Aphasia and a Dual-Stream Language Model in a 4-Year-Old Female with Landau-Kleffner Syndrome.

Landau-Kleffner syndrome (LKS) is a rare neurological disorder characterized by acquired aphasia. LKS presents with distinctive electroencephalography (EEG) findings, including diffuse continuous spike and wave complexes (CSW), particularly during sleep. There has been little research on the mechanisms of aphasia and its origin within the brain and how it recovers. We diagnosed LKS in a 4-year-old female with an epileptogenic zone located primarily in the right superior temporal gyrus or STG (nondominant side). In the course of her illness, she had early signs of motor aphasia recovery but was slow to regain language comprehension and recover from hearing loss. We suggest that the findings from our patient's brain imaging and the disparity between her recovery from expressive and receptive aphasias are consistent with the dual-stream model of speech processing in which the nondominant hemisphere also plays a significant role in language comprehension. Unlike aphasia in adults, the right-hemisphere disorder has been reported to cause delays in language comprehension and gestures in early childhood. In the period of language acquisition, it requires a process of understanding what the words mean by integrating and understanding the visual, auditory, and contextual information. It is thought that the right hemisphere works predominantly with respect to its integrating role.

Pitch-class distribution modulates the statistical learning of atonal chord sequences.

The present study investigated whether neural responses could demonstrate the statistical learning of chord sequences and how the perception underlying a pitch class can affect the statistical learning of chord sequences. Neuromagnetic responses to two chord sequences of augmented triads that were presented every 0.5s were recorded from fourteen right-handed participants. One sequence was a series of 360 chord triplets, each of which consisted of three chords in the same pitch class (clustered pitch-classes sequences). The other sequence was a series of 360 chord triplets, each of which consisted of three chords in different pitch classes (dispersed pitch-classes sequences). The order of the triplets was constrained by a first-order Markov stochastic model such that a forthcoming triplet was statistically defined by the most recent triplet (80% for one; 20% for the other two). We performed a repeated-measures ANOVA with the peak amplitude and latency of the P1m, N1m and P2m. In the clustered pitch-classes sequences, the P1m responses to the triplets that appeared with higher transitional probability were significantly reduced compared with those with lower transitional probability, whereas no significant result was detected in the dispersed pitch-classes sequences. Neuromagnetic significance was concordant with the results of familiarity interviews conducted after each learning session. The P1m response is a useful index for the statistical learning of chord sequences. Domain-specific perception based on the pitch class may facilitate the domain-general statistical learning of chord sequences.

Magnetoencephalographic recording of auditory mismatch negativity in response to duration and frequency deviants in a single session in patients with schizophrenia.

AIM: Auditory mismatch negativity (MMN) and its magnetoencephalographic (MEG) counterpart (MMNm) are an established biological index in schizophrenia research. MMN in response to duration and frequency deviants may have differential relevance to the pathophysiology and clinical stages of schizophrenia. MEG has advantage in that it almost purely detects MMNm arising from the auditory cortex. However, few previous MEG studies on schizophrenia have simultaneously assessed MMNm in response to duration and frequency deviants or examined the effect of chronicity on the group difference. METHODS: Forty-two patients with chronic schizophrenia and 74 matched control subjects participated in the study. Using a whole-head MEG, MMNm in response to duration and frequency deviants of tones was recorded while participants passively listened to an auditory sequence. RESULTS: Compared to healthy subjects, patients with schizophrenia exhibited significantly reduced powers of MMNm in response to duration deviant in both hemispheres, whereas MMNm in response to frequency deviant did not differ between the two groups. These results did not change according to the chronicity of the illness. CONCLUSION: These results, obtained by using a sequence-enabling simultaneous assessment of both types of MMNm, suggest that MEG recording of MMN in response to duration deviant may be a more sensitive biological marker of schizophrenia than MMN in response to frequency deviant. Our findings represent an important first step towards establishment of MMN as a biomarker for schizophrenia in real-world clinical psychiatry settings.

Statistical learning of music- and language-like sequences and tolerance for spectral shifts.

In our previous study (Daikoku, Yatomi, & Yumoto, 2014), we demonstrated that the N1m response could be a marker for the statistical learning process of pitch sequence, in which each tone was ordered by a Markov stochastic model. The aim of the present study was to investigate how the statistical learning of music- and language-like auditory sequences is reflected in the N1m responses based on the assumption that both language and music share domain generality. By using vowel sounds generated by a formant synthesizer, we devised music- and language-like auditory sequences in which higher-ordered transitional rules were embedded according to a Markov stochastic model by controlling fundamental (F0) and/or formant frequencies (F1-F2). In each sequence, F0 and/or F1-F2 were spectrally shifted in the last one-third of the tone sequence. Neuromagnetic responses to the tone sequences were recorded from 14 right-handed normal volunteers. In the music- and language-like sequences with pitch change, the N1m responses to the tones that appeared with higher transitional probability were significantly decreased compared with the responses to the tones that appeared with lower transitional probability within the first two-thirds of each sequence. Moreover, the amplitude difference was even retained within the last one-third of the sequence after the spectral shifts. However, in the language-like sequence without pitch change, no significant difference could be detected. The pitch change may facilitate the statistical learning in language and music. Statistically acquired knowledge may be appropriated to process altered auditory sequences with spectral shifts. The relative processing of spectral sequences may be a domain-general auditory mechanism that is innate to humans.

Origin coordinate influence on performance of temporally extended signal space separation in magnetoencephalography.

OBJECTIVE: Temporally extended signal space separation (tSSS) is a powerful method for artifact suppression in magnetoencephalography (MEG). Because tSSS first separates MEG signals coming from inside and outside a certain sphere, definition of the sphere origin is important. For this study, we explored the influence of origin choice on tSSS performance in spontaneous and evoked activity from epilepsy patients. METHODS: Interictal epileptiform discharges (IEDs) and somatosensory evoked fields (SEFs) were processed with two tSSSs: one with the default origin of (0, 0, 40 mm) in the head coordinate, and the other with an individual origin estimated using each patient's anatomical magnetic resonance imaging (MRI). Equivalent current dipoles (ECDs) were calculated for the data. The ECD location and quality of estimation were compared across conditions. RESULTS: MEG data from 21 patients revealed marginal differences in ECD location, but the estimation quality inferred from goodness of fit (GOF) and confidence volume (CV) was better for the tSSS with individual origins. This choice affected IEDs more than it affected SEFs. CONCLUSIONS: Individual sphere model resulted in better GOF and CV. SIGNIFICANCE: Application of tSSS using an individual origin would be more desirable when available. This parameter might influence spontaneous activity more strongly.

Order of statistical learning depends on perceptive uncertainty.

Statistical learning (SL) is an innate mechanism by which the brain automatically encodes the n-th order transition probability (TP) of a sequence and grasps the uncertainty of the TP distribution. Through SL, the brain predicts a subsequent event (e n+1 ) based on the preceding events (e n ) that have a length of "n". It is now known that uncertainty modulates prediction in top-down processing by the human predictive brain. However, the manner in which the human brain modulates the order of SL strategies based on the degree of uncertainty remains an open question. The present study examined how uncertainty modulates the neural effects of SL and whether differences in uncertainty alter the order of SL strategies. It used auditory sequences in which the uncertainty of sequential information is manipulated based on the conditional entropy. Three sequences with different TP ratios of 90:10, 80:20, and 67:33 were prepared as low-, intermediate, and high-uncertainty sequences, respectively (conditional entropy: 0.47, 0.72, and 0.92 bit, respectively). Neural responses were recorded when the participants listened to the three sequences. The results showed that stimuli with lower TPs elicited a stronger neural response than those with higher TPs, as demonstrated by a number of previous studies. Furthermore, we found that participants adopted higher-order SL strategies in the high uncertainty sequence. These results may indicate that the human brain has an ability to flexibly alter the order based on the uncertainty. This uncertainty may be an important factor that determines the order of SL strategies. Particularly, considering that a higher-order SL strategy mathematically allows the reduction of uncertainty in information, we assumed that the brain may take higher-order SL strategies when encountering high uncertain information in order to reduce the uncertainty. The present study may shed new light on understanding individual differences in SL performance across different uncertain situations.

Correlation of motor-auditory cross-modal and auditory unimodal N1 and mismatch responses of schizophrenic patients and normal subjects: an MEG study.

Introduction: It has been suggested that the positive symptoms of schizophrenic patients (hallucinations, delusions, and passivity experience) are caused by dysfunction of their internal and external sensory prediction errors. This is often discussed as related to dysfunction of the forward model that executes self-monitoring. Several reports have suggested that dysfunction of the forward model in schizophrenia causes misattributions of self-generated thoughts and actions to external sources. There is some evidence that the forward model can be measured using the electroencephalography (EEG) and magnetoencephalography (MEG) components such as N1 (m) and mismatch negativity (MMN) (m). The objective in this MEG study is to investigate differences in the N1m and MMNm-like activity generated in motor-auditory cross-modal tasks in normal control (NC) subjects and schizophrenic (SC) patients, and compared that activity with N1m and MMNm in the auditory unimodal task. Methods: The N1m and MMNm/MMNm-like activity were recorded in 15 SC patients and 12 matched NC subjects. The N1m-attenuation effects and peak amplitude of MMNm/MMNm-like activity of the NC and SC groups were compared. Additionally, correlations between MEG measures (N1m suppression rate, MMNm, and MMNm-like activity) and clinical variables (Positive and Negative Syndrome Scale (PANSS) scores and antipsychotic drug (APD) dosages) in SC patients were investigated. Results: It was found that (i) there was no significant difference in N1m-attenuation for the NC and SC groups, and that (ii) MMNm in the unimodal task in the SC group was significantly smaller than that in the NC group. Further, the MMNm-like activity in the cross-modal task was smaller than that of the MMNm in the unimodal task in the NC group, but there was no significant difference in the SC group. The PANSS positive symptoms and general psychopathology score were moderately negatively correlated with the amplitudes of the MMNm-like activity, and the APD dosage was moderately negatively correlated with the N1m suppression rate. However, none of these correlations reached statistical significance. Discussion: The findings suggest that schizophrenic patients perform altered predictive processes differently from healthy subjects in latencies reflecting MMNm, depending on whether they are under forward model generation or not. This may support the hypothesis that schizophrenic patients tend to misattribute their inner experience to external agents, thus leading to the characteristic schizophrenia symptoms.

Investigating the technical feasibility of magnetoencephalography during transcranial direct current stimulation.

Introduction: Magnetoencephalography (MEG) can measure weak magnetic fields produced by electrical brain activity. Transcranial direct current stimulation (tDCS) can affect such brain activities. The concurrent application of both, however, is challenging because tDCS presents artifacts on the MEG signal. If brain activity during tDCS can be elucidated by MEG, mechanisms of plasticity-inducing and other effects of tDCS would be more comprehensively understood. We tested the technical feasibility of MEG during tDCS using a phantom that produces an artificial current dipole simulating focal brain activity. An earlier study investigated estimation of a single oscillating phantom dipole during tDCS, and we systematically tested multiple dipole locations with a different MEG device. Methods: A phantom provided by the manufacturer was used to produce current dipoles from 32 locations. For the 32 dipoles, MEG was recorded with and without tDCS. Temporally extended signal space separation (tSSS) was applied for artifact rejection. Current dipole sources were estimated as equivalent current dipoles (ECDs). The ECD modeling quality was assessed using localization error, amplitude error, and goodness of fit (GOF). The ECD modeling performance with and without tDCS, and with and without tSSS was assessed. Results: Mean localization errors of the 32 dipoles were 1.70 ± 0.72 mm (tDCS off, tSSS off, mean ± standard deviation), 6.13 ± 3.32 mm (tDCS on, tSSS off), 1.78 ± 0.83 mm (tDCS off, tSSS on), and 5.73 ± 1.60 mm (tDCS on, tSSS on). Mean GOF findings were, respectively, 92.3, 87.4, 97.5, and 96.7%. Modeling was affected by tDCS and restored by tSSS, but improvement of the localization error was marginal, even with tSSS. Also, the quality was dependent on the dipole location. Discussion: Concurrent tDCS-MEG recording is feasible, especially when tSSS is applied for artifact rejection and when the assumed location of the source of activity is favorable for modeling. More technical studies must be conducted to confirm its feasibility with different source modeling methods and stimulation protocols. Recovery of single-trial activity under tDCS warrants further research.

Refined analysis of complex language representations by non-invasive neuroimaging techniques.

OBJECTIVE: The determination of language lateralisation is important for patients with medically intractable epilepsy or a brain tumour near the language areas to avoid the risk of post-surgical language deficits. The aim of this study was to evaluate the clinical usefulness of near-infrared spectroscopy (NIRS) to identify language lateralisation compared with functional MRI (fMRI) and magnetoencephalography (MEG) in multiple language tasks. METHODS: We investigated 28 patients whose language dominance was evaluated by the Wada test. fMRI, MEG and NIRS were performed to investigate language representation. All patients were asked to read three-letter words silently for fMRI and MEG (Kana reading) and to write words beginning with a visually presented letter (word generation) for NIRS. The laterality index was calculated to assess language lateralisation in each investigation. RESULTS: In 24 cases (85.7%), of which two investigations showed the same laterality, the results had perfect concordance with the Wada test. In patients with left dominance, the sensitivity and specificity of fMRI, MEG and NIRS was 95.0% and 62.5%, 100% and 87.5%, 75.0% and 87.5%, respectively. In three patients with right lateralization, only NIRS showed a significant increase of oxygenated-haemoglobin in the right inferior frontal region, indicating right dominance. CONCLUSION: We established a method to determine language lateralisation by co-utilising fMRI, MEG and NIRS with high reliability. NIRS recognised atypical language representation, in addition to fMRI and MEG. While fMRI, MEG and NIRS are not currently as accurate as the Wada test in determining language lateralisation, this non-invasive and repeatable method has great potential as an alternative to the Wada test in time following further research and refinement of these techniques.

Perceptual uncertainty modulates auditory statistical learning: A magnetoencephalography study.

Statistical learning allows comprehension of structured information, such as that in language and music. The brain computes a sequence's transition probability and predicts future states to minimise sensory reaction and derive entropy (uncertainty) from sequential information. Neurophysiological studies have revealed that early event-related neural responses (P1 and N1) reflect statistical learning - when the brain encodes transition probability in stimulus sequences, it predicts an upcoming stimulus with a high transition probability and suppresses the early event-related responses to a stimulus with a high transition probability. This amplitude difference between high and low transition probabilities reflects statistical learning effects. However, how a sequence's transition probability ratio affects neural responses contributing to statistical learning effects remains unknown. This study investigated how transition-probability ratios or conditional entropy (uncertainty) in auditory sequences modulate the early event-related neuromagnetic responses of P1m and N1m. Sequence uncertainties were manipulated using three different transition-probability ratios: 90:10%, 80:20%, and 67:33% (conditional entropy: 0.47, 0.72, and 0.92 bits, respectively). Neuromagnetic responses were recorded when participants listened to sequential sounds with these three transition probabilities. Amplitude differences between lower and higher probabilities were larger in sequences with transition-probability ratios of 90:10% and smaller in sequences with those of 67:33%, compared to sequences with those of 80:20%. This suggests that the transition-probability ratio finely tunes P1m and N1m. Our study also showed larger amplitude differences between frequent- and rare-transition stimuli in P1m than in N1m. This indicates that information about transition-probability differences may be calculated in earlier cognitive processes.

Musical expertise facilitates statistical learning of rhythm and the perceptive uncertainty: A cross-cultural study.

The brain extracts statistical regularities from sequential information around our environment. This is referred to as statistical learning (SL). Statistical learning is considered an innate function in the human brain and contributes to the brain's development. Within the framework of predictive coding, this learning system allows us to predict a future state to minimize sensory reaction and resolve uncertainty around the world. By auditory statistical learning, over the brain's development, humans become able to comprehend language and music. An increasing number of studies has revealed that Western-classical musical training optimizes the brain's probabilistic model of music and enhances the accuracy of perceptive uncertainty (entropy) in newly encountered melody. No study, however, investigates how musical training modulates the probabilistic model of rhythm, and how the musical culture tunes them. The present study investigated how SL of temporal sequences with and without a beat is reflected in neural responses, and how the SL is modulated by the two types of musical training in different cultures: Western- and Japanese-classical music (i.e., Hougaku). The neural representation showed evidence that the SL effects of beat sequence were prominent in the left hemisphere. This finding was larger in Western- and Japanese-classical musicians compared with non-musicians. Further, the entropy (uncertainty) of the sequences negatively correlated with neural effects of SL, mainly in the left hemisphere of the both Western- and Japanese-classical musicians. These suggest that, regardless of musical culture, musical training may generally facilitate SL of rhythm. However, the specific neural components showed differences between groups of musicians: an earlier component, referred to as P1, represented the left lateralization for perceptive uncertainty in both groups of musicians, whereas a later component, referred to as N1, represented the left lateralization only in Japanese Classical musicians. These findings may suggest that the types of musical training differently modulate neural representation of underlying temporal SL, particularly global processing of uncertainty rather than local processing of transitional probability. The present study sheds new light on the neurophysiological account of Japanese classical music.

Long-Term Undiagnosed Nonconvulsive Status Epilepticus Identified by Urgent Electroencephalography with Hyperventilation Activation.

Nonconvulsive status epilepticus (NCSE) might be underdiagnosed in cases where clinical symptoms are ambiguous. If a patient exhibits ictal psychiatric symptoms such as NCSE presentation and is misdiagnosed as having a psychiatric disorder, the patient may be treated in psychiatry settings, where continuous electroencephalography (cEEG), the gold standard for NCSE diagnosis, is typically not used. Herein, we report our experience with a patient having NCSE who exhibited psychiatric symptoms and remained misdiagnosed for many years. We also included a brief review of the relevant literature. Our experience with this patient presents two clinically significant points: (1) clinicians should consider NCSE in the differential diagnosis of interictal psychosis when patients with epilepsy, in whom the seizure type is unknown, repeatedly present transient psychiatric symptoms, and (2) urgent EEG with hyperventilation activation during acute periods may help diagnose patients with suspected NCSE.

Concurrent Statistical Learning of Ignored and Attended Sound Sequences: An MEG Study.

In an auditory environment, humans are frequently exposed to overlapping sound sequences such as those made by human voices and musical instruments, and we can acquire information embedded in these sequences via attentional and nonattentional accesses. Whether the knowledge acquired by attentional accesses interacts with that acquired by nonattentional accesses is unknown, however. The present study examined how the statistical learning (SL) of two overlapping sound sequences is reflected in neurophysiological and behavioral responses, and how the learning effects are modulated by attention to each sequence. SL in this experimental paradigm was reflected in a neuromagnetic response predominantly in the right hemisphere, and the learning effects were not retained when attention to the tone streams was switched during the learning session. These results suggest that attentional and nonattentional learning scarcely interact with each other and that there may be a specific system for nonattentional learning, which is independent of attentional learning.

Aphasic status epilepticus preceding tumefactive left hemisphere lesion in anti-MOG antibody associated disease.

INTRODUCTION: Anti-myelin oligodendrocyte glycoprotein (MOG) antibodies have recently been associated with epilepsy with FLAIR hyperintense cortical lesions on MRI. Association between anti-MOG antibodies and epilepsy without detectable structural brain lesion on MRI is unknown. CASE REPORT: A 48-year-old right-handed man with a four-and-a-half year history of anti-MOG antibody associated demyelinating disease presented with persistent global aphasia. Brain MRI showed no new lesion or cortical lesion in the left hemisphere. Electroencephalogram, magnetoencephalography, and brain perfusion single-photon emission computed tomography suggested epileptic foci in the left temporal and parietal lobes, and the patient's aphasia transiently responded to intravenous diazepam, compatible with aphasic status epilepticus. Cerebrospinal fluid showed mildly elevated cell count and positive oligoclonal bands. The patient only partially responded to antiepileptic drugs but responded to steroid pulse therapy. Six months later, the patient again exhibited global aphasia. Brain MRI showed tumefactive white matter lesion in the left temporo-parietal lobes. CONCLUSION: Autoimmune epilepsy without obvious causative lesion on MRI can be seen in the course of anti-MOG antibody associated demyelinating disease. The subsequent emergence of tumefactive lesion closely located to the epileptic foci may suggest some association between autoimmune epilepsy and demyelinating lesions.

Perceptual change in response to a bistable picture increases neuromagnetic beta-band activities.

The purpose of the present study was to examine by whole-head magnetoencephalography (MEG) brain oscillatory responses related to visual perceptual change of short-term duration in the absence of morphologic change. Twenty healthy volunteers participated in this study. We used three pictures: a bistable picture with ambiguous contours that could represent two different objects ('target') and two preceding pictures that were clear representations of either object ('face' or 'saxophone'). Two types of stimulus conditions were created, the 'face-target' (F-T) condition and the 'saxophone-target' (S-T) condition, and data acquisition was performed mainly during presentation of the 'target' picture. Time-frequency analysis was performed by means of fast Fourier transform. All subjects reported that they perceived the 'target' picture predominantly as a 'face' regardless of the preceding picture. We suspect that perceptual change occurred more frequently in the S-T condition than in the F-T condition. We found significantly greater synchronization in the beta (14-30-Hz) frequency band, ranging from 250 to 450ms predominantly over the occipital and parietal regions, after stimulus alternation for the S-T condition than for the F-T condition. Results of the present study show that the change in beta-band activity reflects a change in visual perception.

The influence of gender and personality traits on individual difference in auditory mismatch: a magnetoencephalographic (MMNm) study.

The mismatch negativity (MMN; and its magnetic counterpart, MMNm) is widely used to assess early-stage auditory cortical function in humans and its impairment in various neuropsychiatric disorders. To establish MMN as a useful clinical tool for objective monitoring of auditory cortical function in an individual, we investigated the effect of gender and personality traits on individual difference in MMNm in healthy subjects. Participants were 88 healthy adults (31 women and 57 men). The MMNm in response to the duration or frequency change of tones and those in response to across-phoneme change between vowels /a/ and /o/ were recorded using 204-channel whole-head magnetoencephalography. The temperament and character inventory (TCI) was used to assess individual personality traits. Women were associated with significantly delayed peak latency of phonetic MMNm for the right hemisphere compared with men. Men had greater strength of tonal duration MMNm for the left hemisphere than women. Additionally, the persistence score predicted the strength of phonetic MMNm for the left hemisphere in the combined sample and the tonal duration MMNm for the left hemisphere in men; reward dependence predicted the latency of the tonal duration MMNm for the left hemisphere in men; and cooperativeness predicted the strength of the tonal frequency MMNm for the right hemisphere in women. These results suggest that gender and personality traits have an effect on individual variability of the MMNm. Our observation may provide useful information to establish MMN/MMNm as a clinical tool for monitoring auditory cortical function on an individual basis.

Lack of correlation between phonetic magnetic mismatch field and plasma d-serine levels in humans.

OBJECTIVE: Uncovering molecular bases for auditory language processing in the human brain is a fundamental scientific challenge. The power and latency of the magnetic mismatch field (MMF) elicited by phoneme change, which are magnetoencephalographic indices of language function in its early stage of information processing, are theoretically thought to be modulated by N-methyl-d-aspartate-type glutamate receptor (NMDAR) function, but no study has yet assessed this possibility. We have thus sought to demonstrate an association between phonetic MMF power/latency and levels of plasma d-serine, an intrinsic co-agonist of glycine binding sites on NMDAR, in adults. METHODS: The MMF response to phoneme changes was recorded using 204-channel magnetoencephalography in 61 healthy, right-handed, Japanese adults. Plasma levels of d- and l-serine were measured for each participant. RESULTS: We did not find a significant correlation between MMF power/latency and plasma serine levels. CONCLUSIONS: Despite a sufficient sample size, we failed to find an association between the physiological markers of the early stage of information processing of language in the auditory cortex and biomarkers indexing glutamatergic function. SIGNIFICANCE: Our study did not indicate that a molecular index of glutamatergic function could be a surrogate marker for the early stage of information processing of language in humans.

Latency variation of auditory N1m responses to vocal and nonvocal sounds.

To investigate the temporal aspect of timbre processing, we recorded auditory-evoked neuromagnetic responses to periodic complex sounds, which were matched in all acoustic parameters except for two fundamental frequencies (F0s) and 12 spectral envelopes of vocal and nonvocal categories. Only for nonvocal sounds, a significant difference in N1m latency for F0 was detected in both hemispheres. A significant difference among stimuli was detected in both hemispheres for vocal and linear sounds, whereas only in the right hemisphere for instrumental sounds. Moreover, the results of paired comparison among F0s revealed that not only the vocal sounds but also some of the nonvocal sounds were F0-independent. This latency independence may be attributed to the relatively high power in the higher frequency spectrum.

Single, but not dual, attention facilitates statistical learning of two concurrent auditory sequences.

When we are exposed to a novel stimulus sequence, we can learn the sequence by extracting a statistical structure that is potentially embedded in the sequence. This mechanism is called statistical learning, and is considered a fundamental and domain-general process that is innate in humans. In the real-world environment, humans are inevitably exposed to auditory sequences that often overlap with one another, such as speech sound streams from multiple speakers or entangled melody lines generated by multiple instruments. The present study investigated how single and dual attention modulates brain activity, reflecting statistical learning when two auditory sequences were presented simultaneously. The results demonstrated that the effect of statistical learning had more pronounced neural activity when listeners paid attention to only one sequence and ignored the other, rather than paying attention to both sequences. Biased attention may thus be an essential strategy when learners are exposed to multiple information streams.

Statistical learning of an auditory sequence and reorganization of acquired knowledge: A time course of word segmentation and ordering.

Previous neural studies have supported the hypothesis that statistical learning mechanisms are used broadly across different domains such as language and music. However, these studies have only investigated a single aspect of statistical learning at a time, such as recognizing word boundaries or learning word order patterns. In this study, we neutrally investigated how the two levels of statistical learning for recognizing word boundaries and word ordering could be reflected in neuromagnetic responses and how acquired statistical knowledge is reorganised when the syntactic rules are revised. Neuromagnetic responses to the Japanese-vowel sequence (a, e, i, o, and u), presented every .45s, were recorded from 14 right-handed Japanese participants. The vowel order was constrained by a Markov stochastic model such that five nonsense words (aue, eao, iea, oiu, and uoi) were chained with an either-or rule: the probability of the forthcoming word was statistically defined (80% for one word; 20% for the other word) by the most recent two words. All of the word transition probabilities (80% and 20%) were switched in the middle of the sequence. In the first and second quarters of the sequence, the neuromagnetic responses to the words that appeared with higher transitional probability were significantly reduced compared with those that appeared with a lower transitional probability. After switching the word transition probabilities, the response reduction was replicated in the last quarter of the sequence. The responses to the final vowels in the words were significantly reduced compared with those to the initial vowels in the last quarter of the sequence. The results suggest that both within-word and between-word statistical learning are reflected in neural responses. The present study supports the hypothesis that listeners learn larger structures such as phrases first, and they subsequently extract smaller structures, such as words, from the learned phrases. The present study provides the first neurophysiological evidence that the correction of statistical knowledge requires more time than the acquisition of new statistical knowledge.