An ERP study of regular and irregular English past tense inflection

Abstract

Compositionality is a critical and universal characteristic of human language. It is found at numerous levels, including the combination of morphemes into words and of words into phrases and sentences. These compositional patterns can generally be characterized by rules. For example, the past tense of most English verbs ("regulars") is formed by adding an -ed suffix. However, many complex linguistic forms have rather idiosyncratic mappings. For example, "irregular" English verbs have past tense forms that cannot be derived from their stems in a consistent manner. Whether regular and irregular forms depend on fundamentally distinct neurocognitive processes (rule-governed combination vs. lexical memorization), or whether a single processing system is sufficient to explain the phenomena, has engendered considerable investigation and debate. We recorded event-related potentials while participants read English sentences that were either correct or had violations of regular past tense inflection, irregular past tense inflection, syntactic phrase structure, or lexical semantics. Violations of regular past tense and phrase structure, but not of irregular past tense or lexical semantics, elicited left-lateralized anterior negativities (LANs). These seem to reflect neurocognitive substrates that underlie compositional processes across linguistic domains, including morphology and syntax. Regular, irregular, and phrase structure violations all elicited later positivities that were maximal over midline parietal sites (P600s), and seem to index aspects of controlled syntactic processing of both phrase structure and morphosyntax. The results suggest distinct neurocognitive substrates for processing regular and irregular past tense forms: regulars depending on compositional processing, and irregulars stored in lexical memory.

Figure 1

Grand average ERPs for violation (dashed lines) and control (solid lines) target words in each condition. Waveforms for correct and incorrect target words are superimposed. The ordinate indicates the onset of the target word. Timing is given in milliseconds. Negative voltage is plotted upwards.

Figure 1

Grand average ERPs for violation (dashed lines) and control (solid lines) target words in each condition. Waveforms for correct and incorrect target words are superimposed. The ordinate indicates the onset of the target word. Timing is given in milliseconds. Negative voltage is plotted upwards.

Figure 2

Scalp topographic maps showing the distribution of the ERP components of interest in the early (a) and late (b) epochs. To capture the peak difference between violation and control words, 50 msec time widows were chosen for each condition centered around the peaks identified on the basis of examination of the waveforms (Figure 1).