P1 amplitude. The data reported here indicate that establishing degree of latency jitter within each participant is possible, and should be an essential part of ERP analysis if conclusions are to be drawn to regarding the origin of observed group differences. Before leaving this point, it is important to point out that a number of physiological factors contribute to ERP amplitude. Although ICA was able to isolate the signal associated with perceptual encoding from the total EEG, and therefore facilitate comparison of within-participant variables such as variability, it cannot address the potentially confounding factors of individual differences that may lead to differences in ERP amplitude between groups including differences in cortical convolution, position of the calcarine sulcus, and/or conductivity of underlying tissue, etc. Given that there is some evidence of cortical folding abnormalities in children with ASD (Nordahl et al., 2007), direct comparison of EEG amplitude or EEG power between experimental groups, without first normalizing the data, may not be a reliable technique.
