The detection of an irregular, potentially relevant change (deviance) in the regular, unattended acoustic environment is ensured by the automatic deviance detection mechanism. It underlies the formation of a regularity representation and a comparison of an incoming sound with this representation. A mismatch outcome of this comparison evokes the mismatch negativity (MMN) of the event-related potential. For unattended pure tones the automatic deviance detection mechanism operates most efficiently for initial sound parts, which is why these are suggested to contribute more to sound representation than later parts. A transient that physically segments the sounds can overcome this temporal constraint in sound representation. Whether the resulting individual (initial and terminal) sound segments or the joined two-segments give rise to the regularity representation is addressed here. We took advantage that the MMN attenuation to the second of two successive deviances (deviance-repetition effect) is more pronounced when the deviances belong to the same unit of representation. We measured MMN for two deviances (frequency modulations) within segmented sounds that either occurred within the initial or the terminal segment, or that were split across both segments. Unexpectedly, we did not obtain a deviance-repetition effect. Instead, we obtained a temporal distance effect: With increasing temporal distance from deviance-onset relative to segment-onset the MMN amplitude decreased. Furthermore, this effect did not depend on whether the deviance occurred in the initial or in the terminal segment. Thus, (for the current approach) we suggest that the regularity representation is based on the individual rather than joined segments.
“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. A 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], [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 favourable to use pseudowords for investigating phonological effects by means of MMN.
from Brain Research
Mismatch Negativity and Adaptation Measures of the Late Auditory Evoked Potential in Cochlear Implant Users
A better understanding of the neural correlates of large variability in cochlear implant (CI) patients’ speech performance may allow us to find solutions to further improve CI benefits. The present study examined the mismatch negativity (MMN) and the adaptation of the late auditory evoked potential (LAEP) in 10 CI users. The speech syllable /da/ and 1-kHz tone burst were used to examine the LAEP adaptation. The amount of LAEP adaptation was calculated according to the averaged N1-P2 amplitude for the LAEPs evoked by the last 3 stimuli and the amplitude evoked by the first stimulus. For the MMN recordings, the standard stimulus (1-kHz tone) and the deviant stimulus (2-kHz tone) were presented in an oddball condition. Additionally, the deviants alone were presented in a control condition. The MMN was derived by subtracting the response to the deviants in the control condition from the oddball condition. Results showed that good CI performers displayed a more prominent LAEP adaptation than moderate-to-poor performers. Speech performance was significantly correlated to the amount of LAEP adaptation for the 1-kHz tone bursts. Good performers displayed large MMNs and moderate-to-poor performers had small or absent MMNs. The abnormal electrophysiological findings in moderate-to-poor performers suggest that long-term deafness may cause damage not only at the auditory cortical level, but also at the cognitive level.
from Hearing Research
Occurrence of Mismatch Negativity in Response to Changes in the Durations of Short Pauses during Continuous Auditory Stimulation
Mismatch negativity (MMN) is a component of the auditory evoked potential which is widely used in research and clinical investigations. Using the oddball paradigm, which is traditional for obtaining mismatch negativity, we recorded MMN-like responses to changes in the duration of short pauses (standard = 25 msec; deviant = 50 msec, and vice versa) on the background of continuous auditory stimulation (1 kHz, 50 dB). Our data show that this is the first description of this type of mismatch negativity. We compared the responses to changes in pause duration with “classical” mismatch negativity to changes in pause duration with the same time characteristics. Mismatch negativity to changes in pauses was characterized by longer latent periods and the absence of significant inversion in the mastoid leads. Both responses, to changes in sound duration and to changes in pause duration, demonstrated shorter latent periods when the deviants were longer than the standards as compared with the reverse situation. This new type of mismatch negativity may widen the potential for its use in clinical and research studies.
Interhemisphere Asymmetry of Auditory Evoked Potentials in Humans and Mismatch Negativity during Sound Source Localization
Results of studies in humans of long-latency auditory evoked potentials and mismatch negativity in conditions of dichotic stimulation during presentation of deviant stimuli producing instantaneous changes in stimulus azimuth from the null to +22.5° or movement at rates of 11.25–112.5°/sec from the midline of the head across the left and right hemispheres towards each ear are presented. These studies showed that the total amplitude of the components of the N1–P2 complex of auditory evoked potentials in the frontal lead of the right hemisphere was greater than that in the left hemisphere. Mismatch negativity parameters showed significant relationships with the spatial position of the sound source, namely, its displacement into the right hemisphere from the position of the sound image of the standard signal. Questions of the involvement of the right hemisphere in discriminating the spatial characteristics of sound sources are discussed.
Electrophysiological Indices of Discrimination of Long-Duration, Phonetically Similar Vowels in Children With Typical and Atypical Language Development
Conclusions: Increased vowel duration can improve discrimination in children with SLI. However, poor identification of these longer vowels by some children with SLI suggests a deficit in long-term phonological representations or accessing these representations.
The mismatch negativity (MMN) component of the auditory event-related potential can be used to study automatic perceptual inference. This study was designed to explore “Conditional Inference” in the MMN system – the capacity of the auditory system to use current input to switch between inference models in memory. We presented a “Random” sequence comprising a standard repeating sound occasionally interrupted by a change in frequency, duration or intensity (louder or softer). We also presented the same sequence with a conditional linkage between deviants – that is, frequency and duration deviants always followed an intensity change. We explored whether the auditory system could use intensity deviance to change the inference from “expect the standard to repeat” to “expect a frequency or duration violation” and quantified this as the proportion decline in the MMN elicited to duration and frequency deviant sounds in the linked versus random sequence. We report three main outcomes on a sample of 25 healthy young adults: (1) there was a significant conditional inference effect (a reduction in MMN amplitude in linked versus random sequences) to duration but not frequency deviants; (2) larger simple MMN and larger conditional inference effect on duration MMN were correlated with higher Digit Span; and (3) the conditional inference effect but not simple MMN to duration deviants, was strongly correlated with working memory ability (rs=.78, p<.001). The results are discussed with respect to the differential cognitive demands of simple MMN and conditional inference, and the possible involvement of prefrontal cortex in implementing conditional inference in the MMN system.
from Brain Research