INSTANTANEOUS FREQUENCY MAPS, DIPOLE MODELS AND POTENTIAL DISTRIBUTIONS OF PATTERN REVERSAL-EVOKED POTENTIAL FIELDS FOR CORRECT RECOGNITIONOF STIMULATED HEMIRETINAE

Lateral hemifield pattern-reversal visual evoked potential (PVEP) fiel d data were evaluated using potential distributions, dipole modelling and distributions of Hilbert transformation-based instantaneous freque ncy in order to determine the stimulated hemisphere. Twenty channel re cords were collected from 35 normal volunteers in two laboratories usi ng similar stimulus conditions (11-20.5 degrees target, 60-75 min chec ks, 2/s reversal, 500 ms analysis epoch). P100 latency was determined in each average by the global field power maximum between 90 and 120 m s. Using the data from O1 and O2 at P100 latency, the stimulated hemis phere was identified by maximal potential or minimal instantaneous fre quency on the stimulus-contralateral side, or, using the 20-electrodes data at P100 by the ipsilateral lateralization of the dipole model. C orrect classification of the stimulated 70 hemiretinae was achieved by potential distribution in 44 cases, by dipole modelling in 54 cases a nd by instantaneous frequencies in 68 cases. Errors in the classificat ion by potential distribution and dipole location were twice as freque nt for decisions based on expected locations over the left than over t he right hemisphere. This finding might be caused by the relatively la rger size of the left occipital lobe. We conclude that a single value of instantaneous frequency which implies a massive data reduction can serve as a robust parameter for the characterization of the input cond itions of hemifield PVEP (i.e. the stimulated hemiretina). It is more successful than potential distribution or dipole modelling, probably b ecause instantaneous frequency incorporates considerably more informat ion than the other two measures. It is suggested to explore instantane ous frequency as a parameter to recognize small retinal area stimuli i n perimetry studies.