Familiarity affects environmental sound processing outside the focus of attention: An event-related potential study

ObjectiveThis study investigated the influence of the familiarity of an environmental sound on sound processing outside the focus of attention.MethodsBy comparing ERPs elicited by a familiar, animal sound and an acoustically matched, but unfamiliar, complex sound, three issues were addressed: (a) general differences in the processing of the familiar and the unfamiliar sound, (b) influences of sound familiarity on the processing of deviants unrelated to familiarity and (c) familiarity-specific processing depending on the sound context. Participants watched a silent, subtitled movie.ResultsThe familiar sound elicited a centro-parietal enhancement of the N1, a frontocentrally enhanced P2 and an additional P250. Auditory deviance processing elicited by deviants in sound location was not influenced by the familiarity of the sounds. However, after an involuntary switch of attention to the deviant, an N400-like deflection indicated enhanced semantic analysis of the familiar deviant. Familiarity-specific ERP effects as a consequence of the sound context occurred between 300 and 500 ms after stimulus onset.ConclusionWhereas familiarity of an environmental sound elicited enhanced stimulus processing before 300 ms, influences of the sound context were observed subsequent to 300 ms.SignificanceFamiliarity of a complex environmental sound influences several stages of auditory processing outside the focus of attention.     

Deconvolution of magnetic acoustic change complex (mACC)

ObjectiveThe aim of this study was to design a novel experimental approach to investigate the morphological characteristics of auditory cortical responses elicited by rapidly changing synthesized speech sounds.MethodsSix sound-evoked magnetoencephalographic (MEG) responses were measured to a synthesized train of speech sounds using the vowels /e/ and /u/ in 17 normal hearing young adults. Responses were measured to: (i) the onset of the speech train, (ii) an F0 increment; (iii) an F0 decrement; (iv) an F2 decrement; (v) an F2 increment; and (vi) the offset of the speech train using short (jittered around 135 ms) and long (1500 ms) stimulus onset asynchronies (SOAs). The least squares (LS) deconvolution technique was used to disentangle the overlapping MEG responses in the short SOA condition only.ResultsComparison between the morphology of the recovered cortical responses in the short and long SOAs conditions showed high similarity, suggesting that the LS deconvolution technique was successful in disentangling the MEG waveforms. Waveform latencies and amplitudes were different for the two SOAs conditions and were influenced by the spectro-temporal properties of the sound sequence. The magnetic acoustic change complex (mACC) for the short SOA condition showed significantly lower amplitudes and shorter latencies compared to the long SOA condition. The F0 transition showed a larger reduction in amplitude from long to short SOA compared to the F2 transition. Lateralization of the cortical responses were observed under some stimulus conditions and appeared to be associated with the spectro-temporal properties of the acoustic stimulus.ConclusionsThe LS deconvolution technique provides a new tool to study the properties of the auditory cortical response to rapidly changing sound stimuli. The presence of the cortical auditory evoked responses for rapid transition of synthesized speech stimuli suggests that the temporal code is preserved at the level of the auditory cortex. Further, the reduced amplitudes and shorter latencies might reflect intrinsic properties of the cortical neurons to rapidly presented sounds.SignificanceThis is the first demonstration of the separation of overlapping cortical responses to rapidly changing speech sounds and offers a potential new biomarker of discrimination of rapid transition of sound.     

Infants’ brain responses for speech sound changes in fast multifeature MMN paradigm

ObjectiveWe investigated whether newborn speech-sound discrimination can be studied in 40 min using fast multifeature mismatch negativity (MMN) paradigm and do the results differ from those obtained with the traditional oddball paradigm.MethodsNewborns’ MMN responses to five types of changes (consonant identity, F0, intensity, vowel duration and vowel identity) were recorded in the multifeature group (N = 15) and vowel duration and vowel identity changes in the oddball group (N = 13), after which the MMNs from both groups were compared with each others.ResultsStatistically significant MMNs in the 190–600 ms time range from the stimulus onset were found for most change types in both paradigms. Newborn MMN responses were predominantly positive but a small number of participants elicited negative MMNs instead. MMN amplitudes did not differ between the multifeature and oddball groups.ConclusionsNewborn speech-sound discrimination can be assessed in a short recording time using the fast multifeature paradigm.SignificanceThe paradigm presented here can be used to record extensive auditory discrimination profiles in newborns and assess development of speech-sound discrimination and its difficulties.     

Mismatch Negativity (MMN) evoked by sound duration contrasts: An unexpected major effect of deviance direction on amplitudes

ObjectiveVerify and explore unexpected results suggesting an effect of deviance direction (shorter or longer deviants) on the amplitude of MMNs evoked by sound duration contrasts.MethodsMMNs were recorded using the oddball paradigm on ten adults. Four standard stimulus durations (100, 150, 200 and 250 ms) were used and deviants were 50% shorter or longer. Behavioral data (hit rates, d′, and reaction times) were collected after the electrophysiological sessions.ResultsMMNs were larger for short than for long deviants. There was no effect on MMN latencies. Hit rates and d′ data were almost at ceiling level for all conditions even for the longest standard – long deviant combination in which the MMN was abolished.ConclusionsWe argue that the deviance direction effect on MMN amplitudes can be explained by the delay between the moment of deviance detection and the end of the deviance quantification process.SignificanceA major effect of deviance direction on amplitudes was confirmed. This effect, which was confined to electrophysiological data, is to be taken into account when using duration contrasts to probe the processing of temporal information.     

Children’s brain responses to sound changes in pseudo words in a multifeature paradigm

ObjectiveThe multifeature mismatch negativity (MMN) paradigm has previously been used to study MMN responses to changes in tones or isolated syllables. We tested 4–12 year old children’s MMNs to changes in a naturally produced pseudo word context.MethodsWe studied preschoolers’ (under the age of 7 years, N = 15, mean age 5 years 4 months) and school childrens’ (over the age of 7 years, N = 15, mean age 9 years 3 months) MMNs to five types of changes (vowel duration, fundamental frequency, gap, intensity, vowel identity) in the middle syllable of a pseudo word [tɑtɑtɑ] using a multifeature paradigm.ResultsVowel duration and gap changes elicited larger frontocentral MMN responses than other change types and the vowel identity change also produced an early positive p-MMR. The presence of the MMN was also determined at the individual level, and it was found that vowel duration and gap deviants produced MMNs in most of the participants.ConclusionsThe current study shows that children’s neural speech sound discrimination can be assessed in a word context in a short recording time (30 min) by using the multifeature paradigm.SignificanceA paradigm which can be used to investigate the discrimination of several change types of speech-sounds in a natural context can be useful for investigating speech development and deficits.     

Event-related potentials (MMN and novelty P3) in permanent vegetative or minimally conscious states

ObjectiveTo assess markers of cognition, if any, in patients in a permanent vegetative state (PVS).MethodsEvent-related potential (ERP) mapping was performed on 27 patients in permanent (4–261 months after coma onset) vegetative (PVS, n = 16) or minimally conscious states (MCS, n = 11) due to anoxia (n = 18) or other aetiologies (n = 9). Mismatch negativity (MMN) to duration-deviant tones and novelty P3 (nP3) to the subject’s own name were recorded according to a paradigm previously validated in healthy volunteers and comatose patients. SEPs, MLAEPs and BAEPs were also recorded.ResultsMMN was present in 5/27 and nP3 in 7/27 patients. ERPs were not related to the time from coma onset and not different in MCS and in PVS. Normal SEPs and MLAEPs, and present nP3s were less frequent in anoxia than in other aetiologies.ConclusionsIrrespective of their clinical assessment, a few patients are likely to process sound deviance (MMN) or novelty (nP3), mainly when their state is not due to anoxia.SignificanceSome PVS patients may be able to put certain awareness marker processes to work. The diagnostic criteria for PVS or MCS, currently based on mere behaviour, should also include functional brain investigations, such as ERPs, related to the aetiology.     

Neonatal frequency discrimination in 250–4000-Hz range: Electrophysiological evidence

ObjectiveThe precision of sound frequency discrimination in newborn infants in the 250–4000-Hz frequency range was determined using the neonatal electrophysiological mismatch response (MMR), the infant equivalent of adult mismatch negativity (MMN).MethodsThe electroencephalogram (EEG) was recorded in 11 full-term sleeping newborn infants mostly in active sleep (67% of the time). Pure tones were presented through loudspeakers in an oddball paradigm with a 800-ms stimulus onset asynchrony (SOA). Each stimulus block contained a standard (p = 0.76) of 250, 1000, or 4000 Hz in frequency (in separate blocks) and deviants with a frequency change of either 5% or 20% of the standard (p = 0.12 of each).ResultsA positive ERP deflection was found at 200–300 ms from stimulus onset in response to the 20% deviation from the 250, 1000, and 4000 Hz standard frequencies. The amplitude of the response in the 200–300 ms time window was significantly larger for the 20% than 5% deviation.ConclusionsWe observed in newborn infants automatic frequency discrimination as reflected by a positive MMR. The newborns were able to discriminate frequency change of 20% in the 250–4000-Hz frequency range, whereas the discrimination of the 5% frequency change was not statistically confirmed.SignificanceThe present data hence suggest that the neonatal frequency discrimination has lower resolution than that in adult and older children data.     

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.     

Memory-based mismatch response to changes in duration of auditory stimuli: An MEG study

ObjectiveDifferences in physical features and occurrence probability between standards and deviants in oddball paradigms provide contributions to magnetic mismatch negativity (MMNm). We aimed to reduce these influential factors and extract memory-based MMNm by adding a control paradigm.MethodsMagnetoencephalographic responses were recorded in 13 healthy adults with an oddball paradigm (125-ms standard and 50-ms deviant tones) and an equiprobable control paradigm (50-ms control and four other duration-varying tones). The stimulus onset asynchrony was 500 ms. Controlled MMNm was obtained by subtracting control-evoked responses from deviant-evoked responses.ResultsWith respect to the onset of stimulus difference, the peak latency of controlled MMNm was compatible with previous intracranial MMN recordings. Both controlled and traditional MMNm were generated around the superior temporal cortex, whereas the controlled MMNm amplitude was about 70% of traditional MMNm amplitude. Right-hemispheric dominance was observed in traditional MMNm but not in controlled MMNm. N100m amplitude was smaller in standard-evoked than in deviant- or control-evoked responses.ConclusionsControlled MMNm reflects memory-based processing of duration changes, whereas traditional MMNm additionally involves non-memory activations related to differential refractoriness states and physical properties between standard and deviant stimuli.SignificanceThe memory-based processing of auditory deviants may be preferentially extracted by adding a control paradigm.     

Effects of spatial separation and stimulus probability on the event-related potentials elicited by occasional changes in sound location

The ability to extract information about the spatial location of sounds plays an important role in auditory scene analysis. The present study examined the effects of spatial separation and stimulus probability on auditory event-related potentials (ERPs) to changes in sound location. In Experiment 1, we found that difference waves between ERPs elicited by standard and deviant stimuli showed a biphasic negative-positive response peaking around 126 and 226 ms after deviant onset. The amplitude of both responses increased with decreasing deviant stimulus probability, and increasing stimulus deviance. When the same stimuli were presented with equal probability for all locations (Experiment 2), there were no significant differences in the ERP amplitude and latency. These results suggest that the data reported in Experiment 1 are the result of contextual changes, rather than changes in simple acoustic features. Brain electrical source analyses are consistent with generators located in auditory cortices posterior to Heschel's gyrus. Although occasional changes in sound location elicit earlier peaks than the mismatch negativity (MMN) response reported for other types of deviation, their topographical distribution and behavior are consistent with MMN. The early latency of MMN for changes in sound location is interpreted in the context of an early-warning system to alert the organism to new sound sources in the environment.     

The time course of temporal discrimination: An ERP study

ObjectiveThe question of how temporal information is processed by the brain is still a matter of debate. This study aimed to elucidate the brain electrical activity associated with a visual temporal discrimination task.MethodsFor this purpose, 44 participants were required to compare pairs of sequentially presented time intervals: a fixed standard interval (1000 ms), and an equal-to-standard, longer (1200 ms) or shorter (800 ms) comparison interval. Behavioural data and event-related potentials (ERPs) were analyzed.ResultsLong intervals were more rapidly identified than short intervals. The amplitude of the contingent negative variation (CNV) found at frontocentral sites before the end of the comparison interval was significantly affected by the difference between its duration and the standard one. The amplitude and the scalp distribution of ERPs registered after the offset of the comparison interval were linearly modulated by its absolute duration.ConclusionsERP components associated with the offset of the comparison intervals clarified the involvement of working memory processes and different brain structures in temporal discrimination.SignificanceThis study further improves our understanding of the cognitive processes and neural substrates underlying temporal discrimination in healthy subjects and lays the ground for the investigation of clinical samples with time processing deficits.     

Intensity changes in a continuous tone: Auditory cortical potentials comparison with frequency changes

ObjectivesTo examine auditory cortical potentials in normal-hearing subjects to intensity increments in a continuous pure tone at low, mid, and high frequency.MethodsElectrical scalp potentials were recorded in response to randomly occurring 100 ms intensity increments of continuous 250, 1000, and 4000 Hz tones every 1.4 s. The magnitude of intensity change varied between 0, 2, 4, 6, and 8 dB above the 80 dB SPL continuous tone.ResultsPotentials included N100, P200, and a slow negative (SN) wave. N100 latencies were delayed whereas amplitudes were not affected for 250 Hz compared to 1000 and 4000 Hz. Functions relating the magnitude of the intensity change and N100 latency/amplitude did not differ in their slope among the three frequencies. No consistent relationship between intensity increment and SN was observed. Cortical dipole sources for N100 did not differ in location or orientation between the three frequencies.ConclusionsThe relationship between intensity increments and N100 latency/amplitude did not differ between tonal frequencies. A cortical tonotopic arrangement was not observed for intensity increments. Our results are in contrast to prior studies of brain activities to brief frequency changes showing cortical tonotopic organization.SignificanceThese results suggest that intensity and frequency discrimination employ distinct central processes.     

Event-related potential measures of gap detection threshold during natural sleep

ObjectiveThe minimum time interval between two stimuli that can be reliably detected is called the gap detection threshold. The present study examines whether an unconscious state, natural sleep affects the gap detection threshold.MethodsEvent-related potentials were recorded in 10 young adults while awake and during all-night sleep to provide an objective estimate of this threshold. These subjects were presented with 2, 4, 8 or 16 ms gaps occurring in 1.5 duration white noise.ResultsDuring wakefulness, a significant N1 was elicited for the 8 and 16 ms gaps. N1 was difficult to observe during stage N2 sleep, even for the longest gap. A large P2 was however elicited and was significant for the 8 and 16 ms gaps. Also, a later, very large N350 was elicited by the 16 ms gap. An N1 and P2 was significant only for the 16 ms gap during REM sleep.SignificanceERPs to gaps occurring in noise segments can therefore be successfully elicited during natural sleep. The gap detection threshold is similar in the waking and sleeping states.     

Fast vigilance decrement in closed head injury patients as reflected by the mismatch negativity (MMN)

Event-related potentials (ERPs) were measured from 24 chronic closed head injury (CHI) patients and 18 age- and education-matched controls. The oddball paradigm was applied while subjects were watching a silent movie. The standard (p=0.8) sound of 75 ms duration had a basic frequency of 500 Hz with harmonic partials of 1000 Hz and 1500 Hz, whereas these frequencies for the pitch deviant were each 10% higher. The frequencies of the duration deviant matched with those of the standard but was 25 ms in duration. The MMN (mismatch negativity), generated by the brain's automatic auditory change-detector mechanism, was elicited by both deviants. No significant differences in the MMN latency or amplitude for either pitch or duration deviants were found between the groups. However, the MMN amplitude for the pitch deviant decreased in the patient group during the experiment considerably faster than in controls, suggesting a faster vigilance decrement in the patients.     

A mechanistic model of mismatch negativity in the ageing brain

ObjectiveWe investigated the neurophysiological mechanisms underpinning the generation of the mismatch negativity (MMN) in the ageing brain.MethodsWe used dynamic causal modelling (DCM) to study connectivity models for healthy young and old subjects. MMN was elicited with an auditory odd-ball paradigm in two groups of healthy subjects with mean age 74 (n = 30) and 26 (n = 26). DCM was implemented using up to five cortical nodes. We tested models with different hierarchical complexities.ResultsWe showed that the network generating MMN consisted of 5 nodes that could modulate all intra- and inter-nodal connections. The inversion of this model showed that old subjects had increased input from rSTG to the rIFG (p < 0.01) together with increased inhibition of pyramidal cells (p < 0.05). Furthermore, there was reduced modulation of activity within rIFG (p < 0.02) on stimulus change.ConclusionThe age related change in MMN is due to a decline in frontal-based control mechanisms, with alterations in connectivity between temporal and frontal regions together with a dysregulation of the excitatory–inhibitory balance in the rIFG.SignificanceThis study provides for the first time a neurobiological explanation for the age related changes of the MMN in the ageing brain.     

Post-exercise exhaustion in Lambert–Eaton myasthenic syndrome

ObjectivesTo study post-exercise exhaustion by decrement (PEE-D) systematically in 24 repetitive nerve stimulation (RNS) tests in 14 patients with Lambert–Eaton myasthenic syndrome (LEMS).MethodsIn the abductor digiti quinti muscle, the compound muscle action potential (CMAP) amplitude and 3 Hz responses for 2 s were obtained with the supramaximal stimulation at rest, immediately after (PE0), 30 s after (PE30s), and at 1, 2, 3, and 4 m after 10-s exercise.ResultsThere was a 377% increment in the CMAP amplitude at PE0 and a mild increment (+26%) at PE30s. A transient but significant improvement (−22%) in the decremental response was observed at PE0, and a gradual worsening of decrement in subsequent tests, with the worst decrement noted (−50%) at PE2m.ConclusionPEE-D was found 2 m after exercise in LEMS.SignificancePEE-D may be physiologically closest to the reversible myasthenic fatigue after exercise observed in LEMS patients.     

Neuromagnetic activation of primary and secondary somatosensory cortex following tactile-on and tactile-off stimulation

ObjectiveMagnetoencephalography (MEG) recordings were performed to investigate the cortical activation following tactile-on and tactile-off stimulation.MethodsWe used a 306-ch whole-head MEG system and a tactile stimulator driven by a piezoelectric actuator. Tactile stimuli were applied to the tip of right index finger. The interstimulus interval was set at 2000 ms, which included a constant stimulus of 1000 ms duration.ResultsProminent somatosensory evoked magnetic fields were recorded from the contralateral hemisphere at 57.5 ms and 133.0 ms after the onset of tactile-on stimulation and at 58.2 ms and 138.5 ms after the onset of tactile-off stimulation. All corresponding equivalent current dipoles (ECDs) were located in the primary somatosensory cortex (SI). Moreover, long-latency responses (168.7 ms after tactile-on stimulation, 169.8 ms after tactile-off stimulation) were detected from the ipsilateral hemisphere. The ECDs of these signals were identified in the secondary somatosensory cortex (SII).ConclusionsThe somatosensory evoked magnetic fields waveforms elicited by the two tactile stimuli (tactile-on and tactile-off stimuli) with a mechanical stimulator were strikingly similar. These mechanical stimuli elicited both contralateral SI and ipsilateral SII activities.SignificanceTactile stimulation with a mechanical stimulator provides new possibilities for experimental designs in studies of the human mechanoreceptor system.     

The effect of gaze direction on the ocular vestibular evoked myogenic potential produced by air-conducted sound

ObjectiveTo assess the effects of vertical and horizontal gaze, head rotation, body position, and vision on the ocular vestibular evoked myogenic potential (OVEMP) produced by air-conducted (AC) sound.MethodsTen normal subjects were stimulated by 500 Hz 2 ms AC tone bursts at 136–142 dB peak SPL. OVEMPs were recorded from electrodes placed beneath the eyes. Angles of vertical gaze ranged from maximal downward to upward gaze in increments of 5–10°. Horizontal gaze was measured during elevation and ranged from 20° adduction to 20° abduction.ResultsIncreasing vertical gaze increased OVEMP amplitude, especially for the contralateral eye (neutral vs maximal upward gaze; contra: 1.0 vs 2.6 μV; ipsi: 0.8 vs 0.9 μV; P < 0.001). OVEMPs from the contralateral eye peaked significantly earlier in the upward gaze positions (contra: 9.2 ms; ipsi: 10.4 ms; P < 0.001), but peaked later during downward gaze (contra: 14.2 ms; ipsi: 11.4 ms; P = 0.014). There were small effects of horizontal gaze and supine body position, but no effects of head rotation or vision.ConclusionsOVEMP amplitudes are strongly modulated by gaze position. Truncal position also affects OVEMP amplitude.SignificanceThis study quantifies the effect of gaze on the OVEMP and demonstrates the importance of controlling for gaze in clinical and experimental studies.     

Differing response properties of cervical and ocular vestibular evoked myogenic potentials evoked by air-conducted stimulation

ObjectiveTo determine the amplitude changes of vestibular evoked myogenic potentials (VEMPs) recorded simultaneously from the neck (cVEMPs) and eyes (oVEMPs) in response to 500 Hz, 2 ms air-conducted sound pips over a 30 dB range.MethodsFifteen healthy volunteers (mean age 29, range 18–57 years old) and one patient with unilateral superior canal dehiscence (SCD) were studied. The stimulus was reduced in increments to 105 dB pSPL for the normals (81 dB pSPL for the SCD patient). A statistical criterion was used to detect responses.ResultsIpsilateral (i-p13/n23) and contralateral (c-n12/p24/n30) peaks for the cVEMP montage and contralateral (c-n10/p16/n21) and ipsilateral (i-n13) peaks for the oVEMP montage were present for the baseline intensity. For the lowest intensity, 6/15 subjects had responses for the i-p13 cVEMP potential and 4/15 had c-n10 oVEMP responses. The SCD patient showed larger responses for nearly all intensities. The cVEMP potentials were generally well fitted by a power law relationship, but the oVEMP c-n10, p16 and n21 potentials showed a significant increase in gradient for the higher intensities.ConclusionMost oVEMP and cVEMP responses follow a power law relationship but crossed oVEMP responses showed a change in gradient above a threshold.SignificanceThe pattern of response to AC stimulation may be a property of the pathways underlying the potentials.     

Distinct pre-attentive responses to non-scale notes: An auditory mismatch negativity (MMN) study

Objective: The aim of the present study was to examine patterns of neural activity in response to variations in scale notes and alterations from a scale note to a non-scale note.Methods: Event-related potentials (ERPs) were recorded in response to scale and non-scale violin notes using an odd-ball mismatch negativity (MMN) paradigm. Standard stimuli were set to the scale note A4 (440 Hz). Deviant stimuli included two scale notes (scale-B, B4 = 494 Hz; scale-C, C5 = 523 Hz) and a non-scale note halfway between them (non-scale, B4 + 42¢ = 506 Hz).Results: MMN amplitude elicited by the non-scale was significantly larger than that elicited by the scale-B and scale-C, which did not differ significantly from one another.Conclusion: The current results suggest that the human brain may possess pre-attentive mechanisms for extracting relational aspects among sounds of the musical scale.Significance: The results indicate that non-scale notes may be processed in a different way even in the pre-attentive stage than scale notes.