Papers by Antonia Hamilton
Detection and Interpretation of Animacy, Agency, and Intention, 2013
Comprehension of actions is a core social skill. Here we provide a critical review of the dominan... more Comprehension of actions is a core social skill. Here we provide a critical review of the dominant mirror neuron theory of action comprehension. Recent data demonstrate that parts of the mirror system respond to actions performed by non-human shapes, and are insensitive to actor identity. Regions beyond the mirror system are also important for action comprehension. We suggest this data is not compatible with a strong mirror system hypothesis, and outline alternative theories.
Autism Research, 2015
Previous research has suggested that people with Autism Spectrum Conditions (ASC) may have diffic... more Previous research has suggested that people with Autism Spectrum Conditions (ASC) may have difficulty with visual perspective taking (VPT), but it is not clear how this relates to different strategies that can be used in perspective taking tasks. The current study examined VPT in 30 children with autism and 30 verbal mental age matched typical children, in comparison to mental rotation abilities and body representation abilities. Using a similar paradigm to Hamilton et al. (2009) all children completed three tasks: a VPT task in which children decided what a toy on a table would look like from a different points of view; a mental rotation task in which the child decided what a toy would look like after it had been rotated; and a body posture matching task, in which children matched pictures of a body
Frontiers in human neuroscience, 2014
Humans are able to mentally adopt the spatial perspective of others and understand the world from... more Humans are able to mentally adopt the spatial perspective of others and understand the world from their point of view. We propose that spatial perspective taking (SPT) could have developed from the physical alignment of perspectives. This would support the notion that others have put forward claiming that SPT is an embodied cognitive process. We investigated this issue by contrasting several accounts in terms of the assumed processes and the nature of the embodiment. In a series of four experiments we found substantial evidence that the transformations during SPT comprise large parts of the body schema, which we did not observe for object rotation. We further conclude that the embodiment of SPT is best conceptualised as the self-initiated emulation of a body movement, supporting the notion of endogenous motoric embodiment. Overall our results are much more in agreement with an 'embodied' transformation account than with the notion of sensorimotor interference. Finally we discuss our findings in terms of SPT as a possible evolutionary stepping stone towards more complex alignments of socio-cognitive perspectives.
Numerous studies have established that inferior frontal cortex is active when hand actions are pl... more Numerous studies have established that inferior frontal cortex is active when hand actions are planned [1], imagined [2], remembered , imitated , and even observed . Furthermore, it has been proposed that these activations reflect a process of simulating the observed action to allow it to be understood and thus fully perceived. However, direct evidence for a perceptual role for left inferior frontal cortex is rare, and linguistic [8] or motor contributions to the reported activations have not been ruled out. We used repetitive transcranial magnetic stimulation (rTMS) over inferior frontal gyrus during a perceptual weightjudgement task to test the hypothesis that this region contributes to action understanding. rTMS at this site impaired judgments of the weight of a box lifted by a person, but not judgements of the weight of a bouncing ball or of stimulus duration, and rTMS at control sites had no impact. This demonstrates that the integrity of left inferior frontal gyrus is necessary to make accurate perceptual judgments about other people's actions.
Social Cognitive and Affective Neuroscience, 2014
The neural and cognitive mechanisms by which primed constructs can impact on social behavior are ... more The neural and cognitive mechanisms by which primed constructs can impact on social behavior are poorly understood. In the present study, we used functional magnetic resonance imaging (fMRI) to explore how scrambled sentence priming can impact on mimicry behavior. Sentences involving pro/ antisocial events from a first/third-person point of view were presented in short blocks, followed by a reaction-time assessment of mimicry. Behavioral results showed that both prosociality and viewpoint impact on mimicry, and fMRI analysis showed this effect is implemented by anterior medial prefrontal cortex (amPFC). We suggest that social primes may subtly modulate processing in amPFC in a manner linked to the later behavior, and that this same region also implements the top-down control of mimicry responses. This priming may be linked to processing of self-schemas in amPFC. Our findings demonstrate how social priming can be studied with fMRI, and have important implications for our understanding of the underlying mechanisms of prime-to-behavior effects as well as for current theories in social psychology.
JOURNAL OF NEUROPHYSIOLOGY, 2002
It has been proposed that the invariant kinematics observed during goal-directed movements result... more It has been proposed that the invariant kinematics observed during goal-directed movements result from reducing the consequences of signal-dependent noise (SDN) on motor output. The purpose of this study was to investigate the presence of SDN during isometric force production and determine how central and peripheral components contribute to this feature of motor control. Peripheral and central components were distinguished experimentally by comparing voluntary contractions to those elicited by electrical stimulation of the extensor pollicis longus muscle. To determine other factors of motor-unit physiology that may contribute to SDN, a model was constructed and its output compared with the empirical data. SDN was evident in voluntary isometric contractions as a linear scaling of force variability (SD) with respect to the mean force level. However, during electrically stimulated contractions to the same force levels, the variability remained constant over the same range of mean forces. When the subjects were asked to combine voluntary with stimulation-induced contractions, the linear scaling relationship between the SD and mean force returned. The modeling results highlight that much of the basic physiological organization of the motor-unit pool, such as range of twitch amplitudes and range of recruitment thresholds, biases force output to exhibit linearly scaled SDN. This is in contrast to the square root scaling of variability with mean force present in any individual motor-unit of the pool. Orderly recruitment by twitch amplitude was a necessary condition for producing linearly scaled SDN. Surprisingly, the scaling of SDN was independent of the variability of motoneuron firing and therefore by inference, independent of presynaptic noise in the motor command. We conclude that the linear scaling of SDN during voluntary isometric contractions is a natural by-product of the organization of the motor-unit pool that does not depend on signal-dependent noise in the motor command. Synaptic noise in the motor command and common drive, which give rise to the variability and synchronization of motoneuron spiking, determine the magnitude of the force variability at a given level of mean force output.
JOURNAL OF NEUROPHYSIOLOGY, 2002
Frontiers in Human Neuroscience, 2012
As a distinct feature of human social interactions, spontaneous mimicry has been widely investiga... more As a distinct feature of human social interactions, spontaneous mimicry has been widely investigated in the past decade. Research suggests that mimicry is a subtle and flexible social behavior which plays an important role for communication and affiliation. However, fundamental questions like why and how people mimic still remain unclear. In this paper, we evaluate past theories of why people mimic and the brain systems that implement mimicry in social psychology and cognitive neuroscience. By reviewing recent behavioral and neuroimaging studies on the control of mimicry by social signals, we conclude that the subtlety and sophistication of mimicry in social contexts reflect a social top-down response modulation (STORM) which increases one's social advantage and this mechanism is most likely implemented by medial prefrontal cortex (mPFC). We suggest that this STORM account of mimicry is important for our understanding of social behavior and social cognition, and provides implications for future research in autism.
Social Cognitive and Affective Neuroscience, 2012
When you see someone reach into a cookie jar, their goal remains obvious even if you know that th... more When you see someone reach into a cookie jar, their goal remains obvious even if you know that the last cookie has already been eaten. Thus, it is possible to infer the goal of an action even if you know that the goal cannot be achieved. Previous research has identified distinct brain networks for processing information about object locations, actions and mental-state inferences. However, the relationship between brain networks for action understanding in social contexts remains unclear. Using functional magnetic resonance imaging, this study assesses the role of these networks in understanding another person searching for hidden objects. Participants watched movie clips depicting a toy animal hiding and an actor, who was ignorant of the hiding place, searching in the filled or empty location. When the toy animal hid in the same location repeatedly, the blood oxygen level-dependent (BOLD) response was suppressed in occipital, posterior temporal and posterior parietal brain regions, consistent with processing object properties and spatial attention. When the actor searched in the same location repeatedly, the BOLD signal was suppressed in the inferior frontal gyrus, consistent with the observation of hand actions. In contrast, searches towards the filled location compared to the empty location were associated with a greater response in the medial prefrontal cortex and right temporal pole, which are both associated with mental state inference. These findings show that when observing another person search for a hidden object, brain networks for processing information about object properties, actions and mental state inferences work together in a complementary fashion. This supports the hypothesis that brain regions within and beyond the putative human mirror neuron system are involved in action comprehension within social contexts.
NeuroImage, 2006
Research on action simulation identifies brain areas that are active while imagining or performin... more Research on action simulation identifies brain areas that are active while imagining or performing simple overlearned actions. Are areas engaged during imagined movement sensitive to the amount of actual physical practice? In the present study, participants were expert dancers who learned and rehearsed novel, complex whole-body dance sequences 5 h a week across 5 weeks. Brain activity was recorded weekly by fMRI as dancers observed and imagined performing different movement sequences. Half these sequences were rehearsed and half were unpracticed control movements. After each trial, participants rated how well they could perform the movement. We hypothesized that activity in premotor areas would increase as participants observed and simulated movements that they had learnt outside the scanner. Dancers' ratings of their ability to perform rehearsed sequences, but not the control sequences, increased with training. When dancers observed and simulated another dancer's movements, brain regions classically associated with both action simulation and action observation were active, including inferior parietal lobule, cingulate and supplementary motor areas, ventral premotor cortex, superior temporal sulcus and primary motor cortex. Critically, inferior parietal lobule and ventral premotor activity was modulated as a function of dancers' ratings of their own ability to perform the observed movements and their motor experience. These data demonstrate that a complex motor resonance can be built de novo over 5 weeks of rehearsal. Furthermore, activity in premotor and parietal areas during action simulation is enhanced by the ability to execute a learned action irrespective of stimulus familiarity or semantic label. D
Trends in Cognitive Sciences, 2008
The 'broken mirror' theory of autism has received considerable attention far beyond the scientifi... more The 'broken mirror' theory of autism has received considerable attention far beyond the scientific community. This theory proposes that the varied socialcognitive difficulties characteristic of autism could be explained by dysfunction of the mirror neuron system, thought to play a role in imitation. We examine this theory and argue that explaining typical imitation behavior, and the failure to imitate in autism, requires much more than the mirror neuron system. Furthermore, evidence for the role of the mirror neuron system in autism is weak. We suggest the broken mirror theory of autism is premature and that better cognitive models of social behavior within and beyond the mirror neuron system are required to understand the causes of poor social interaction in autism.
Journal of Neuroscience, 2011
Spontaneous mimicry of other people's actions serves an important social function, enhancing affi... more Spontaneous mimicry of other people's actions serves an important social function, enhancing affiliation and social interaction. This mimicry can be subtly modulated by different social contexts. We recently found behavioral evidence that direct eye gaze rapidly and specifically enhances mimicry of intransitive hand movements (Wang et al., 2011). Based on past findings linking medial prefrontal cortex (mPFC) to both eye contact and the control of mimicry, we hypothesized that mPFC might be the neural origin of this behavioral effect. The present study aimed to test this hypothesis. During functional magnetic resonance imaging (fMRI) scanning, 20 human participants performed a simple mimicry or no-mimicry task, as previously described (Wang et al., 2011), with direct gaze present on half of the trials. As predicted, fMRI results showed that performing the task activated mirror systems, while direct gaze and inhibition of the natural tendency to mimic both engaged mPFC. Critically, we found an interaction between mimicry and eye contact in mPFC, superior temporal sulcus (STS) and inferior frontal gyrus. We then used dynamic causal modeling to contrast 12 possible models of information processing in this network. Results supported a model in which eye contact controls mimicry by modulating the connection strength from mPFC to STS. This suggests that mPFC is the originator of the gaze-mimicry interaction and that it modulates sensory input to the mirror system. Thus, our results demonstrate how different components of the social brain work together to on-line control mimicry according to the social context.
Social Neuroscience, 2013
Social Neuroscience, 2007
It has previously been shown that observing an action made by a human, but not by a robot, interf... more It has previously been shown that observing an action made by a human, but not by a robot, interferes with executed actions . Here, we investigated what aspect of human movement causes this interference effect. Subjects made arm movements while observing a video of either a human making an arm movement or a ball moving across the screen. Both human and ball videos contained either biological (minimum jerk) or non-biological (constant velocity) movements. The executed and observed arm movements were either congruent (same direction) or incongruent (tangential direction) with each other. The results showed that observed movements are processed differently according to whether they are made by a human or a ball. For the ball videos, both biological and non-biological incongruent movements interfered with executed arm movements. In contrast, for the human videos, the velocity profile of the movement was the critical factor: only incongruent, biological human movements interfered with executed arm movements. We propose that the interference effect could be due either to the information the brain has about different types of movement stimuli or to the impact of prior experience with different types of form and motion.
Psychological Research, 2007
When accepting a parcel from another person, we are able to use information about that person's m... more When accepting a parcel from another person, we are able to use information about that person's movement to estimate in advance the weight of the parcel, that is, to judge its weight from observed action. Perceptual weight judgment provides a powerful method to study our interpretation of other people's actions, but it is not known what sources of information are used in judging weight. We have manipulated full form videos to obtain precise control of the perceived kinematics of a box lifting action, and use this technique to explore the kinematic cues that affect weight judgment. We find that observers rely most on the duration of the lifting movement to judge weight, and make less use of the durations of the grasp phase, when the box is first gripped, or the place phase, when the box is put down. These findings can be compared to the kinematics of natural box lifting behaviour, where we find that the duration of the grasp component is the best predictor of true box weight. The lack of accord between the optimal cues predicted by the natural behaviour and the cues actually used in the perceptual task has implications for our understanding of action observation in terms of a motor simulation.
Psychological Research, 2012
During social interactions, how do we predict what other people are going to do next? One view is... more During social interactions, how do we predict what other people are going to do next? One view is that we use our own motor experience to simulate and predict other people's actions. For example, when we see Sally look at a coffee cup or grasp a hammer, our own motor system provides a signal that anticipates her next action. Previous research has typically examined such gaze and grasp-based simulation processes separately, and it is not known whether similar cognitive and brain systems underpin the perception of object-directed gaze and grasp. Here we use functional magnetic resonance imaging to examine to what extent gaze-and grasp-perception rely on common or distinct brain networks. Using a 'peeping window' protocol, we controlled what an observed actor could see and grasp. The actor could peep through one window to see if an object was present and reach through a different window to grasp the object. However, the actor could not peep and grasp at the same time. We compared gaze and grasp conditions where an object was present with matched conditions where the object was absent. When participants observed another person gaze at an object, left anterior inferior parietal lobule (aIPL) and parietal operculum showed a greater response than when the object was absent. In contrast, when participants observed the actor grasp an object, premotor, posterior parietal, fusiform and middle occipital brain regions showed a greater response than when the object was absent. These results point towards a division in the neural substrates for different types of motor simulation. We suggest that left aIPL and parietal operculum are involved in a predictive process that signals a future hand interaction with an object based on another person's eye gaze, whereas a broader set of brain areas, including parts of the action observation network, are engaged during observation of an ongoing object-directed hand action.
PLoS ONE, 2014
Children copy the actions of others with high fidelity, even when they are not causally relevant.... more Children copy the actions of others with high fidelity, even when they are not causally relevant. This copying of visibly unnecessary actions is termed overimitation. Many competing theories propose mechanisms for overimitation behaviour. The present study examines these theories by studying the social factors that lead children to overimitate actions. Ninetyfour children aged 5-to 8-years each completed five trials of an overimitation task. Each trial provided the opportunity to overimitate an action on familiar objects with minimal causal reasoning demands. Social cues (live or video demonstration) and eye contact from the demonstrator were manipulated. After the imitation, children's ratings of action rationality were collected. Substantial overimitation was seen which increased with age. In older children, overimitation was higher when watching a live demonstrator and when eye contact was absent. Actions rated as irrational were more likely to be imitated than those rated as rational. Children overimitated actions on familiar objects even when they rated those actions as irrational, suggesting that failure of causal reasoning cannot be driving overimitation. Our data support social explanations of overimitation and show that the influence of social factors increases with age over the 5-to 8-year-old age range.
Neuropsychologia, 2012
What does it mean to ''know'' what an object is? Viewing objects from different categories (e.g.,... more What does it mean to ''know'' what an object is? Viewing objects from different categories (e.g., tools vs. animals) engages distinct brain regions, but it is unclear whether these differences reflect object categories themselves or the tendency to interact differently with objects from different categories (grasping tools, not animals). Here we test how the brain constructs representations of objects that one learns to name or physically manipulate. Participants learned to name or tie different knots and brain activity was measured whilst performing a perceptual discrimination task with these knots before and after training. Activation in anterior intraparietal sulcus, a region involved in object manipulation, was specifically engaged when participants viewed knots they learned to tie. This suggests that object knowledge is linked to sensorimotor experience and its associated neural systems for object manipulation. Findings are consistent with a theory of embodiment in which there can be clear overlap in brain systems that support conceptual knowledge and control of object manipulation.
Neuropsychologia, 2007
The motor mirror neuron system supports imitation and goal understanding in typical adults. Recen... more The motor mirror neuron system supports imitation and goal understanding in typical adults. Recently, it has been proposed that a deficit in this mirror neuron system might contribute to poor imitation performance in children with autistic spectrum disorders (ASD) and might be a cause of poor social abilities in these children. We aimed to test this hypothesis by examining the performance of 25 children with ASD and 31 typical children of the same verbal mental age on four action representation tasks and a theory of mind battery. Both typical and autistic children had the same tendency to imitate an adult's goals, to imitate in a mirror fashion and to imitate grasps in a motor planning task. Children with ASD showed superior performance on a gesture recognition task. These imitation and gesture recognition tasks all rely on the mirror neuron system in typical adults, but performance was not impaired in children with ASD. In contrast, the ASD group were impaired on the theory of mind tasks. These results provide clear evidence against a general imitation impairment and a global mirror neuron system deficit in children with autism. We suggest this data can best be understood in terms of multiple brain systems for different types of imitation and action understanding, and that the ability to understand and imitate the goals of hand actions is intact in children with ASD.
NeuroImage, 2006
Activation of premotor cortex during the observation and imitation of human actions is now increa... more Activation of premotor cortex during the observation and imitation of human actions is now increasingly accepted, but it remains unclear how the CNS is able to resolve potential conflicts between the observation of another person's action and the ongoing control of one's own action. Recent data suggest that this overlap leads to a systematic bias, where lifting a box influences participant's perceptual judgments of the weight of a box lifted by another person. We now investigate the neural basis of this bias effect using fMRI. Seventeen participants performed a perceptual weight judgment task or two control conditions while lifting a light box, a heavy box or no box during scanning. Brain regions related to perceptual bias were localized by correlating individual differences in bias with BOLD signal. Five regions were found to show correlations with psychophysical bias: left inferior frontal gyrus, left central sulcus, left extrastriate body area, left lingual gyrus and right intraparietal sulcus. The cluster in primary motor cortex was also activated by box lifting, and the cluster in extrastriate body area by the observation of hand actions and the weight judgment task. We suggest that these brain areas are part of a network where motor processing modulates perceptual judgment of observed human actions, and thus visual and motor processes cannot be thought of as two distinct systems, but instead interact at many levels. D
Uploads
Papers by Antonia Hamilton