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Chunk #14 — Methods — Current Source Density (CSD), N1 Latency Jitter, and Principal Components Analysis (PCA)

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A neurophysiological deficit in early visual processing in schizophrenia patients with auditory hallucinations.
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ERP component latency jitter, either between conditions or between subjects, is a well-known problem for quantifying ERP peaks (e.g., Möcks, 1986). For each paradigm (RM, WM) and task (face, word), individual CSD waveform topographies were temporally adjusted for N1 sink peak latency to create optimized subepochs (−50 to 400 ms) focused on N1 sink activity. After determining the most negative deflection for pooled CSD waveforms using sites P7 and P9 (word; 91–223 ms interval) or P7, P8, P9 and P10 (face; 79–223 ms), all 67 CSD waveforms were jointly aligned with the mean N1 sink peak latency for each task (face, word) and paradigm (RM, WM). For example, if an individual N1 sink peaked at 141 ms in the RM paradigm using words (i.e., using the average of the corresponding CSD waveforms at P7 and P9), all CSDs for this participant, task and paradigm were shifted 2 samples (approximately +8 ms) so that the N1 sink maximum would match the respective mean N1 sink peak latency for words during the RM paradigm (approximately 149 ms). Local N1 sink maxima were