Though activation of Broca's region in the combinatorial processing of symbols (language, music) has been revealed by neurometabolic studies, most previous neurophysiological research found the earliest grammar indices in the temporal cortex, with inferior-frontal generators becoming active at relatively late stages. We use the attention- and task-free syntactic mismatch negativity (sMMN) event-related potential (ERP) to measure rapid and automatic sensitivity of the human brain to grammatical information in participants' native language (French). Further, sources underlying the MMN were estimated by applying the Parametrical Empirical Bayesian (PEB) approach, with the Multiple Sparse Priors (MSP) technique. Results showed reliable grammar-related activation focused on Broca's region already in the 150-190 ms time window, providing robust documentation of its involvement in the first stages of syntactic processing.

Humans show variable degrees of success in acquiring a second language (L2). In many cases, morphological and syntactic knowledge remain deficient, although some learners succeed in reaching nativelike levels, even if they begin acquiring their L2 relatively late. In this study, we use psycholinguistic, online language proficiency tests and a neurophysiological index of syntactic processing, the syntactic mismatch negativity (sMMN) to local agreement violations, to compare behavioural and neurophysiological markers of grammar processing between native speakers (NS) of English and non-native speakers (NNS). Variable grammar proficiency was measured by psycholinguistic tests. When NS heard ungrammatical word sequences lacking agreement between subject and verb (e.g. *we kicks), the MMN was enhanced compared with syntactically legal sentences (e.g. he kicks). More proficient NNS also showed this difference, but less proficient NNS did not. The main cortical sources of the MMN responses were localised in bilateral superior temporal areas, where, crucially, source strength of grammar-related neuronal activity correlated significantly with grammatical proficiency of individual L2 speakers as revealed by the psycholinguistic tests. As our results show similar, early MMN indices to morpho-syntactic agreement violations among both native speakers and non-native speakers with high grammar proficiency, they appear consistent with the use of similar brain mechanisms for at least certain aspects of L1 and L2 grammars.

Complex words can be seen as combinations of elementary units, decomposable into stems and affixes according to morphological rules. Alternatively, complex forms may be stored as single lexical entries and accessed as whole forms. This study uses an event-related potential brain response capable of indexing both whole-form retrieval and combinatorial processing, the Mismatch Negativity (MMN), to investigate early brain activity elicited by morphologically complex derived words in German. We presented complex words consisting of stems “sicher” (secure), or “sauber” (clean) combined with abstract nominalizing derivational affixes -heit or -keit, to form either congruent derived words: “Sicherheit” (security) and “Sauberkeit” (cleanliness), or incongruent derived pseudowords: *“Sicherkeit”, and *“Sauberheit”. Using this orthogonal design, it was possible to record brain responses for -heit and -keit in both congruent and incongruent contexts, therefore balancing acoustic variance. Previous research has shown that incongruent combinations of symbols elicit a stronger MMN than congruent combinations, but that single words or constructions stored as whole forms elicit a stronger MMN than pseudowords or non-existent constructions. We found that congruent derived words elicited a stronger MMN than incongruent derived words, beginning about 150 ms after perception of the critical morpheme. This pattern of results is consistent with whole-form storage of morphologically complex derived words as lexical units, or mini-constructions. Using distributed source localization methods, the MMN enhancement for well-formed derivationally complex words appeared to be most prominent in the left inferior anterior-temporal, bilateral superior parietal and bilateral post-central, supra-marginal areas. In addition, neurophysiological results reflected the frequency of derived forms, thus providing further converging evidence for whole form storage and against a combinatorial mechanism.

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The human brain stores an immense repertoire of linguistic symbols (morphemes, words) and combines them into a virtually unlimited set of well-formed strings (phrases, sentences) that serve as efficient communicative tools. Communication is hampered, however, if strings include meaningless items (e.g., "pseudomorphemes"), or if the rules for combining string elements are violated. Prior research suggests that, when participants attentively process sentences in a linguistic task, syntactic processing can occur quite early, but lexicosemantic processing, or any interaction involving this factor, is manifest later in time (ca. 400 msec or later). In contrast, recent evidence from passive speech perception paradigms suggests early processing of both combinatorial (morphosyntactic) and storage-related (lexicosemantic) properties. A crucial question is whether these parallel processes might also interact early in processing. Using ERPs in an orthogonal design, we presented spoken word strings to participants while they were distracted from incoming speech to obtain information about automatic language processing mechanisms unaffected by task-related strategies. Stimuli were either (1) well-formed miniconstructions (short pronoun-verb sentences), (2) "unstored" strings containing a pseudomorpheme, (3) "ill-combined" strings violating subject-verb agreement rules, or (4) double violations including both types of errors. We found that by 70-210 msec after the onset of the phrase-final syllable that disambiguated the strings, interactions of lexicosemantic and morphosyntactic deviance were evident in the ERPs. These results argue against serial processing of lexical storage, morphosyntactic combination and their interaction, and in favor of early, simultaneous, and interactive processing of symbols and their combinatorial structures.

Transmission loss over the range of the direct arrival is examined for a receiver lying on a deep, sedimentary ocean bottom and is found to exhibit interference structure not explained by water-borne paths alone. It is suggested that this structure can be understood in terms of energy refracted through the sediments back to the receiver. The velocity structure in the sediments required to account for the interference is quite consistent with the velocity structure inferred from seismic profiling the vicinity of the receivers.

Calculations of transmission loss using a Parabolic Equation (PE) model are compared to measured transmission loss from a North Pacific propagation experiment. In the range-dependent environment various combinations of two source depths, three receiver depths, and three frequencies permitted a thorough examination of the influence of PE model input parameters. Sensitivity of calculated transmission loss to variations in the input parameters is discussed and some omissions in the measurements are found to be significant when evaluating the model. When known measurement uncertainties are used to vary the model’s input, changes in the model’s predicted transmission loss are of the same scale as the differences seen in model-to-data comparisons. Repeatability of the measurement was determined by two comparable measurement events. Data-to-data statistical comparisons of those two measurement events are no better than the model-to-data comparisons. The data-to-data comparisons showed mean differences up to 1.5 dB with standard deviations between 1 and 3.5 dB. Model-to-data comparisons yield comparable means and standard deviations. It is concluded that the PE model permits comparisons with the data at a level of detail which demands more information from measurements than is available from even this unusually comprehensive data set.

Background:Many magnetoencephalographs (MEG) contain, in addition to data channels, a set of reference channels positioned relatively far from the head that provide information on magnetic fields not originating from the brain. This information is used to subtract sources of non-neural origin, with either geometrical or least mean squares (LMS) methods. LMS methods in particular tend to be biased toward more constant noise sources and are often unable to remove intermittent noise. New Method:To better identify and eliminate external magnetic noise, we propose performing ICA directly on the MEG reference channels. This in most cases produces several components which are clear summaries of external noise sources with distinct spatio-temporal patterns. We present two algorithms for identifying and removing such noise components from the data which can in many cases significantly improve data quality. Results:We performed simulations using forward models that contained both brain sources and external noise sources. First, traditional LMS-based methods were applied. While this removed a large amount of noise, a significant portion still remained. In many cases, this portion could be removed using the proposed technique, with little to no false positives. Comparison with existing method(s):The proposed method removes significant amounts of noise to which existing LMS-based methods tend to be insensitive. Conclusions:The proposed method complements and extends traditional reference based noise correction with little extra computational cost and low chances of false positives. Any MEG system with reference channels could profit from its use, particularly in labs with intermittent noise sources.