The EEG differs from event-related potentials (ERPs), which are waveform analyses of the brain electrical responses within the EEG signal, time-locked to a specific set of stimuli. ERPs are used to capture snapshots of brain responses to discrete stimuli associated with the recognition of familiar and novel objects or sounds. ERP events are brief, typically 500 milliseconds. Many trials are required because the ERP waveform is extracted by averaging across all trials of the same stimulus so that the background EEG signal drops out and the specific response to a particular stimulus is observable. An advantage of ERPs is that the various positive and negative components of the waveform at different latencies from stimulus onset have been associated with specific cognitive processes. A disadvantage is the relatively large number of trials required, such that the attrition rate in ERP studies with infants can range from 35–75% (de Haan, 2006). A discussion of ERPs in studies of cognitive development can be found elsewhere (e.g., DeBoer et al., 2006; Fox, Schmidt, Henderson, & Marshall, 2007).
