Signal-to-noise ratio sensitivity in ERPs to stimulus and task complexity: different effects for early and late components

Traditionally, early and late ERP components are evaluated by the latency and amplitude of their components. We investigated their signal-to-noise (S/N) ratio: how well individual ERP trials correlate with their overall averaged ERP. High correlations indicate minimal noise or individual trial variability while low correlations reflect greater trial variability. Continuous EEG activity was recorded from 57 university students during single- and dual-task conditions in a within-subjects paradigm (easy and difficult tone discrimination; with and without verbal working memory task). For early components, the addition of the second task increased the correlations between the individual trials and the averaged ERPs. For the late components, both the addition of the second task and an increase in stimulus difficulty decreased individual trial correlations. Results suggest that the S/N ratio analysis is a useful method for highlighting differences between early and late components associated with stimulus processing manipulations.