SPEED OF ELEMENTARY VISUAL RECOGNITION OPERATIONS IN PARKINSONS-DISEASE AS MEASURED BY THE MUTUAL MASKING METHOD

Pairs of mutually different, spatially overlapping letters were expose d for recognition to groups of patients with Parkinson's disease (PD) and the age-matched control group. Stimulus onset asynchrony (SOA), me dical treatment status (de novo vs. treated), and predominant symptoms (tremor vs. hypokinetic rigidity) were an other main variables. The h ighly significant main effects of SOA and health status demonstrated s lowing of elementary visual recognition operations in Parkinson's dise ase; the results are based on the experimental method that requires ne ither fast manual responses nor Cracking of the display events by sacc adic eye movements. Significant interaction between the temporal order of stimulus exposure and health status showed that impairment due to PD was more pronounced for the first stimulus, including the de novo g roup. Qualitatively similar recognition functions in the binocular and dichoptic conditions showed that the typical pattern of results - pre valence of S2 over S1 at intermediate SOAs - cannot be attributed to r etinal processes and should be originating from central processes. An earlier finding (Bachmann, 1994) that PD patients whose nonspecific th alamic nuclei were stimulated intracranially produced qualitatively un usual recognition functions that should have been the result of stimul ation, rather than PD as such.