4.2 Peak-to-peak Amplitude Measurement in Single Trials
Using a peak-to-peak measure to report the amplitude of an ERP component has several advantages compared to reporting baseline-to-peak measures or averaged amplitude within a window (i.e., STW approach). Firstly, baseline-to-peak and STW measures are centered on a baseline obtained in a step in the preprocessing stage for creating ERPs. This processing step may not always be successful in producing a constant zero-voltage baseline prior to the stimulus onset. In these cases, measuring in relation to the baseline can be problematic as the deflection of interest may move more positive or more negative than a true zero baseline would guarantee. Secondly, previous research demonstrates that measuring amplitude using a peak-to-peak approach produces a more reliable measure of amplitude compared to baseline-to-peak or average voltage in a window, suggesting that there is less measurement error in the peak-to-peak amplitude measure (Gavin et al., 2019; Lin et al., 2020; Taylor et al., 2016). Finally, previous studies have shown that in a stream of processing from stimulus presentation to behavior (e.g., response time) each phase is not independent from the next, i.e., successive phases are interrelated (Lin, et al., 2021; Taylor, 2019). These interrelationships are consistent with the concept of phase sequences proposed by connectionist theory (Bear & Cooper, 1990; Hebb, 1949; Lowe et al., 2016; McNaughton & Nadel, 1990). Thus, using a peak-to-peak measure preserves the interrelationship between brain process reflected by each component. However, it should be noted that using multiple peak-to-peak measures from single ST ERPs or averaged ERPs can lead to multicollinearity, so caution needs to be heeded when using these measures in statistical analyses.
In the current study, the use of the STP peak-to-peak amplitude measures demonstrated enhanced reliability and measurement sensitivity compared to the STP baseline-to-peak and the STW amplitude measures. The split-half correlation coefficients were greater when examining STP peak-to-peak amplitudes (see Table 6) compared to the STP baseline-to-peak and STW amplitudes (see Table 5). This suggests that there was more stability in the peak-to-peak measure. In addition, the changes within a session were more pronounced for each component when using the STP peak-to-peak measure compared to the STP baseline-to-peak and STW amplitude measures (see Figure 2). This suggests that the smaller measurement error in the STP peak-to-peak measure increases the sensitivity to voltage fluctuations across trials demonstrating changes within a session, at least when examining the ST ERPs during the speeded flanker task. The interrelationship between processing phases required to successfully complete the speeded flanker task are captured when using the peak-to-peak measure when observing changes across a session.