REVERSIBLE DISSOCIATION OF SENSITIVITY TO DYNAMIC STIMULI IN PARKINSONS-DISEASE - IS MAGNOCELLULAR FUNCTION ESSENTIAL TO READING MOTION-DEFINED LETTERS

A group of 20 control subjects carried out the following visual tests: Snellen acuity; contrast detection threshold for a temporally unmodul ated grating and for temporally modulated grating; speed threshold for recognising motion-defined dotted letters, Normal limits were defined as 2.5 standard deviations from the respective control means, A patie nt with Parkinson's disease carried out the tests 12 hr after medicati on was withheld at a time when symtoms were evident (''off'' stage), a nd after administration of medication when it had taken full effect (' 'on'' stage), Confirming previous reports, contrast detection threshol d for the temporally modulated grating was much higher during the ''of f'' stage than during the ''on'' stage, but contrast detection thresho ld for the temporally unmodulated grating showed little difference. Sp eed threshold for recognising motion-defined letters did not, however, fall during the ''on'' stage, We suggest that magnocellular function is not essential for the recognition of motion-defined form, (C) 1997 Elsevier Science Ltd.