Perceptual-motor adaptation in hemianopes wearing peripheral prisms is possible: Preliminary results

Abstract

Purpose: For hemianopia, peripheral prism (p-prism) glasses are used to optically shift peripheral areas of the blind hemifield 20°-30° toward the seeing side. This improves detection immediately however perceived location of prism side obstacles is incorrect. With general wear, some hemianopes make cognitive corrections for the displacement, but perceptual adaptation does not occur (Giorgi et al 2009). We are conducting a pilot study to evaluate whether intensive perceptual-motor training improves adaptation and generalizes to improved collision judgments in a walking simulator.

Methods: Seven hemianopes wearing 57Δ oblique p-prisms received 120 minutes of computerized training over 3 weeks consisting of reaching out to touch peripheral stimuli presented on a touch screen under fixed gaze conditions. Training included 5 levels of difficulty starting with slow but accurate reaching to blind side stimuli (level 1), reaching to stimuli in both hemifields (level 2), increasing speed (level 3), cognitive loading (level 4), and use of background visual cues (level 5). Collision judgment data under fixed gaze conditions were collected in a video walking simulator before and after training.

Results: Touch accuracy error to targets presented in prism areas improved significantly (p=0.02) from median (x,y) (17°, 6°) to (1° , 0.5°) (equivalent to seeing-side accuracy). The median difference between seeing and prism side reaction times reduced significantly (p=0.04) from 880ms to 110ms. Preliminary analyses of collision judgment data suggest no or only modest improvements in performance post-training.

Conclusions: These pilot data suggest that hemianopes wearing p-prisms can be trained to perform similarly on the blind and seeing side during a perceptual-motor task. We suspect the mechanism of adaptation for most participants was realignment of the felt position of the arm (as opposed to retinotopic coordinates), and so did not generalize. We are developing pre- and post- test measures to investigating this hypothesis by looking for transfer to the untrained hand.

Keywords: 759 visual impairment: neuro-ophthalmological disease • 753 vision and action • 650 plasticity