Electrophysiological evidence for the morpheme-based combinatoric processing of English compounds

Abstract

The extent to which the processing of compounds (e.g., “catfish”) makes recourse to morphological-level representations remains a matter of debate. Moreover, positing a morpheme-level route to complex word recognition entails not only access to morphological constituents, but also combinatoric processes operating on the constituent representations; however, the neurophysiological mechanisms subserving decomposition, and in particular morpheme combination, have yet to be fully elucidated. The current study presents electrophysiological evidence for the morpheme-based processing of both lexicalized (e.g., “teacup”) and novel (e.g., “tombnote”) visually presented English compounds; these brain responses appear prior to and are dissociable from the eventual overt lexical decision response. The electrophysiological results reveal increased negativities for conditions with compound structure, including effects shared by lexicalized and novel compounds, as well as effects unique to each compound type, which may be related to aspects of morpheme combination. These findings support models positing across-the-board morphological decomposition, counter to models proposing that putatively complex words are primarily or solely processed as undecomposed representations, and motivate further electrophysiological research toward a more precise characterization of the nature and neurophysiological instantiation of complex word recognition.

Keywords:

• Compound words
• Lexical access
• Lexical decision
• Morphology
• Electroencephalography.

We would like to thank Stephen Politzer-Ahles, Utako Minai, and Natalie S. Pak for their assistance in the preparation of this manuscript.

Notes

1 See also Pratarelli (1995) for a study on English auditorily presented compounds using a picture–word priming task, showing N400 responses sensitive to semantic relatedness among the picture and a subsequently presented compound with either full overlap or overlap of a shared morpheme among the picture and compound word.

2 Care was also taken to keep bigram frequency as similar as possible across conditions. No significant differences emerge at the morpheme level between the lexicalized and novel compounds, either for the first or for the second morpheme. At the whole-word level, we were able to achieve similar bigram frequencies for all conditions save the long monomorphemic words (with the long monomorphemic words higher in bigram frequency than the other three conditions). While this potentially complicates the direct comparison of the long monomorphemic words and the lexicalized compounds, it is worth noting that, although there remain few studies on ERP responses related to phonological/orthographic probability/familiarity, we may predict that high probability should yield larger N400-like responses than lower probability (e.g., Friedrich & Friederici, 2005; Rossi et al., 2011). Thus, results showing a higher amplitude response for the long monomorphemic words would be consistent with a probability effect, although higher amplitude responses for the compounds would suggest a contravening (structural) factor distinguishing the conditions; we report the latter finding in the current study. Moreover, we note that probability was controlled within the novel compound versus novel nonword comparison, and within the lexicalized versus novel compound comparison; thus, these comparisons provide probes for effects of morphological constituency and for postdecompositional processing, respectively, which are not complicated by bigram differences.

3 We thank an anonymous reviewer for recommending that we analyse this part of the waveforms.

4 We report the difference between a participant's accuracy with nonwords and their accuracy with novel compounds as the behavioural correlate here; however, we also verified that the same holds if the novel compound accuracy itself is used as the behavioural correlate, thus ensuring that the pattern is not due to variability within the nonwords rather than the novel compounds.