1.4 Variability in Single Trials - It Can Be Systematic
While often dismissed as measurement error, the EEG/ERP research community has long recognized that information inherent within trial-to-trial variation is lost through averaging (Jung et al., 2001; Walsh, Gunzelmann, & Anderson, 2017; Yajing et al., 2020). When trial-to-trial variability in either latency or amplitude is systematic rather than random, analysis of single trials can show valuable information such as the state of the participant, the presence of a disability or disorder, or the ability to learn over time (Jongsma et al. 2006; Pfefferbaum, Ford, Wenegrat, Roth, & Kopell, 1984; Pfefferbaum, Wenegrat, Ford, Roth, & Kopell, 1984; Saville et al., 2015). Several researchers have explored trial-to-trial variability (latency jitter) using ST techniques and have shown individual or group differences, especially in children or individuals with disabilities (Gavin et al., 2019; Milne, 2011; Unsal & Segalowitz, 1995). Roth and colleagues (2007) found increased latency and amplitude variability in participants with schizophrenia compared to typical adults. ST analyses have also been used to examine systematic changes in amplitude or latency across the duration of the ERP task to identify informative patterns that may represent learning over time (Quian Quiroga et al., 2007; Rey et al., 2015). For example, Jongsma et al. (2006) observed slightly faster response times with frequently presented targets versus infrequently presented targets showing learning in healthy adults.