SYMMETRY DISCRIMINATION IN PATIENTS WITH RETINITIS-PIGMENTOSA

To investigate the relative sensory and perceptual contributions to ce ntral visual function of patients with retinitis pigmentosa (RP), we t ested symmetry discrimination using block patterns with varying types of symmetric organization, Eleven control subjects with normal vision and 11 patients with RP with 20/30 visual acuity or better, viewed pat terns presented for 255 msec, The patterns differed in the type of sym metric organization and the subjects were required to identify the typ e, The control subjects performed significantly better (89.2%) than th e patients (74.5%). Four hypotheses to account for these findings were tested and the results were as follows, (1) A reduction in pattern lu minance did not change symmetry discrimination performance in the cont rol subjects, (2) Large reductions in pattern contrast did not alter s ymmetry discrimination in the control subjects, (3) Reductions in stim ulus duration, likewise, did not produce similar error patterns in the central subjects as those observed in the patients with RP, (4) Alter ations in spatial sampling density did not completely account for the patients' deficits, None of the retinally based explanations alone was sufficient to account for our findings, Additionally, we suggest that alterations of sensory input may affect the perceptual encoding of th e relationship among pattern elements.