Multichannel evoked potential fields show different properties of human upper and lower hemiretina systems

Scalp potential fields in human subjects were evoked by checkerboard reversals to the upper and lower hermiretinae, using 1.6 and 3.2 reversals/s. Averaged fields were sampled along a saggital midline row of electrodes (field profiles) in 20 subjects, and from a 47 electrode array (field maps) in five subjects. In five subjects, profile peaks and troughs between 84 and 128 ms latency resided within the recorded electrode row surrounded by lesser potential values, and thus met the evaluation criteria. Response latency defined as maximal voltage difference between two electrodes within the profiles was significantly shorter (medians 12 and 11 ms, respectively) for upper than for lower hemiretina stimuli at both frequencies. There was a significant difference between latencies to 3.2 and 1.6 stimuli/s in the upper but not in the lower hemiretina system, suggesting different system behavior of the two retinal halves. Pertinent anatomical, electrophysiological, and behavioral data are reviewed.