How to get by with half a loop - An investigation of visual and auditory codes in a case of impaired phonological short-term memory (pSTM).

In the field of cognitive neuropsychology of phonological short-term memory (pSTM), a key debate surrounds the issue of how impairment on tasks deemed to tap this system imply a dissociable phonological input and output buffer system, with the implication that impairments can be fractionated across disruption to separate functional components (Nickels, Howard & Best, 1997). This study presents CT, a conduction aphasic who showed no impairment on basic auditory discrimination tasks, but had very poor nonword repetition. Clear-cut examples of such cases are very rare (see Jacquemot, Dupoux & Bachoud-Levi, 2007), and we interpret the case with reference to a pSTM model that includes input and output buffers. The dissociation between performance on auditory phonological tasks and visual phonological tasks we interpret as consistent with disruption to the link from input buffer to output buffer without concurrent damage to connections from output to input. Previous research has also shown that patients with impairments of pSTM can make visual confusions with orthographically presented items in tasks seeking to tap this mechanism (Warrington & Shallice, 1972), which might stem from having an incomplete pSTM loop. In light of this we examined whether CT's ability on tests of ISR was affected by visual orthographic similarity among list items, and this is indeed what we observed. On balance then, CT's overall profile is considered best interpreted with respect to a dual buffer pSTM model (e.g., Vallar & Papagno, 2002).

Phonotactic processing deficit following left-hemisphere stroke.

The neural basis of speech processing is still a matter of great debate. Phonotactic knowledge-knowledge of the allowable sound combinations in a language-remains particularly understudied. The purpose of this study was to investigate the brain regions crucial to phonotactic knowledge in left-hemisphere stroke survivors. Results were compared to areas in which gray matter anatomy related to phonotactic knowledge in healthy controls. 44 patients with chronic left-hemisphere stroke, and 32 controls performed an English-likeness rating task on 60 auditory non-words of varying phonotactic regularities. They were asked to rate on a 1-5 scale, how close each non-word sounded to English. Patients' performance was compared to that of healthy controls, using mixed effects modeling. Multivariate lesion-symptom mapping and voxel-based morphometry were used to find the brain regions important for phonotactic processing in patients and controls respectively. The results showed that compared to controls, stroke survivors were less sensitive to phonotactic regularity differences. Lesion-symptom mapping demonstrated that a loss of sensitivity to phonotactic regularities was associated with lesions in left angular gyrus and posterior middle temporal gyrus. Voxel-based morphometry also revealed a positive correlation between gray matter density in left angular gyrus and sensitivity to phonotactic regularities in controls. We suggest that the angular gyrus is used to compare the incoming speech stream to internal predictions based on the frequency of sound sequences in the language derived from stored lexical representations in the posterior middle temporal gyrus.

Neural organization of spoken language revealed by lesion-symptom mapping.

Studies of patients with acquired cognitive deficits following brain damage and studies using contemporary neuroimaging techniques form two distinct streams of research on the neural basis of cognition. In this study, we combine high-quality structural neuroimaging analysis techniques and extensive behavioural assessment of patients with persistent acquired language deficits to study the neural basis of language. Our results reveal two major divisions within the language system-meaning versus form and recognition versus production-and their instantiation in the brain. Phonological form deficits are associated with lesions in peri-Sylvian regions, whereas semantic production and recognition deficits are associated with damage to the left anterior temporal lobe and white matter connectivity with frontal cortex, respectively. These findings provide a novel synthesis of traditional and contemporary views of the cognitive and neural architecture of language processing, emphasizing dual routes for speech processing and convergence of white matter tracts for semantic control and/or integration.

The relationship between verbal and nonverbal auditory signal processing in conduction aphasia: behavioral and anatomical evidence for common decoding mechanisms.

The processing of nonverbal auditory stimuli has not yet been sufficiently investigated in patients with aphasia. On the basis of a duration discrimination task, we examined whether patients with left-sided cerebrovascular lesions were able to perceive time differences in the scale of approximately 150 ms. Further linguistic and memory-related tasks were used to characterize more exactly the relationships in the performances between auditory nonverbal task and selective linguistic or mnemonic disturbances. All examined conduction aphasics showed increased thresholds in the duration discrimination task. The low thresholds on this task were in a strong correlative relation to the reduced performances in repetition and working memory task. This was interpreted as an indication of a pronounced disturbance in integrating auditory verbal information into a long-term window (sampling disturbance) resulting in an additional load of working memory. In order to determine the lesion topography of patients with sampling disturbances, the anatomical and psychophysical data were correlated on the basis of a voxelwise statistical approach. It was found that tissue damage extending through the insula, the posterior superior temporal gyrus, and the supramarginal gyrus causes impairments in sequencing of time-sensitive information.

Conduction aphasia with intact visual object naming.

Conduction aphasia, most often caused by damage to the inferior parietal lobe and arcuate fasciculus, is usually characterized by mildly dysfluent speech with frequent phonemic paraphasic errors, impaired repetition, and impaired word finding and naming, but with relatively spared comprehension. We report an 86-year-old right-handed man with conduction aphasia caused by an infarction that damaged his right temporoparietal region. On testing with the Western Aphasia Battery, however, he named objects almost perfectly. To test his naming ability further, we showed him half the items in the Boston Naming Test; we described or defined the other half of the items, but did not show them to the patient. He performed excellently when naming the objects that he could see, but he had difficulty naming the objects that were only described or defined. These observations suggest that visual word naming may be mediated by a network that is somewhat independent of the networks that mediate spontaneous word finding and word finding based on verbal descriptions or definitions.

The cortical organization of speech processing: feedback control and predictive coding the context of a dual-stream model.

Speech recognition is an active process that involves some form of predictive coding. This statement is relatively uncontroversial. What is less clear is the source of the prediction. The dual-stream model of speech processing suggests that there are two possible sources of predictive coding in speech perception: the motor speech system and the lexical-conceptual system. Here I provide an overview of the dual-stream model of speech processing and then discuss evidence concerning the source of predictive coding during speech recognition. I conclude that, in contrast to recent theoretical trends, the dorsal sensory-motor stream is not a source of forward prediction that can facilitate speech recognition. Rather, it is forward prediction coming out of the ventral stream that serves this function.

Arcuate fasciculus variability and repetition: the left sometimes can be right.

Repetition ability is a major criterion for classifying aphasic syndromes and its status is helpful in the determination of the involved neural structures. It is widely assumed that repetition deficits correlate with injury to the left perisylvian core including the arcuate fasciculus (AF). However, descriptions of normal repetition despite damage to the AF or impaired repetition without AF involvement cast doubts on its role in repetition. To explain these paradoxes, we analyse two different aphasic syndromes - in which repetition is selectively impaired (conduction aphasia) or spared (transcortical aphasias) - in light of recent neuroimaging findings. We suggest that the AF and other white matter bundles are the anatomical signatures of language repetition and that individual variability in their anatomy and lateralisation may explain negative cases.

What can iconic gestures tell us about the language system? A case of conduction aphasia.

BACKGROUND: Speech and language therapists rarely analyse iconic gesture when assessing a client with aphasia, despite a growing body of research suggesting that language and gesture are part of either the same system or two highly integrated systems. This may be because there has been limited research that has systematically analysed iconic gesture production by people with aphasia. AIMS: The aim was to determine whether the gesture production of a participant with conduction aphasia was able to provide information about her language system. METHODS & PROCEDURES: The iconic gestures produced by a participant with conduction aphasia (LT) and five control participants produced during the retelling of a cartoon were analysed. In particular, the iconic gestures produced during lexical retrieval difficulties (co-tip-of-the-tongue (co-TOT) gestures) were compared with the iconic gestures produced during fluent speech (co-speech gestures). OUTCOMES & RESULTS: It was found that LT produced 57 co-speech gestures that were similar in form to the co-speech gestures produced by the control participants (mean = 34.2, standard deviation (SD) = 22.2). LT also produced an additional eleven co-TOT gestures that were unlike her co-speech gestures and unlike the co-speech gestures produced by the control participants. While the co-speech gestures depicted events, the co-TOT gestures depicted 'things' (for example, objects and animals). Furthermore, all but one of the co-TOT gestures produced by LT was classified as a shape-outline gesture, whereas co-speech gestures were rarely classified as shape-outline gestures. LT also produced a new type of gesture that has not previously been described in the literature: a homophone gesture. This co-TOT homophone gesture depicted the homophone of the target word. The iconic gestures produced by LT suggest that she had an intact semantic system but had difficulties with phonological encoding, consistent with a diagnosis of conduction aphasia. This raises the possibility that iconic gesture production can provide evidence about the level of breakdown in the language system. CONCLUSIONS & IMPLICATIONS: A larger study exploring the gestures produced by participants with aphasia is required. The research also highlights the importance of including gesture assessments in SLT's work with adults with acquired language disorder.

Atypical conduction aphasia and the right hemisphere: Cross-hemispheric plasticity of phonology in a developmentally dyslexic and dysgraphic patient with early left frontal damage.

We report the rare case of a patient, JNR, with history of mixed handedness, developmental dyslexia, dysgraphia, and attentional deficits associated with a Klippel-Trenaunay syndrome and a small subcortical frontal lesion involving the left arcuate fasciculus. In adulthood, he suffered a large right perisylvian stroke and developed atypical conduction aphasia with deficits in input and output phonological processing and poor auditory-verbal short-term memory. Lexical-semantic processing for single words was intact, but he was unable to access meaning in sentence comprehension and repetition. Reading and writing deficits worsened after the stroke and he presented a combination of developmental and acquired dysgraphia and dyslexia with mixed lexical and phonological processing deficits. This case suggest that a small lesion sustained prenatally or early in life could induce a selective rightward shift of phonology sparing the standard left hemisphere lateralisation of lexical-semantic functions.

Temporal processing capabilities in repetition conduction aphasia.

This study investigates the temporal resolution capacities of the central-auditory system in a subject (NP) suffering from repetition conduction aphasia. More specifically, the patient was asked to detect brief gaps between two stretches of broadband noise (gap detection task) and to evaluate the duration of two biphasic (WN-3) continuous noise elements, starting with white noise (WN) followed by 3kHz bandpass-filtered noise (duration discrimination task). During the gap detection task, the two portions of each stimulus were either identical ("intra-channel condition") or differed ("inter-channel condition") in the spectral characteristics of the leading and trailing acoustic segments. NP did not exhibit any deficits in the intra-channel condition of the gap detection task, indicating intact auditory temporal resolution across intervals of 1-3ms. By contrast, the inter-channel condition yielded increased threshold values. Based upon the "multiple-looks" model of central-auditory processing, this profile points at a defective integration window operating across a few tens of milliseconds - a temporal range associated with critical features of the acoustic speech signal such as voice onset time and formant transitions. Additionally, NP was found impaired during a duration discrimination task addressing longer integration windows (ca. 150ms). Concerning speech, this latter time domain approximately corresponds to the duration of stationary segmental units such as fricatives and long vowels. On the basis of our results we suggest, that the patient's auditory timing deficits in non-speech tasks may account, at least partially, for his impairments in speech processing.

Density pervades: an analysis of phonological neighbourhood density effects in aphasic speakers with different types of naming impairment.

We investigated the influence of phonological neighbourhood density (PND) on the performance of aphasic speakers whose naming impairments differentially implicate phonological or semantic stages of lexical access. A word comes from a dense phonological neighbourhood if many words sound like it. Limited evidence suggests that higher density facilitates naming in aphasic speakers, as it does in healthy speakers. Using well-controlled stimuli, Experiment 1 confirmed the influence of PND on accuracy and phonological error rates in two aphasic speakers with phonological processing deficits. In Experiments 2 and 3, we extended the investigation to an aphasic speaker who is prone to semantic errors, indicating a semantic deficit and/or a deficit in the mapping from semantics to words. This individual had higher accuracy, and fewer semantic errors, in naming targets from high- than from low-density neighbourhoods. It is argued that the Results provide strong support for interactive approaches to lexical access, where reverberatory feedback between word- and phoneme-level lexical representations not only facilitates phonological level processes but also privileges the selection of a target word over its semantic competitors.

The role of the arcuate fasciculus in conduction aphasia.

In aphasia literature, it has been considered that a speech repetition defect represents the main constituent of conduction aphasia. Conduction aphasia has frequently been interpreted as a language impairment due to lesions of the arcuate fasciculus (AF) that disconnect receptive language areas from expressive ones. Modern neuroradiological studies suggest that the AF connects posterior receptive areas with premotor/motor areas, and not with Broca's area. Some clinical and neurophysiological findings challenge the role of the AF in language transferring. Unusual cases of inter-hemispheric dissociation of language lateralization (e.g. Broca's area in the left, and Wernicke's area in the right hemisphere) have been reported without evident repetition defects; electrocortical studies have found that the AF not only transmits information from temporal to frontal areas, but also in the opposite direction; transferring of speech information from the temporal to the frontal lobe utilizes two different streams and conduction aphasia can be found in cases of cortical damage without subcortical extension. Taken altogether, these findings may suggest that the AF is not required for repetition although could have a subsidiary role in it. A new language network model is proposed, emphasizing that the AF connects posterior brain areas with Broca's area via a relay station in the premotor/motor areas.

Visuomotor tracking abilities of speakers with apraxia of speech or conduction aphasia.

This investigation examined the visuomotor tracking abilities of persons with apraxia of speech (AOS) or conduction aphasia (CA). In addition, tracking performance was correlated with perceptual judgments of speech accuracy. Five individuals with AOS and four with CA served as participants, as well as an equal number of healthy controls matched by age and gender. Participants tracked predictable (sinusoidal) and unpredictable signals using jaw and lip movements transduced with strain gauges. Tracking performance in participants with AOS was poorest for predictable signals, with decreased kinematic measures of cross-correlation and gain ratio and increased target-tracker difference. In contrast, tracking of the unpredictable signal by participants with AOS was performed as well as for other groups (e.g. participants with CA, healthy controls). Performance of the subjects with AOS on the predictable tracking task was found to strongly correlate with perceptual judgments of speech. These findings suggest that motor control capabilities are impaired in AOS, but not in CA. Results suggest that AOS has its basis in motor programming deficits, not impaired motor execution.

The many places of frequency: evidence for a novel locus of the lexical frequency effect in word production.

The effect of lexical frequency on language-processing tasks is exceptionally reliable. For example, pictures with higher frequency names are named faster and more accurately than those with lower frequency names. Experiments with normal participants and patients strongly suggest that this production effect arises at the level of lexical access. Further work has suggested that within lexical access this effect arises at the level of lexical representations. Here we present patient E.C. who shows an effect of lexical frequency on his nonword error rate. The best explanation of his performance is that there is an additional locus of frequency at the interface of lexical and segmental representational levels. We confirm this hypothesis by showing that only computational models with frequency at this new locus can produce a similar error pattern to that of patient E.C. Finally, in an analysis of a large group of Italian patients, we show that there exist patients who replicate E.C.'s pattern of results and others who show the complementary pattern of frequency effects on semantic error rates. Our results combined with previous findings suggest that frequency plays a role throughout the process of lexical access.

It's either a cook or a baker: patients with conduction aphasia get the gist but lose the trace.

Patients with conduction aphasia have been characterized as having a short-term memory deficit that leads to relative difficulty on span and repetition tasks. It has also been observed that these same patients often get the gist of what is said to them, even if they are unable to repeat the information verbatim. To study this phenomenon experimentally, patients with conduction aphasia and left hemisphere-injured controls were tested on a repetition recognition task that required them to listen to a sentence and immediately point to one of three sentences that matched it. On some trials, the distractor sentences contained substituted words that were semantically-related to the target, and on other trials, the distractor sentences contained semantically-distinct words. Patients with conduction aphasia and controls performed well on the latter condition, when distractors were semantically-distinct. However, when the distractor sentences were semantically-related, the patients with conduction aphasia were impaired at identifying the target sentence, suggesting that these patients could not rely on the verbatim trace. To further understand these results, we also tested elderly controls on the same task, except that a delay was introduced between study and test. Like the patients with conduction aphasia, the elderly controls were worse at identifying target sentences when there were semantically-related distractors. Taken together, these results suggest that patients with conduction aphasia rely on non-phonologic cues, such as lexical-semantics, to support their short-term memory, just as normal participants must do in long-term memory tasks when the phonological trace is no longer present.

[Neurolinguistic approaches to aphasia]. / Aproximaciones lingüísticas a la afasiología en torno a la repetición.

Aphasias are language pathologies, therefore the acquaintance of its structure is required for proper understanding. Language is a cultural interaction system, logical, set much above common natural. It separates the symbolic function, which establishes the distinction between significant and signification. We establish a neurolinguistic classification of aphasias, refuting improper expressions. We broach the wrongly called "conduction aphasia". We detach the unit of speech act and we distinguish the existence of a joint project that sheds light on all sentences brought forth. The complex texture of the "transcorticalism" qualify is analyzed. Aphasia field and some forms of its unfolding are questions aborded under the light of basic neurolinguistic concepts. We detach the unit of speech act and we distinguish the existence of a common project that sheds light on all sentences brought forth.

Aproximaciones lingüísticas a la afasiología en torno a la repetición / Neurolinguistic approaches about aphasia

Las afasias son una patología del lenguaje y éste es un sistema de mediación cultural lógica, situado netamente por encima de lo meramente natural. Arranca de la función simbólica, que establece la distinción y el nexo entre significante y significado. Se establece, a grandes rasgos, una clasificación neurolingüística de las afasias, rechazando las expresiones inadecuadas de sensitiva o sensorial y motora. Se insiste particularmente aquí sobre la cuestión de la "repetición" en la semiología afásica, tanto en lo que se refiere a su pérdida como a su "exaltación". Ello conduce a una revisión de la mal llamada afasia "de conducción" y del "transcorticalismo".

Aphasias are language pathologies, therefore the acquaintance of its structure is required for proper understanding. Language is a cultural interaction system, logical, set much above common natural. It separates the symbolic function, which establishes the distinction between significant and signification. We establish a neurolinguistic classification of aphasias, refuting improper expressions. We broach the wrongly called "conduction aphasia". We detach the unit of speech act and we distinguish the existence of a joint project that sheds light on all sentences brought forth. The complex texture of the "transcorticalism" qualify is analyzed. Aphasia field and some forms of its unfolding are questions aborded under the light of basic neurolinguistic concepts. We detach the unit of speech act and we distinguish the existence of a common project that sheds light on all sentences brought forth.

Reaction time and accuracy in individuals with aphasia during auditory vigilance tasks.

Research indicates that attentional deficits exist in aphasic individuals. However, relatively little is known about auditory vigilance performance in individuals with aphasia. The current study explores reaction time (RT) and accuracy in 10 aphasic participants and 10 nonbrain-damaged controls during linguistic and nonlinguistic auditory vigilance tasks. Findings indicate that the aphasic group was less accurate during both tasks than the control group, but was not slower in their accurate responses. Further examination of the data revealed variability in the aphasic participants' RT contributing to the lower accuracy scores.

The rises and falls of disconnection syndromes.

In a brain composed of localized but connected specialized areas, disconnection leads to dysfunction. This simple formulation underlay a range of 19th century neurological disorders, referred to collectively as disconnection syndromes. Although disconnectionism fell out of favour with the move against localized brain theories in the early 20th century, in 1965, an American neurologist brought disconnection to the fore once more in a paper entitled, 'Disconnexion syndromes in animals and man'. In what was to become the manifesto of behavioural neurology, Norman Geschwind outlined a pure disconnectionist framework which revolutionized both clinical neurology and the neurosciences in general. For him, disconnection syndromes were higher function deficits that resulted from white matter lesions or lesions of the association cortices, the latter acting as relay stations between primary motor, sensory and limbic areas. From a clinical perspective, the work reawakened interest in single case studies by providing a useful framework for correlating lesion locations with clinical deficits. In the neurosciences, it helped develop contemporary distributed network and connectionist theories of brain function. Geschwind's general disconnectionist paradigm ruled clinical neurology for 20 years but in the late 1980s, with the re-emergence of specialized functional roles for association cortex, the orbit of its remit began to diminish and it became incorporated into more general models of higher dysfunction. By the 1990s, textbooks of neurology were devoting only a few pages to classical disconnection theory. Today, new techniques to study connections in the living human brain allow us, for the first time, to test the classical formulation directly and broaden it beyond disconnections to include disorders of hyperconnectivity. In this review, on the 40th anniversary of Geschwind's publication, we describe the changing fortunes of disconnection theory and adapt the general framework that evolved from it to encompass the entire spectrum of higher function disorders in neurology and psychiatry.

Functional MRI follow-up study of language processes in healthy subjects and during recovery in a case of aphasia.

BACKGROUND AND PURPOSE: The goal of this study was to develop a functional MRI (fMRI) paradigm robust and reproducible enough in healthy subjects to be adapted for a follow-up study aiming at evaluating the anatomical substratum of recovery in poststroke aphasia. METHODS: Ten right-handed subjects were studied longitudinally using fMRI (7 of them being scanned twice) and compared with a patient with conduction aphasia during the first year of stroke recovery. RESULTS: Controls exhibited reproducible activation patterns between subjects and between sessions during language tasks. In contrast, the patient exhibited dynamic changes in brain activation pattern, particularly in the phonological task, during the 2 fMRI sessions. At 1 month after stroke, language homotopic right areas were recruited, whereas large perilesional left involvement occurred later (12 months). CONCLUSIONS: We first demonstrate intersubject robustness and intrasubject reproducibility of our paradigm in 10 healthy subjects and thus its validity in a patient follow-up study over a stroke recovery time course. Indeed, results suggest a spatiotemporal poststroke brain reorganization involving both hemispheres during the recovery course, with an early implication of a new contralateral functional neural network and a later implication of an ipsilateral one.