Electrocortical correlates of intra-subject variability in reaction times: average and single-trial analyses.

Intra-subject variability of reaction times (ISV), generally considered secondary to measures of central tendency, has become increasingly important for cognitive neuroscience. Event-related potential (ERP) research suggests an inverse relationship between ISV and P3b amplitude; however ERP methods' reliance on averaged waveforms may be unsuitable for studying ISV due to potentially distorting effects of latency jitter. The present study investigates the neural bases of ISV through single-trial analysis of P3bs in groups with low and high ISV, using Infomax-rotated principal components analysis of ERP data. Results indicate that while latency jitter contributes to the reduced P3b amplitude seen in average ERPs of high ISV participants, group differences in amplitude survive the use of single-trial methods that are robust to such distortions. A decoupling of P3b and RT was also seen in the high ISV group. The results are discussed in the context of the P3b's dimensionality, and its possible catecholaminergic underpinnings.