Effects of three stimulus parameters on eye position in cerebral palsied adults.

Bilateral eye position was measured in 6 cerebral palsied adults to assess the effects of stimulus dimensions (horizontal, vertical), amplitude (+/- 4 degrees, +/- 6 degrees, +/- 8 degrees), and frequency (0.3, 0.5, 0.7 Hz) on saccadic and pursuit movements. The head-free, corneal reflection method was used for 54 10-sec. trials of square, triangle, and sine wave stimuli. Shared variance between each eye's position and the stimulus was tested by Wilcoxon T (dimension) and Friedman analysis of variance (amplitude, frequency) showing that the effects of saccadic and pursuit dimension and amplitude were individualized with regard to subject and right and left eye positions. The bilateral eye position of 5 of 6 subjects was affected by saccadic frequency; pursuit frequency affected bilateral eye position of 4 of 6 subjects. The lowest shared variance (critical difference in ranks) was at 0.7 Hz. The results are discussed with regard to subjects' disability, stimulus velocity, and frequency of directional reversal. Reversal may be the most critical stimulus property.