1.5 The Aims of the Present Study
Most studies looking at single-trial data analyzed one or two components, typically the P300 and N200. By looking at multiple components, including baseline, researchers can determine if the variability is random or systematic (Gaspar, Rousselet, & Pernet, 2011). If within-subject variability is systematic, it would be helpful to find a reliable method to analyze single-trial data that preserves individual differences and can demonstrate systematic changes during task performance within and across individuals. Therefore, the purpose of this study was to determine the feasibility and validity of measuring multiple ERP components (e.g., the N1, P2, N2, and P3 peaks) using a simple computational strategy to obtain ST measurements. The feasibility of these ST measures was considered by computing the SNR for the traditional averaged ERP, the STP approach, and the Single Trial Average Time Window (STW) approach. Reliability was determined through the comparison of split-half and test-retest reliability measures of amplitude and latency computed for single trials to those computed for measures of amplitude for the STW approach and amplitude and latencies obtained from the traditional averaged ERP. We expect that both the SNR and correlations for reliability measures will demonstrate similarities in the different ST approaches. Validity was considered by comparing the standard measurement error (SME) of the STP and STW approaches. The validity of the ST measures was further determined by computing how well an individual’s mean ST amplitude, ST amplitude variability, ST latency variability, and mean ST noise predict the individual’s peak amplitude measures of the averaged ERP. Given issues of SNR, we expect measures of reliability and validity to improve across the phases of cognitive processing, reflected by successive ERP components. Furthermore, we used curve fitting to look for the presence of systematic changes across trials. If the process of identifying ERP components within ST data can be shown to be reliable and valid, the methodology can then be used to demonstrate that systematic changes do occur within a paradigm from one trial to the next.