Mismatch Negativity during Exposure to Acoustic Stimuli Simulating Fused Auditory Images

The authors consider the results of study of the phenomenon of mismatch negativity (MMN) during exposure to acoustic stimuli simulating fused auditory images with different spatial localization: along the head midline (a standard stimulus used in all series), near either of the ears (lateralized), and moving from the midline to or from an ear. All deviant stimuli evoked the mismatch negativity; the minimum MMN amplitude with the longest latency was observed when the stimulus simulated motion of the auditory image from the midline to either ear. When the deviant auditory images were localized on the left of the midline, the contralateral MMN dominance was more pronounced and responses to various deviant stimuli differed more than when the images were localized on the right. The mismatch negativity as a criterion of discrimination accuracy for signals with different localization features is discussed.     

Perceptual categories for auditory motion as reflected in mismatch negativity

Auditory evoked response and mismatch negativity potential have been studied using the reversed oddball paradigm of standard and deviant stimulus presentation. In the experiments, three types of spatial sound stimuli (stationary and moving gradually or abruptly from the head midline) were presented in three configurations. In each configuration, one stimulus type served as the standard one, and the other two, as deviants. The reversal of the configuration of the presentation of the standard and deviant stimuli was shown to significantly influence the evoked response and mismatch negativity. The results are discussed as possible evidence of the categorical perception of auditory motion at early stages of sound processing in the hearing system.     

Mismatch negativity (MMN) for sequences of auditory and visual stimuli: evidence for a mechanism specific to the auditory modality

ERPs to sequences of standard and deviant sinusoidal 100 msec tone pips, high-contrast sinusoidal gratings and to their simultaneously presented combinations were recorded. Mismatch negativity (MMN), an ERP component elicited by deviant stimuli, was estimated for the different stimulus sequences in order to find out whether it reflects modality-specific processes or non-specific attentive phenomena. In addition to the auditory modality, we studied whether the mismatch response could be evoked by a deviant visual stimulus in a visual sequence or by a deviant stimulus in either modality. The results show that only auditory stimuli produced the mismatch response, suggesting that MMN is not a manifestation of a general attentional mechanism but is probably specific to the auditory modality.     

Mismatch negativity in the auditory event-related potentials in response to abrupt and smooth displacements of virtual sound source

The work investigated event-related potentials, mismatch negativity (MMN), and P3a component under dichotic stimulation with deviant stimuli simulating abrupt or smooth displacement of auditory images to the left or to the right from the head midline by means of interaural time delay introduced into the deviant stimuli. Repetitive standard stimuli were localized near the head midline. All deviant stimuli elicited mismatch negativity and P3a component. It was shown the MMN for smooth deviant motion was lower than that for the abrupt deviant displacement. MMN amplitude for both deviant types obviously depended on interaural time delay, which confirms that MMN might be considered as a measure of the auditory system spatial discriminative ability. The P3a component demonstrated the same amplitude dependences as the MMN. The results obtained are discussed in respect to manifestation of the processes underlying the auditory motion detection in the event-related potentials.     

Mismatch negativity as a characteristic of the distinguishing locating capacity of the human auditory system

Mismatch negativity has been studied under the conditions of dichotic stimulation by deviant stimuli that either changed their azimuth from zero to 4.5°, 13.5°, and 22.5° or moved with small velocities from the head midline to one of the ears. The reference stimuli were located along the head midline. Our experiments have shown that both a discontinuous increase in the azimuth and an increase in the velocity of moving stimuli are accompanied by an increase in the amplitude of mismatch negativity. This process is more pronounced in the cases of (1) an instantaneous change in the deviant azimuth compared to its movement, (2) a longer duration of the deviant sound, (3) action of the deviant in the right hemisphere, and (4) the frontal derivation. The correlations of changes in the mismatch negativity with psychophysical data on the resolution of the human auditory system are considered.     

A mismatch negativity elicited with stationary and moving auditory images of different azimuth positions

Characteristics of mismatch negativity elicited by dichotic stimulation were examined using deviant stimuli simulating movement of fused auditory images towards the standard stimuli or in the reverse direction. The effect of stationary deviants localized at 90 degrees in respect to standards was also measured. The standard stimuli were localized near either of ears or along the head midline. The spatial locations were produced by introducing interaural time differences into the click trains. All deviant stimuli evoked the mismatch negativity. The deviants moving from standards seem to evoke the lowest mismatch negativity with the longest latency at all azimuthal locations of standard stimuli. Besides, the deviant shift from standards proved to be the only direction at which the characteristics of mismatch negativity depended upon the standard's azimuth. It is seems that the discrimination of interaural time delay is essentially dependent on the pattern of interaural delay changes at the moment when the deviant occurs.     

Integrated mismatch negativity (MMNi): a noise-free representation of evoked responses allowing single-point distribution-free statistical tests

If the repeated presentation of a single (standard) auditory stimulus is randomly interspersed with a second acoustically different (deviant) stimulus, the cortical activity evoked by the deviant stimulus can contain a negative component known as the mismatch negativity (MMN). The MMN is derived by subtracting the averaged response evoked by the standard stimulus from that evoked by the deviant stimulus. When the magnitude of the response is small or the signal-to-noise ratio is poor, it is difficult to judge the presence or absence of the MMN simply by visual inspection, and statistical detection techniques become necessary. A method of analysis is proposed to quantify the magnitude and statistically evaluate the presence of the MMN based on time-integrated evoked responses. This paper demonstrates the use of this integrated mismatch negativity (MMN_i) analysis to detect the MMN evoked by stimulus contrasts near the perceptual threshold of two subjects. The MMN_i, by virtue of being equivalent to a low-pass filtered response, presents an almost noise-free estimate of MMN magnitude. A single measure of the integrated evoked response at a fixed time point is used in a distribution-free statistic that compares the magnitude of the averaged response evoked by the deviant stimulus with a magnitude distribution derived from 200 subaveraged responses to the standard stimulus (with the number of sweeps per average equal to that of the deviant stimulus). This allows a calculation of the exact probability for the null hypothesis that the negative magnitude of the response evoked by the deviant stimulus is drawn from the magnitude distribution of responses evoked by the standard stimulus. Rejection of this hypothesis provides objective evidence of the presence of the MMN.     

Frequency Change Detection in Human Auditory Cortex

We offer a model of how human cortex detects changes in the auditory environment. Auditory change detection has recently been the object of intense investigation via the mismatch negativity (MMN). MMN is a preattentive response to sudden changes in stimulation, measured noninvasively in the electroencephalogram (EEG) and the magnetoencephalogram (MEG). It is elicited in the oddball paradigm, where infrequent deviant tones intersperse a series of repetitive standard tones. However, little apart from the participation of tonotopically organized auditory cortex is known about the neural mechanisms underlying change detection and the MMN. In the present study, we investigate how poststimulus inhibition might account for MMN and compare the effects of adaptation with those of lateral inhibition in a model describing tonotopically organized cortex. To test the predictions of our model, we performed MEG and EEG measurements on human subjects and used both small- (<1/3 octave) and large- (>5 octaves) frequency differences between the standard and deviant tones. The experimental results bear out the prediction that MMN is due to both adaptation and lateral inhibition. Finally, we suggest that MMN might serve as a probe of what stimulus features are mapped by human auditory cortex.     

Mechanisms of generation of mismatch negativity and their role in discrimination of short acoustical stimuli

The effect of stimulus duration on the mismatch negativity in the auditory event-related potentials was used to study the role of mismatch negativity (MMN) in discrimination of short acoustical stimuli. We compared discrimination of different short acoustical stimuli in active variant of "odd ball" paradigm. It was shown that it is possible to discriminate between standard and deviant acoustical stimuli which do not produce MMN in passive condition. It makes possible to estimate behavioural significance of MMN in active discrimination task. If the MMN had not been recorded in passive condition, that leads to an increase of reaction time in active paradigm approximately by 50 ms.     

Event-related potentials in an auditory oddball situation in the rat

Evoked potentials were recorded from the auditory cortex of both freely moving and anesthetized rats when deviant sounds were presented in a homogenous series of standard sounds (oddball condition). A component of the evoked response to deviant sounds, the mismatch negativity (MMN), may underlie the ability to discriminate acoustic differences, a fundamental aspect of auditory perception. Whereas most MMN studies in animals have been done using simple sounds, this study involved a more complex set of sounds (synthesized vowels). The freely moving rats had previously undergone behavioral training in which they learned to respond differentially to these sounds. Although we found little evidence in this preparation for the typical, epidurally recorded, MMN response, a significant difference between deviant and standard evoked potentials was noted for the freely moving animals in the 100-200 ms range following stimulus onset. No such difference was found in the anesthetized animals.     

Auditory event-related potentials to deviant stimuli during drowsiness and stage 2 sleep

Twelve subjects were tested using a 3-tone auditory oddball paradigm consisting of a standard 1000 Hz tone (P = 80%) and two deviants, namely, a 1200 Hz tone and a 2000 Hz tone (both P = 10%). Testing took place in 3 conditions: (1) attend, in which the subject had to count one of the deviant tones; (2) ignore, in which the subject read a book; and (3) sleep, in which the subject was encouraged to go to sleep during presentation of the tones.In the awake conditions stimulus deviance elicited mismatch negativity (MMN) and P3. During drowsiness, no separate mismatch negativity (MMN) could be detected, but the 2000 Hz tone evoked a broad fronto-central early negative deflection, suggesting an overlap of N₁ and MMN. In the same condition, P210, N330 and P430 appeared, all being sensitive to magnitude of deviance. During stage 2, the P210, N330 and P430 amplitudes increased, most notably to the large deviant.These data indicate that differential processing of auditory inputs is maintained during drowsiness and stage 2 sleep, but do not support the notion that MMN or P3 activity comparable to the waking state occurs to oddball stimuli during this stage. It is hypothesised that during light sleep, scanning of the environment is performed by a different system than in the awake state and that during drowsiness a gradual switch between these two systems takes place.     

Fast detection of unexpected sound intensity decrements as revealed by human evoked potentials

The detection of deviant sounds is a crucial function of the auditory system and is reflected by the automatically elicited mismatch negativity (MMN), an auditory evoked potential at 100 to 250 ms from stimulus onset. It has recently been shown that rarely occurring frequency and location deviants in an oddball paradigm trigger a more negative response than standard sounds at very early latencies in the middle latency response of the human auditory evoked potential. This fast and early ability of the auditory system is corroborated by the finding of neurons in the animal auditory cortex and subcortical structures, which restore their adapted responsiveness to standard sounds, when a rare change in a sound feature occurs. In this study, we investigated whether the detection of intensity deviants is also reflected at shorter latencies than those of the MMN. Auditory evoked potentials in response to click sounds were analyzed regarding the auditory brain stem response, the middle latency response (MLR) and the MMN. Rare stimuli with a lower intensity level than standard stimuli elicited (in addition to an MMN) a more negative potential in the MLR at the transition from the Na to the Pa component at circa 24 ms from stimulus onset. This finding, together with the studies about frequency and location changes, suggests that the early automatic detection of deviant sounds in an oddball paradigm is a general property of the auditory system.     

Moving sound source discrimination in humans: Mismatch negativity and psychophysics

The ability to discriminate moving sounds sources with different dynamic properties was studied in humans. Mismatch negativity was studied in an experiment on dichotic stimulation, with deviant stimuli simulating the instantaneous movement of the auditory image to the right or left of the head midline in the horizontal plane. Standard stimuli simulated continuous movement of the sound source to the right or to the left to the same angular distances. It was also established that both deviant stimuli caused mismatch negativity, its parameters being independent on the direction of sound movement. Psychophysical testing of the same group of subjects showed that discrimination between the stimuli was below the psychophysical threshold. The results obtained are discussed from the point of view of current theories of moving sound localization. The correlation between the objective and subjective levels of discrimination of moving auditory images are discussed.     

Mismatch negativity to changes in a continuous tone with regularly varying frequencies

By using the mismatch negativity (MMN) component of the event-related potential, it was demonstrated that changes within a repetitively presented tone pattern can be automatically (i.e., involuntarily and attention-independently) detected by the human brain. Patterns consisting of 5 tones, immediately succeeding one another and differing in frequency, were delivered to subjects reading a self-selected book. There was a frequent , “standard” (P = 0.90) and an infrequent, “deviant” (P = 0.10) pattern presented in random order. The deviant pattern elicited the MMN even when the auditory stimulation was continuous, that is, no empty between-pattern interval indicated the beginning of a tone pattern. It may be concluded that the MMN mechanism is not necessarily timed by an “external” reference but is able to use “internal” units extracted from the repetitive structure inherent in the incessant flow of acoustic signals. The MMN paradigm seems to provide a tool to illuminate the organization of acoustic signals into auditory units.     

Mismatch negativity in the brain evoked potentials induced by short duration acoustic stimuli in adolescents in the norm and those with attention deficit

The effect of stimulus duration on the mismatch negativity of the auditory event-related potentials was studied in healthy children and those with attention-deficit symptoms. The minimum stimulus duration with which a MMN was elicited by frequency deviant was 50 ms in healthy children. The MMN was absent with shorter stimuli (11 ms and 30 ms). These parametres are close to those in adults. As to children with attention-deficit symptoms the MMN was insignificant with all tested stimulus durations (11 ms, 30 ms, 50 ms).     

Role of phasic changes in sound signal in localization of auditory image

The work presents experimental data on certain changes in electrical responses of the auditory system's midbrain centre in a contraphasic binaural presentation of sound impulse series. Neuronal cortical activity is selective in respect to dynamic interaural changes of signals' phasic spectre which may serve as a basis for the mechanisms of localising a moving source of sound. Human auditory evoked potentials reveal a manifestation of memorizing the auditory image movement direction as shown by appearance of stimuli deviant from standard mismatch negativity.     

Changes of evoked potentials caused by sound signals with different localization characteristics

Characteristics of the mismatch negativity (MMN) were studied by presenting the subjects with four blocks of stimuli containing standard series of clicks (90%) simulating a stationery sound image located in the head midline, and one of three different deviant series of clicks (10%) simulating either a stationary sound image located near the left ear or a moving sound image which shifted from the head midline to the left ear or in the opposite direction. All the deviant stimuli elicited the MMN with the minimal peak amplitude and the greatest latency evoked by the deviant series of clicks simulating the sound image moving from the head midline to the left ear. These findings suggest that the MMN may be considered as a pre-perceptual physiological measure of the discrimination accuracy for the sound signals with various spatial locations.     

Preattentive auditory information processing under exposure to the 902 MHz GSM mobile phone electromagnetic field: A mismatch negativity (MMN) study

Previous studies on the effects of the mobile phone electromagnetic field (EMF) on various event‐related potential (ERP) components have yielded inconsistent and even contradictory results, and often failed in replication. The mismatch negativity (MMN) is an auditory ERP component elicited by infrequent (deviant) stimuli differing in some physical features from the repetitive frequent (standard) stimuli in a sound sequence. The MMN provides a sensitive measure for cortical auditory stimulus feature discrimination, regardless of attention and other contaminating factors. In this study, MMN responses to duration, intensity, frequency, and gap changes were recorded in healthy young adults (n = 17), using a multifeature paradigm including several types of auditory change in the same stimulus sequence, while a GSM mobile phone was placed on either ear with the EMF (902 MHz pulsed at 217 Hz; SAR_1g = 1.14 W/kg, SAR_10g = 0.82 W/kg, peak value = 1.21 W/kg, measured with an SAM phantom) on or off. An MMN was elicited by all deviant types, while its amplitude and latency showed no significant differences due to EMF exposure for any deviant types. In the present study, we found no conclusive evidence that acute exposure to GSM mobile phone EMF affects cortical auditory change detection processing reflected by the MMN. Bioelectromagnetics 30:241–248, 2009. © 2009 Wiley‐Liss, Inc.     

Impaired mismatch negativity (MMN) generation in schizophrenia as a function of stimulus deviance,probability, and interstimulus/interdeviant interval

Schizophrenia is a severe mental disorder associated with disturbances in perception and cognition. Event-related potentials (ERP) provide a mechanism for evaluating potential mechanisms underlying neurophysiological dysfunction in schizophrenia. Mismatch negativity (MMN) is a short-duration auditory cognitive ERP component that indexes operation of the auditory sensory (`echoic') memory system. Prior studies have demonstrated impaired MMN generation in schizophrenia along with deficits in auditory sensory memory performance. MMN is elicited in an auditory oddball paradigm in which a sequence of repetitive standard tones is interrupted infrequently by a physically deviant (`oddball') stimulus. The present study evaluates MMN generation as a function of deviant stimulus probability, interstimulus interval, interdeviant interval and the degree of pitch separation between the standard and deviant stimuli. The major findings of the present study are first, that MMN amplitude is decreased in schizophrenia across a broad range of stimulus conditions, and second, that the degree of deficit in schizophrenia is largest under conditions when MMN is normally largest. The pattern of deficit observed in schizophrenia differs from the pattern observed in other conditions associated with MMN dysfunction, including Alzheimer's disease, stroke, and alcohol intoxication.     

Interstimulus interval and auditory event-related potentials in children: evidence for multiple generators

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7–9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, `standard' and 1100 Hz rare, `deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.