The importance of single trials: temporal and spatial resolution in event-related potential research.

In event-related potential (ERP) research, the average potential over many trials is a useful measure, but it obscures temporal variability across trials that may be functionally significant. Familiar ERP components have been shown to reflect the phase shifting of oscillatory activity that is present in varying degrees before the event. Even with single trials, understanding the underlying neural activity may require methods of dealing with the spatial superposition of neural signals at the head surface electrodes. We conclude with an illustration in which the modulation of averaged ERPs by trait anxiety may be related to underlying sources of theta oscillations.