Minding the PS, queues, and PXQs: uniformity of semantic processing across multiple stimulus types

Abstract

An assumption in the reading literature is that access to semantics is gated by stimulus properties such as orthographic regularity or familiarity. In the electrophysiological domain, this assumption has led to a debate about the features necessary to initiate semantic processing as indexed by the N400 event-related potential (ERP) component. To examine this, we recorded ERPs to sentences with endings that were familiar and legal (words), familiar and illegal (acronyms), or unfamiliar and illegal (consonant or vowel strings). N400 congruency effects (reduced negativity to expected relative to unexpected endings) were observed for words and acronyms; these were identical in size, timing, and scalp distribution. Notably, clear N400 potentials were also elicited by unfamiliar, illegal strings, suggesting that, at least in a verbal context, semantic access may be attempted for any letter string, regardless of familiarity or regularity.

Figure 1

Grand average waveforms elicited by unexpected and expected sentence-final acronyms at all 26 scalp channels. Expected acronym ERPs are notably more positive in the 250–450-ms N400 window than are unexpected acronym ERPs.

Figure 2

Grand average ERPs elicited to unexpected and expected acronyms and words at the middle parietal channel. Response to expected endings is more positive in the N400 window for both item types. The apparent positivity for unexpected word endings is not statistically reliable in the post-N400 window.

Figure 3

Grand average waveforms elicited by unexpected words, unexpected acronyms, and illegal strings at a representative selection of central parietal channels; the unexpected acronym and illegal string categories of sentence ending type are similar in their orthographic illegality and their low lexical density. In the 250–450-ms N400 window, the ERPs to words are reliably more negative than those to unexpected acronyms or illegal strings whereas the responses to unexpected acronyms and illegal strings are indistinguishable.