It is also worth noting that in the early days there were heated arguments over whether the N400 was, for example, simply a longer-latency member of the N200 family of responses (typically preceding P3b’s to unexpected events) (e.g., Deacon et al 1991) or resolution of yet another component. Linking a newer response with a better-characterized one is useful in allowing new predictions and generalizations. Critically, however, such classifications often matter little for how the measure can be used. What is essential whether linking a newly-discovered response with an older one or splitting a well-studied response into subcomponents is that the measure be reliably identifiable in data and its sensitivity to stimulus and task properties mapped out; only then can it be used to meaningfully answer questions about cognitive and neural function. By 1988, the N400 had reached the status of a fairly well-characterized neural marker (“component”) and began to be usefully applied to a variety of questions, including those that were difficult or impossible to test with other metrics, and to challenge core assumptions about cognitive processing, especially in the domain of language (Kutas & Van Petten 1988; Kutas & Van Petten 1994).
