That sounds awful! Does sound unpleasantness modulate the mismatch negativity and its habituation?

There are sounds that most people perceive as highly unpleasant, for instance, the sound of rubbing pieces of polystyrene together. Previous research showed larger physiological and neural responses for such aversive compared to neutral sounds. Hitherto, it remains unclear whether habituation, i.e., diminished responses to repeated stimulus presentation, which is typically reported for neutral sounds, occurs to the same extent for aversive stimuli. We measured the mismatch negativity (MMN) in response to rare occurrences of aversive or neutral deviant sounds within an auditory oddball sequence in 24 healthy participants, while they performed a demanding visual distractor task. Deviants occurred as single events (i.e., between two standards) or as double deviants (i.e., repeating the identical deviant sound in two consecutive trials). All deviants elicited a clear MMN, and amplitudes were larger for aversive than for neutral deviants (irrespective of their position within a deviant pair). This supports the claim of preattentive emotion evaluation during early auditory processing. In contrast to our expectations, MMN amplitudes did not show habituation, but increased in response to deviant repetition-similarly for aversive and neutral deviants. A more fine-grained analysis of individual MMN amplitudes in relation to individual arousal and valence ratings of each sound item revealed that stimulus-specific MMN amplitudes were best predicted by the interaction of deviant position and perceived arousal, but not by valence. Deviants with perceived higher arousal elicited larger MMN amplitudes only at the first deviant position, indicating that the MMN reflects preattentive processing of the emotional content of sounds.

Neural signatures of automatic repetition detection in temporally regular and jittered acoustic sequences.

Detection of repeating patterns within continuous sound streams is crucial for efficient auditory perception. Previous studies demonstrated a remarkable sensitivity of the human auditory system to periodic repetitions in unfamiliar, meaningless sounds. Automatic repetition detection was reflected in different EEG markers, including sustained activity, neural synchronisation, and event-related responses to pattern occurrences. The current study investigated how listeners' attention and the temporal regularity of a sound modulate repetition perception, and how this influence is reflected in different EEG markers that were previously suggested to subserve dissociable functions. We reanalysed data of a previous study in which listeners were presented with sequences of unfamiliar artificial sounds that either contained repetitions of a certain sound segment or not. Repeating patterns occurred either regularly or with a temporal jitter within the sequences, and participants' attention was directed either towards the pattern repetitions or away from the auditory stimulation. Across both regular and jittered sequences during both attention and in-attention, pattern repetitions led to increased sustained activity throughout the sequence, evoked a characteristic positivity-negativity complex in the event-related potential, and enhanced inter-trial phase coherence of low-frequency oscillatory activity time-locked to repeating pattern onsets. While regularity only had a minor (if any) influence, attention significantly strengthened pattern repetition perception, which was consistently reflected in all three EEG markers. These findings suggest that the detection of pattern repetitions within continuous sounds relies on a flexible mechanism that is robust against in-attention and temporal irregularity, both of which typically occur in naturalistic listening situations. Yet, attention to the auditory input can enhance processing of repeating patterns and improve repetition detection.

Deviants violating higher-order auditory regularities can become predictive and facilitate behaviour.

The human auditory system is believed to represent regularities inherent in auditory information in internal models. Sounds not matching the standard regularity (deviants) elicit prediction error, alerting the system to information not explainable within currently active models. Here, we examine the widely neglected characteristic of deviants bearing predictive information themselves. In a modified version of the oddball paradigm, using higher-order regularities, we set up different expectations regarding the sound following a deviant. Higher-order regularities were defined by the relation of pitch within tone pairs (rather than absolute pitch of individual tones). In a deviant detection task participants listened to oddball sequences including two deviant types following diametrically opposed rules: one occurred mostly in succession (high repetition probability) and the other mostly in isolation (low repetition probability). Participants in Experiment 1 were not informed (naïve), whereas in Experiment 2 they were made aware of the repetition rules. Response times significantly decreased from first to second deviant when repetition probability was high-albeit more in the presence of explicit rule knowledge. There was no evidence of a facilitation effect when repetition probability was low. Significantly more false alarms occurred in response to standards following high compared with low repetition probability deviants, but only in participants aware of the repetition rules. These findings provide evidence that not only deviants violating lower- but also higher-order regularities can inform predictions about auditory events. More generally, they confirm the utility of this new paradigm to gather further insights into the predictive properties of the human brain.

Auditory representations for long lasting sounds: Insights from event-related brain potentials and neural oscillations.

The basic features of short sounds, such as frequency and intensity including their temporal dynamics, are integrated in a unitary representation. Knowledge on how our brain processes long lasting sounds is scarce. We review research utilizing the Mismatch Negativity event-related potential and neural oscillatory activity for studying representations for long lasting simple versus complex sounds such as sinusoidal tones versus speech. There is evidence for a temporal constraint in the formation of auditory representations: Auditory edges like sound onsets within long lasting sounds open a temporal window of about 350 ms in which the sounds' dynamics are integrated into a representation, while information beyond that window contributes less to that representation. This integration window segments the auditory input into short chunks. We argue that the representations established in adjacent integration windows can be concatenated into an auditory representation of a long sound, thus, overcoming the temporal constraint.

Within- and between-subject consistency of perceptual segmentation in periodic noise: A combined behavioral tapping and EEG study.

It is remarkable that human listeners can perceive periodicity in noise, as the isochronous repetition of a particular noise segment is not accompanied by salient physical cues in the acoustic signal. Previous research suggested that listeners rely on short temporally local and idiosyncratic features to perceptually segment periodic noise sequences. The present study sought to test this assumption by disentangling consistency of perceptual segmentation within and between listeners. Presented periodic noise sequences either consisted of seamless repetitions of a 500-ms segment or of repetitions of a 200-ms segment that were interleaved with 300-ms portions of random noise. Both within- and between-subject consistency was stronger for interleaved (compared with seamless) periodic sequences. The increased consistency likely resulted from reduced temporal jitter of potential features used for perceptual segmentation when the recurring segment was shorter and occurred interleaved with random noise. These results support the notion that perceptual segmentation of periodic noise relies on subtle temporally local features. However, the finding that some specific noise sequences were segmented more consistently across listeners than others challenges the assumption that the features are necessarily idiosyncratic. Instead, in some specific noise samples, a preference for certain spectral features is shared between individuals.

Change detection of auditory tonal patterns defined by absolute versus relative pitch information. A combined behavioural and EEG study.

The human auditory system often relies on relative pitch information to extract and identify auditory objects; such as when the same melody is played in different keys. The current study investigated the mental chronometry underlying the active discrimination of unfamiliar melodic six-tone patterns by measuring behavioural performance and event-related potentials (ERPs). In a roving standard paradigm, such patterns were either repeated identically within a stimulus train, carrying absolute frequency information about the pattern, or shifted in pitch (transposed) between repetitions, so only relative pitch information was available to extract the pattern identity. Results showed that participants were able to use relative pitch to detect when a new melodic pattern occurred. Though in the absence of absolute pitch sensitivity significantly decreased and behavioural reaction time to pattern changes increased. Mismatch-Negativity (MMN), an ERP indicator of auditory deviance detection, was elicited at approximately 206 ms after stimulus onset at frontocentral electrodes, even when only relative pitch was available to inform pattern discrimination. A P3a was elicited in both conditions, comparable in amplitude and latency. Increased latencies but no differences in amplitudes of N2b, and P3b suggest that processing at higher levels is affected when, in the absence of absolute pitch cues, relative pitch has to be extracted to inform pattern discrimination. Interestingly, the response delay of approximately 70 ms on the behavioural level, already fully manifests at the level of N2b. This is in accordance with recent findings on implicit auditory learning processes and suggests that in the absence of absolute pitch cues a slowing of target selection rather than a slowing of the auditory pattern change detection process causes the deterioration in behavioural performance.

Neural signatures of temporal regularity and recurring patterns in random tonal sound sequences.

The auditory system is highly sensitive to recurring patterns in the acoustic input - even in otherwise unstructured material, such as white noise or random tonal sequences. Electroencephalography (EEG) research revealed a characteristic negative potential to periodically recurring auditory patterns - a response, which has been interpreted as memory trace-related and specific, rather than as a sign of periodicity-driven entrainment. Here, we aim to disentangle these two possible contributions by investigating the influence of a periodic sound sequence's inherent temporal regularity on event-related potentials. Participants were presented continuous sequences of short tones of random pitch, with some sequences containing a recurring pattern, and asked to indicate whether they heard a repetition. Patterns were either spaced equally across the random sequence (isochronous condition) or with a temporal jitter (jittered condition), which enabled us to differentiate between event-related potentials (and thus processing operations associated with a memory trace for a repeated pattern) and the periodic nature of the repetitions. A negative recurrence-related component could be observed independently of temporal regularity, was pattern-specific, and modulated by across trial repetition of the pattern. Critically, isochronous pattern repetition induced an additional early periodicity-related positive component, which started to build up already before the pattern onset and which was elicited undampedly even when the repeated pattern was occasionally not presented. This positive component likely reflects a sensory driven entrainment process that could be the foundation of a behavioural benefit in detecting temporally regular repetitions.

Electrophysiological Correlates of Speaker Segregation and Foreground-Background Selection in Ambiguous Listening Situations.

In everyday listening environments, a main task for our auditory system is to follow one out of multiple speakers talking simultaneously. The present study was designed to find electrophysiological indicators of two central processes involved - segregating the speech mixture into distinct speech sequences corresponding to the two speakers, and then attending to one of the speech sequences. We generated multistable speech stimuli that were set up to create ambiguity as to whether only one or two speakers are talking. Thereby we were able to investigate three perceptual alternatives (no segregation, segregated - speaker A in the foreground, segregated - speaker B in the foreground) without any confounding stimulus changes. Participants listened to a continuously repeating sequence of syllables, which were uttered alternately by two human speakers, and indicated whether they perceived the sequence as an inseparable mixture or as originating from two separate speakers. In the latter case, they distinguished which speaker was in their attentional foreground. Our data show a long-lasting event-related potential (ERP) modulation starting at 130ms after stimulus onset, which can be explained by the perceptual organization of the two speech sequences into attended foreground and ignored background streams. Our paradigm extends previous work with pure-tone sequences toward speech stimuli and adds the possibility to obtain neural correlates of the difficulty to segregate a speech mixture into distinct streams.

Exploiting temporal predictability: Event-related potential correlates of task-supportive temporal cue processing in auditory distraction.

The human cognitive system has various functions to enhance performance in tasks requiring responses to stimuli. When potentially occurring stimuli are known, we can establish selective attention sets and ignore task-irrelevant events while attending task-relevant ones. When the stimulation is temporally structured, we can rely on constant temporal relationships between stimulus events to prepare for the task-relevant moments. Most distraction paradigms feature task-irrelevant events which are followed by task-relevant ones within a constant interval, and distraction is induced by randomly replacing some of the standard task-irrelevant events. The constant time interval transforms irrelevant events to task-supportive temporal cues, which are integrated into the task-behavior by the participants. The present study investigated whether distracters could be utilized as temporal cues to support task-related processing in a continuous auditory stimulation paradigm. A continuous tone featuring short and long gaps, and pitch glides was presented. Participants performed a gap duration discrimination task, while ignoring glides. Glides could be presented frequently or rarely. In the informative condition, 80% of the glides predicted the presentation time of the forthcoming gap (400ms), while in the uninformative condition, the occurrence of gaps and glides was independent. Rare glides elicited an enhanced N1, mismatch negativity, and P3 event-related potentials in both informative and uninformative conditions. In informative conditions glides were followed by a contingent negative variation; and rare informative glides elicited an N2b, suggesting that despite triggering distraction-related processes, distracters could be integrated into the task-behavior, and could be utilized as task-supportive cues.

Functional dissociation between regularity encoding and deviance detection along the auditory hierarchy.

Auditory deviance detection based on regularity encoding appears as one of the basic functional properties of the auditory system. It has traditionally been assessed with the mismatch negativity (MMN) long-latency component of the auditory evoked potential (AEP). Recent studies have found earlier correlates of deviance detection based on regularity encoding. They occur in humans in the first 50 ms after sound onset, at the level of the middle-latency response of the AEP, and parallel findings of stimulus-specific adaptation observed in animal studies. However, the functional relationship between these different levels of regularity encoding and deviance detection along the auditory hierarchy has not yet been clarified. Here we addressed this issue by examining deviant-related responses at different levels of the auditory hierarchy to stimulus changes varying in their degree of deviation regarding the spatial location of a repeated standard stimulus. Auditory stimuli were presented randomly from five loudspeakers at azimuthal angles of 0°, 12°, 24°, 36° and 48° during oddball and reversed-oddball conditions. Middle-latency responses and MMN were measured. Our results revealed that middle-latency responses were sensitive to deviance but not the degree of deviation, whereas the MMN amplitude increased as a function of deviance magnitude. These findings indicated that acoustic regularity can be encoded at the level of the middle-latency response but that it takes a higher step in the auditory hierarchy for deviance magnitude to be encoded, thus providing a functional dissociation between regularity encoding and deviance detection along the auditory hierarchy.

Involvement of the human midbrain and thalamus in auditory deviance detection.

Prompt detection of unexpected changes in the sensory environment is critical for survival. In the auditory domain, the occurrence of a rare stimulus triggers a cascade of neurophysiological events spanning over multiple time-scales. Besides the role of the mismatch negativity (MMN), whose cortical generators are located in supratemporal areas, cumulative evidence suggests that violations of auditory regularities can be detected earlier and lower in the auditory hierarchy. Recent human scalp recordings have shown signatures of auditory mismatch responses at shorter latencies than those of the MMN. Moreover, animal single-unit recordings have demonstrated that rare stimulus changes cause a release from stimulus-specific adaptation in neurons of the primary auditory cortex, the medial geniculate body (MGB), and the inferior colliculus (IC). Although these data suggest that change detection is a pervasive property of the auditory system which may reside upstream cortical sites, direct evidence for the involvement of subcortical stages in the human auditory novelty system is lacking. Using event-related functional magnetic resonance imaging during a frequency oddball paradigm, we here report that auditory deviance detection occurs in the MGB and the IC of healthy human participants. By implementing a random condition controlling for neural refractoriness effects, we show that auditory change detection in these subcortical stations involves the encoding of statistical regularities from the acoustic input. These results provide the first direct evidence of the existence of multiple mismatch detectors nested at different levels along the human ascending auditory pathway.

Repetition suppression and repetition enhancement underlie auditory memory-trace formation in the human brain: an MEG study.

The formation of echoic memory traces has traditionally been inferred from the enhanced responses to its deviations. The mismatch negativity (MMN), an auditory event-related potential (ERP) elicited between 100 and 250ms after sound deviation is an indirect index of regularity encoding that reflects a memory-based comparison process. Recently, repetition positivity (RP) has been described as a candidate ERP correlate of direct memory trace formation. RP consists of repetition suppression and enhancement effects occurring in different auditory components between 50 and 250ms after sound onset. However, the neuronal generators engaged in the encoding of repeated stimulus features have received little interest. This study intends to investigate the neuronal sources underlying the formation and strengthening of new memory traces by employing a roving-standard paradigm, where trains of different frequencies and different lengths are presented randomly. Source generators of repetition enhanced (RE) and suppressed (RS) activity were modeled using magnetoencephalography (MEG) in healthy subjects. Our results show that, in line with RP findings, N1m (~95-150ms) activity is suppressed with stimulus repetition. In addition, we observed the emergence of a sustained field (~230-270ms) that showed RE. Source analysis revealed neuronal generators of RS and RE located in both auditory and non-auditory areas, like the medial parietal cortex and frontal areas. The different timing and location of neural generators involved in RS and RE points to the existence of functionally separated mechanisms devoted to acoustic memory-trace formation in different auditory processing stages of the human brain.

Encoding of nested levels of acoustic regularity in hierarchically organized areas of the human auditory cortex.

Our auditory system is able to encode acoustic regularity of growing levels of complexity to model and predict incoming events. Recent evidence suggests that early indices of deviance detection in the time range of the middle-latency responses (MLR) precede the mismatch negativity (MMN), a well-established error response associated with deviance detection. While studies suggest that only the MMN, but not early deviance-related MLR, underlie complex regularity levels, it is not clear whether these two mechanisms interplay during scene analysis by encoding nested levels of acoustic regularity, and whether neuronal sources underlying local and global deviations are hierarchically organized. We registered magnetoencephalographic evoked fields to rapidly presented four-tone local sequences containing a frequency change. Temporally integrated local events, in turn, defined global regularities, which were infrequently violated by a tone repetition. A global magnetic mismatch negativity (MMNm) was obtained at 140-220 ms when breaking the global regularity, but no deviance-related effects were shown in early latencies. Conversely, Nbm (45-55 ms) and Pbm (60-75 ms) deflections of the MLR, and an earlier MMNm response at 120-160 ms, responded to local violations. Distinct neuronal generators in the auditory cortex underlay the processing of local and global regularity violations, suggesting that nested levels of complexity of auditory object representations are represented in separated cortical areas. Our results suggest that the different processing stages and anatomical areas involved in the encoding of auditory representations, and the subsequent detection of its violations, are hierarchically organized in the human auditory cortex.

Two sequential processes of change detection in hierarchically ordered areas of the human auditory cortex.

Auditory deviance detection occurs around 150 ms after the onset of a deviant sound. Recent studies in animals and humans have described change-related processes occurring during the first 50 ms after sound onset. However, it still remains an open question whether these early and late processes of deviance detection are organized hierarchically in the human auditory cortex. We applied a beamforming source reconstruction approach in order to estimate brain sources associated with 2 temporally distinct markers of deviance detection. Results showed that rare frequency changes elicit an enhancement of the Nbm component of the middle latency response (MLR) peaking at 43 ms, in addition to the magnetic mismatch negativity (MMNm) peaking at 115 ms. Sources of MMNm, located in the right superior temporal gyrus, were lateral and posterior to the deviance-related MLR activity being generated in the right primary auditory cortex. Source reconstruction analyses revealed that detection of changes in the acoustic environment is a process accomplished in 2 different time ranges, by spatially separated auditory regions. Paralleling animal studies, our findings suggest that primary and secondary areas are involved in successive stages of deviance detection and support the existence of a hierarchical network devoted to auditory change detection.

Regularity encoding and deviance detection of frequency modulated sweeps: human middle- and long-latency auditory evoked potentials.

Fast encoding of frequency modulated (FM) sweeps is crucial for communication. In humans, FM sweeps deviating from the acoustic regularity elicit the mismatch negativity (MMN) evoked potential. Yet, direction sensitivity to FM sweeps is found in animals' primary auditory cortex, upstream of MMN sources found in humans. Here, we were interested in whether direction deviants of complex FM sweeps modulated brain responses earlier than MMN. We used a controlled oddball paradigm, and measured the middle latency responses (MLRs) and the MMN. Our results showed a repetition enhancement to the standards at the Pa component of the MLR and a genuine MMN in the later response range. These results show that, early in the cortical hierarchy, the system is sensitive to the physical characteristics of the repetitive stimuli, but a higher-order mechanism is needed to detect violations of the acoustic regularity.

Simple and complex acoustic regularities are encoded at different levels of the auditory hierarchy.

The detection of auditory stimuli that deviate from a simple or complex auditory regularity is reflected by the mismatch negativity component of the human auditory evoked potential. Moreover, simple deviants of an oddball paradigm modulate the preceding middle-latency response of the auditory evoked potential. For the frequency oddball paradigms it has been shown that the Nb wave, at approximately 40 ms from stimulus onset, is enhanced in response to deviant compared with standard stimuli. In this study we tested whether the detection of auditory deviants in a (frequency-location) feature-conjunction paradigm is reflected by modulations of the Na, Pa or Nb wave of healthy human participants. In addition, a frequency oddball paradigm was applied to directly contrast the results of a simple and a complex invariance. Feature-conjunction deviants did not elicit any modulations of the tested middle-latency waves. Deviants of the frequency oddball paradigm, by contrast, elicited an enhancement of the Nb wave, confirming the outcome of precedent studies. In both conditions a significant mismatch negativity component was elicited, which showed larger amplitudes and shorter latencies in the oddball condition than in the feature-conjunction condition. These findings corroborate the idea that simple auditory regularities are encoded upstream of those of more complex auditory features and are in line with the idea of a hierarchically working auditory novelty system.

Electrophysiological index of acoustic temporal regularity violation in the middle latency range.

OBJECTIVE: Acoustic violations in temporal regularity have been traditionally indexed by mismatch negativity (MMN). However, recent studies have demonstrated that humans can detect auditory changes in physical sound features, such as frequency, location and intensity, in the first 50 ms after sound onset. Our aim was to examine if temporal regularity violations could be detected in the middle latency range. METHODS: We used an oddball paradigm with 290 ms as standard stimulus onset asynchrony (SOA) and 200 ms as deviant SOA. We also employed a control paradigm that comprised of seven SOAs including 200 and 290 ms, in order to control for differences due to refractoriness. RESULTS: In the middle latency range, temporal regularity violations led to enhanced Pa and Nb responses, which behaved differently to the corresponding SOAs in the control condition. In the long latency range, temporal regularity violations led to similar behaviours in both oddball and control paradigms. CONCLUSIONS: These findings suggest that with a fast presentation rate, human brains are capable to detect temporal regularity violations in the middle latency range. SIGNIFICANCE: Together with previous studies that found early change detection responses, the current study emphasises that the human brain can encode simple regularity violation as early as approximately 50 ms post-stimulus onset.

Is fast auditory change detection feature specific? An electrophysiological study in humans.

Recent oddball studies showed that auditory change detection responses exist in the first 50 ms after sound onset, upstream of mismatch negativity (MMN). We examined if these early responses could be elicited by feature-specific changes, meaning changes in the value of one attribute of a stimulus, regardless of whether other attributes of the stimulus are changing or not. We used a multifeature paradigm with four types of deviants: frequency, duration, intensity, and interaural time difference. In the middle latency range, only frequency deviants led to an enhanced Nb response. All four feature changes generated significant MMNs. Our results indicate that human brain is capable of detecting a feature-specific change for frequency attributes in the middle latency. The different levels of information being encoded in two separate event-related potential time ranges support the notion of a hierarchical organization of auditory deviance detection.

Ultrafast tracking of sound location changes as revealed by human auditory evoked potentials.

The rapid discrimination of auditory location information enables grouping and selectively attending to specific sound sources. The typical indicator of auditory change detection is the mismatch negativity (MMN) occurring at a latency of about 100-250 ms. However, recent studies have revealed the existence of earlier markers of frequency deviance detection in the middle-latency response (MLR). Here, we measured the MLR and MMN to changes in sound location. Clicks were presented in either the left or right hemifields during oddball (rare 30°-shifts in location), reversed oddball, and control (sounds occurring equiprobably from five locations) conditions. Clicks at deviant locations elicited an MMN and an enhanced Na component of the MLR peaking at 20 ms compared to clicks at standard or control locations. Whereas MMN was not significantly lateralized, the Na effect showed a contralateral dominance. These findings indicate that, also for sound location changes, early detection processes exist upstream of MMN.

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.