Brain-damaged Subjects Research Articles

A new method for detecting unilateral spatial neglect with tracing tasks using the Rey-Osterrieth complex figure: a pilot study.

To explore efficacy of the "Rey-Osterrieth complex figure (ROCF) tracing task" as a new test to detect unilateral spatial neglect (USN). Subjects were 40 healthy control (HC) and 20 right brain-damaged patients with (USN + , n = 10) or without USN (USN - , n = 10). After the ROCF copying task, the tracing task was performed under conditions that did not leave any tracing lines on the sample figure. Evaluation used the conventional 36-point scoring system, laterality index (LI) as the ratio of the left and right structure scores, and the number of overlaps for each of the left and right structures scored. In the tracing task, USN + showed a lower LI than HC. Furthermore, left-sided neglect was sometimes more evident than in the copying task. Regarding the total overlapping score, USN + showed a greater score than HC. The right-sided overlapping scores in USN + and USN - were also greater than that in HC. In the right brain-damaged subjects, clinically meaningful correlations were not found between evaluations in the ROCF tracing task and in conventional USN screening tests. Receiver-operating-characteristic analysis to test the power of detection showed moderate performance for the tracing LI (AUC = 0.76, 95% CI = 0.54-0.97), which was greater than that of other tests. Further, the total overlapping score in the tracing task showed sensitivity 0.9 (highest among the tests performed), specificity 0.5, and AUC 0.68 (95% CI = 0.43-0.92). The ROCF tracing task might be a convenient method to detect USN and to reveal the extent of spatial working memory impairment.

Intracranial Self-Stimulation and Memory in Rats: A Sistematic Review.

Intracranial self-stimulation (ICSS) is a technique by which rats press a lever to stimulate their brains through an electrode chronically implanted in brain reward areas. Currently only two laboratories in the world, one in India and one in Spain, are intensively studying the effect of this kind of deep brain stimulation on learning and memory. This paper will present the main findings. Different groups of young and old healthy and brain-damaged rats with electrodes implanted in the medial forebrain bundle received a treatment of ICSS after being trained in several paradigms of implicit and explicit learning. Memory was tested over short and long-term periods. Structural and molecular post-mortem analyses of their brains were examined in relation to memory results. ICSS enhances implicit and explicit memory, especially in animals showing poor performance in the learning tasks, such as brain-damaged subjects. At the structural and molecular level, ICSS enhances size and dendritic arborization and promotes neurogenesis in specific hippocampal areas. ICSS also regulates the expression of genes related to learning and memory. Through activating reward and neural plasticity mechanisms, ICSS in the medial forebrain bundle is a promising technique for memory-enhancing treatments.

Arm Ability Training (AAT) Promotes Dexterity Recovery After a Stroke-a Review of Its Design, Clinical Effectiveness, and the Neurobiology of the Actions.

Arm Ability Training (AAT) has been specifically designed to promote manual dexterity recovery for stroke patients who have mild to moderate arm paresis. The motor control problems that these patients suffer from relate to a lack of efficiency in terms of the sensorimotor integration needed for dexterity. Various sensorimotor arm and hand abilities such as speed of selective movements, the capacity to make precise goal-directed arm movements, coordinated visually guided movements, steadiness, and finger dexterity all contribute to our “dexterity” in daily life. All these abilities are deficient in stroke patients who have mild to moderate paresis causing focal disability. The AAT explicitly and repetitively trains all these sensorimotor abilities at the individual's performance limit with eight different tasks; it further implements various task difficulty levels and integrates augmented feedback in the form of intermittent knowledge of results. The evidence from two randomized controlled trials indicates the clinical effectiveness of the AAT with regard to the promotion of “dexterity” recovery and the reduction of focal disability in stroke patients with mild to moderate arm paresis. In addition, the effects have been shown to be superior to time-equivalent “best conventional therapy.” Further, studies in healthy subjects showed that the AAT induced substantial sensorimotor learning. The observed learning dynamics indicate that different underlying sensorimotor arm and hand abilities are trained. Capacities strengthened by the training can, in part, be used by both arms. Non-invasive brain stimulation experiments and functional magnetic resonance imaging data documented that at an early stage in the training cortical sensorimotor network areas are involved in learning induced by the AAT, yet differentially for the tasks trained. With prolonged training over 2 to 3 weeks, subcortical structures seem to take over. While behavioral similarities in training responses have been observed in healthy volunteers and patients, training-induced functional re-organization in survivors of a subcortical stroke uniquely involved the ipsilesional premotor cortex as an adaptive recruitment of this secondary motor area. Thus, training-induced plasticity in healthy and brain-damaged subjects are not necessarily the same.

When is a wh-in-situ question identified in standard Persian?

ABSTRACTPrevious literature demonstrated the influential role of prediction in processing speech [Brazil, 1981. The place of intonation in a discourse model. In C. Malcolm & M. Montgomery (Eds.), Studies in discourse analysis (pp. 146–157). London: Routledge & Kegan Paul; Grosjean, 1983. How long is the sentence? Prediction and prosody in the on-line processing of language. Linguistics, 21, 501–529, 1996a. Using prosody to predict the end of sentences in English and French: Normal and brain damaged subjects. Language and Cognitive Processes, 11, 107–134; Snedeker & Trueswell, 2003. Using prosody to avoid ambiguity: Effects of speaker awareness and referential context. Journal of Memory and Language, 48, 103–130], and of prosody in predicting the eventual syntactic structure of ambiguous sentences [e.g. Snedeker & Trueswell, 2003. Using prosody to avoid ambiguity: Effects of speaker awareness and referential context. Journal of Memory and Language, 48, 103–130]. Wh-in-situ questions contain temporary syntactic ambiguity. One of the languages characterised by wh-in-situ questions is Persian. The current research adopted the gating paradigm [Grosjean, 1980. Spoken word recognition processes and the gating paradigm. Perception and Psychophysics, 28, 267–283] to investigate when distinctive prosodic cues of the pre-wh part enable correct identification of wh-in-situ questions in Persian. A perception experiment was designed in which gated stimuli were played to Persian native speakers in a forced-choice sentence identification task. In line with our expectation, correct identification responses were given from the beginning of the sentence. The result is discussed in the context of proposals regarding the need to integrate prosody and prediction into models of language and speech processing [Beach, 1991. The interpretation of prosodic patterns at points of syntactic structure ambiguity: Evidence for cue trading relations. Journal of Memory and Language, 30, 644–663; Grosjean, 1983. How long is the sentence? Prediction and prosody in the on-line processing of language. Linguistics, 21, 501–529, 1996a. Using prosody to predict the end of sentences in English and French: Normal and brain damaged subjects. Language and Cognitive Processes, 11, 107–134].

Two visual systems in Molyneux subjects

Molyneux’s question famously asks about whether a newly sighted subject might immediately recognize, by sight alone, shapes that were already familiar to her from a tactile point of view. This paper addresses three crucial points concerning this puzzle. First, (a) the presence of two different questions: the classic one concerning visual recognition and another one concerning vision-for-action (the second question has been almost completely neglected in the literature and even those who mention this second formulation do not fully investigate it). Second, (b) the explicit distinction, reported in the literature, between ocular and cortical blindness. Third, (c) the importance of making reference to our best neuroscientific account on vision, ‘the two visual systems model’, in order to better address Molyneux’s problem(s). Then, by offering a new, deeper analysis of the relation between (a), (b) and (c), this paper suggests that the subjects of Molyneux’s two different questions show the same visual impairment as brain-damaged subjects with different lesions of the visual cortex. In particular, the subject of the first (classic) question shows the same impairment in visual recognition as a visual agnosic subject, while the subject of the second question shows the same visual impairment in visuomotor processing as an optic ataxic subject. These impairments still hold even if ocular processing is restored. Therefore, I suggest the following. For the first classic question, the required experimental setting cannot be properly reached. By contrast, concerning the second question, based on the interpretation we select, either the answer is negative, or, as with the first question, the experimental setting cannot be properly reached. This proposal constitutes, with the other approaches offered in the literature, a further attempt to tackle the enormous complexity of Molyneux’s puzzle.

Visual and tactile material recognition in elderly and brain-damaged subjects

Visual and tactile material recognition in elderly and brain-damaged subjects

Neural correlates of consciousness: what we know and what we have to learn!

Consciousness is a multifaceted concept with two major components: awareness of environment and of self (i.e., the content of consciousness) and wakefulness (i.e., the level of consciousness). Medically speaking, consciousness is the state of the patient's awareness of self and environment and his responsiveness to external stimulation and inner need. A basic understanding of consciousness and its neural correlates is of major importance for all clinicians, especially those involved with patients suffering from altered states of consciousness. To this end, in this review it is shown that consciousness is dependent on the brainstem and thalamus for arousal; that basic cognition is supported by recurrent electrical activity between the cortex and the thalamus at gamma band frequencies; and that some kind of working memory must, at least fleetingly, be present for awareness to occur. New advances in neuroimaging studies are also presented in order to better understand and demonstrate the neurophysiological basis of consciousness. In particular, recent functional magnetic resonance imaging studies have offered the possibility to measure directly and non-invasively normal and severely brain damaged subjects' brain activity, whilst diffusion tensor imaging studies have allowed evaluating white matter integrity in normal subjects and patients with disorder of consciousness.

Beyond the Non-Specific Attentional Effect of Caloric Vestibular Stimulation: Evidence from Healthy Subjects and Patients.

Caloric vestibular stimulation (CVS) is a simple physiological manipulation that has been used for a long time in different clinical fields due to its rapid and relevant effects on behaviour. One of the most debated issues in this research field concerns the degree of specificity of such stimulation, namely whether the effects of CVS can be, and to what extent are, independent of the mere influence of non-specific factors such as general arousal, ocular movements or attentional shift towards the stimulated side. The hypothesis that CVS might cause a shift of attention towards the side of the stimulation has been largely supported; moreover, a large amount of evidence is available nowadays to corroborate the specific effect of CVS, providing behavioural and neurophysiological data in both patients and normal subjects. These data converge in indicating that the effects of CVS can be independent of eye deviation and general arousal, can modulate different symptoms in different directions, and do not merely depend on a general shift of attention. The present article is divided into three main sections. In the first section, we describe classical studies that investigate the effects of CVS on neglect and related symptoms. In the second and third parts, we provide an overview of the modulatory effects of CVS on somatosensory processes and body representation in both brain-damaged patients and healthy subjects. Finally, we conclude by discussing the relevance of these new findings for the understanding of the neural mechanisms underlying the modulatory effects of CVS.

Effets bénéfiques de la musique préférée sur les capacités cognitives des patients en état de conscience minimale

Several studies have shown that music can boost cognitive functions in normal and brain-damaged subjects. A few studies have suggested a beneficial effect of music in patients with a disorder of consciousness but it is difficult to conclude since they did not use quantified measures and a control condition/group. The aim of the present study was to compare the effect of music to that of a continuous sound on the relational behavior of patients in a minimally conscious state (MCS). Behavioral responses of six MCS patients were evaluated using items from the Coma Recovery Scale-Revised. Weekly evaluation sessions were carried out, over four weeks, under two conditions: following the presentation of either the patient's preferred music, or following a continuous sound (control condition). Qualitative and quantitative analyses showed that twelve of the eighteen sessions (66.6%) showed a better result for the music condition than for the control condition. This new protocol suggests that preferred music has a beneficial effect on the cognitive abilities of MCS patients. The results further suggest that cerebral plasticity may be enhanced in autobiographical (emotional and familiar) contexts. These findings should now be further extended with an increased number of patients to further validate the hypothesis of the beneficial effect of music on cognitive recovery.

El papel de la morfología en el reconocimiento léxico, España

En el léxico se almacenan y procesan un enorme número de palabras. Este almacenamiento supone un coste cognitivo que no parece asumible por las capacidades del cerebro si no fuera por la especial organización del léxico, que ordena las entradas de modo que economiza el coste de este gran caudal de palabras. En la investigación de dicha organización léxica, destaca desde hace tres décadas el estudio del papel que desempeña la morfología. Diversas investigaciones, tanto con personas con lesión cerebral como sin lesión, han mostrado que la morfología efectivamente cumple un papel muy importante para el reconocimiento léxico. Este papel, sin embargo, no es conocido en profundidad. En este trabajo realizamos una revisión en profundidad de las principales investigaciones al respecto y discutimos los resultados a la luz de los diversos modelos teóricos propuestos.

Prism adaptation in the healthy brain: The shift in line bisection judgments is long lasting and fluctuates

Rightward prism adaptation has been shown to ameliorate visuospatial biases in right brain-damaged patients with neglect, and a single session of prism adaptation can lead to improvements that last up to several hours. Leftward prism adaptation in neurologically healthy individuals induces neglect-like biases in visuospatial tasks. The duration of these effects in healthy individuals, typically assumed to be ephemeral, has never been investigated. Here we assessed the time-course of the adaptation-induced modifications in a classical perceptual line bisection task that was repeatedly administered for approximately 40min after a single session of adaptation to either a leftward or rightward prismatic deviation. Consistent with previous reports, only adaptation to leftward-deviating prisms induced a visuospatial shift on perceptual line bisection judgments. The typical pattern of pseudoneglect was counteracted by a rightward shift in midline judgments, which became significant between 5 and 10min after adaptation, fluctuated between being significant or not several times in the 40min following adaptation, and was present as late as 35min. In contrast, the sensorimotor aftereffect was present immediately after adaptation to both rightward and leftward deviating prisms, decayed initially then remained stable until 40min. These results demonstrate that both the sensorimotor and visuospatial effects last for at least 35min, but that the visuospatial shift needs time to fully develop and fluctuates. By showing that the effects of prism adaptation in the undamaged brain are not ephemeral, these findings reveal the presence of another, so-far neglected dimension in the domain of the cognitive effects induced by prism adaptation, namely time. The prolonged duration of the induced visuospatial shift, previously considered to be a feature of prism adaptation unique to brain-damaged subjects, also applies to the normal brain.

A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior

One challenging aspect of the clinical assessment of brain-injured, unresponsive patients is the lack of an objective measure of consciousness that is independent of the subject's ability to interact with the external environment. Theoretical considerations suggest that consciousness depends on the brain's ability to support complex activity patterns that are, at once, distributed among interacting cortical areas (integrated) and differentiated in space and time (information-rich). We introduce and test a theory-driven index of the level of consciousness called the perturbational complexity index (PCI). PCI is calculated by (i) perturbing the cortex with transcranial magnetic stimulation (TMS) to engage distributed interactions in the brain (integration) and (ii) compressing the spatiotemporal pattern of these electrocortical responses to measure their algorithmic complexity (information). We test PCI on a large data set of TMS-evoked potentials recorded in healthy subjects during wakefulness, dreaming, nonrapid eye movement sleep, and different levels of sedation induced by anesthetic agents (midazolam, xenon, and propofol), as well as in patients who had emerged from coma (vegetative state, minimally conscious state, and locked-in syndrome). PCI reliably discriminated the level of consciousness in single individuals during wakefulness, sleep, and anesthesia, as well as in patients who had emerged from coma and recovered a minimal level of consciousness. PCI can potentially be used for objective determination of the level of consciousness at the bedside.

The effectiveness of computer-assisted cognitive rehabilitation in brain-damaged patients

AbstractThis study examined the effects of computer-assisted cognitive rehabilitation in a group of 16 brain-damaged patients. Therapeutic effectiveness was assessed by improvement on computer tasks, the results of neuropsychological tests and quality of life ratings. Participants suffered from mild to moderate attention and memory problems or aphasia. The procedure involved baseline assessment (pretest), a 15-week course of therapy conducted twice a week (30 hours in total) and posttest. Neuropsychological tests assessing attention, memory and language problems and quality of life ratings were administered twice: in pre- and posttests. Twelve healthy controls were also examined twice (with a 15-week interval) using the same battery of neuropsychological tests. The RehaCom program and the Polish computer therapy program for aphasics called Afa-System were used for rehabilitation. The computer-assisted rehabilitation tasks were selected individually for each patient. The results showed significant improvement on computer-assisted tasks in all braindamaged subjects. However, none or very little improvement was observed on neuropsychological tests and quality of life ratings. The results of the study confirm the importance of using different types of measures to estimate the effectiveness of computer-assisted neuropsychological rehabilitation as well as the necessity of applying various kinds of therapy to improve cognitive, emotional and social functioning in brain-damaged patients.

Dissociated repetition deficits in aphasia can reflect flexible interactions between left dorsal and ventral streams and gender-dimorphic architecture of the right dorsal stream

Assessment of brain-damaged subjects presenting with dissociated repetition deficits after selective injury to either the left dorsal or ventral auditory pathways can provide further insight on their respective roles in verbal repetition. We evaluated repetition performance and its neural correlates using multimodal imaging (anatomical MRI, DTI, fMRI, and18FDG-PET) in a female patient with transcortical motor aphasia (TCMA) and in a male patient with conduction aphasia (CA) who had small contiguous but non-overlapping left perisylvian infarctions. Repetition in the TCMA patient was fully preserved except for a mild impairment in nonwords and digits, whereas the CA patient had impaired repetition of nonwords, digits and word triplet lists. Sentence repetition was impaired, but he repeated novel sentences significantly better than clichés. The TCMA patient had tissue damage and reduced metabolism in the left sensorimotor cortex and insula. DTI showed damage to the left temporo-frontal and parieto-frontal segments of the arcuate fasciculus (AF) and part of the left ventral stream together with well-developed right dorsal and ventral streams, as has been reported in more than one-third of females. The CA patient had tissue damage and reduced metabolic activity in the left temporoparietal cortex with additional metabolic decrements in the left frontal lobe. DTI showed damage to the left temporo-parietal and temporo-frontal segments of the AF, but the ventral stream was spared. The direct segment of the AF in the right hemisphere was also absent with only vestigial remains of the other dorsal subcomponents present, as is often found in males. fMRI during word and nonword repetition revealed bilateral perisylvian activation in the TCMA patient suggesting recruitment of spared segments of the left dorsal stream and right dorsal stream with propagation of signals to temporal lobe structures suggesting a compensatory reallocation of resources via the ventral streams. The CA patient showed a greater activation of these cortical areas than the TCMA patient, but these changes did not result in normal performance. Repetition of word triplet lists activated bilateral perisylvian cortices in both patients, but activation in the CA patient with very poor performance was restricted to small frontal and posterior temporal foci bilaterally. These findings suggest that dissociated repetition deficits in our cases are probably reliant on flexible interactions between left dorsal stream (spared segments, short tracts remains) and left ventral stream and on gender-dimorphic architecture of the right dorsal stream.

Intrathecal baclofen treatment in early stage of severe brain damaged subjects: Case-report and literature review

Intrathecal baclofen treatment in early stage of severe brain damaged subjects: Case-report and literature review

Correction: Spatio-Temporal Features of Visual Exploration in Unilaterally Brain-Damaged Subjects with or without Neglect: Results from a Touchscreen Test

Correction: Spatio-Temporal Features of Visual Exploration in Unilaterally Brain-Damaged Subjects with or without Neglect: Results from a Touchscreen Test

Spatio-Temporal Features of Visual Exploration in Unilaterally Brain-Damaged Subjects with or without Neglect: Results from a Touchscreen Test

Cognitive assessment in a clinical setting is generally made by pencil-and-paper tests, while computer-based tests enable the measurement and the extraction of additional performance indexes. Previous studies have demonstrated that in a research context exploration deficits occur also in patients without evidence of unilateral neglect at pencil-and-paper tests. The objective of this study is to apply a touchscreen-based cancellation test, feasible also in a clinical context, to large groups of control subjects and unilaterally brain-damaged patients, with and without unilateral spatial neglect (USN), in order to assess disturbances of the exploratory skills. A computerized cancellation test on a touchscreen interface was used for assessing the performance of 119 neurologically unimpaired control subjects and 193 patients with unilateral right or left hemispheric brain damage, either with or without USN. A set of performance indexes were defined including Latency, Proximity, Crossings and their spatial lateral gradients, and Preferred Search Direction. Classic outcome scores were computed as well. Results show statistically significant differences among groups (assumed p<0.05). Right-brain-damaged patients with USN were significantly slower (median latency per detected item was 1.18 s) and less efficient (about 13 search-path crossings) in the search than controls (median latency 0.64 s; about 3 crossings). Their preferred search direction (53.6% downward, 36.7% leftward) was different from the one in control patients (88.2% downward, 2.1% leftward). Right-brain-damaged patients without USN showed a significantly abnormal behavior (median latency 0.84 s, about 5 crossings, 83.3% downward and 9.1% leftward direction) situated half way between controls and right-brain-damaged patients with USN. Left-brain-damaged patients without USN were significantly slower and less efficient than controls (latency 1.19 s, about 7 crossings), preserving a normal preferred search direction (93.7% downward). Therefore, the proposed touchscreen-based assessment had evidenced disorders in spatial exploration also in patients without clinically diagnosed USN.

Atividade metalinguística em discussão: a refacção textual escrita de sujeitos afásicos

Although there have been several studies about the processses of rewriting texts there is none related to aphasia. Even thou rewriting is considered as an alternative to promote reflection, to searching for new ways and, therefore, as a new possibility of sigfiynig in a text, in language, it was never studied with brain damaged subjects. When the subjects recognizes the need to rewrite his text in order to make themselves understood in a more accurate way by his partners, they change their strategies, adjusts their language and positions themselves as a social subjects. The theory on which this work is based is the Neurolinguistics developed by Coudry (1986) and Morato (1995), discoursively oriented, which assumes the close relation between language and speech, language and cognition and between the subject and the social practices. Three aphasic subjects were followed while the process of writing texts about their history on aphasia, mainly about the consequences that the condition of being aphasics brought to their lives. The process of writing was carried together with the investigator, when they talked about their doubts and about the hyphotesis they made about the process of writing. The analysis shows that the cognitive aspects related to the knowledge of the roles and structures of a written text are preserved. In fact, they were able to recognize when something is not properly organized. In general, the research shows that the work with rewriting allows the subject to recover and/or improve their competence in reading and writing.

Transcranial Direct Current Stimulation Improves Word Retrieval in Healthy and Nonfluent Aphasic Subjects

A number of studies have shown that modulating cortical activity by means of transcranial direct current stimulation (tDCS) affects performances of both healthy and brain-damaged subjects. In this study, we investigated the potential of tDCS to enhance associative verbal learning in 10 healthy individuals and to improve word retrieval deficits in three patients with stroke-induced aphasia. In healthy individuals, tDCS (20 min, 1 mA) was applied over Wernicke's area (position CP5 of the International 10-20 EEG System) while they learned 20 new "words" (legal nonwords arbitrarily assigned to 20 different pictures). The healthy subjects participated in a randomized counterbalanced double-blind procedure in which they were subjected to one session of anodic tDCS over left Wernicke's area, one sham session over this location and one session of anodic tDCS stimulating the right occipito-parietal area. Each experimental session was performed during a different week (over three consecutive weeks) with 6 days of intersession interval. Over 2 weeks, three aphasic subjects participated in a randomized double-blind experiment involving intensive language training for their anomic difficulties in two tDCS conditions. Each subject participated in five consecutive daily sessions of anodic tDCS (20 min, 1 mA) and sham stimulation over Wernicke's area while they performed a picture-naming task. By the end of each week, anodic tDCS had significantly improved their accuracy on the picture-naming task. Both normal subjects and aphasic patients also had shorter naming latencies during anodic tDCS than during sham condition. At two follow-ups (1 and 3 weeks after the end of treatment), performed only in two aphasic subjects, response accuracy and reaction times were still significantly better in the anodic than in the sham condition, suggesting a long-term effect on recovery of their anomic disturbances.

Electrical stimulation over the left inferior frontal gyrus (IFG) determines long-term effects in the recovery of speech apraxia in three chronic aphasics

A number of studies have shown that modulating cortical activity by means of transcranial direct current stimulation (tDCS) affects the performance of both healthy and brain-damaged subjects. In this study, we investigated the potential of tDCS for the recovery of apraxia of speech in 3 patients with stroke-induced aphasia. Over 2 weeks, three aphasic subjects participated in a randomized double-blinded experiment involving intensive language training for their articulatory difficulties in two tDCS conditions. Each subject participated in five consecutive daily sessions of anodic tDCS (20 min, 1 mA) and sham stimulation over the left inferior frontal gyrus (referred to as Broca's area) while they performed a repetition task. By the end of each week, a significant improvement was found in both conditions. However, all three subjects showed greater response accuracy in the anodic than in the sham condition. Moreover, results for transfer of treatment effects, although different across subjects, indicate a generalization of the recovery at the language test. Subjects 2 and 3 showed a significant improvement in oral production tasks, such as word repetition and reading, while Subjects 1 and 2 had an unexpected significant recovery in written naming and word writing under dictation tasks. At three follow-ups (1 week, 1 and 2 months after the end of treatment), response accuracy was still significantly better in the anodic than in sham condition, suggesting a long-term effect on the recovery of their articulatory gestures.