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Biomedical subjects

C D Frith

Publications and source records attributed to C D Frith.

At least 19 recordsLinked to original sources
PubMed2005

Kinematic cues in perceptual weight judgement and their origins in box lifting.

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. The differences between perceptual and motor behaviour are evidence against a strong version of the motor simulation hypothesis.

Adolescent↗
PubMed2005

Brain abnormalities underlying altered activation in dyslexia: a voxel based morphometry study.

Voxel-based morphometry was used to assess the consistency among functional imaging and brain morphometry data in developmental dyslexia. Subjects, from three different cultural contexts (UK, France and Italy), were the same as those described in a previous PET activation paper, which revealed a common pattern of reduced activation during reading tasks in the left temporal and occipital lobes. We provide evidence that altered activation observed within the reading system is associated with altered density of grey and white matter of specific brain regions, such as the left middle and inferior temporal gyri and the left arcuate fasciculus. This supports the view that dyslexia is associated with both local grey matter dysfunction and with altered connectivity among phonological/reading areas. The differences were replicable across samples confirming that the neurological disorder underlying dyslexia is the same across the cultures investigated in the study.

Adult↗
PubMed2005

Multisensory stimulation with or without saccades: fMRI evidence for crossmodal effects on sensory-specific cortices that reflect multisensory location-congruence rather than task-relevance.

During covert attention to peripheral visual targets, presenting a concurrent tactile stimulus at the same location as a visual target can boost neural responses to it, even in sensory-specific occipital areas. Here, we examined any such crossmodal spatial-congruence effects in the context of overt spatial orienting, when saccadic eye-movements were directed to each peripheral target or central fixation maintained. In addition, we tested whether crossmodal spatial-congruence effects depend on the task-relevance of visual or tactile stimuli. On each trial, subjects received spatially congruent (same location) or incongruent (opposite hemifields) visuo-tactile stimulation. In different blocks, they made saccades either to the location of each visual stimulus, or to the location of each tactile stimulus; or else passively received the multisensory stimulation. Activity in visual extrastriate areas and in somatosensory parietal operculum was modulated by spatial congruence of the multisensory stimulation, with stronger activations when concurrent visual and tactile stimuli were both delivered at the same contralateral location. Critically, lateral occipital cortex and parietal operculum showed such crossmodal spatial effects irrespective of which modality was task relevant; and also of whether the stimuli were used to guide eye-movements or were just passively received. These results reveal crossmodal spatial-congruence effects upon visual and somatosensory sensory-specific areas that are relatively 'automatic', determined by the spatial relation of multisensory input rather than by its task-relevance.

Adolescent↗
PubMed2004

On the benefits of not trying: brain activity and connectivity reflecting the interactions of explicit and implicit sequence learning.

Under certain circumstances, implicit, automatic learning may be attenuated by explicit memory processes. We explored the brain basis of this phenomenon in a functional magnetic resonance imaging (fMRI) study of motor sequence learning. Using a factorial design that crossed subjective intention to learn (explicit versus implicit) with sequence difficulty (a standard versus a more complex alternating sequence), we show that explicit attempts to learn the difficult sequence produce a failure of implicit learning and, in a follow-up behavioural experiment, that this failure represents a suppression of learning itself rather than of the expression of learning. This suppression is associated with sustained right frontal activation and attenuation of learning-related changes in the medial temporal lobe and the thalamus. Furthermore, this condition is characterized by a reversal of the fronto-thalamic connectivity observed with unimpaired implicit learning. The findings demonstrate a neural basis for a well-known behavioural effect: the deleterious impact of an explicit search upon implicit learning.

Adult↗
PubMed2004

Inferring false beliefs from the actions of oneself and others: an fMRI study.

The ability to make judgments about mental states is critical to social interactions. Simulation theory suggests that the observer covertly mimics the activity of the observed person, leading to shared states of mind between the observer and the person observed. We tested this hypothesis by investigating the neural networks activated while subjects watched videos of themselves and of others lifting a box, and judged the beliefs of the actors about the weight of the box. A parietal premotor circuit was recruited during action perception, and the activity started earlier when making judgments about one's own actions as opposed to those of others. This earlier activity in action-related structures can be explained by simulation theory on the basis that when one observes one's own actions, there is a closer match between the simulated and perceived action than there is when one observes the actions of others. When the observers judged the actions to reflect a false belief, there was activation in the superior temporal sulcus, orbitofrontal, paracingulate cortex and cerebellum. We suggest that this reflects a mismatch between the perceived action and the predicted action's outcomes derived from simulation.

Brain Mapping↗
PubMed2004

Orienting attention to locations in perceptual versus mental representations.

Extensive clinical and imaging research has characterized the neural networks mediating the adaptive distribution of spatial attention. In everyday behavior, the distribution of attention is guided not only by extrapersonal targets but also by mental representations of their spatial layout. We used event-related functional magnetic resonance imaging to identify the neural system involved in directing attention to locations in arrays held as mental representations, and to compare it with the system for directing spatial attention to locations in the external world. We found that these two crucial aspects of spatial cognition are subserved by extensively overlapping networks. However, we also found that a region of right parietal cortex selectively participated in orienting attention to the extrapersonal space, whereas several frontal lobe regions selectively participated in orienting attention within on-line mental representations.

Adult↗
PubMed2003

Preparatory states in crossmodal spatial attention: spatial specificity and possible control mechanisms.

We used event-related functional magnetic resonance imaging to study the neural correlates of endogenous spatial attention for vision and touch. We examined activity associated with attention-directing cues (central auditory pure tones), symbolically instructing subjects to attend to one hemifield or the other prior to upcoming stimuli, for a visual or tactile task. In different sessions, subjects discriminated either visual or tactile stimuli at the covertly attended side, during bilateral visuotactile stimulation. To distinguish cue-related preparatory activity from any modulation of stimulus processing, unpredictably on some trials only the auditory cue was presented. The use of attend-vision and attend-touch blocks revealed whether preparatory attentional effects were modality-specific or multimodal. Unimodal effects of spatial attention were found in somatosensory cortex for attention to touch, and in occipital areas for attention to vision, both contralateral to the attended side. Multimodal spatial effects (i.e. effects of attended side irrespective of task-relevant modality) were detected in contralateral intraparietal sulcus, traditionally considered a multimodal brain region; and also in the middle occipital gyrus, an area traditionally considered purely visual. Critically, all these activations were observed even on cue-only trials, when no visual or tactile stimuli were subsequently presented. Endogenous shifts of spatial attention result in changes of brain activity prior to the presentation of target stimulation (baseline shifts). Here, we show for the first time the separable multimodal and unimodal components of such preparatory activations. Additionally, irrespective of the attended side and modality, attention-directing auditory cues activated a network of superior frontal and parietal association areas that may play a role in voluntary control of spatial attention for both vision and touch.

Attention↗
PubMed2003

Brain activations during visual search: contributions of search efficiency versus feature binding.

We investigated the involvement of the parietal cortex in binding features during visual search using functional magnetic resonance imaging. We tested 10 subjects in four visual search tasks across which we independently manipulated (1) the requirement to integrate different types of features in a stimulus (feature or conjunction search) and (2) the degree of search efficiency (efficient or inefficient). We identified brain areas that were common to all conditions of visual search and areas that were sensitive to the factors of efficiency and feature binding. Visual search engaged an extensive network of parietal, frontal, and occipital areas. The factor of efficiency exerted a strong influence on parietal activations along the intraparietal sulcus and in the superior parietal lobule. These regions showed a main effect of efficiency and showed a simple effect when inefficient conditions were compared directly with efficient pop-out conditions in the absence of feature binding. Furthermore, a correlation analysis supported a tight correspondence between posterior parietal activation and the slope of reaction-time search functions. Conversely, feature binding during efficient pop-out search was not sufficient to modulate the parietal cortex. The results confirm the important role of the parietal cortex in visual search, but suggest that feature binding is not a requirement to engage its contribution.

Adolescent↗
PubMed2003

Delusions of alien control in the normal brain.

Delusions of alien control, or passivity experiences, are symptoms associated with schizophrenia in which patients misattribute self-generated actions to an external source. In this study hypnosis was used to induce a similar misattribution of self-generated movement in normal, healthy individuals. Positron Emission Tomography (PET) was employed to investigate the neural correlates of active movements correctly attributed to the self, compared with identical active movements misattributed to an external source. Active movements attributed to an external source resulted in significantly higher activations in the parietal cortex and cerebellum than identical active movements correctly attributed to the self. We suggest that, as a result of hypnotic suggestion, the functioning of this cerebellar-parietal network is altered so that self-produced actions are experienced as being external. These results have implications for the brain mechanisms underlying delusions of control, which may be associated with overactivation of the cerebellar-parietal network.

Adult↗
PubMed2003

Modulating the experience of agency: a positron emission tomography study.

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.

Adult↗
PubMed2002

Crossmodal spatial influences of touch on extrastriate visual areas take current gaze direction into account.

Recent results indicate that crossmodal interactions can affect activity in cortical regions traditionally regarded as "unimodal." Previously we found that combining touch on one hand with visual stimulation in the anatomically corresponding hemifield could boost responses in contralateral visual cortex. Here we manipulated which visual hemifield corresponded to the location of the stimulated hand, by changing gaze direction such that right-hand touch could now arise in either the left or right visual field. Crossmodal effects on visual cortex switched from one hemisphere to the other, depending on gaze direction, regardless of whether the hand was seen. This indicates that crossmodal influences of touch upon visual cortex depend on spatial alignment for the multimodal stimuli, with gaze posture taken into account.

Adult↗
PubMed2002

Supramodal effects of covert spatial orienting triggered by visual or tactile events.

Event-related functional magnetic resonance imaging was used to identify brain areas involved in spatial attention and determine whether these operate unimodally or supramodally for vision and touch. On a trial-by-trial basis, a symbolic auditory cue indicated the most likely side for the subsequent target, thus directing covert attention to one side. A subsequent target appeared in vision or touch on the cued or uncued side. Invalidly cued trials (as compared with valid trials) activated the temporo-parietal junction and regions of inferior frontal cortex, regardless of target modality. These brain areas have been associated with multimodal spatial coding in physiological studies of the monkey brain and were linked to a change in the location that must be attended to in the present study. The intraparietal sulcus and superior frontal cortex were also activated in our task, again, regardless of target modality, but did not show any specificity for invalidly cued trials. These results identify a supramodal network for spatial attention and reveal differential activity for inferior circuits involving the temporo-parietal junction and inferior frontal cortex (specific to invalid trials) versus more superior intraparietal-frontal circuits (common to valid and invalid trials).

Adult↗
PubMed2002

A role for the ventral visual stream in reporting movements.

In this experiment we contrast the neural activity associated with reporting a stimulus attribute with the activity that occurs when the same stimulus attribute is used to guide behavior. Reporting the characteristics of a stimulus differs from simply tracking that stimulus since reporting requires that a stimulus is explicitly recognized and associated with an arbitrary response. In one condition the subject used his right finger to follow a square that moved randomly on a screen. In a second condition he had to indicate changes in the direction of the square's movements by touching one of two report buttons with his right finger. Two other conditions were added to control for the differences in the form of movement between the two primary conditions. When the reporting condition was contrasted with the tracking condition (controlling for the differences in the form of movement), areas in the ventral visual system (the left ventral prefrontal cortex and the left inferior temporal cortex) were activated. This study shows that contrasting a manual task which involves a report with a manual task which does not activates the ventral visual system. However, the observation of additional activity in other areas suggests that, while activity in the ventral stream is necessary for reporting, it is not sufficient.

Adult↗
PubMed2002

Experiencing oneself vs another person as being the cause of an action: the neural correlates of the experience of agency.

The present study is aimed at identifying the neural correlates of two kinds of attribution: experiencing oneself as the cause of an action (the sense of agency) or experiencing another person as being the cause of that action. The experimental conditions were chosen so that they differed only in their requirement to attribute an action to another person or to oneself. The same motor task and the same visual stimuli were used in the experimental conditions. Subjects used a joystick to drive a circle along a T-shaped path. They were told that the circle would be driven either by themselves or by the experimenter. In the former case subjects were requested to drive the circle, to be aware that they drove the circle, and thus to mentally attribute the action seen on the screen to themselves. In the latter case they were also requested to perform the task, but they were aware that action seen on the screen was driven by the experimenter. In accord with previous studies, the results showed that being aware of causing an action was associated with activation in the anterior insula, whereas being aware of not causing the action and attributing it to another person was associated with activation in the inferior parietal cortex. These two regions are involved in the perception of complex representations of the self and of its interactions with the external world. We suggest that the anterior insula is concerned with the integration of all the concordant multimodal sensory signals associated with voluntary movements. The inferior parietal cortex, in contrast, represents movements in an allocentric coding system that can be applied to the actions of others as well as the self.

Adult↗
PubMed2002

Filtering of distractors during visual search studied by positron emission tomography.

We investigated the sensitivity of brain areas to the presence of filtering operations during overt visual search in crowded displays. Task conditions involved either visual search or predetermined simple eye movements for the detection of target digits. Furthermore, visual displays either contained letter foils that required filtering or contained only target digits. Brain imaging using positron emission tomography showed extensive overlap between areas involved in overt visual search and eye movements. Selective filtering of foils affected visual processing in ventral areas associated with object recognition and in primary visual cortex.

Adult↗
PubMed2002

The role of the dorsolateral prefrontal cortex: evidence from the effects of contextual constraint in a sentence completion task.

Although the prefrontal cortices, in particular the dorsolateral prefrontal cortex (DLPFC), have been examined in numerous imaging and neuropsychological studies, it has proved difficult to assign a specific function to this brain region. The aim of this study was therefore to delineate the function of the DLPFC first by using positron emission tomography with a word generation task and second by comparing these findings with a series of different circumstances in which the DLPFC is activated in association with response selection. Six healthy volunteers were presented with a sentence completion task based on the Hayling test. In each of two conditions, (A) response initiation and (B) response suppression, volunteers saw a sentence with the final word omitted. In condition A they had to provide a word that fitted at the end of the sentence and in condition B they had to provide a word that did not fit. The corpus of sentences used varied systematically in their level of contextual constraint, ranging from low to high. With all levels of constraint combined, significant greater activation was observed in the left DLPFC (BA46/9) under the suppression condition and in the medial orbitofrontal cortex (BA11) under the initiation condition. Under the high-constraint condition with both tasks combined, significant right middle temporal activity (BA21) was observed, whereas under low constraint, the left DLPFC was significantly activated. An interaction of task and constraint revealed that the left DLPFC was significantly more active in the suppression task at all levels of constraint, but only under the low-constraint conditions in the initiation task. The reaction time analyses mirrored the pattern of activity observed, with slower reaction times under conditions of suppression and under conditions of initiation with low constraint. By comparing these findings with other studies of response selection, we argue that the most likely single cognitive function of the DLPFC is to specify a set of responses suitable for a given task and to bias these for selection (sculpting the response space). This function resembles the biasing of competition between stimuli in the model of Desimone and Duncan and is analogous to the component of the Supervisory Attentional System that modulates the contention scheduling system.

Adult↗
PubMed2002

Whose arm is it anyway? An fMRI case study of supernumerary phantom limb.

Under normal circumstances, information from a number of sources is combined to compute a unitary percept of the body. However, after pathology these influences may be perceived simultaneously, resulting in multiple dissociated conscious representations. In a recent paper, we described subject E.P., a right-handed female stroke patient with a right frontomesial lesion who sporadically experiences a supernumerary 'ghost' left arm that occupies the previous position of the real left arm after a delay of 60-90 s. We used a delayed response paradigm with functional MRI to examine the haemodynamic correlates of E.P.'s illusion. Comparison of periods of time during scanning when the ghost arm was present against when it was not revealed a single cluster (9 voxels, t = 5.11, P < 0.012 corrected for multiple comparisons) located on the right medial wall in the supplementary motor area ('SMA proper'). Our results suggest that areas traditionally classified as part of the motor system can influence the conscious perception of the body. We propose that, as a consequence of her injury, E.P. is aware of the position of the phantom limb in this 'action space' while also continuing to be aware of the true position of her real limb on the basis of afferent somatosensory information.

Adult↗