Auditory language comprehension: an event-related fMRI study on the processing of syntactic and lexical information

The functional specificity of different brain regions recruited in auditory language processing was investigated by means of event-related functional magnetic resonance imaging (fMRI) while subjects listened to speech input varying in the presence or absence of semantic and syntactic information. There were two sentence conditions containing syntactic structure, i.e., normal speech (consisting of function and content words), syntactic speech (consisting of function words and pseudowords), and two word-list conditions, i.e., real words and pseudowords. The processing of auditory language, in general, correlates with significant activation in the primary auditory cortices and in adjacent compartments of the superior temporal gyrus bilaterally. Processing of normal speech appeared to have a special status, as no frontal activation was observed in this case but was seen in the other three conditions. This difference may point toward a certain automaticity of the linguistic processes used during normal speech comprehension. When considering the three other conditions, we found that these were correlated with activation in both left and right frontal cortices. An increase of activation in the planum polare bilaterally and in the deep portion of the left frontal operculum was found exclusively when syntactic processes were in focus. Thus, the present data may be taken to suggest an involvement of the left frontal and bilateral temporal cortex when processing syntactic information during comprehension.     

Neural correlates of temporal auditory processing in developmental dyslexia during German vowel length discrimination: an fMRI study

This fMRI study investigated phonological vs. auditory temporal processing in developmental dyslexia by means of a German vowel length discrimination paradigm (Groth, Lachmann, Riecker, Muthmann, & Steinbrink, 2011). Behavioral and fMRI data were collected from dyslexics and controls while performing same-different judgments of vowel duration in two experimental conditions. In the temporal, but not in the phonological condition, hemodynamic brain activation was observed bilaterally within the anterior insular cortices in both groups and within the left inferior frontal gyrus (IFG) in controls, indicating that the left IFG and the anterior insular cortices are part of a neural network involved in temporal auditory processing. Group subtraction analyses did not demonstrate significant effects. However, in a subgroup analysis, participants performing low in the temporal condition (all dyslexic) showed decreased activation of the insular cortices and the left IFG, suggesting that this processing network might form the neural basis of temporal auditory processing deficits in dyslexia.     

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

Speech production is inextricably linked to speech perception, yet they are usually investigated in isolation. In this study, we employed a verbal-repetition task to identify the neural substrates of speech processing with two ends active simultaneously using functional MRI. Subjects verbally repeated auditory stimuli containing an ambiguous vowel sound that could be perceived as either a word or a pseudoword depending on the interpretation of the vowel. We found verbal repetition commonly activated the audition-articulation interface bilaterally at Sylvian fissures and superior temporal sulci. Contrasting word-versus-pseudoword trials revealed neural activities unique to word repetition in the left posterior middle temporal areas and activities unique to pseudoword repetition in the left inferior frontal gyrus. These findings imply that the tasks are carried out using different speech codes: an articulation-based code of pseudowords and an acoustic-phonetic code of words. It also supports the dual-stream model and imitative learning of vocabulary.     

The effects of attention on speech perception: an fMRI study

Focusing of attention to a specific speech source plays an important role in everyday speech perception. However, little is known of the neuronal substrates of focused attention in speech perception. Thus, the present study investigated the effects on neuronal activation of directed attention to auditory stimuli that differed in semantic content. Using an event-related fMRI protocol, single vowels, three-phoneme pseudowords and three- and four-phoneme real nouns and words were randomly presented to the subjects during four different instructional conditions. One condition was passive listening without any specific instructions of focusing of attention. The other conditions were attention focused on either the vowels, the pseudowords or the words. Thus, the acoustic stimulation was constant across conditions. The subjects were 13 healthy adults. Functional MRI was performed with a 1.5 T scanner, using an event-related design. During passive listening, there were significant activations bilaterally in the superior temporal gyrus. Instruction to attend to the pseudowords caused activation in middle temporal lobe areas, extending more anterior compared to the activations seen during passive listening. Instruction to attend to the vowel sounds caused an increase in activation in the superior/medial temporal lobe, with a leftward asymmetry. Instruction to attend to the words caused a leftward asymmetry, particularly in the middle and superior temporal gyri. It is concluded that attention plays a modulatory role in neuronal activation to speech sounds, producing specific activations to specific stimulus categories that may act to facilitate speech perception.     

Reversing spoken items--mind twisting not tongue twisting

Using 12 participants we conducted an fMRI study involving two tasks, word reversal and rhyme judgment, based on pairs of natural speech stimuli, to study the neural correlates of manipulating auditory imagery under taxing conditions. Both tasks engaged the left anterior superior temporal gyrus, reflecting previously established perceptual mechanisms. Engagement of the left inferior frontal gyrus in both tasks relative to baseline could only be revealed by applying small volume corrections to the region of interest, suggesting that phonological segmentation played only a minor role and providing further support for factorial dissociation of rhyming and segmentation in phonological awareness. Most importantly, subtraction of rhyme judgment from word reversal revealed activation of the parietal lobes bilaterally and the right inferior frontal cortex, suggesting that the dynamic manipulation of auditory imagery involved in mental reversal of words seems to engage mechanisms similar to those involved in visuospatial working memory and mental rotation. This suggests that reversing spoken items is a matter of mind twisting rather than tongue twisting and provides support for a link between language processing and manipulation of mental imagery.     

An event-related fMRI study of syntactic and semantic violations

We used event-related functional magnetic resonance imaging to identify brain regions involved in syntactic and semantic processing. Healthy adult males read well-formed sentences randomly intermixed with sentences which either contained violations of syntactic structure or were semantically implausible. Reading anomalous sentences, as compared to well-formed sentences, yielded distinct patterns of activation for the two violation types. Syntactic violations elicited significantly greater activation than semantic violations primarily in superior frontal cortex. Semantically incongruent sentences elicited greater activation than syntactic violations in the left hippocampal and parahippocampal gyri, the angular gyri bilaterally, the right middle temporal gyrus, and the left inferior frontal sulcus. These results demonstrate that syntactic and semantic processing result in nonidentical patterns of activation, including greater frontal engagement during syntactic processing and larger increases in temporal and temporo-parietal regions during semantic analyses.     

Co-localisation of abnormal brain structure and function in specific language impairment

We assessed the relationship between brain structure and function in 10 individuals with specific language impairment (SLI), compared to six unaffected siblings, and 16 unrelated control participants with typical language. Voxel-based morphometry indicated that grey matter in the SLI group, relative to controls, was increased in the left inferior frontal cortex and decreased in the right caudate nucleus and superior temporal cortex bilaterally. The unaffected siblings also showed reduced grey matter in the caudate nucleus relative to controls. In an auditory covert naming task, the SLI group showed reduced activation in the left inferior frontal cortex, right putamen, and in the superior temporal cortex bilaterally. Despite spatially coincident structural and functional abnormalities in frontal and temporal areas, the relationships between structure and function in these regions were different. These findings suggest multiple structural and functional abnormalities in SLI that are differently associated with receptive and expressive language processing.     

The effect of sublexical and lexical frequency on speech production: An fMRI investigation

There is no consensus regarding the fundamental phonetic units that underlie speech production. There is, however, general agreement that the frequency of occurrence of these units is a significant factor. Investigators often use the effects of manipulating frequency to support the importance of particular units. Studies of pseudoword production have been used to show the importance of sublexical units, such as initial syllables, phonemes, and biphones. However, it is not clear that these units play the same role when the production of pseudowords is compared to the production of real words. In this study, participants overtly repeated real and pseudowords that were similar for length, complexity, and initial syllable frequency while undergoing functional magnetic resonance imaging. Compared to real words, production of pseudowords produced greater activation in much of the speech production network, including bilateral inferior frontal cortex, precentral gyri and supplementary motor areas and left superior temporal cortex and anterior insula. Only middle right frontal gyrus showed greater activation for real words than for pseudowords. Compared to a no-speech control condition, production of pseudowords or real words resulted in activation of all of the areas shown to comprise the speech production network. Our data, in conjunction with previous studies, suggest that the unit that is identified as the basic unit of speech production is influenced by the nature of the speech that is being studied, i.e., real words as compared to other real words, pseudowords as compared to other pseudowords, or real words as compared to pseudowords.     

The reading ability of good and poor temporal processors among a group of college students

In this study, we examined whether good auditory and good visual temporal processors were better than their poor counterparts on certain reading measures. Various visual and auditory temporal tasks were administered to 105 undergraduates. They read some phonologically regular pseudowords and irregular words that were presented sequentially in the same ("word" condition) and in different ("line" condition) locations. Results indicated that auditory temporal acuity was more relevant to reading, whereas visual temporal acuity was more relevant to spelling. Good auditory temporal processors did not have the advantage in processing pseudowords, even though pseudoword reading correlated significantly with auditory temporal processing. These results suggested that some higher cognitive or phonological processes mediated the relationship between auditory temporal processing and pseudoword reading. Good visual temporal processors did not have the advantage in processing irregular words. They also did not process the line condition more accurately than the word condition. The discrepancy might be attributed to the use of normal adults and the unnatural reading situation that did not fully capture the function of the visual temporal processes. The distributions of auditory and visual temporal processing abilities were co-occurring to some degree, but they maintained considerable independence. There was also a lack of a relationship between the type and severity of reading deficits and the type and number of temporal deficits.     

汉语双字词在心理词典中的表征方式:来自fNIRS的证据

以汉语双字构成的真词与假词为实验材料,22名大学生为被试,采用功能性近红外脑成像技术(f NIRS)和事件相关设计,考察被试在完成词汇判断任务时的大脑激活模式,探索汉语双字词在心理词典中的表征方式。结果发现:(1)在完成真假词判断任务时,被试大脑左侧额叶和左侧颞叶均被激活;(2)与判断假词相比,被试在判断真词时显著地激活左额上回和左额中回。这一结果说明汉语双字词在心理词典中是混合表征的。     

The neonate brain's sensitivity to repetition-based structure: Specific to speech?

Newborns are able to extract and learn repetition-based regularities from the speech input, that is, they show greater brain activation in the bilateral temporal and left inferior frontal regions to trisyllabic pseudowords of the form AAB (e.g., “babamu”) than to random ABC sequences (e.g., “bamuge”). Whether this ability is specific to speech or also applies to other auditory stimuli remains unexplored. To investigate this, we tested whether newborns are sensitive to regularities in musical tones. Neonates listened to AAB and ABC tones sequences, while their brain activity was recorded using functional Near-Infrared Spectroscopy (fNIRS). The paradigm, the frequency of occurrence and the distribution of the tones were identical to those of the syllables used in previous studies with speech. We observed a greater inverted (negative) hemodynamic response to AAB than to ABC sequences in the bilateral temporal and fronto-parietal areas. This inverted response was caused by a decrease in response amplitude, attributed to habituation, over the course of the experiment in the left fronto-temporal region for the ABC condition and in the right fronto-temporal region for both conditions. These findings show that newborns’ ability to discriminate AAB from ABC sequences is not specific to speech. However, the neural response to musical tones and spoken language is markedly different. Tones gave rise to habituation, whereas speech was shown to trigger increasing responses over the time course of the study. Relatedly, the repetition regularity gave rise to an inverted hemodynamic response when carried by tones, while it was canonical for speech. Thus, newborns’ ability to detect repetition is not speech-specific, but it engages distinct brain mechanisms for speech and music.

Research Highlights

• The ability of newborns’ to detect repetition-based regularities is not specific to speech, but also extends to other auditory modalities.
• The brain mechanisms underlying speech and music processing are markedly different.

     

Brain activity varies with modulation of dynamic pitch variance in sentence melody

Fourteen native speakers of German heard normal sentences, sentences which were either lacking dynamic pitch variation (flattened speech), or comprised of intonation contour exclusively (degraded speech). Participants were to listen carefully to the sentences and to perform a rehearsal task. Passive listening to flattened speech compared to normal speech produced strong brain responses in right cortical areas, particularly in the posterior superior temporal gyrus (pSTG). Passive listening to degraded speech compared to either normal or flattened speech particularly involved fronto-opercular and subcortical (Putamen, Caudate Nucleus) regions bilaterally. Additionally the Rolandic operculum (premotor cortex) in the right hemisphere subserved processing of neat sentence intonation. As a function of explicit rehearsing sentence intonation we found several activation foci in the left inferior frontal gyrus (Broca's area), the left inferior precentral sulcus, and the left Rolandic fissure. The data allow several suggestions: First, both flattened and degraded speech evoked differential brain responses in the pSTG, particularly in the planum temporale (PT) bilaterally indicating that this region mediates integration of slowly and rapidly changing acoustic cues during comprehension of spoken language. Second, the bilateral circuit active whilst participants receive degraded speech reflects general effort allocation. Third, the differential finding for passive perception and explicit rehearsal of intonation contour suggests a right fronto-lateral network for processing and a left fronto-lateral network for producing prosodic information. Finally, it appears that brain areas which subserve speech (frontal operculum) and premotor functions (Rolandic operculum) coincidently support the processing of intonation contour in spoken sentence comprehension.     

Dorsal and ventral streams: a framework for understanding aspects of the functional anatomy of language

Despite intensive work on language-brain relations, and a fairly impressive accumulation of knowledge over the last several decades, there has been little progress in developing large-scale models of the functional anatomy of language that integrate neuropsychological, neuroimaging, and psycholinguistic data. Drawing on relatively recent developments in the cortical organization of vision, and on data from a variety of sources, we propose a new framework for understanding aspects of the functional anatomy of language which moves towards remedying this situation. The framework posits that early cortical stages of speech perception involve auditory fields in the superior temporal gyrus bilaterally (although asymmetrically). This cortical processing system then diverges into two broad processing streams, a ventral stream, which is involved in mapping sound onto meaning, and a dorsal stream, which is involved in mapping sound onto articulatory-based representations. The ventral stream projects ventro-laterally toward inferior posterior temporal cortex (posterior middle temporal gyrus) which serves as an interface between sound-based representations of speech in the superior temporal gyrus (again bilaterally) and widely distributed conceptual representations. The dorsal stream projects dorso-posteriorly involving a region in the posterior Sylvian fissure at the parietal-temporal boundary (area Spt), and ultimately projecting to frontal regions. This network provides a mechanism for the development and maintenance of "parity" between auditory and motor representations of speech. Although the proposed dorsal stream represents a very tight connection between processes involved in speech perception and speech production, it does not appear to be a critical component of the speech perception process under normal (ecologically natural) listening conditions, that is, when speech input is mapped onto a conceptual representation. We also propose some degree of bi-directionality in both the dorsal and ventral pathways. We discuss some recent empirical tests of this framework that utilize a range of methods. We also show how damage to different components of this framework can account for the major symptom clusters of the fluent aphasias, and discuss some recent evidence concerning how sentence-level processing might be integrated into the framework.     

Syntactic, prosodic, and semantic processes in the brain: evidence from event-related neuroimaging

The neural network supporting aspects of syntactic, prosodic, and semantic information processing is specified on the basis of two experiments using functional magnetic resonance imaging (fMRI). In these two studies, the presence/absence of lexical-semantic and syntactic information is systematically varied in spoken language stimuli. Inferior frontal and temporal brain areas in the left and the right hemisphere are identified to support different aspects of auditory language processing. Two additional experiments using event-related brain potentials investigate the possible interaction of syntactic and prosodic information, on the one hand, and syntactic and semantic information, on the other. While the first two information types were shown to interact early during processing, the latter two information types do not. Implications for models of auditory language comprehension are discussed.     

Neural circuitry underlying perception of duration depends on language experience

Thai, a language which exhibits a phonemic opposition in vowel length, allows us to compare temporal patterns in linguistic and nonlinguistic contexts. Functional MRI data were collected from Thai and English subjects in a speeded-response, selective attention paradigm as they performed same/different judgments of vowel duration and consonants (Thai speech) and hum duration (nonspeech). Activation occurred predominantly in left inferior prefrontal cortex in both speech tasks for the Thai group, but only in the consonant task for the English group. The Thai group exhibited activation in the left mid superior temporal gyrus in both speech tasks; the English group in the posterior superior temporal gyrus bilaterally. In the hum duration task, peak activation was observed bilaterally in prefrontal cortex for both groups. These crosslinguistic data demonstrate that encoding of complex auditory signals is influenced by their functional role in a particular language.     

The anatomy of auditory word processing: individual variability

This study used functional magnetic resonance imaging (fMRI) to investigate the neural substrate underlying the processing of single words, comparing activation patterns across subjects and within individuals. In a word repetition task, subjects repeated single words aloud with instructions not to move their jaws. In a control condition involving reverse speech, subjects heard a digitally reversed speech token and said aloud the word "crime." The averaged fMRI results showed activation in the left posterior temporal and inferior frontal regions and in the supplementary motor area, similar to previous PET studies. However, the individual subject data revealed variability in the location of the temporal and frontal activation. Although these results support previous imaging studies, demonstrating an averaged localization of auditory word processing in the posterior superior temporal gyrus (STG), they are more consistent with traditional neuropsychological data, which suggest both a typical posterior STG localization and substantial individual variability. By using careful head restraint and movement analysis and correction methods, the present study further demonstrates the feasibility of using overt articulation in fMRI experiments.     

Shared language: overlap and segregation of the neuronal infrastructure for speaking and listening revealed by functional MRI

Whether the brain's speech-production system is also involved in speech comprehension is a topic of much debate. Research has focused on whether motor areas are involved in listening, but overlap between speaking and listening might occur not only at primary sensory and motor levels, but also at linguistic levels (where semantic, lexical, and syntactic processes occur). Using functional MRI adaptation during speech comprehension and production, we found that the brain areas involved in semantic, lexical, and syntactic processing are mostly the same for speaking and for listening. Effects of primary processing load (indicative of sensory and motor processes) overlapped in auditory cortex and left inferior frontal cortex, but not in motor cortex, where processing load affected activity only in speaking. These results indicate that the linguistic parts of the language system are used for both speaking and listening, but that the motor system does not seem to provide a crucial contribution to listening.     

The contribution of rapid visual and auditory processing to the reading of irregular words and pseudowords presented singly and in contiguity

This study examined the relative involvement of rapid auditory and visual temporal resolution mechanisms in the reading of phonologically regular pseudowords and English irregular words presented both in isolation and in contiguity as a series of six words. Seventy-nine undergraduates participated in a range of reading, visual temporal, and auditory temporal tasks. The correlation analyses suggested a general timing mechanism across modalities. There were more significant correlations between the visual temporal measures and irregular word reading and between the auditory measures and pseudoword reading. Auditory gap detection predicted pseudoword reading accuracies. The low temporal frequency flicker contrast sensitivity measure predicted the accuracies of isolated irregular words and pseudowords presented in contiguity. However, when a combined speed-accuracy score was used, visible persistence at both low and high spatial frequencies and auditory gap detection were active in the reading of pseudowords presented in contiguity. Sensory processing skills in both visual and auditory modalities accounted for some of the variance in the reading performance of normal undergraduates, not just reading-impaired students.     

Brain imaging of tongue-twister sentence comprehension: twisting the tongue and the brain

This study used fMRI to investigate the neural basis of the tongue-twister effect in a sentence comprehension task. Participants silently read sentences equated for the syntactic structure and the lexical frequency of the constituent words, but differing in the proportion of words that shared similar initial phonemes. The manipulation affected not only the reading times and comprehension performance, but also the amount of activation seen in a number of language-related cortical areas. The effect was not restricted to cortical areas known to be involved in articulatory speech programming or rehearsal processes (the inferior frontal gyrus and anterior insula), but also extended to areas associated with other aspects of language processing (inferior parietal cortex) associated with phonological processing and storage.