consistent set of ocular motor strategies to compensate for their specific visual handicap.