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PubMed2006

A probabilistic model of gaze imitation and shared attention.

An important component of language acquisition and cognitive learning is gaze imitation. Infants as young as one year of age can follow the gaze of an adult to determine the object the adult is focusing on. The ability to follow gaze is a precursor to shared attention, wherein two or more agents simultaneously focus their attention on a single object in the environment. Shared attention is a necessary skill for many complex, natural forms of learning, including learning based on imitation. This paper presents a probabilistic model of gaze imitation and shared attention that is inspired by Meltzoff and Moore's AIM model for imitation in infants. Our model combines a probabilistic algorithm for estimating gaze vectors with bottom-up saliency maps of visual scenes to produce maximum a posteriori (MAP) estimates of objects being looked at by an observed instructor. We test our model using a robotic system involving a pan-tilt camera head and show that combining saliency maps with gaze estimates leads to greater accuracy than using gaze alone. We additionally show that the system can learn instructor-specific probability distributions over objects, leading to increasing gaze accuracy over successive interactions with the instructor. Our results provide further support for probabilistic models of imitation and suggest new ways of implementing robotic systems that can interact with humans over an extended period of time.

Attention↗
PubMed2003

Pantomime of object use: a challenge to cerebral localization of cognitive function.

The paper illustrates difficulties and insecurities of localizing cognitive functions with the example of pantomime of object use. Numerous studies have established a particular sensitivity of this task to left brain damage (LBD), but there is no agreement as to how components of its cognitive architecture are related to the laterality and intrahemispheric location of responsible lesions. Apraxia and asymbolia have been suspected to be crucial for explaining the vulnerability of pantomime to LBD, but analysis of correlations between impairments of pantomime, imitation of gestures, drawing from memory, and language in patients with LBD and aphasia suggests that neither of these putative deficits can adequately account for the data. It rather appears that pantomime taps a central aspect of left hemisphere function which affects performance on a great number of otherwise widely different tasks and which is not bound to any particular location within the hemisphere. I discuss ways to resolve apparent conflicts between this interpretation and the findings of double dissociations between pantomime and imitation in clinical case studies and of circumscribed left parietal activation during pantomime in functional neuroimaging.

Aphasia↗
PubMed2004

Functional imaging of face and hand imitation: towards a motor theory of empathy.

Empathy requires the ability to map the feelings of others onto our own nervous system. Until recently, there was no plausible mechanism to explain how such a mapping might occur. The discovery of mirror neurons, however, suggests that the nervous system is capable of mapping the observed actions of others onto the premotor cortex of the self, at least for reaching and grasping movements. Is there a mirroring system for emotive actions, such as facial expression? Subjects (N = 15; all right-handed; eight men, seven women) watched movies of facial expressions (smile or frown) and hand movements (move index or middle finger) while brain activity was imaged using functional magnetic resonance imaging (fMRI). Subjects watched the movies under three different conditions: passive viewing, active imitation, and an active motor control. Subjects also performed a verb generation task to functionally identify language-processing areas. We found evidence for a common cortical imitation circuit for both face and hand imitation, consisting of Broca's area, bilateral dorsal and ventral premotor areas, right superior temporal gyrus (STG), supplementary motor area, posterior temporo-occipital cortex, and cerebellar areas. For faces, passive viewing led to significant activation in the right ventral premotor area, whereas imitation produced bilateral activation. This result is consistent with evidence for right hemisphere (RH) dominance for emotional processing, and suggests that there may be a right hemisphere mirroring system that could provide a neural substrate for empathy.

Adult↗
PubMed2004

Activation of the human primary motor cortex during observation of tool use.

Tool use is a characteristic human trait, requiring motor skills that are largely learned by imitation. A neural system that supports imitation and action understanding by directly matching observed actions and their motor counterparts has been found in the human premotor and motor cortices. To test whether this "mirror-neuron system" (MNS) would be activated by observation of tool use, we recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects while they observed the experimenter to use chopsticks in a goal-directed and non-goal-directed manner. The left and right median nerves were stimulated alternatingly, and the poststimulus rebounds of the approximately 20-Hz motor-cortex rhythms were quantified. Compared with the rest condition, the level of the approximately 20-Hz rhythm was suppressed during observation of both types of tool use, indicating activation of the primary motor cortex. The suppression was on average 15-17% stronger during observation of goal-directed than non-goal-directed tool use, and this difference correlated positively with the frequency of subjects' chopstick use during the last year. These results support the view that the motor-cortex activation is related to the observer's ability to understand and imitate motor acts.

Adult↗
PubMed2005

An fMRI study of joint attention experience.

Although much is now known about eye movement detection, little is known about the higher cognitive processes involved in joint attention. We developed video stimuli which when watched, engender an experience of joint attention in the observer. This allowed us to compare an experience of joint attention to nonjoint attention within an fMRI scanning environment. Joint attention was associated with activity in the ventromedial frontal cortex, the left superior frontal gyrus (BA10), cingulate cortex, and caudate nuclei. The ventromedial frontal cortex has been consistently shown to be activated during mental state attribution tasks. BA10 may serve a cognitive integration function, which in this case seems to utilize a perception-action matching process. The activation we identified in BA10 overlaps with a location of increased grey matter density that we recently found to be associated with autistic spectrum disorder. This study therefore constitutes evidence that the neural substrate of joint attention also serves a mentalizing function. The developmental failure of this substrate in the left anterior frontal lobe may be important in the etiology of autistic spectrum disorder.

Adolescent↗
PubMed2005

CASL fMRI of subcortico-cortical perfusion changes during memory-guided finger sequences.

Arterial spin labeling (ASL) perfusion functional magnetic resonance imaging (fMRI) is an attractive alternative to BOLD fMRI. Nevertheless, current ASL fMRI techniques are limited by several factors that hamper more routine applications in humans. One of these factors is restricted brain coverage so that whole-brain ASL fMRI studies have never been reported. The present study tested the ability of a multislice continuous ASL (CASL) fMRI approach using a small surface coil placed on the subject's neck to map changes in regional cerebral blood flow (rCBF) throughout the brain while healthy individuals (N = 15) performed memory-guided sequential finger movements at a mean rate of approximately 0.5 Hz. As predicted by results from a large number of studies, reliable task-related increases in flow were detected across subjects not only in primary and associative cortical areas but also in subcortical brain regions. When normalized to baseline, rCBF increased 31% in the hand representation area (HRA) of left primary motor cortex (M1), 13% in the left supplementary motor area proper (SMA), 10% in the left dorsolateral prefrontal cortex (DLPFC), 10-18% in the bilateral intraparietal sulci, 6% in the HRA of left putamen, 10% in the left thalamus, and 17% in the right anterior cerebellum. In addition to these increases, 6% and 4% decreases in rCBF were detected in the HRA of the right M1 and the bilateral posterior cingulate sulci, respectively. These results demonstrate that perfusion-based fMRI using CASL with a separate labeling coil can now be used to characterize task-related flow changes in most of the brain volume with adequate accuracy and sensitivity.

Adult↗
PubMed2005

The selection of intended actions and the observation of others' actions: a time-resolved fMRI study.

Whenever we plan, imagine, or observe an action, the motor systems that would be involved in preparing and executing that action are similarly engaged. The way in which such common motor activation is formed, however, is likely to differ depending on whether it arises from our own intentional selection of action or from the observation of another's action. In this study, we use time-resolved event-related functional MRI to tease apart neural processes specifically related to the processing of observed actions, the selection of our own intended actions, the preparation for movement, and motor response execution. Participants observed a finger gesture movement or a cue indicating they should select their own finger gesture to perform, followed by a 5-s delay period; participants then performed the observed or self-selected action. During the preparation and readiness for action, prior to initiation, we found activation in a common network of higher motor areas, including dorsal and ventral premotor areas and the pre-supplementary motor area (pre-SMA); the more caudal SMA showed greater activation during movement execution. Importantly, the route to this common motor activation differed depending on whether participants freely selected the actions to perform or whether they observed the actions performed by another person. Observation of action specifically involved activation of inferior and superior parietal regions, reflecting involvement of the dorsal visual pathway in visuomotor processing required for planning the action. In contrast, the selection of action specifically involved the dorsal lateral prefrontal and anterior cingulate cortex, reflecting the role of these prefrontal areas in attentional selection and guiding the selection of responses.

Adult↗
PubMed2004

Hemispheric specialisation for imitation of hand-head positions and finger configurations: a controlled study in patients with complete callosotomy.

Several studies of patients with unilateral brain damage and a patient with spontaneous callosal disconnection [Journal of Neurology, Neurosurgery, and Psychiatry 61 (1996) 176; Neuropsychologia 37 (1999) 559; Neuropsychologia 39 (2001) 1432] suggest that the imitation of positions of the hand relative to the head is a strongly lateralised left hemispheric function. In contrast, the imitation of finger configurations draws on resources of both hemispheres with a predominance of the right hemisphere. While these findings suggest a specific pattern of imitation impairment in split-brain patients, thus far, no imitation deficits have been reported in split-brain patients. Three patients with complete callosotomy and two control groups, four patients with partial callosotomy and 10 healthy subjects, imitated hand-head positions and finger configurations with non-lateralised and tachistoscopic stimulus presentation. In addition, the influence of visual control on the imitation performance was examined. One split-brain patient showed the predicted dissociation as she had severe right hemispheric deficit in imitating hand-head positions, while finger configuration imitation was preserved. The other two split-brain patients had no impairment in hand-head position imitation. Withdrawal of visual control significantly deteriorated imitation of finger configurations in the split-brain group, but not in the controls, demonstrating that the split-brain patients relied heavily on visual control as a compensatory strategy indicating an imitation deficit in the separate hemispheres. The findings question the previously held belief that in split-brain patients both hemispheres are perfectly capable of imitating gestures and that imitation is not dependent on hemispherically specialised functions.

Adolescent↗
PubMed2004

Action observation and speech production: study on children and adults.

The present study aimed to determine whether observation of upper limb actions selectively influences speech production. We compared the effects on children with those on adults, hypothesizing that action observation is used by children for speech learning. Children and adults observed an actor either grasping a cherry or an apple, or bringing the same fruits to his mouth. They pronounced the syllable/ba/ at the end of the action. In a control experiment, children and adults executed the two bringing-to-the-mouth actions, still pronouncing/ba/. As previously found ([Euro. J. Neurosci., 17 (2003) 179]; [Euro. J. Neurosci., 19 (2004) 192]), the observed kinematics of the action, which were different according to the fruit size, influenced lip shaping kinematics and voice formants. In addition, the effect was selective for the action since the observations of actions such as grasping and bringing-to-the-mouth affected formant 1 and formant 2 in the voice spectra, respectively. The effects on speech were greater in the children than in the adults. By contrast, the effects on lip shaping did not differ between the two groups. Effects similar to those found for action observation were found for action execution in spite of a different arm kinematics between children and adults. The results of the present study are discussed according to the hypothesis that action observation induces in the viewer action recognition and activation of the successive mouth act (probably grasping-with-the-mouth when observing grasping-with-the-hand and chewing when observing bringing-to-the-mouth). This subsequently seems to affect characteristics peculiar to the emitted vowel. This mechanism might have been used by humans to transfer a primitive arm gesture communication system from the arm to the mouth and may be further used by children for speech learning.

Adult↗
PubMed2005

Deficient internal models for planning hand-object interactions in apraxia.

Motor imagery (MI) has been associated with planning stages of motor production, and in particular, with internal models that predict the sensory consequences of motor commands and specify the motor commands required to achieve a given outcome. In this study we investigated several predictions derived from the hypothesis that ideomotor apraxia (IM), a deficit in pantomime and imitation of skilled actions, may be attributable in part to deficits in internal models for planning object-related actions, in the face of relatively intact on-line, feedback-driven control of action. This hypothesis predicts that in IM, motor imagery should be (a) strongly correlated with other motor tasks not providing strong visual, tactile, and proprioceptive feedback from objects, i.e., object-related pantomime and imitation; (b) poorly correlated with performance tasks providing strong environmental feedback about the locations of effectors and targets, i.e., actual interaction with objects; and (c) particularly deficient in conditions that are computationally difficult for the motor planning system. Eight left fronto-parietal stroke patients with IM, five stroke patients without IM, and six healthy matched controls imagined grasping dowels and widgets presented at varying orientations, and actually grasped the same objects. The experimental predictions were confirmed. In addition, patients with IM and motor imagery deficits were significantly more likely than the non-apraxic group to have lesions in the intraparietal sulcus, a region previously implicated in imagery for hand-object interactions. The findings suggest a principled explanation for the deficits of IM patients in object-related gesture pantomime, imitation, and learning of new object-related gestures.

Adult↗
PubMed2005

Left inferior parietal dominance in gesture imitation: an fMRI study.

The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exist between clinical studies in apraxic patients and neuroimaging findings on imitation. We therefore aimed to investigate: (1) which areas are recruited during imitation under conditions similar to clinical tests for apraxic deficits; (2) whether there are common lateralized areas subserving imitation irrespective of the acting limb side; and also (3) whether there are differences between hand and finger gestures. We used fMRI in 12 healthy, right handed subjects to investigate the imitation of four types of variable gestures that were presented by video clips (16 different finger and 16 different hand gestures with either the right or the left arm). The respective control conditions consisted of stereotyped gestures (only two gestures presented in pseudorandom order). Subtraction analysis of each type of gesture imitation (variable>stereotyped) revealed a bilateral activation pattern including the inferior parietal cortex Brodmann Area (BA 40), the superior parietal cortex, the inferior frontal cortex (opercular region), the prefrontal motor cortex, the lateral occipito-temporal junction, and the cerebellum. These results were supported by statistical conjunction of all four subtraction analyses and by the common analysis of all four types of gesture imitation. The direct comparison of the right and left hemispheric activation revealed a lateralization to the left only of the inferior parietal cortex. Comparisons between different types of gesture imitation yielded no significant results. In conclusion, gesture imitation recruits bilateral fronto-parietal regions, with significant lateralization of only one area, namely the left inferior parietal cortex. These in vivo data indicate left inferior parietal dominance for gesture imitation in right handers, confirming lesion-based theories of apraxia.

Adult↗
PubMed2005

Neural mechanisms of imitation and 'mirror neuron' functioning in autistic spectrum disorder.

An association between autistic spectrum disorder and imitative impairment might result from dysfunction in mirror neurons (MNs) that serve to relate observed actions to motor codings. To explore this hypothesis, we employed a functional magnetic resonance imaging (fMRI) protocol previously used to identify the neural substrate of imitation, and human MN function, to compare 16 adolescent males of normal intelligence with autistic spectrum disorder (ASD) and age, sex and IQ matched controls. In the control group, in accord with previous findings, we identified activity attributable to MNs in areas of the right parietal lobe. Activity in this area was less extensive in the ASD group and was absent during non-imitative action execution. Broca's area was minimally active during imitation in controls. Differential patterns of activity during imitation and action observation in ASD and controls were most evident in an area at the right temporo-parietal junction also associated with a 'theory of mind' (ToM) function. ASD participants also failed to show modulation of left amygdala activity during imitation that was evident in the controls. This may have implications for understanding the imitation of emotional stimuli in ASD. Overall, we suggest that ASD is associated with altered patterns of brain activity during imitation, which could stem from poor integration between areas serving visual, motor, proprioceptive and emotional functions. Such poor integration is likely to adversely affect the development of ToM through imitation as well as other aspects of social cognitive function in ASD.

Adolescent↗
PubMed2005

Tapping, grasping and aiming in ideomotor apraxia.

Very few studies have investigated sensorimotor control in apraxia using tasks that differ in movement complexity. Nevertheless, there is some evidence to suggest that spontaneous behaviour, although relatively preserved, can be rather clumsy or awkward, and that patients with ideomotor apraxia may have subtle kinematic abnormalities in movements made in the laboratory. It remains unclear whether patients with ideomotor apraxia perform normally on movements such as visually guided aiming, that may not depend on higher-order, more cognitive, processes and that are relatively unguided by overlearned contexts. In this study, three different sensorimotor tasks were given to the same sample of patients with quantified apraxic disturbance. Finger tapping, goal-directed grasping and aiming with and without visual feedback were examined in these patients. A clear dissociation was found between grossly impaired gesture imitation and intact motor programming of goal-directed movements with visual feedback. Apraxic patients were, however, impaired on aiming movements without visual feedback, suggesting that apraxia is associated with an increased reliance on integration of online visual information with feedforward/feedback somatosensory and motor signals. Furthermore, patients were impaired on single finger tapping which was a surprisingly good predictor of apraxia severity.

Aged↗
PubMed2006

A new account of face apraxia based on a longitudinal study.

The aim of this paper is to provide an interpretation of face apraxia which accounts also for the role of right hemisphere lesions. Thirty-one patients with left hemisphere (L/pts) and 31 patients with right hemisphere (R/pts) lesions entered a cross-sectional study to identify those presenting with either lower or upper face apraxia. The 16L/pts and 8R/pts who presented with face apraxia in the acute stage and could be retested 4 months later, were followed up longitudinally. The degree of recovery did not differ between the two groups of patients. The traditional hypothesis of face apraxia based on the presence of a left-sided praxis centre could not account for these findings. A new trade-off model of face praxis resources distributed across the two hemispheres is presented. This model, based on individual differences in the healthy brain, accounts for the presence and persistence of face apraxia in a proportion of R/pts.

Aged↗
PubMed2006

Hemisphere asymmetry for imitation of hand and finger movements, Goldenberg's hypothesis reworked.

Goldenberg and co-workers put forward the hypothesis that coding of hand gestures with respect to body parts depends upon the functioning of the left hemisphere while the right hemisphere would be involved in imitation of finger postures. They supported this claim with experimental evidence from lesion studies, however, they failed to back it up with functional neuroimaging data. To verify Goldenberg's hypothesis on hemisphere asymmetries for hand/finger postures imitation, the performance of 35 patients with left hemisphere lesion (L/pts), of 24 patients with right hemisphere lesion (R/pts) and that of 41 matched controls was assessed in two imitation tasks, respectively, taxing hand or finger postures. The data, adjusted for the performance of the controls and for the effect of age were analysed using a multivariate, nonparametric approach. The outcome partly supports Goldenberg and colleagues' hypothesis: hand minus finger performance did differs between the R/pts and L/pts patients, even considering the pertinent hand-finger performances by control participants, however, in line with neuroimaging evidence, the left hemisphere's contribution is greater than that of the right for both finger and hand posture imitation.

Adult↗
PubMed2006

Differential cerebral activation during observation of expressive gestures and motor acts.

We compared brain activation involved in the observation of isolated right hand movements (e.g. twisting a lid), body-referred movements (e.g. brushing teeth) and expressive gestures (e.g. threatening) in 20 healthy subjects by using functional magnetic resonance imaging (fMRI). Perception-related areas in the occipital and inferior temporal lobe but also the mirror neuron system in the lateral frontal (ventral premotor cortex and BA 44) and superior parietal lobe were active during all three conditions. Observation of body-referred compared to common hand actions induced increased activity in the bilateral posterior superior temporal sulcus (STS), the left temporo-parietal lobe and left BA 45. Expressive gestures involved additional areas related to social perception (bilateral STS, temporal poles, medial prefrontal lobe), emotional processing (bilateral amygdala, bilateral ventrolateral prefrontal cortex (VLPFC), speech and language processing (Broca's and Wernicke's areas) and the pre-supplementary motor area (pre-SMA). In comparison to body-referred actions, expressive gestures evoked additional activity only in the left VLPFC (BA 47). The valence-ratings for expressive gestures correlated significantly with activation intensity in the VLPFC during expressive gesture observation. Valence-ratings for negative expressive gestures correlated with right STS-activity. Our data suggest that both, the VLPFC and the STS are coding for differential emotional valence during the observation of expressive gestures.

Adult↗
PubMed2006

Spatial and kinematic features of apraxic movement depend on the mode of execution.

Knowledge about the dependency of apraxic movements on the mode of execution may enhance the understanding of apraxia and of the cerebral representation of actions. We examined a common tool-use action in nine patients with left hemisphere damage and apraxia. Arm movements during the use of a handsaw were measured and tested in three different modes of execution: pantomime, pantomime with a bar shaped like the handle of the saw, and actual sawing. Analysis concentrated on spatial and kinematic features of the wrist trajectories during these repetitive movements. In healthy control subjects, both pantomime conditions differed from actual use mainly by larger amplitudes during miming. Apraxic patients executed large proportions of their pantomiming movements in an incorrect direction away from the appropriate anteroposterior direction, while other movement features were normal. The availability of the handle-like bar did not improve performance. During actual use, movement direction was constraint by mechanical demands. In this condition patients moved with moderately decreased velocity. However, this deficit was not related to the errors in movement direction characteristic of pantomiming. These data suggest that pantomiming and actual execution of an action are dictated by different external requirements and constraints, pantomiming serves to convey information, while actual use has to obey the mechanical demands of the task. Due to these differences, spatial and kinematic movement features in healthy subjects vary between the modes of execution, movements are differently vulnerable to apraxia, and deficits in patients may dissociate.

Adult↗
PubMed2006

Imitation during phoneme production.

Does listening to and observing the speaking interlocutor influence phoneme production? In two experiments female participants were required to recognize and, then, to repeat the string-of-phonemes /aba/ presented by actors visually, acoustically and audiovisually. In experiment 1 a male actor presented the string-of-phonemes and the participants' lip kinematics and voice spectra were compared with those of a reading control condition. In experiment 2 female and male actors presented the string-of-phonemes and the lip kinematics and the voice spectra of the participants' responses to the male actors were compared with those to the female actors (control condition). In both experiments 1 and 2, the lip kinematics in the visual presentations and the voice spectra in the acoustical presentations changed in the comparison with the control conditions approaching the male actors' values, which were different from those of the female participants and actors. The variation in lip kinematics induced changes also in voice formants but only in the visual presentation. The data suggest that both features of the lip kinematics and of the voice spectra tend to be automatically imitated when repeating a string-of-phonemes presented by a visible and/or audible speaking interlocutor. The use of imitation, in place of the usual lip kinematics and vocal features, suggests an automatic and unconscious tendency of the perceiver to interact closely with the interlocutor. This is in accordance with the idea that resonant circuits are activated by the activity of the mirror system, which relates observation to execution of arm and mouth gestures.

Adult↗