Ensemble characteristics of visual evoked cortical potentials in noise
Timothy C. Doyle · 1969
To date, most investigations of evoked potentials monitored at the human scalp have utilized the average of a series of responses recorded from a single subject to define components of the evoked response, ER.This technique has provided a fairly consistent estimate of an individual's average ER.However, with this method it is not uncommon to obtain quite dissimilar averages from different subjects under identical experimental conditions.This contrast in the ER estimates across a population has hindered the interpretation of the effects of stimulus parameters on the ER and frustrated the attenpt to use this average for clinical diamosis.The present stud>' investigated one metliod of obtaining infonna- tion about the diaracter of the response to visual stimuli common to a considered normal subject population.The estimation technique utilized was to average across an ensemble of fift>' subject EEC's containing evoked activity.This method permitted estimation of common inter-subject response activity evoked by a single stimulus.Vlll IX By averaging tiie resultant waveforms of tiiis enseinble average across stimuli, a reliable, relatively noise-free inter-subject response template was obtained.The resemblance of the ensemble of cortical potentials to a classical stochastic process enabled the author to investigate three prevalent assumptions about the statistical character of the evoked response and background noise activity.These three assumptions are: (1) the response and background noise are independent; (2) the background noise is stationary ; and (3) the response and noise are additive.Tlie results presented in this dissertation lend some measure of support to each of the three assumptions.