Effects of spectral complexity and sound duration on automatic complex-sound pitch processing in humans - a mismatch negativity study

Linking the neural basis of distributional statistical learning with transitional statistical learning: The paradox of attention

Statistical learning, the process of tracking distributional information and discovering embedded patterns, is traditionally regarded as a form of implicit learning. However, recent studies proposed that both implicit (attention-independent) and explicit (attention-dependent) learning systems are involved in statistical learning. To understand the role of attention in statistical learning, the current study investigates the cortical processing of distributional patterns in speech across local and global contexts. We then ask how these cortical responses relate to statistical learning behavior in a word segmentation task. We found Event-Related Potential (ERP) evidence of pre-attentive processing of both the local (mismatching negativity) and global distributional information (late discriminative negativity). However, as speech elements became less frequent and more surprising, some participants showed an involuntary attentional shift, reflected in a P3a response. Individuals who displayed attentive neural tracking of distributional information showed faster learning in a speech statistical learning task. These results suggest that an involuntary attentional shift might play a facilitatory, but not essential, role in statistical learning.

A Review of Research on the Neurocognition for Timbre Perception

As one of the basic elements in acoustic events, timbre influences the brain collectively with other factors such as pitch and loudness. Research on timbre perception involve interdisciplinary fields, including physical acoustics, auditory psychology, neurocognitive science and music theory, etc. From the perspectives of psychology and physiology, this article summarizes the features and functions of timbre perception as well as their correlation, among which the multi-dimensional scaling modeling methods to define timbre are the focus; the neurocognition and perception of timbre (including sensitivity, adaptability, memory capability, etc.) are outlined; related experiment findings (by using EEG/ERP, fMRI, etc.) on the deeper level of timbre perception in terms of neural cognition are summarized. In the meantime, potential problems in the process of experiments on timbre perception and future possibilities are also discussed. Thought sorting out the existing research contents, methods and findings of timbre perception, this article aims to provide heuristic guidance for researchers in related fields of timbre perception psychology, physiology and neural mechanism. It is believed that the study of timbre perception will be essential in various fields in the future, including neuroaesthetics, psychological intervention, artistic creation, rehabilitation, etc.

Suppression, Maintenance, and Surprise: Neuronal Correlates of Predictive Processing Specialization for Musical Rhythm

Auditory repetition suppression and omission activation are opposite neural phenomena and manifestations of principles of predictive processing. Repetition suppression describes the temporal decrease in neural activity when a stimulus is constant or repeated in an expected temporal fashion; omission activity is the transient increase in neural activity when a stimulus is temporarily and unexpectedly absent. The temporal, repetitive nature of musical rhythms is ideal for investigating these phenomena. During an fMRI session, 10 healthy participants underwent scanning while listening to musical rhythms with two levels of metric complexity, and with beat omissions with different positional complexity. Participants first listened to 16-s-long presentations of continuous rhythms, before listening to a longer continuous presentation with beat omissions quasi-randomly introduced. We found deactivation in bilateral superior temporal gyri during the repeated presentation of the normal, unaltered rhythmic stimulus, with more suppression of activity in the left hemisphere. Omission activation of bilateral middle temporal gyri was right lateralized. Persistent activity was found in areas including the supplementary motor area, caudate nucleus, anterior insula, frontal areas, and middle and posterior cingulate cortex, not overlapping with either listening, suppression, or omission activation. This suggests that the areas are perhaps specialized for working memory maintenance. We found no effect of metric complexity for either the normal presentation or omissions, but we found evidence for a small effect of omission position—at an uncorrected threshold—where omissions in the more metrical salient position, i.e., the first position in the bar, showed higher activation in anterior cingulate/medial superior frontal gyrus, compared to omissions in the less salient position, in line with the role of the anterior cingulate cortex for saliency detection. The results are consistent with findings in our previous studies on Parkinson’s disease, but are put into a bigger theoretical frameset.

Improved Auditory Function Caused by Music Versus Foreign Language Training at School Age: Is There a Difference?

In adults, music and speech share many neurocognitive functions, but how do they interact in a developing brain? We compared the effects of music and foreign language training on auditory neurocognition in Chinese children aged 8–11 years. We delivered group-based training programs in music and foreign language using a randomized controlled trial. A passive control group was also included. Before and after these year-long extracurricular programs, auditory event-related potentials were recorded (n = 123 and 85 before and after the program, respectively). Through these recordings, we probed early auditory predictive brain processes.

To our surprise, the language program facilitated the children’s early auditory predictive brain processes significantly more than did the music program. This facilitation was most evident in pitch encoding when the experimental paradigm was musically relevant. When these processes were probed by a paradigm more focused on basic sound features, we found early predictive pitch encoding to be facilitated by music training.

Thus, a foreign language program is able to foster auditory and music neurocognition, at least in tonal language speakers, in a manner comparable to that by a music program. Our results support the tight coupling of musical and linguistic brain functions also in the developing brain.

Auditory Pattern Representations Under Conditions of Uncertainty-An ERP Study

The auditory system is able to recognize auditory objects and is thought to form predictive models of them even though the acoustic information arriving at our ears is often imperfect, intermixed, or distorted. We investigated implicit regularity extraction for acoustically intact versus disrupted six-tone sound patterns via event-related potentials (ERPs). In an exact-repetition condition, identical patterns were repeated; in two distorted-repetition conditions, one randomly chosen segment in each sound pattern was replaced either by white noise or by a wrong pitch. In a roving-standard paradigm, sound patterns were repeated 1-12 times (standards) in a row before a new pattern (deviant) occurred. The participants were not informed about the roving rule and had to detect rarely occurring loudness changes. Behavioral detectability of pattern changes was assessed in a subsequent behavioral task. Pattern changes (standard vs. deviant) elicited mismatch negativity (MMN) and P3a, and were behaviorally detected above the chance level in all conditions, suggesting that the auditory system extracts regularities despite distortions in the acoustic input. However, MMN and P3a amplitude were decreased by distortions. At the level of MMN, both types of distortions caused similar impairments, suggesting that auditory regularity extraction is largely determined by the stimulus statistics of matching information. At the level of P3a, wrong-pitch distortions caused larger decreases than white-noise distortions. Wrong-pitch distortions likely prevented the engagement of restoration mechanisms and the segregation of disrupted from true pattern segments, causing stronger informational interference with the relevant pattern information.

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.

Asymmetries in Accessing Vowel Representations Are Driven by Phonological and Acoustic Properties: Neural and Behavioral Evidence From Natural German Minimal Pairs

In vowel discrimination, commonly found discrimination patterns are directional asymmetries where discrimination is faster (or easier) if differing vowels are presented in a certain sequence compared to the reversed sequence. Different models of speech sound processing try to account for these asymmetries based on either phonetic or phonological properties. In this study, we tested and compared two of those often-discussed models, namely the Featurally Underspecified Lexicon (FUL) model (Lahiri and Reetz, 2002) and the Natural Referent Vowel (NRV) framework (Polka and Bohn, 2011). While most studies presented isolated vowels, we investigated a large stimulus set of German vowels in a more naturalistic setting within minimal pairs. We conducted an mismatch negativity (MMN) study in a passive and a reaction time study in an active oddball paradigm. In both data sets, we found directional asymmetries that can be explained by either phonological or phonetic theories. While behaviorally, the vowel discrimination was based on phonological properties, both tested models failed to explain the found neural patterns comprehensively. Therefore, we additionally examined the influence of a variety of articulatory, acoustical, and lexical factors (e.g., formant structure, intensity, duration, and frequency of occurrence) but also the influence of factors beyond the well-known (perceived loudness of vowels, degree of openness) in depth via multiple regression analyses. The analyses revealed that the perceptual factor of perceived loudness has a greater impact than considered in the literature and should be taken stronger into consideration when analyzing preattentive natural vowel processing.

A generic deviance detection principle for cortical On/Off responses, omission response, and mismatch negativity

Neural responses to sudden changes can be observed in many parts of the sensory pathways at different organizational levels. For example, deviants that violate regularity at various levels of abstraction can be observed as simple On/Off responses of individual neurons or as cumulative responses of neural populations. The cortical deviance-related responses supporting different functionalities (e.g., gap detection, chunking, etc.) seem unlikely to arise from different function-specific neural circuits, given the relatively uniform and self-similar wiring patterns across cortical areas and spatial scales. Additionally, reciprocal wiring patterns (with heterogeneous combinations of excitatory and inhibitory connections) in the cortex naturally speak in favor of a generic deviance detection principle. Based on this concept, we propose a network model consisting of reciprocally coupled neural masses as a blueprint of a universal change detector. Simulation examples reproduce properties of cortical deviance-related responses including the On/Off responses, the omitted-stimulus response (OSR), and the mismatch negativity (MMN). We propose that the emergence of change detectors relies on the involvement of disinhibition. An analysis of network connection settings further suggests a supportive effect of synaptic adaptation and a destructive effect of N-methyl-D-aspartate receptor (NMDA-r) antagonists on change detection. We conclude that the nature of cortical reciprocal wiring gives rise to a whole range of local change detectors supporting the notion of a generic deviance detection principle. Several testable predictions are provided based on the network model. Notably, we predict that the NMDA-r antagonists would generally dampen the cortical Off response, the cortical OSR, and the MMN.

Deviance detection in sound frequency in simple and complex sounds in urethane-anesthetized rats

Mismatch negativity (MMN), which is an electrophysiological response demonstrated in humans and animals, reflects memory-based deviance detection in a series of sounds. However, only a few studies on rodents have used control conditions that were sufficient in eliminating confounding factors that could also explain differential responses to deviant sounds. Furthermore, it is unclear if change detection occurs similarly for sinusoidal and complex sounds. In this study, we investigated frequency change detection in urethane-anesthetized rats by recording local-field potentials from the dura above the auditory cortex. We studied change detection in sinusoidal and complex sounds in a series of experiments, controlling for sound frequency, probability, and pattern in a series of sounds. For sinusoidal sounds, the MMN controlled for frequency, adaptation, and pattern, was elicited at approximately 200 ms onset latency. For complex sounds, the MMN controlled for frequency and adaptation, was elicited at 60 ms onset latency. Sound frequency affected the differential responses. MMN amplitude was larger for the sinusoidal sounds than for the complex sounds. These findings indicate the importance of controlling for sound frequency and stimulus probabilities, which have not been fully controlled for in most previous animal and human studies. Future studies should confirm the preference for sinusoidal sounds over complex sounds in rats.

Compensatory task-specific hypersensitivity in bilateral planum temporale and right superior temporal gyrus during auditory rhythm and omission processing in Parkinson's disease

Persons with Parkinson's disease have general timing deficits and have difficulties in rhythm discrimination tasks. The basal ganglia, a crucial part of Parkinson's disease pathology, is believed to play an important role in rhythm and beat processing, with a possible modulation of basal ganglia activity by level of rhythmic complexity. As dysfunction in basal ganglia impacts function in other brain areas in Parkinson's disease during temporal processing, investigating the neuronal basis for rhythm processing is important as it could shed light on the nature of basal ganglia dysfunction and compensatory mechanisms. We constructed an auditory beat-omission fMRI paradigm with two levels of rhythm complexity, to investigate if and where persons with Parkinson's disease showed abnormal activation during rhythm and omission processing, and whether such activations were modulated by the level of rhythmic complexity. We found no effect of complexity, but found crucial group differences. For the processing of normal rhythm presentations, the Parkinson-group showed higher bilateral planum temporal activity, an area previously associated with the processing of complex patterns. For the omissions, the Parkinson-group showed higher activity in an area in the right superior temporal gyrus previously associated with detection of auditory omissions. We believe this shows a pattern of "hypersensitive" activity, indicative of task-specific, compensatory mechanisms in the processing of temporal auditory information in persons with Parkinson's disease.

Spatial Properties of Mismatch Negativity in Patients with Disorders of Consciousness

In recent decades, event-related potentials have been used for the clinical electrophysiological assessment of patients with disorders of consciousness (DOCs). In this paper, an oddball paradigm with two types of frequency-deviant stimulus (standard stimuli were pure tones of 1000 Hz; small deviant stimuli were pure tones of 1050 Hz; large deviant stimuli were pure tones of 1200 Hz) was applied to elicit mismatch negativity (MMN) in 30 patients with DOCs diagnosed using the JFK Coma Recovery Scale-Revised (CRS-R). The results showed that the peak amplitudes of MMN elicited by both large and small deviant stimuli were significantly different from baseline. In terms of the spatial properties of MMN, a significant interaction effect between conditions (small and large deviant stimuli) and electrode nodes was centered at the frontocentral area. Furthermore, correlation coefficients were calculated between MMN amplitudes and CRS-R scores for each electrode among all participants to generate topographic maps. Meanwhile, a significant negative correlation between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores was also found at the frontocentral area. In consequence, our results combine the above spatial properties of MMN in patients with DOCs, and provide a more precise location (frontocentral area) at which to evaluate the correlation between clinical electrophysiological assessment and the level of consciousness.

Usage of drip drops as stimuli in an auditory P300 BCI paradigm

Recently, many auditory BCIs are using beeps as auditory stimuli, while beeps sound unnatural and unpleasant for some people. It is proved that natural sounds make people feel comfortable, decrease fatigue, and improve the performance of auditory BCI systems. Drip drop is a kind of natural sounds that makes humans feel relaxed and comfortable. In this work, three kinds of drip drops were used as stimuli in an auditory-based BCI system to improve the user-friendness of the system. This study explored whether drip drops could be used as stimuli in the auditory BCI system. The auditory BCI paradigm with drip-drop stimuli, which was called the drip-drop paradigm (DP), was compared with the auditory paradigm with beep stimuli, also known as the beep paradigm (BP), in items of event-related potential amplitudes, online accuracies and scores on the likability and difficulty to demonstrate the advantages of DP. DP obtained significantly higher online accuracy and information transfer rate than the BP (p < 0.05, Wilcoxon signed test; p < 0.05, Wilcoxon signed test). Besides, DP obtained higher scores on the likability with no significant difference on the difficulty (p < 0.05, Wilcoxon signed test). The results showed that the drip drops were reliable acoustic materials as stimuli in an auditory BCI system.

Nicotine enhances an auditory Event-Related Potential component which is inversely related to habituation

Nicotine is a psychoactive substance that is commonly consumed in the context of music. However, the reason why music and nicotine are co-consumed is uncertain. One possibility is that nicotine affects cognitive processes relevant to aspects of music appreciation in a beneficial way. Here we investigated this possibility using Event-Related Potentials. Participants underwent a simple decision-making task (to maintain attentional focus), responses to which were signalled by auditory stimuli. Unlike previous research looking at the effects of nicotine on auditory processing, we used complex tones that varied in pitch, a fundamental element of music. In addition, unlike most other studies, we tested non-smoking subjects to avoid withdrawal-related complications. We found that nicotine (4.0 mg, administered as gum) increased P2 amplitude in the frontal region. Since a decrease in P2 amplitude and latency is related to habituation processes, and an enhanced ability to disengage from irrelevant stimuli, our findings suggest that nicotine may cause a reduction in habituation, resulting in non-smokers being less able to adapt to repeated stimuli. A corollary of that decrease in adaptation may be that nicotine extends the temporal window during which a listener is able and willing to engage with a piece of music.

How regularity representations of short sound patterns that are based on relative or absolute pitch information establish over time: An EEG study

The recognition of sound patterns in speech or music (e.g., a melody that is played in different keys) requires knowledge about pitch relations between successive sounds. We investigated the formation of regularity representations for sound patterns in an event-related potential (ERP) study. A pattern, which consisted of six concatenated 50 ms tone segments differing in fundamental frequency, was presented 1, 2, 3, 6, or 12 times and then replaced by another pattern by randomly changing the pitch of the tonal segments (roving standard paradigm). In an absolute repetition condition, patterns were repeated identically, whereas in a transposed condition, only the pitch relations of the tonal segments of the patterns were repeated, while the entire patterns were shifted up or down in pitch. During ERP measurement participants were not informed about the pattern repetition rule, but were instructed to discriminate rarely occurring targets of lower or higher sound intensity. EPRs for pattern changes (mismatch negativity, MMN; and P3a) and for pattern repetitions (repetition positivity, RP) revealed that the auditory system is able to rapidly extract regularities from unfamiliar complex sound patterns even when absolute pitch varies. Yet, enhanced RP and P3a amplitudes, and improved behavioral performance measured in a post-hoc test, in the absolute as compared with the transposed condition suggest that it is more difficult to encode patterns without absolute pitch information. This is explained by dissociable processing of standards and deviants as well as a back propagation mechanism to early sensory processing stages, which is effective after less repetitions of a standard stimulus for absolute pitch.

Early auditory processing in musicians and dancers during a contemporary dance piece

The neural responses to simple tones and short sound sequences have been studied extensively. However, in reality the sounds surrounding us are spectrally and temporally complex, dynamic and overlapping. Thus, research using natural sounds is crucial in understanding the operation of the brain in its natural environment. Music is an excellent example of natural stimulation which, in addition to sensory responses, elicits vast cognitive and emotional processes in the brain. Here we show that the preattentive P50 response evoked by rapid increases in timbral brightness during continuous music is enhanced in dancers when compared to musicians and laymen. In dance, fast changes in brightness are often emphasized with a significant change in movement. In addition, the auditory N100 and P200 responses are suppressed and sped up in dancers, musicians and laymen when music is accompanied with a dance choreography. These results were obtained with a novel event-related potential (ERP) method for natural music. They suggest that we can begin studying the brain with long pieces of natural music using the ERP method of electroencephalography (EEG) as has already been done with functional magnetic resonance (fMRI), these two brain imaging methods complementing each other.

Music in Research and Rehabilitation of Disorders of Consciousness: Psychological and Neurophysiological Foundations

According to a prevailing view, the visual system works by dissecting stimuli into primitives, whereas the auditory system processes simple and complex stimuli with their corresponding features in parallel. This makes musical stimulation particularly suitable for patients with disorders of consciousness (DoC), because the processing pathways related to complex stimulus features can be preserved even when those related to simple features are no longer available. An additional factor speaking in favor of musical stimulation in DoC is the low efficiency of visual stimulation due to prevalent maladies of vision or gaze fixation in DoC patients. Hearing disorders, in contrast, are much less frequent in DoC, which allows us to use auditory stimulation at various levels of complexity. The current paper overviews empirical data concerning the four main domains of brain functioning in DoC patients that musical stimulation can address: perception (e.g., pitch, timbre, and harmony), cognition (e.g., musical syntax and meaning), emotions, and motor functions. Music can approach basic levels of patients' self-consciousness, which may even exist when all higher-level cognitions are lost, whereas music induced emotions and rhythmic stimulation can affect the dopaminergic reward-system and activity in the motor system respectively, thus serving as a starting point for rehabilitation.

Event-related brain responses while listening to entire pieces of music

Brain responses to discrete short sounds have been studied intensively using the event-related potential (ERP) method, in which the electroencephalogram (EEG) signal is divided into epochs time-locked to stimuli of interest. Here we introduce and apply a novel technique which enables one to isolate ERPs in human elicited by continuous music. The ERPs were recorded during listening to a Tango Nuevo piece, a deep techno track and an acoustic lullaby. Acoustic features related to timbre, harmony, and dynamics of the audio signal were computationally extracted from the musical pieces. Negative deflation occurring around 100 milliseconds after the stimulus onset (N100) and positive deflation occurring around 200 milliseconds after the stimulus onset (P200) ERP responses to peak changes in the acoustic features were distinguishable and were often largest for Tango Nuevo. In addition to large changes in these musical features, long phases of low values that precede a rapid increase - and that we will call Preceding Low-Feature Phases - followed by a rapid increase enhanced the amplitudes of N100 and P200 responses. These ERP responses resembled those to simpler sounds, making it possible to utilize the tradition of ERP research with naturalistic paradigms.

Auditory mismatch impairments are characterized by core neural dysfunctions in schizophrenia

Major theories on the neural basis of schizophrenic core symptoms highlight aberrant salience network activity (insula and anterior cingulate cortex), prefrontal hypoactivation, sensory processing deficits as well as an impaired connectivity between temporal and prefrontal cortices. The mismatch negativity is a potential biomarker of schizophrenia and its reduction might be a consequence of each of these mechanisms. In contrast to the previous electroencephalographic studies, functional magnetic resonance imaging may disentangle the involved brain networks at high spatial resolution and determine contributions from localized brain responses and functional connectivity to the schizophrenic impairments. Twenty-four patients and 24 matched control subjects underwent functional magnetic resonance imaging during an optimized auditory mismatch task. Haemodynamic responses and functional connectivity were compared between groups. These data sets further entered a diagnostic classification analysis to assess impairments on the individual patient level. In the control group, mismatch responses were detected in the auditory cortex, prefrontal cortex and the salience network (insula and anterior cingulate cortex). Furthermore, mismatch processing was associated with a deactivation of the visual system and the dorsal attention network indicating a shift of resources from the visual to the auditory domain. The patients exhibited reduced activation in all of the respective systems (right auditory cortex, prefrontal cortex, and the salience network) as well as reduced deactivation of the visual system and the dorsal attention network. Group differences were most prominent in the anterior cingulate cortex and adjacent prefrontal areas. The latter regions also exhibited a reduced functional connectivity with the auditory cortex in the patients. In the classification analysis, haemodynamic responses yielded a maximal accuracy of 83% based on four features; functional connectivity data performed similarly or worse for up to about 10 features. However, connectivity data yielded a better performance when including more than 10 features yielding up to 90% accuracy. Among others, the most discriminating features represented functional connections between the auditory cortex and the anterior cingulate cortex as well as adjacent prefrontal areas. Auditory mismatch impairments incorporate major neural dysfunctions in schizophrenia. Our data suggest synergistic effects of sensory processing deficits, aberrant salience attribution, prefrontal hypoactivation as well as a disrupted connectivity between temporal and prefrontal cortices. These deficits are associated with subsequent disturbances in modality-specific resource allocation. Capturing different schizophrenic core dysfunctions, functional magnetic resonance imaging during this optimized mismatch paradigm reveals processing impairments on the individual patient level, rendering it a potential biomarker of schizophrenia.

Questioning the dichotomy between vegetative state and minimally conscious state: a review of the statistical evidence

Given the enormous consequences that the diagnosis of vegetative state (VS) vs. minimally conscious state (MCS) may have for the treatment of patients with disorders of consciousness, it is particularly important to empirically legitimate the distinction between these two discrete levels of consciousness. Therefore, the aim of this contribution is to review all the articles reporting statistical evidence concerning the performance of patients in VS vs. patients in MCS, on behavioral or neurophysiological measures. Twenty-three articles matched these inclusion criteria, and comprised behavioral, electroencephalographic (EEG), positron emission tomography (PET) and magnetic resonance imaging (MRI) measures. The analysis of these articles yielded 47 different statistical findings. More than half of these findings (n = 24) did not reveal any statistically significant difference between VS and MCS. Overall, there was no combination of variables that allowed reliably discriminating between VS and MCS. This pattern of results casts doubt on the empirical validity of the distinction between VS and MCS.

Musicianship facilitates the processing of Western music chords--an ERP and behavioral study

The present study addressed the effects of musicianship on neural and behavioral discrimination of Western music chords. In abstract oddball paradigms, minor chords and inverted major chords were presented in the context of major chords to musician and non-musician participants in a passive listening task (with EEG recordings) and in an active discrimination task. Both sinusoidal sounds and harmonically rich piano sounds were used. Musicians outperformed non-musicians in the discrimination task. Change-related mismatch negativity (MMN) was evoked to minor and inverted major chords in musicians only, and N1 amplitude was larger in musicians than non-musicians. While MMN was absent in non-musicians, both groups showed decreased N1 in response to minor compared to major chords. The results indicate that processing of complex musical stimuli is enhanced in musicians both behaviorally and neurally, but that major-minor chord categorization is present to some extent also in the absence of music training.

Fast measurement of auditory event-related potential profiles in 2-3-year-olds

Auditory discrimination, memory, and attention-related functions were investigated in healthy 2-3-year-olds by recording event-related potentials (ERPs) to changes in five auditory features and two types of novel sounds using the fast multifeature paradigm (MFP). ERP profiles consisting of the mismatch negativity (MMN), P3a, and prominent late discriminative negativities (LDN) were obtained, for the first time, from this age group in a considerably shorter time compared to the traditional paradigms. Statistically significant responses from individual children were obtained mainly for the novel sounds. Thus, the MFP shows promise as a time-efficient paradigm for investigating central auditory functions in toddlers.

Effects of voice harmonic complexity on ERP responses to pitch-shifted auditory feedback

OBJECTIVE

The present study investigated the neural mechanisms of voice pitch control for different levels of harmonic complexity in the auditory feedback.

METHODS

Event-related potentials (ERPs) were recorded in response to+200 cents pitch perturbations in the auditory feedback of self-produced natural human vocalizations, complex and pure tone stimuli during active vocalization and passive listening conditions.

RESULTS

During active vocal production, ERP amplitudes were largest in response to pitch shifts in the natural voice, moderately large for non-voice complex stimuli and smallest for the pure tones. However, during passive listening, neural responses were equally large for pitch shifts in voice and non-voice complex stimuli but still larger than that for pure tones.

CONCLUSIONS

These findings suggest that pitch change detection is facilitated for spectrally rich sounds such as natural human voice and non-voice complex stimuli compared with pure tones. Vocalization-induced increase in neural responses for voice feedback suggests that sensory processing of naturally-produced complex sounds such as human voice is enhanced by means of motor-driven mechanisms (e.g. efference copies) during vocal production.

SIGNIFICANCE

This enhancement may enable the audio-vocal system to more effectively detect and correct for vocal errors in the feedback of natural human vocalizations to maintain an intended vocal output for speaking.

Preserved oscillatory response but lack of mismatch negativity in patients with disorders of consciousness

OBJECTIVE

The diagnostic validity of non-phase-locked oscillations (NPLOs) and mismatch negativity (MMN) in an oddball task for assessing attentional reactivity in patients with disordered consciousness was examined.

METHODS

Patients in a minimally conscious (MCS, n = 6) or vegetative (VS, n = 16) state and healthy controls (n = 15) were assessed. MMN and NPLOs were analyzed with single-subject, non-parametric statistics.

RESULTS

In 11 healthy controls and 2 VS patients, MMN was detected. More subjects showed NPLO differences in the alpha than in the theta or beta frequency ranges. In 14 healthy controls, 4 MCS patients, and 5 VS patients, lower amplitudes after deviants were found in the alpha frequency range. One healthy subject and one VS patient showed higher amplitudes after deviants.

CONCLUSIONS

Neither ERPs nor NPLOs could reliably distinguish MCS from VS patients. However, NPLOs were more sensitive than ERPs for detecting significantly different activity, and they possibly identified preserved processing better than ERPs.

SIGNIFICANCE

Intact neurophysiological attentional responses observed in the NPLOs of VS patients may indicate a need for other diagnostic techniques. Inter-individual differences in the direction of the effect should be considered as normal variance.

MMN evidence for asymmetry in detection of IOI shortening and lengthening at behavioral indifference tempo

Most behavioral investigations indicated an indifference interval of 500-700 ms, at which the detection of inter-onset interval (IOI) shortening and lengthening are equally difficult and no perceptual bias would be expected. However, some event-related potential (ERPs) studies showed that even at this behavioral indifference time, the detection of shortening and lengthening might rely on different aspects of information processing. This work was aimed to investigate whether the pre-attentive processing of local tempo perturbations, i.e., IOI shortening and lengthening, are different when the basic tempo is at the behavioral indifference area. Tempo perturbations were introduced by shortening or lengthening the third IOI by 10% of the base IOI of the 5-beat isochronous sequence. ERPs recorded in a passive experiment showed that both tempo perturbations elicited a distinct frontal mismatch negativity (MMN). The low resolution electromagnetic tomography (LORETA) source estimation indicated a left prefrontal predominance activity around the MMN peak, implicating an important role of the frontal lobe in the processing of local tempo perturbations. Statistical analysis revealed that the MMN to IOI shortening had an earlier and greater peak than that to IOI lengthening, implying that IOI shortening might be more easily to be detected than IOI lengthening even at indifference tempo. Our results suggested that local IOI perturbations at behavioral indifference area have an asymmetric effect on the pre-attentive processing of temporal variation detection.

Effect of inverting electrode on mismatch negativity presence for perceptible/imperceptible tonal frequency contrasts

The effect of inverting electrode location and stimulus perceptibility on the presence of the mismatch negativity (MMN) evoked response was investigated in 20 normal-hearing adult females. Perceptible and imperceptible frequency contrasts were employed in an oddball paradigm. The perceptible contrast consisted of an 1122 Hz standard and a 1000 Hz target, while the imperceptible contrast consisted of an 1122 Hz standard and an 1120 Hz target. Data were referenced separately to the tip of the nose, the ipsilateral mastoid, and the mathematical average of the two mastoids. Presence of a response was determined according to strict criteria established a priori. The correspondence between MMN findings and parallel behavioral discrimination data was not systematic. Inverting electrode had an effect of MMN presence. MMNs were more likely to be present for mastoid-referenced data than nose-referenced data. Thus, when using the current paradigm, a mastoid reference is suggested to optimize the detection of the MMN response.

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

OBJECTIVE

Verify and explore unexpected results suggesting an effect of deviance direction (shorter or longer deviants) on the amplitude of MMNs evoked by sound duration contrasts.

METHODS

MMNs were recorded using the oddball paradigm on ten adults. Four standard stimulus durations (100, 150, 200 and 250ms) were used and deviants were 50% shorter or longer. Behavioral data (hit rates, d', and reaction times) were collected after the electrophysiological sessions.

RESULTS

MMNs 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.

CONCLUSIONS

We 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.

SIGNIFICANCE

A 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.

Brain hyper-reactivity to auditory novel targets in children with high-functioning autism

Although communication and social difficulties in autism have received a great deal of research attention, the other key diagnostic feature, extreme repetitive behaviour and unusual narrow interests, has been addressed less often. Also known as 'resistance to change' this may be related to atypical processing of infrequent, novel stimuli. This can be tested at sensory and neural levels. Our aims were to (i) examine auditory novelty detection and its neural basis in children with autism spectrum conditions (ASC) and (ii) test for brain activation patterns that correlate quantitatively with number of autistic traits as a test of the dimensional nature of ASC. The present study employed event-related fMRI during a novel auditory detection paradigm. Participants were twelve 10- to 15-year-old children with ASC and a group of 12 age-, IQ- and sex-matched typical controls. The ASC group responded faster to novel target stimuli. Group differences in brain activity mainly involved the right prefrontal-premotor and the left inferior parietal regions, which were more activated in the ASC group than in controls. In both groups, activation of prefrontal regions during target detection was positively correlated with Autism Spectrum Quotient scores measuring the number of autistic traits. These findings suggest that target detection in autism is associated not only with superior behavioural performance (shorter reaction time) but also with activation of a more widespread network of brain regions. This pattern also shows quantitative variation with number of autistic traits, in a continuum that extends to the normal population. This finding may shed light on the neurophysiological process underlying narrow interests and what clinically is called 'need for sameness'.

The effects of learning on event-related potential correlates of musical expectancy

Musical processing studies have shown that unexpected endings in familiar musical sequences produce extended latencies of the P300 component. The present study sought to identify event-related potential (ERP) correlates of musical expectancy by entraining participants with rule-governed chord sequences and testing whether unexpected endings created similar responses. Two experiments were conducted in which participants performed grammaticality classifications without training (Experiment 1) and with training (Experiment 2). In both experiments, deviant chords differing in instrumental timbre elicited a MMN/P3a waveform complex. Violations related to learned patterns elicited an early right anterior negativity and P3b. Latency and amplitude of peak components were modulated by the physical characteristics of the chords, expectations due to prior knowledge of musical harmony, and contextually defined expectations developed through entrainment.

The mismatch negativity (MMN) in basic research of central auditory processing: a review

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Representation of harmonic frequencies in auditory memory: A mismatch negativity study

Most natural sounds are composed of a mixture of frequencies, which activate separate neurons in the tonotopic auditory cortex. Nevertheless, we perceive this mixture as an integrated sound with unique acoustic properties. We used the Mismatch Negativity (MMN), a marker of auditory change detection, to determine whether individual harmonics are represented in sensory memory. The MMN elicited by duration and pitch deviations were compared for harmonic and pure tones. Controlled for acoustic differences between standards and deviants and their relative probabilities, the MMN was larger for harmonic than pure tones for duration but not for pitch deviance. Because the magnitude of the MMN reflects the number of concurrent changes in the acoustic input relative to a preexistent acoustic representation, these results suggest that duration is represented and compared separately for individual frequencies, whereas pitch comparison occurs after integration.

Optical imaging of temporal integration in human auditory cortex

Behavioral and physiological studies have indicated the existence of a temporal window of auditory integration (TWI), within which similar sounds are perceptually grouped. The current study exploits the combined temporal and spatial resolution of fast optical imaging (the event-related optical signal, EROS) to show that brain activity elicited by sounds within and outside the TWI differs in location and latency. In a previous event-related brain potential (ERP) study [Sable, Gratton, and Fabiani (2003) European Journal of Neuroscience, 17, 2492-2496], we found that the mismatch negativity (MMN; a brain response to acoustic irregularities) elicited by deviations in stimulus onset asynchronies (SOAs) had a unique shape when the deviant SOA was within the TWI. In the present study, we extended these ERP results using EROS. Participants heard trains of five tones. The first four tones had SOAs of 96, 192, 288 or 384 ms. The SOA of the fourth and fifth tones was either the same (standard) or one of the other three (deviant) SOAs. With a deviant SOA of 96 ms, the cortical response was approximately 2 cm anterior to responses to longer SOA deviants, and was followed by a later response that was absent in the other conditions. Similarly to the electrical MMN, the optical mismatch response amplitudes were proportional to the magnitude of interval deviance. These results, in combination with our previous findings, indicate that the temporal integration of sounds is reflected in cortical mismatch responses that differ from the typical response to interval deviance.

Frequency specific impairment of automatic pitch change detection by fMRI acoustic noise: an MEG study

The loud acoustic noise produced by the magnetic resonance scanner is a major source of interference in auditory fMRI research. Whole-head magnetoencephalography (MEG) was used to investigate the interaction between the frequency range of auditory stimulation and fMRI acoustic noise. Pure tones and 3-harmonic complexes varying between 240 and 1240 Hz in frequency were presented while participants attended to a silent subtitled film. Continuous fMRI acoustic noise was presented during half of the blocks. The activity in six regions of interest was analyzed in 100-200 and 200-300 ms time windows to evaluate the magnetic counterparts of the mismatch negativity (MMN) and P3a brain responses. The results suggested that fMRI noise significantly reduced the amplitude of these responses. The effect of the noise on the automatic processing of the tones was more prominent for the tones with frequencies higher than 500 Hz. It is recommended that in the MMN protocols using continuous fMRI acquisition the sound stimuli should be spectrally separated from the fMRI scanner noise spectrum.

Change detection in children with autism: An auditory event-related fMRI study

Autism involves impairments in communication and social interaction, as well as high levels of repetitive, stereotypic, and ritualistic behaviours, and extreme resistance to change. This latter dimension, whilst required for a diagnosis, has received less research attention. We hypothesise that this extreme resistance to change in autism is rooted in atypical processing of unexpected stimuli. We tested this using auditory event-related fMRI to determine regional brain activity associated with passive detection of infrequently occurring frequency-deviant and complex novel sounds in a no-task condition. Participants were twelve 10- to 15-year-old children with autism and a group of 12 age- and sex-matched healthy controls. During deviance detection, significant activation common to both groups was located in the superior temporal and inferior frontal gyri. During 'novelty detection', both groups showed activity in the superior temporal gyrus, the temporo-parietal junction, the superior and inferior frontal gyri, and the cingulate gyrus. Children with autism showed reduced activation of the left anterior cingulate cortex during both deviance and novelty detection. During novelty detection, children with autism also showed reduced activation in the bilateral temporo-parietal region and in the right inferior and middle frontal areas. This study confirms previous evidence from ERP studies of atypical brain function related to automatic change detection in autism. Abnormalities involved a cortical network known to have a role in attention switching and attentional resource distribution. These results throw light on the neurophysiological processes underlying autistic 'resistance to change'.

Information processing in severe disorders of consciousness: Vegetative state and minimally conscious state

OBJECTIVE

To study the presence of electrophysiological indicators of remaining cortical functions in patients with persistent vegetative state (PVS) and minimally conscious state (MCS). Previous electrophysiological and PET data indicated that some PVS patients have partially intact cortical processing functions. However, it remains unclear whether the reported patients were representative for PVS population or just some exceptional cases.

METHODS

Event-related brain responses to stimuli of different complexity levels, recorded in 98 patients with extremely severe diffuse brain injuries, 50 of which in PVS. Four main indicators of cortical functions were: (i) N1-P2 complex as an index of simple, undifferentiated cortical processing; (ii) mismatch negativity as an index of pre-attentive, probably unconscious, cortical orientation; (iii) P3 wave as an index of deep cortical analysis of physical stimuli, and (iv) brain responses to semantic stimuli.

RESULTS

Cortical responses were found in all PVS patients with a background EEG activity > 4 Hz. All responses investigated, including those to semantic stimuli that indicated comprehension of meaning, occurred significantly above chance, though less frequently than in patients with severe brain injuries who were conscious.

CONCLUSIONS

Cortical responses were lacking in most patients with severe EEG slowing (< 4 Hz). Follow-up data revealed that the presence of a mismatch negativity, a short disease duration, and the traumatic etiology were related to a better outcome.

SIGNIFICANCE

The data show that in a subpopulation of PVS patients with preserved thalamocortical feedback connections, remaining cortical information processing is a consistent finding and may even involve semantic levels of processing.

Test–retest stability of the magnetic mismatch response (MMNm)

OBJECTIVE

We investigated the replicability of the magnetically measured mismatch negativity (MMNm).

METHODS

The MMNm was recorded twice by using a 122-channel whole-head magnetometer in 15 healthy young adults. The MMNm responses for duration, intensity and frequency deviants were analyzed separately in left and right hemispheres for the response strength, latency, dipole moment, and generator loci.

RESULTS

In the right hemisphere, the test-retest correlations were statistically significant for all MMNm parameters (r = 0.49-0.89). In the left hemisphere, the majority of the MMNm parameters also demonstrated statistically significant test-retest correlations (r = 0.61-0.82). In addition, the MMNm generator loci were stable for all deviants.

CONCLUSIONS AND SIGNIFICANCE

The present results are encouraging in terms of both research and clinical use of MMNm in studying human auditory discrimination in its normal and deteriorated states.

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.

Event-related potential measures of consciousness: two equations with three unknowns

This is a brief review of event-related brain potentials (ERPs) as indices of cortical information processing in conditions in which conscious perception of stimuli is supposed to be absent: sleep, coma, vegetative state, general anesthesia, neglect as well as presentation of subliminal or masked stimuli. Exogenous ERP components such as N1 and P2 are much more likely to remain in all these conditions than endogenous components. Further, all varieties of the late posterior positive ERP waves (e.g., P3b, P600, late positive complex) are most difficult to be elicited in such conditions, indicating that the cortical activity underlying the late posterior positivity may have a particularly close relationship to brain mechanisms of conscious perception. Contrary to what might be expected, reliable ERP effects indicating complex analysis of semantic stimulus features (i.e., meaning) can be recorded without conscious awareness, generally, as easy as (in some conditions, even easier than) ERP components related to rather simple physical stimulus features. It should be emphasized, however, that we never should overestimate our confidence about the degree of subjects' unawareness. Particularly in the conditions in which no behavioral response can be obtained (e.g., sleep, coma, anesthesia), residual conscious processing, at least in some subjects and on some trials, cannot be ruled out.

Pitch discrimination accuracy in musicians vs nonmusicians: an event-related potential and behavioral study

Previously, professional violin players were found to automatically discriminate tiny pitch changes, not discriminable by nonmusicians. The present study addressed the pitch processing accuracy in musicians with expertise in playing a wide selection of instruments (e.g., piano; wind and string instruments). Of specific interest was whether also musicians with such divergent backgrounds have facilitated accuracy in automatic and/or attentive levels of auditory processing. Thirteen professional musicians and 13 nonmusicians were presented with frequent standard sounds and rare deviant sounds (0.8, 2, or 4% higher in frequency). Auditory event-related potentials evoked by these sounds were recorded while first the subjects read a self-chosen book and second they indicated behaviorally the detection of sounds with deviant frequency. Musicians detected the pitch changes faster and more accurately than nonmusicians. The N2b and P3 responses recorded during attentive listening had larger amplitude in musicians than in nonmusicians. Interestingly, the superiority in pitch discrimination accuracy in musicians over nonmusicians was observed not only with the 0.8% but also with the 2% frequency changes. Moreover, also nonmusicians detected quite reliably the smallest pitch changes of 0.8%. However, the mismatch negativity (MMN) and P3a recorded during a reading condition did not differentiate musicians and nonmusicians. These results suggest that musical expertise may exert its effects merely at attentive levels of processing and not necessarily already at the preattentive levels.

Assessment of cognitive functions in severely paralysed and severely brain-damaged patients: neuropsychological and electrophysiological methods

A systematic neuropsychological assessment technique is described for use with severely physically disabled individuals, possibly with combined motor and cognitive disorders. Target neurological conditions may be, e.g., an incomplete locked-in state, a minimally conscious state, or severe combinations of paralysis, agnosia, and apraxia. Neuropsychological assessment in these patients is difficult, because standard neuropsychological tests require fast motor responses, which can be manual, verbal, or both. To assess the cognitive status of patients with residual motor function, tests have been applied that can be answered by a binary (yes/no) signal and whose outcomes were not based on reaction times. Further, a battery of neurophysiological examination procedures based on event-related brain potentials has been developed. These procedures can be performed directly at a patient's bedside (at home or in a hospital) and applied for assessment of cognitive functions even in patients without residual motor function.

Frequency discrimination at different frequency levels as indexed by electrophysiological and behavioral measures

The present study systematically compared the neural and behavioral accuracy of discriminating a frequency change ("deviant") in a repetitive tone ("standard") across a frequency range of 250-4000 Hz. The sound structure (pure sinusoidal vs. harmonically rich tones) and the magnitude of frequency change (2.5%, 5%, 10%, 20%) were also varied. The accuracy of neural frequency-change detector was determined by comparing the auditory event-related potentials (ERP) elicited by deviant and standard stimuli in the absence of attention. In a separate behavioral task, subjects were to indicate when they noticed a frequency change. The ranges of the across-subject means of ERP parameters across the conditions were: the mismatch negativity (MMN) amplitude -0.9 to -4.9 microV, latency 125-218 ms, the P3a amplitude 0.3-3.2 microV, latency 239-304 ms. The ERP latency was shortest for the standard-stimulus frequency from 1000 to 2000 Hz suggesting that automatic frequency discrimination was the most accurate in that range. The ERP latencies and amplitudes correlated with the hit rate (HR) and reaction time (RT), with highest correlation found between the MMN amplitude and the HR (r=0.8). The harmonical tones elicited MMN and P3a with shorter latencies and larger amplitudes, than did pure sinusoidal tones in all frequency bands. The results may have implication to pitch-perception theories.

Stimulus complexity enhances auditory discrimination in patients with extremely severe brain injuries

There is controversy as to what extent the processing of spectrally rich sounds in the human auditory cortex is related to the processing of singular frequencies. An informative index of the function of the auditory cortex, particularly important in neurological patients, is the mismatch negativity (MMN), a component of auditory event-related potentials. In the present study the MMN was recorded in 79 patients with extremely severe diffuse brain injuries, most of them in persistent vegetative state or minimal consciousness state. Both sinusoidal ('pure') and complex musical tones were used. Different statistical approaches converged in that musical tones elicited an MMN significantly more frequently, and of a larger amplitude, than simple sine tones. This implies that using simple stimuli in clinical populations may lead to a severe underestimation of the functional state of a patient's auditory system. The findings are also in line with behavioral and physiological data indicating independent processing of complex sounds in the auditory cortex.

Prefrontal cortex involvement in preattentive auditory deviance detection: neuroimaging and electrophysiological evidence

Previous electrophysiological and neuroimaging studies suggest that the mismatch negativity (MMN) is generated by a temporofrontal network subserving preattentive auditory change detection. In two experiments we employed event-related brain potentials (ERP) and event-related functional magnetic resonance imaging (fMRI) to examine neural and hemodynamic activity related to deviance processing, using three types of deviant tones (small, medium, and large) in both a pitch and a space condition. In the pitch condition, hemodynamic activity in the right superior temporal gyrus (STG) increased as a function of deviance. Comparisons between small and medium and between small and large deviants revealed right prefrontal activation in the inferior frontal gyrus (IFG; BA 44/45) and middle frontal gyrus (MFG; BA 46), whereas large relative to medium deviants led to left and right IFG (BA 44/45) activation. In the ERP experiment the amplitude of the early MMN (90-120 ms) increased as a function of deviance, by this paralleling the right STG activation in the fMRI experiment. A U-shaped relationship between MMN amplitude and the degree of deviance was observed in a late time window (140-170 ms) resembling the right IFG activation pattern. In a subsequent source analysis constrained by fMRI activation foci, early and late MMN activity could be modeled by dipoles placed in the STG and IFG, respectively. In the spatial condition no reliable hemodynamic activation could be observed. The MMN amplitude was substantially smaller than in the pitch condition for all three spatial deviants in the ERP experiment. In contrast to the pitch condition it increased as a function of deviance in the early and in the late time window. We argue that the right IFG mediates auditory deviance detection in case of low discriminability between a sensory memory trace and auditory input. This prefrontal mechanism might be part of top-down modulation of the deviance detection system in the STG.

The Promises of Change-Related Brain Potentials in Cognitive Neuroscience of Music

Even when simultaneously performing a task unrelated to sounds, the human auditory cortex can precisely model the invariances of the acoustic environment. Data acquired in a mismatch negativity (MMN) paradigm have shown that temporally and spectrally complex sounds as well as their relations are automatically represented in the human auditory cortex. Furthermore, MMN data indicate that these neural sound representations are spatially distinct from phonetic and musical sounds within and between the cerebral hemispheres. Most MMN studies were conducted in pitch dimension, but temporal aspects of sound processing are also under increasing experimentation. To some extent, musical expertise is also reflected in sound representation accuracy as indexed by the MMN paradigm.

Phonetic perception and the temporal cortex

Recent functional neuroimaging studies have emphasized the role of the different areas within the left superior temporal sulcus (STS) for the perception of various speech stimuli. We report here the results of three independent studies additionally demonstrating hemodynamic responses in the vicinity of the planum temporale (PT). In these studies we used consonant-vowel (CV) syllables, tones, white noise, and vowels as acoustic stimuli in the context of whole-head functional magnetic resonance imaging, applying a long TR to attenuate possible masking effects by the scanner noise. To summarize, we obtained the following results for the contrasts comparing hemodynamic responses obtained during the perception of CV syllables compared to tones or white noise: (i) stronger activation in the vicinity of the left PT with two distinct foci of activation, one in a lateral position and the other more medial in the vicinity of Heschl's sulcus; (ii) stronger activation in the vicinity of the right PT; and (iii) stronger bilateral activation within the mid-STS. Further contrasts revealed the following findings: (iv) stronger bilateral activation to CV syllables than to vowels in the medial PT, (v) stronger left-sided activation to CV syllables than to vowels in the mid-STS, and (vi) stronger activation to CV syllables with voiceless initial consonants than to CV syllables with voiced initial consonants in the left medial PT. The results are compatible with the hypothesis that the STS contains neurons specialized for speech perception. However, these results also emphasize the role of the PT in the analysis of phonetic features, namely the voice-onset-time. Yet this does not mean that the PT is solely specialized for phonetic analysis. We hypothesize rather that the PT contains neurons specialized for the analysis of rapidly changing cues as was suggested by P. Tallal et al. (1993, Ann. N. Y. Acad. Sci. 682: 27-47).