Sari Ylinen

Mismatch negativity (MMN) elicited by changes in phoneme length: A cross-linguistic study

Speech sounds representing different phonetic categories are typically easier to discriminate than sounds belonging to the same category. This phenomenon is referred to as the phoneme boundary effect. We aimed to determine whether, at neural level, this effect is indeed due to crossing the phoneme boundary. The mismatch negativity (MMN) brain response was measured for across- and within-category changes in Finnish phoneme length in native speakers and second-language users of Finnish as well as non-Finnish-speaking subjects. The results showed that the MMN amplitude was enhanced in the native speakers in comparison with the two non-native groups which, in turn, did not differ from each other in MMN amplitude. The response pattern to across- and within-category changes, however, was the same in all groups regardless of whether or not they had the phoneme categories. Thus, the responses could not be determined by crossing the phoneme boundary. Rather, the enhancement of MMN amplitude in the native speakers is likely to be due to the activation of native-language phonetic prototypes. The second-language users, however, did not seem to have automatic access to Finnish prototypes.

The perception of phonological quantity based on durational cues by native speakers, second-language users and nonspeakers of Finnish.

Some languages, such as Finnish, use speech-sound duration as the primary cue for a phonological quantity distinction. For second-language (L2) learners, quantity is often difficult to master if speech-sound duration plays a less important role in the phonology of their native language (L1). By comparing the categorization performance of native speakers of Finnish, Russian L2 users of Finnish, and non-Finnish-speaking Russians, the present study aimed to determine whether the L2 users, whose native language does not have a quantity distinction, have been able to establish categories for Finnish quantity. The results suggest that the native speakers and some of the L2 users that have been exposed to Finnish for a longer time have access to phonological quantity categories, whereas the L2 users with shorter exposure and the non-Finnish-speaking subjects do not. In addition, by comparing categorization and discrimination tasks it was found that the native speakers show a phoneme-boundary effect for quantity that is cued by duration only, whereas the non-Finnish-speaking subjects and the subjects with low proficiency in Finnish do not.

Spatiotemporal Dynamics of the Processing of Spoken Inflected and Derived Words: A Combined EEG and MEG Study

The spatiotemporal dynamics of the neural processing of spoken morphologically complex words are still an open issue. In the current study, we investigated the time course and neural sources of spoken inflected and derived words using simultaneously recorded electroencephalography (EEG) and magnetoencephalography (MEG) responses. Ten participants (native speakers) listened to inflected, derived, and monomorphemic Finnish words and judged their acceptability. EEG and MEG responses were time-locked to both the stimulus onset and the critical point (suffix onset for complex words, uniqueness point for monomorphemic words). The ERP results showed that inflected words elicited a larger left-lateralized negativity than derived and monomorphemic words approximately 200 ms after the critical point. Source modeling of MEG responses showed one bilateral source in the superior temporal area ∼100 ms after the critical point, with derived words eliciting stronger source amplitudes than inflected and monomorphemic words in the right hemisphere. Source modeling also showed two sources in the temporal cortex approximately 200 ms after the critical point. There, inflected words showed a more systematic pattern in source locations and elicited temporally distinct source activity in comparison to the derived word condition. The current results provide electrophysiological evidence for at least partially distinct cortical processing of spoken inflected and derived words. In general, the results support models of morphological processing stating that during the recognition of inflected words, the constituent morphemes are accessed separately. With regard to derived words, stem and suffix morphemes might be at least initially activated along with the whole word representation.

Parameter-specific modulation of the mismatch negativity to duration decrement and increment: evidence for asymmetric processes.

OBJECTIVE The mismatch negativity (MMN) component of event-related potentials (ERPs) reflects a change-detection process in the brain. The present study investigated whether stimulus parameters (sound type and duration) exert a differential influence on the MMN for a duration decrement and increment of an equal magnitude. Some asymmetries were reported in the previous studies; yet no systematical study has been conducted. METHODS ERPs were recorded from 16 healthy adults presented with repetitive standard sounds interspersed with duration changes (deviant sounds). In separate sequences, stimuli were vowels, music chord, sinusoid, or band-pass filtered white noise. The stimulus durations (standard/deviant) were either 200/120 ms or 400/240 ms for decrements, and vice versa for increments. RESULTS The MMN for the increments was abolished in the 400/240 ms condition, whereas the MMN for decrements was significant irrespective of the sound duration. The amplitude of the increment MMN paralleled with the spectral complexity of the stimulus sound, whereas that of the decrement MMN was larger for natural sounds than artificial sounds. CONCLUSIONS The observed interactions demonstrated asymmetries in the MMN for duration increment and decrement. SIGNIFICANCE The present findings suggest that the effects of stimulus parameters should be taken into account when comparing different studies, especially where clinical populations are involved, with one another.

Two Distinct Auditory-Motor Circuits for Monitoring Speech Production as Revealed by Content-Specific Suppression of Auditory Cortex

Speech production, both overt and covert, down-regulates the activation of auditory cortex. This is thought to be due to forward prediction of the sensory consequences of speech, contributing to a feedback control mechanism for speech production. Critically, however, these regulatory effects should be specific to speech content to enable accurate speech monitoring. To determine the extent to which such forward prediction is content-specific, we recorded the brains neuromagnetic responses to heard multisyllabic pseudowords during covert rehearsal in working memory, contrasted with a control task. The cortical auditory processing of target syllables was significantly suppressed during rehearsal compared with control, but only when they matched the rehearsed items. This critical specificity to speech content enables accurate speech monitoring by forward prediction, as proposed by current models of speech production. The one-to-one phonological motor-to-auditory mappings also appear to serve the maintenance of information in phonological working memory. Further findings of right-hemispheric suppression in the case of whole-item matches and left-hemispheric enhancement for last-syllable mismatches suggest that speech production is monitored by 2 auditory-motor circuits operating on different timescales: Finer grain in the left versus coarser grain in the right hemisphere. Taken together, our findings provide hemisphere-specific evidence of the interface between inner and heard speech.

Effects of prosodic familiarity on the automatic processing of words in the human brain.

We aimed to determine the effect of prosodic familiarity on automatic word processing in the brain by comparing the mismatch negativity (MMN) components of the event-related brain potential (ERP) elicited by words and pseudowords with familiar and unfamiliar stress patterns. The results show that the MMN was elicited by a change from unfamiliar to familiar words and a change from a familiar to an unfamiliar word-stress pattern.When familiar words were accompanied by an unfamiliar stress pattern, the MMN response was significantly delayed in comparison with the familiar words with a familiar stress pattern, suggesting that an unfamiliar prosodic pattern increased the computational needs in word recognition but did not prevent it. In addition to the effects of familiarity on the MMN, we found a positive brain response peaking between 100 and 200 ms that could be associated with the processing of familiar auditory objects. The present results expand the understanding of the early stages of speech processing in the human brain by demonstrating how automatic word processing is affected by prosodic cues that play an important role in the segmentation of continuous speech.

Enhanced plasticity in spoken language acquisition for child learners: Evidence from phonetic training studies in child and adult learners of English

Speech sounds that contain multiple phonetic cues are often difficult for foreign-language learners, especially if certain cues are weighted differently in the foreign and native languages. Greek adult and child speakers of English were studied to determine the effect of native language on second-language (L2) cue weighting and, in particular, to explore whether perceptual training could help to improve accuracy in phoneme identification and discrimination. Two forms of stimuli were used: natural (unedited) stimuli and ‘modified’ vowel duration stimuli which were edited to ensure that duration could not be used as a cue in the tasks. Results show the Greek speakers performed poorly when they were unable to use the duration cue as compared with the native English speakers. After high-variability training, performance was improved for both Greek adult (20 –30 years) and child (7 –8 years) groups. However, the degree of improvement was most pronounced for children. This suggests enhanced plasticity for spoken language in this developmental stage. These data have impact on informing the strategies used for teaching spoken language in English as additional language (EAL) populations in different age groups.

Neuroscience illuminating the influence of auditory or phonological intervention on language-related deficits

Remediation programs for language-related learning deficits are urgently needed to enable equal opportunities in education. To meet this need, different training and intervention programs have been developed. Here we review, from an educational perspective, studies that have explored the neural basis of behavioral changes induced by auditory or phonological training in dyslexia, specific language impairment (SLI), and language-learning impairment (LLI). Training has been shown to induce plastic changes in deficient neural networks. In dyslexia, these include, most consistently, increased or normalized activation of previously hypoactive inferior frontal and occipito-temporal areas. In SLI and LLI, studies have shown the strengthening of previously weak auditory brain responses as a result of training. The combination of behavioral and brain measures of remedial gains has potential to increase the understanding of the causes of language-related deficits, which may help to target remedial interventions more accurately to the core problem.

Is there a direct neural correlate for memory-trace formation in audition?

Recently, Haenschel et al. (2005) suggested that a positive event-related potential wave called ‘repetition positivity’ (RP) is a direct neural correlate of the formation of sensory memory traces. We investigated whether RP is elicited by familiar vowels that have previously been suggested to form accurate memory representations faster than unfamiliar sounds. No evidence for RP elicitation was found, however, even though memory representations for the vowels were formed. Instead of finding an increasing positive response along with stimulus repetition predicted by the RP hypothesis, we found that N1 and sustained potential were enhanced in amplitude for the familiar vowels as compared with unfamiliar sounds, indicating stronger activation at the auditory cortex.

Predictive coding of phonological rules in auditory cortex: A mismatch negativity study.

The brain is constantly generating predictions of future sensory input to enable efficient adaptation. In the auditory domain, this applies also to the processing of speech. Here we aimed to determine whether the brain predicts the following segments of speech input on the basis of language-specific phonological rules that concern non-adjacent phonemes. Auditory event-related potentials (ERP) were recorded in a mismatch negativity (MMN) paradigm, where the Finnish vowel harmony, determined by the first syllables of pseudowords, either constrained or did not constrain the phonological composition of pseudoword endings. The phonological rule of vowel harmony was expected to create predictions about phonologically legal pseudoword endings. Results showed that MMN responses were larger for phonologically illegal than legal pseudowords, and P3a was elicited only for illegal pseudowords. This supports the hypothesis that speech input is evaluated against context-dependent phonological predictions that facilitate speech processing.