The Phonological Mapping Negativity (PMN) is not phonology-specific: Sensitivity to speaker voice mismatch

In the electrophysiological time course of speech processing, the Phonological Mapping Negativity (PMN) is a negative-going ERP component thought to specifically index pre-lexical phonological mapping. The response is often used in research investigating the cognitive mechanisms that underlie speech processing, but more recently has been employed in clinical research seeking to identify the specific deficits that contribute to a host of speech and language impairments. The PMN has long been assumed to be sensitive only to phonological manipulations. Here, we test that assumption in a classic phoneme blending task, comparing responses to phonological mismatches and speaker voice mismatches. Participants were instructed to blend nonword primes segmented into onset and rhyme (e.g.,/l/+/ɛk/), which were followed by targets that matched or mismatched based on either phonological expectancy (e.g., match:/lɛk/; mismatch:/wɛk/) or speaker voice expectancy (match: same voice; mismatch: different voice). Analysis of the 150-400 ms post-target window revealed a predicted negative ERP response to phoneme mismatch vs match trials (i.e., the PMN, as typically characterised). Crucially however, analysis of speaker trials revealed a similar pattern of results in response to speaker mismatch vs speaker match. Our findings are discussed in light of ongoing debates about the functional sensitivity and characterization of the PMN, alongside strong recommendations against the use of the component as a biomarker for phonological deficits until further research clarifies the validity of a phonology-specific ERP response.