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.