Inequality across consonantal contrasts in speech perception: evidence from mismatch negativity.

The precise structure of speech sound representations is still a matter of debate. In the present neurobiological study, we compared predictions about differential sensitivity to speech contrasts between models that assume full specification of all phonological information in the mental lexicon with those assuming sparse representations (only contrastive or otherwise not predictable information is stored). In a passive oddball paradigm, we studied the contrast sensitivity as reflected in the mismatch negativity (MMN) response to changes in the manner of articulation, as well as place of articulation of consonants in intervocalic positions of nonwords (manner of articulation: [edi ~ eni], [ezi ~ eni]; place of articulation: [edi ~ egi]). Models that assume full specification of all phonological information in the mental lexicon posit equal MMNs within each contrast (symmetric MMNs), that is, changes from standard [edi] to deviant [eni] elicit a similar MMN response as changes from standard [eni] to deviant [edi]. In contrast, models that assume sparse representations predict that only the [ezi] ~ [eni] reversals will evoke symmetric MMNs because of their conflicting fully specified manner features. Asymmetric MMNs are predicted, however, for the reversals of [edi] ~ [eni] and [edi] ~ [egi] because either a manner or place property in each pair is not fully specified in the mental lexicon. Our results show a pattern of symmetric and asymmetric MMNs that is in line with predictions of the featurally underspecified lexicon model that assumes sparse phonological representations. We conclude that the brain refers to underspecified phonological representations during speech perception.

"What you encode is not necessarily what you store": evidence for sparse feature representations from mismatch negativity.

The present study examines whether vowels embedded in complex stimuli may possess underspecified representations in the mental lexicon. The second goal was to assess the possible interference of the lexical status of stimuli under study. Minimal pairs of German nouns differing only in the stressed vowels [e], [ø], and [o], and derived pseudowords, were used to measure the Mismatch Negativity (MMN) in a passive oddball-paradigm. The differing vowels were chosen such that the place of articulation information was conflicting vs. non-conflicting in the framework of models assuming underspecified representations in the mental lexicon (i.e. minimizing featural information by omitting redundant information in order to ensure efficient speech processing), whereas models assuming fully specified phonological representations would predict equal levels of conflict in all possible contrasts. The observed pattern of MMN amplitude differences was in accordance to predictions of models assuming underspecified phonological representations. As the possible interferences by other levels of linguistic processing was demonstrated, it seems favorable to use pseudowords for investigating phonological effects by means of MMN.

Laryngeal elevation achieved by neuromuscular stimulation at rest.

During swallowing, airway protection is achieved in part by laryngeal elevation. Although multiple muscles are normally active during laryngeal elevation, neuromuscular stimulation of select muscles was evaluated to determine which single muscle or muscle pair best elevates the larynx and should be considered during future studies of neuromuscular stimulation in dysphagic patients. Hooked-wire monopolar electrodes were inserted into mylohyoid, thyrohyoid, and geniohyoid muscle regions in 15 healthy men selected for having a highly visible thyroid prominence for videotaping. During trials of single, bilateral, and combined muscle stimulations, thyroid prominence movements were video recorded, digitized, and normalized relative to elevation during a 2-ml water swallow. Individual muscle stimulation induced approximately 30% of the elevation observed during a swallow and approximately 50% of swallow velocity, whereas paired muscle stimulation resulted in approximately 50% of the elevation and approximately 80% of the velocity produced during a swallow. Paired muscle stimulation produced significantly greater elevation than single muscle stimulation and could assist with laryngeal elevation in dysphagic patients with reduced or delayed laryngeal elevation.