Automatic discriminative sensitivity inside temporal window of sensory memory as a function of time

Neural representation of preceding sound-patterns stored in the human brain, as reflected by mismatch negativity (MMN) related to the automatic discriminative process, is restricted to a duration of 160-170 ms due to the short form of auditory sensory memory termed the temporal window of integration (TWI). To examine the temporal uniformity of deviation-sensitivity inside TWI of sensory memory, magnetic MMN (MMNm) responses were measured with a dual 37-channel magnetometer for complex sounds of 170 ms duration containing an omitted (silent) segment. Frequent standard stimuli (probability of 80%) consisted of five tone segments. Deviant stimuli were different from standard stimuli in that one of four segments was occasionally (probability of 5%) omitted and replaced by a silent segment. The stimulus duration of 170 ms was intended to correspond to the postulated duration of TWI. When the silent segment occurred later in deviant stimulus, the MMNm peak amplitude was attenuated and MMNm peak latency, measured from the onset of each silent segment, was delayed. Thus, automatic deviation-detection sensitivity declines nonlinearly toward the end of TWI in auditory sensory memory. In the second experiment, two types of deviant stimuli, which differed from each other only in the period after the occurrence of the silent segment, elicited MMNm with the same peak latency but with a different peak amplitude. Thus, mismatch process is triggered at the moment of change but still lasts after the detection of deviation. In other words, both standard and deviant stimuli are treated as a unitary event within a TWI.     

Sound perception affected by nonlinear variation of accuracy in memory trace

The mismatch negativity (MMN) reflects the neural representation of the acoustic environment stored in sensory memory. The short phase of sensory memory corresponds to the temporal window of integration (TWI) which integrates the neighboring sounds into a unitary event. We measured the magnetic MMN (MMNm) and the discriminative reaction time (RT) responding to an omitted segment incorporated into a complex sound. Consequently, for the late omitted segments, the MMNm amplitudes were decreased, and those latencies and the RTs were prolonged. The percentages of the correct responses were also reduced for the late omitted segments. In sum, the discriminative sensitivity nonlinearly declined toward the end of the TWI, suggesting that the time-wise accuracy of the neural trace nonlinearly varies in sensory memory.     

Attentional modulation in the detection of irrelevant deviance: a simultaneous ERP/fMRI study

Little is known about the neural mechanisms that control attentional modulation of deviance detection in the auditory modality. In this study, we manipulated the difficulty of a primary task to test the relation between task difficulty and the detection of infrequent, task-irrelevant deviant (D) tones (1,300 Hz) presented among repetitive standard (S) tones (1,000 Hz). Simultaneous functional magnetic resonance imaging (fMRI)/event-related potentials (ERPs) were recorded from 21 subjects performing a two-alternative forced-choice duration discrimination task (short and long tones of equal probability). The duration of the short tone was always 50 msec. The duration of the long tone was 100 msec in the easy task and 60 msec in the difficult task. As expected, response accuracy decreased and response time (RT) increased in the difficult compared with the easy task. Performance was also poorer for D than for S tones, indicating distraction by task-irrelevant frequency information on trials involving D tones. In the difficult task, an amplitude increase was observed in the difference waves for N1 and P3a, ERP components associated with increased attention to deviant sounds. The mismatch negativity (MMN) response, associated with passive deviant detection, was larger in the easy task, demonstrating the susceptibility of this component to attentional manipulations. The fMRI contrast D > S in the difficult task revealed activation on the right superior temporal gyrus (STG) and extending ventrally into the superior temporal sulcus, suggesting this region's involvement in involuntary attention shifting toward unattended, infrequent sounds. Conversely, passive deviance detection, as reflected by the MMN, was associated with more dorsal activation on the STG. These results are consistent with the view that the dorsal STG region is responsive to mismatches between the memory trace of the standard and the incoming deviant sound, whereas the ventral STG region is activated by involuntary shifts of attention to task-irrelevant auditory features.     

Simultaneous storage of two complex temporal sound patterns in auditory sensory memory

We wished to determine whether multiple sound patterns can be simultaneously represented in the temporary auditory buffer (auditory sensory memory), when subjects have no task related to the sounds. To this end we used the mismatch negativity (MMN) event-related potential, an electric brain response elicited when a frequent sound is infrequently replaced by a different sound. The MMN response is based on the presence of the auditory sensory memory trace of the frequent sounds, which exists whether or not these sounds are in the focus of the subject's attention. Subjects watching a movie were presented with sound sequences consisting of two frequent sound patterns, each formed of four different tones and an infrequent pattern consisting of the first two tones of one of the frequent sound pattern and the last two tones of the other frequent sound pattern. The infrequent sound pattern elicited an MMN, indicating that multiple sound patterns are formed at an early, largely automatic stage of auditory processing.     

The use of conditional inference to reduce prediction error—A mismatch negativity (MMN) study

The brain uses regularities in the sound environment to build inference models predicting the most likely attributes of subsequent sounds. When the inference model fails, a prediction-error signal (the mismatch negativity or MMN) is generated. This study is designed to explore the capacity to use information about when a deviant sound will occur to switch between inference models in memory. We measured MMN generated to rare frequency, duration, intensity and spatial deviant sounds randomly occurring in a stream of identical repeating “standard” sounds. We then measured MMN to the same deviants in a linked sequence where deviants were paired—duration deviants followed an intensity change and spatial deviants followed a frequency change. To minimise prediction error, the brain should use the occurrence of the intensity and frequency deviant to prompt a change in the dominant inference (“expect-the-standard”) to anticipate the characteristics of the linked deviant. Anticipation was quantified as the proportion decline in duration and spatial MMN in the linked versus random sequence. We report three main outcomes on a sample of 23 healthy adults: (1) a significant reduction in duration MMN amplitude in linked versus random sequence; (2) a subgroup of participants exhibited significant reduction in spatial MMN amplitude in linked versus random sequence; and (3) the capacity to anticipate a linked deviant (reduce MMN) was a related to performance on the Continuous Performance Task-Identical Pairs. The results are discussed with respect to a possible co-reliance of CPT-IP and inference models on the inferior frontal gyrus.     

Are different kinds of acoustic features processed differently for speech and non-speech sounds?

This study examined how changes in different types of acoustic features are processed in the brain for both speech and non-speech sounds. Event-related potentials (ERPs) were recorded in native Finnish speakers presented with sequences of repetitive vowels (/e/) or complex harmonical tones interspersed with infrequent changes in duration, frequency and either a vowel change (/o/ for vowel sequences) or a double deviant (frequency+duration change for tone sequences). The stimuli were presented monaurally in separate blocks to either the left or right ear. The results showed that speech stimuli were more efficiently processed than harmonical tones as reflected by an enhanced mismatch negativity (MMN) and P3a ERP components. In addition, the duration change in vowels elicited a larger MMN component than the equivalent change in tones. This result might reflect enhanced processing of duration features in the Finnish language in which phoneme duration plays a critical role.     

Duration mismatch negativity in biological relatives of patients with schizophrenia spectrum disorders.

BACKGROUND: One of the most consistent findings in schizophrenia research over the past decade is a reduction in the amplitude of an auditory event-related brain potential known as mismatch negativity (MMN), which is generated whenever a deviant sound occurs in a background of repetitive auditory stimulation. The reduced amplitude of MMN in schizophrenia was first observed for deviant sounds that differ in duration relative to background standard sounds, and similar findings have been observed for sounds that are deviant in frequency. The aim of this study was to determine whether first-degree relatives of schizophrenia patients show a similar reduction in MMN amplitude to duration deviants. METHODS: We measured MMN to duration increments (deviants 100 msec vs. standards 50 msec) in 22 medicated patients with a diagnosis in the schizophrenia spectrum, 17 individuals who were first-degree unaffected relatives of patients, and 21 healthy control subjects. RESULTS: Mismatch negativity amplitude was reduced in patients and relatives compared with control subjects. There were no significant differences between patients and relatives. In contrast, the subsequent positive component, P3a, was larger in relatives compared with patients. CONCLUSIONS: These findings suggest that a reduced MMN amplitude may be an endophenotype marker of the predisposition to schizophrenia.     

Do tone duration changes that elicit the mismatch negativity also affect the preceding middle latency responses?

The human brain can automatically detect sound changes. Previous studies have reported that rare sounds presented within a sequence of repetitive sounds elicit the mismatch negativity (MMN) in the absence of attention in the latency range of 100–250 ms. On the other hand, a previous study discovered that occasional changes in sound location enhance the middle latency response (MLR) elicited in the latency range of 10–50 ms. Several studies have reported an increase in the amplitude of the MLR within the frame of oddball paradigms such as frequency and location changes. However, few studies have been conducted on paradigms employing a duration change. The purpose of the present study was to examine whether the peak amplitudes of the MLR components are enhanced by a change in duration. Twenty healthy Japanese men (age: 23.9 ± 2.9 years) participated in the present study. We used an oddball paradigm that contained standard stimuli with a duration of 10 ms and deviant stimuli with a duration of 5 ms. The peak amplitudes of the MLR for the deviant stimuli were then compared with those for the standard stimuli. No changes were observed in the peak amplitude of the MLR resulting from a duration change, whereas a definite MMN was elicited. The amplitude of the MLR was increased within the frame of oddball paradigms such as frequency and location changes. By contrast, the amplitude of the MLR was not changed within the duration change oddball paradigm that elicited the MMN.     

The development of memory trace depending on the number of the standard stimuli.

The mismatch negativity (MMN) component of the event-related potentials reflects the automatic detection mechanism of sound change. MMN is elicited by a neuronal mismatch process between deviant (infrequent) auditory input and the sensory memory trace of the standard (frequent) stimuli. Although many previous studies have investigated MMN to reveal the sensory memory mechanism, the development of memory representation still remains unclear, in particular, the topographical aspect of the trace-development in sensory memory has not been clarified. We measured the frontal and the temporal MMN components, respectively, when the sound trace was developed as the number of standard stimuli was changed to 1, 3, 5 or 7. In this experiment, the inter-train interval was 15 sec. The stimulus train with the different frequency of 800 Hz, 900 Hz, or 1000 Hz was repeatedly presented. Thus, we reduced the influence of the previous train. For the first time, we found not only the enhanced amplitude but also the shortened latency for both MMN components when the number of standard stimuli was increased. These findings indicate that both frontal and temporal MMN components reflect the development of memory trace depending on the number of standard stimuli.     

Automatic auditory change detection in humans is influenced by visual-auditory associative learning

Automatic detection of auditory changes that violate a regular sound sequence is indexed by the mismatch negativity (MMN) component of the event-related potential. The MMN is considered to reflect an auditory sensory memory and attention switching mechanism. Our aim was to study whether the auditory MMN can be associated with visual cues that have predictive value. By using visual cues that predicted the appearance of a deviant sound in most but not all of the cases, we were able to elicit MMN not only to the deviant sounds but also to those regular sounds that were misleadingly preceded by the visual cue. This result indicates high flexibility in the human automatic auditory change detection system, as it is affected by short-term visual-auditory associative learning.     

New fast mismatch negativity paradigm for determining the neural prerequisites for musical ability

Studies have consistently shown that the mismatch negativity (MMN) for different auditory features correlates with musical skills, and that this effect is more pronounced for stimuli integrated in complex musical contexts. Hence, the MMN can potentially be used for determining the development of auditory skills and musical expertise. MMN paradigms, however, are typically very long in duration, and far from sounding musical. Therefore, we developed a novel multi-feature MMN paradigm with 6 different deviant types integrated in a complex musical context of no more than 20 min in duration. We found significant MMNs for all 6 deviant types. Hence, this short objective measure can putatively be used as an index for auditory and musical development.     

Right hemisphere dominance of different mismatch negativities

Auditory stimulus blocks were presented to 10 reading subjects. Each block consisted of 2 types of stimulus, standard (P = 90%) and deviant (P = 10%), delivered in a random order with short constant inter-stimulus intervals. The standard stimuli were 600 Hz, 80 dB SPL 50 msec sine wave bursts. In different blocks, the deviant stimuli differed from the standards either in frequency (650 Hz), intensity (70 dB) or duration (20 msec). Left- and right-ear stimulations were used in separate blocks. Event-related brain potentials (ERPs) were recorded with 16 electrodes over both hemispheres. All the different types of deviant stimuli elicited an ERP component called the mismatch negativity (MMN). The MMN was larger over the right hemisphere irrespective of the ear stimulated whereas the N1 component, elicited by both standards, and deviants, was larger over the hemisphere contralateral to the ear stimulated. The results provide further evidence for the view that the MMN reflects a neural mismatch process with a memory trace which automatically codes the physical features of the repetitive stimuli.     

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

ObjectiveThe 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.MethodsERPs 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.ResultsThe 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.ConclusionsThe observed interactions demonstrated asymmetries in the MMN for duration increment and decrement.SignificanceThe 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.     

Study of sensory memory reflected by mismatch negativity and its clinical application]

The event-related brain potential called Mismatch negativity (MMN) reflects the auditory detection system which automatically detects subtle change in the surrounding acoustic environment. This system is based on the pre-attentive mechanism of comparison mechanism between the neural trace of background sounds stored in sensory memory and incoming sound change. This "memory trace theory" has raised the importance of MMN. The features of sound information are extracted from the incoming sound in sensory memory, and is integrated into an auditory unit within the temporal window of 160-170 ms. Since the MMN itself is basically free from the influence of attention and requires no task for measurement, MMN can be applied to various clinical studies. There are two generators, the temporal MMN reflecting the change detection in sensory memory and the frontal MMN reflecting the attentional switch. Therefore, MMN has various clinical applications including memory disturbance and attention disorder. For example, reduced amplitude of MMN is a robust finding in schizophrenia. Some basic MMN studies and their promising clinical applications are described here.     

Mismatch negativity for speech sounds in temporal lobe epilepsy

The mismatch negativity (MMN) is an electrophysiological trace of change detection, measured by electroencephalography (EEG), and is a reliable marker for pre-attentive auditory sensory memory. We used a phonetic oddball paradigm in patients with temporal lobe epilepsy (TLE) to elicit the MMN response at fronto-central sites and the mismatch positivity (MMP) response at mastoid sites. The MMN in 26 patients was compared with that of 26 age- and gender-matched healthy control participants. Electroencephalography responses were recorded during the presentation of speech sounds: the vowels 'a' and 'o' in alternation. Average waveforms were obtained for standard and deviant trials. We found that the MMP response at bilateral mastoid sites was reduced, whereas the MMN response at fronto-central sites did not change significantly. These results support the view that the MMN is generated by separable sources in the frontal and temporal lobes and that these sources are differentially affected by TLE.     

Does familiarity facilitate the cortical processing of music sounds?

Automatic cortical sound discrimination, as indexed by the mismatch negativity (MMN) component of the auditory evoked potential, is facilitated for familiar speech sounds (phonemes). In musicians as compared to non-musicians, an enhanced MMN has been observed for complex non-speech sounds. Here, musically trained subjects were presented with sequences of either familiar (tonal) or structurally matched unfamiliar (atonal) triad chords, both with either fixed or randomly transposed chord root pitch. The MMN elicited by deviant chords did not differ for familiar and unfamiliar triad sequences, and was undiminished even to unfamiliar deviant sounds which were consciously undetectable. Only subsequent attention-related components indicated facilitated cognitive processing of familiar sounds, corresponding to higher behavioral detection scores.     

The mismatch negativity (MMN) with no standard stimulus

ObjectiveThe recent fast multi-feature mismatch negativity (MMN) paradigms rest on the assumption that the deviant stimuli, alternating with the standard tone, strengthen the memory trace of the standard in respect to those attributes they have in common. In the present study, we tested whether the MMN can be recorded even without the standard stimulus, with the invariant properties of the deviant stimuli serving as a standard against which to detect the sound changes.MethodsMMN was recorded for changes in sound duration, frequency, intensity, location, gap, brightness, density, and noise level in a new multi-feature paradigm where no standard stimuli were used. In addition, these MMNs were compared with those recorded in the conventional multi-feature paradigm.ResultsAll sound changes elicited significant MMN responses that were highly similar between paradigms.ConclusionsThe MMN can be recorded even without the standard stimulus, as an accurate memory trace is constructed for the invariant features of the auditory input.SignificanceOmitting the standard stimuli results in almost 50% shorter recording time and the larger selection of deviant types with the newly introduced brightness, density, and noise-level changes provides even more information on the individual perceptual profiles than conventional multi-feature paradigms.     

Neurophysiological evidence of memory traces for words in the human brain

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of lexical contrasts in the human brain. The MMN was elicited either by rare words presented among repetitive words or pseudowords, or by pseudowords presented among words. Phonetic and phonological contrasts were identical in all conditions. MMNs elicited by both word deviants were larger than that elicited by the deviant pseudoword. The presence of lexical contrast did not significantly alter the word-elicited MMNs, which were, however, distinct in amplitude and topography from the MMN evoked by pseudowords. Thus, our results indicate the existence of word-related MMN enhancement largely independent of the lexical status of the standard stimulus. This enhancement may reflect the presence of a long-term memory trace for a spoken word.     

Changes in sensitivity to stimulus deviance in Alzheimer's disease: an ERP perspective

The mismatch negativity (MMN) of the event-related brain potential (ERP) reflects the storage of information in sensory memory. MMNs were recorded from eight patients with Alzheimer's disease (AD) and eight controls to small (delta50 Hz), large (delta300 Hz), and a variety of highly deviant, environmental sounds. Both old controls and patients showed robust MMNs to all three classes of deviant events, and robust P3 compounds (indicative of active attention) to the environmental sounds. The data suggest that patients with mild AD have an intact sensory memory mechanism that responds similarly to that of controls to systematic increases in deviance. However, for both older controls and patients, only highly deviant acoustic events are likely to involuntary capture attention.     

Differential auditory processing continues during sleep.

Auditory evoked potentials (AEPs) were used to examine selective stimulus processing in sleep. In waking, repetitive stimuli generate exogenous P1, N1 and P2 components of the auditory evoked potential (AEP). Deviant stimuli generate endogenous cognitive components including the mismatch negativity (MMN), N2 and P3 components. We examined long-latency auditory evoked potentials elicited by repetitive and deviant stimuli during waking and stage II-IV sleep to assess whether stimulus deviance is detected during sleep. The waking P1, N1b and P2 had maximal amplitudes at fronto-central scalp sites, with additional peaks (N1a, N1c) at temporal sites. Deviant tones generated a frontal maximal MMN, and complex novel tones generated an additional P3 component maximal at centro-parietal sites. During stages II-IV sleep N1a, b, c amplitudes were reduced. During stage II sleep all stimuli generated increased P2 amplitudes and a late negative component (N340). Deviant stimuli generated greater P2 and N340 amplitudes than frequent stimuli in stage II sleep, as well as an additional P420 component. In stage III-IV sleep the P420 was absent and the AEP was dominated by a negativity of long duration whose amplitude increased in response to deviant stimuli. These data indicate that auditory evoked activity changes from wakefulness to sleep. The differential response to deviant sounds observed during waking and all sleep stages supports the theory that selective processing of auditory stimuli persists during sleep.