Corresponding author:
William J Gavin
Department of Molecular, Cellular & Integrative Neuroscience
Colorado State University
Fort Collins, CO 80523, USA
Email:
william.gavin@colostate.edu
Phone: 970-227-9999
Abstract
Averaging multiple event-related potential (ERP) segments distorts the
brain’s response to a stimulus given the false assumptions that the ERP
signal is invariant and hidden by background noise. Our Single Trial
Peaks (STP) procedure measures amplitude and latency of multiple peaks
in each segment based on the peak latencies of the individual’s averaged
ERP. This study examined correct trial data from 70 adults performing
two repetitions of a speeded visual flanker task. STP peak data (P1, N1,
P2, N2, and P3) were compared to single-trial averaged voltage in time
windows (STW) and peaks of averaged ERPs. Results indicated that the STP
approach had higher split-half reliability (odd-even, r =
.70-.96) and test-retest reliability (r = .66-.97) than the STW
approach. The mean signal/noise ratios for the amplitude measures for
the STP ranged from 1.62 to 2.9 and were larger than the STW approach,
although averaged ERPs had higher ratios than both. Coefficients of
variation (CV ) for the STP and STW approaches were similar, and
both had smaller CV s than averaged ERPs. The validity of the STP
approach was determined by regression analyses where mean trial-level
peak amplitude, SDs across trials for amplitude and latency, and
noise accounted for a significant amount of variance in corresponding
peaks of the averaged ERPs (R2 = .73-.95).
Curve fitting analyses showed nonlinear systematic patterns in amplitude
over trials similar to changes in response time. These results support
the validity of the STP approach which can be used to investigate
systematic changes of brain activity across trials.
Variability of Single Trial ERP Measures Within a Session is Systematic
and Nonlinear