Methods of acquisition and analysis of auditory evoked potentials

Auditory evoked potentials (AEP) were triggered in real time as a function of ongoing EEG phase. Phase triggering online or retrospective phase selective averaging introduces phase artifacts, such as spurious troughs or peaks, which mask mid-latency and affect the amplitude of late AEPs. We developed a method to control for phase artifacts by phase-selective averaging of trials, which were recorded without stimulation, and used this to uncover a previously unknown phase dependency of AEPs. Not only are such findings inconsistent with the standard additive evoked potential model, but also we identified clear neural correlates at fixed latencies, which are inconsistent with the recently proposed phase resetting model. Our findings suggest that a new conceptualization is required to account for the interplay between the correlates of neural evoked activity and modulation of ongoing EEG that together constitutes evoked potentials.; We investigated the applicability of different analysis methods, such as principal component analysis (PCA) and independent component analysis (ICA), for extraction of AEP from standard averages. The use of ICA in some subjects allowed us to extract AEPs. In other subjects, ICA was not able to separate different AEPs and therefore was not useful. PCA did not separate different AEPs.; We further studied the feasibility of employing linear and quadratic discriminators, obtained using tonal and phonemic response data, to classify AEP to elongated phonemes. The results show that a substantial part of normal subjects process elongated phonemes as tones. This suggests a selection criterion for elongated phonemes training of children with dyslexia.