Identification of the stimulated hemiretinae using a reduced number of PVEP trials

Left and right hemifield pattern-reversal visual evoked potentials (PVEP) a t P100 latency are characterised by typical field distributions of potentia l and the spectral parameter instantaneous frequency (IF). Both parameters can be utilised for the correct identification of the stimulated hemiretina in healthy Volunteers (Hoffmann, K. et al. Electroenceph. clin. Neurophysi ol., 100, 1996: 569-578). The aim of this study was the investigation of th e robustness of instantaneous frequency for reduced numbers of averages. He mifield PVEP of 15 volunteers (20 channel records) were analysed. The numbe r of averages was reduced step-by-step (64-32-16-8-4-1). For each average, the time of P100 latency was determined by the Global field power maximum b etween 90 and 125 ms. The stimulated hemifield was identified using the pot ential or instantaneous frequency values at the occipital electrode positio ns O1 and O2: by maximal potential and instantaneous frequency on the stimu lus-contralateral side. In summary, by reduced numbers of averages (as well as by single trials) the stimulated hemiretina was correctly identified mo re frequently on the basis of instantaneous frequency than of potential dis tribution. A number of 8 averages seems to be sufficient for the correct id entification of the stimulus condition. Consequently, for the identificatio n of left and right hemifield stimulations the recording time could be redu ced immensely. Instantaneous frequency is suggested as an additional and ro bust parameter for the selective averaging of artefact-free trials during t he recording of hemifield PVEP. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.