AUTOMATIC PERIMETRY AND VISUAL P300 - DIFFERENCES BETWEEN UPPER AND LOWER VISUAL-FIELDS STIMULATION IN HEALTHY-SUBJECTS

Human visual-evoked potentials (VEPs) from upper and lower hemifield s timulation are thought to reflect the anatomical and functional differ ences between the hemiretinas and corresponding visual pathways. Confl icting results have, however, been reported in topographic studies on the putative cortical generators. We have estimated by automatic perim etry (Octopus 2000R, Program 32) and compared the sensitivity threshol ds of lower and upper hemifields of the retina in 12 healthy subjects with no history or evidence of visual or neurological diseases. A visu al P3 that is linked to cognitive function was recorded in an odd-ball paradigm with presentation of high-contrast checkerboards at two diff erent spatial frequencies at 20 degrees eccentricity in each hemifield . VEP and P3 were recorded at O-1 and O-2 and at C-z according to the 10/20 international system. Lower sensitivity thresholds were found, a nd higher VEP and event-related potential (ERP) amplitude values were obtained when stimulating the lower, compared with the upper, visual h emifield. The results are consistent with previous findings and anatom ical and physiological evidence in animals and man. Interactions betwe en perceptive process in the visual system and higher cognitive functi ons are a possible explanation for this finding.