Frequency effects and morpheme stripping in English verbs

The ability to combine linguistic units—known as merge—has been shown to be lateralised to the left hemisphere of the brain (Zaccarella & Friederici, 2015). Merge is thought to underlie the combination of stems and affixes in regular verbs (e.g., chews = chew + s). However, some accounts suggest that this applies primarily to infrequent regular verbs, while frequent forms may be stored as whole lexical units (Pinker & Ullman, 2002). If this idea is correct, only infrequent regular verbs should elicit lateralised neural processing. Twenty right-handed native English speakers underwent EEG recording during a mismatch negativity (MMN) task, comparing the pairs chewed–chews (low frequency) and cared–cares (high frequency). All stimuli were phonetically matched, uttered in Received Pronunciation and thus consisting of a CVC sequence. Results showed that only the low-frequency pair chewed–chews elicited a lateralised negativity, while the high-frequency pair cared–cares produced a more distributed pattern of activation. These findings may offer preliminary evidence that frequent regular verbs are less likely to engage merge-based combinatorial processes, whereas infrequent regular verbs are more likely to do so.