In this experiment, we tested whether perceptually delineating the scotoma location and border with a gaze contingent polygon overlay improves reading speed and reading eye movements in patients with bilateral central scotomas.
Eight patients with age-related macular degeneration and bilateral central scotomas read aloud MNRead style sentences with their preferred eye. Eye movement signals from an EyeLink II eyetracker were used to create a gaze contingent display in which a polygon overlay delineating the area of the patient’s scotoma was superimposed on the text during 18 of the 42 trials. Blocks of six trials with the superimposed polygon were alternated with blocks of six trials without the polygon. Reading speed and reading eye movements were assessed before and after the subjects practiced reading with the polygon overlay.
All of the subjects but one showed an increase in reading speed. A paired-samples t-test for the group as a whole revealed a statistically significant increase in reading speed of 0.075 ± 0.060 (SD) log wpm after reading with the superimposed polygon. Individual subjects demonstrated significant changes in reading eye movements, with the greatest number of subjects demonstrating a shift in the average vertical fixation locus. Across subjects, there was no significant difference between the initial and final reading eye movements in terms of saccades per second, average fixation duration, average amplitude of saccades, or proportion of non-horizontal saccades.
The improvement in reading speed (0.075 log wpm or 19%) over the short experimental session for the majority of subjects indicates that making the scotoma location more visible is potentially beneficial for improving reading speed in patients with bilateral central scotomas. Additional research to examine the efficacy of more extended training with this paradigm is warranted.