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Biomedical subjects

Patrick Haggard

Publications and source records attributed to Patrick Haggard.

14 recordsLinked to original sources
PubMed2003

Awareness of action in schizophrenia.

An abnormal sense of agency is among the most characteristic yet perplexing positive symptoms of schizophrenia. Schizophrenics may either attribute the consequences of their own actions to the intentions of others (delusions of influence), or may perceive themselves as causing events which they do not in fact control (megalomania). Previous reports have often described inaccurate agency judgements in schizophrenia, but have not identified the disordered neural mechanisms or psychological processes underlying these judgements. We report the perceived time of a voluntary action and its consequence in eight schizophrenic patients and matched controls. The patients showed an unusually strong binding effect between actions and consequences. Specifically, the temporal interval between action and consequence appeared shorter for patients than for controls. Patients may overassociate their actions with subsequent events, experiencing their actions as having unusual causal efficacy. Disorders of agency may reflect an underlying abnormality in the experience of voluntary action.

Acoustic Stimulation↗
PubMed2003

The effect of attentional cueing on conscious awareness of stimulus and response.

Attending to a cued location in space leads to faster reaction times when a stimulus is presented there. The reasons for this attentional effect, and its specific locus in the information-processing chain between stimulus and response, remain unclear. One suggestion is that attention speeds the conscious detection of stimuli. Surprisingly, this possibility appears not to have been tested directly. To resolve this question, we asked subjects to make simple responses to lateralised targets that followed either a valid, invalid or neutral cue, and to judge the perceived time of the target onset, or of their response, by delayed report of the position of a clock hand. Our results showed that only a small and non-significant part of the attentional effect is due to delayed conscious awareness of the stimulus. The greater part of the attentional effect is localised either subsequent to conscious detection of stimuli or occurs in a separate, parallel processing stream from that which generates the motor response.

Adult↗
PubMed2003

Awareness of somatic events associated with a voluntary action.

How does the brain distinguish actions that we perform from movements imposed on us? To study links between the representations of actions and their somatosensory consequences, we compared the perceived times of voluntary actions or involuntary movements and of a subsequent somatic effect (a TMS-induced twitch of the right index finger). Participants perceived voluntary actions as occurring later and their bodily effects as occurring earlier in the agency context, compared to single-event baseline conditions. When the voluntary action was replaced by a passive, involuntary movement this attraction effect reversed. In a second experiment, subjects rated the intensity of the same TMS-induced somatic effect, again following a voluntary action or a passive movement. When the somatic effect was caused by a voluntary action, it was perceived as significantly less intense than when it followed a passive movement. Our results suggest a binding mechanism integrating awareness of somatic consequences occurring in voluntary action. This 'intentional binding' mechanism might underlie the way in which the mind constructs a strong association between intentions, actions and consequences so as to generate the unique and private phenomenological experience of self-agency.

Adult↗
PubMed2003

Who knows best? Awareness of divided attention difficulty in a neurological rehabilitation setting.

OBJECTIVE: To explore whether patients relearning to walk after acquired brain injury and showing cognitive-motor interference were aware of divided attention difficulty; whether their perceptions concurred with those of treating staff. DESIGN: Patients and neurophysiotherapists (from rehabilitation and disabled wards) completed questionnaires. Factor analyses were applied to responses. Correlations between responses, clinical measures and experimental decrements were examined. RESULTS: Patient/staff responses showed some agreement; staff reported higher levels of perceived difficulty; responses conformed to two factors. One factor (staff/patients alike) reflected expectations about functional/motor status and did not correlate with decrements. The other factor (patients) correlated significantly with dual-task motor decrement, suggesting some genuine awareness of difficulty (cognitive performance prioritized over motor control). The other factor (staff) correlated significantly with cognitive decrement (gait prioritized over sustained attention). CONCLUSIONS: Despite some inaccurate estimation of susceptibility; patients and staff do exhibit awareness of divided attention difficulty, but with a limited degree of concurrence. In fact, our results suggest that patients and staff may be sensitive to different aspects of the deficit. Rather than 'Who knows best?', it is a question of 'Who knows what?'

Adult↗
PubMed2003

Changing patterns of cognitive-motor interference (CMI) over time during recovery from stroke.

OBJECTIVE: To explore the extent and nature of change in cognitive-motor interference (CMI) among rehabilitating stroke patients who showed dual-task gait decrement at initial assessment. DESIGN: Experimental, within-subjects, repeated measures design. SETTING: Rehabilitation centre for adults with acquired, nonprogressive brain injury. SUBJECTS: Ten patients with unilateral stroke, available for reassessment 1-9 months following their participation in a study of CMI after brain injury. MEASURES: Median stride duration; mean word generation. METHODS: Two x one-minute walking trials, two x one-minute word generation trials, two x one-minute trials of simultaneous walking and word generation; 10-metre walking time; Barthel ADL Scale score. RESULTS: Seven out of ten patients showed reduction over time in dual-task gait decrement. Three out of ten showed reduction in cognitive decrement. Only one showed concomitant reduction in gait and word generation decrement. CONCLUSION: Extent of CMI during relearning to walk after a stroke reduced over time in the majority of patients. Effects were more evident in improved stride duration than improved cognitive performance. Measures of multiple task performance should be included in assessment for functional recovery.

Activities of Daily Living↗
PubMed2002

Imitation without awareness.

Imitation is a characteristic but little-understood function of the human brain and of some higher animals. The direct matching hypothesis suggests that a specialised brain circuit is able to extract and directly copy the motor commands of another person's observed actions. Here we investigate how conscious people are of this kind of imitation. We first showed that imitation reactions are faster than simple visual reaction times, consistent with a direct matching circuit in the CNS. We next compared the perceived time of imitation reactions in 17 healthy subjects with other kinds of actions. We found a significant delay in subjects' awareness of their own imitation reactions. Thus, while imitation reactions are unusually fast, subjects are not aware of this. The brain's direct-matching circuit for imitation partly bypasses conscious awareness.

Adult↗
PubMed2002

Action and awareness in pointing tasks.

Subjects' awareness of motor corrections was investigated in a double-step pointing task. An unpredictable lateral target displacement of 10 cm, either left or right, during an ongoing reaching movement led to corrections of the trajectory. Subjects were required either to follow the target (pointing) or move in the opposite direction (anti-pointing). The target jump elicited rapid corrections to the movement in the direction of the target shift. These corrections were in some sense involuntary as they sometimes occurred in anti-point trials, when subjects were instructed to correct in the opposite direction to the target jump. The instructed correction away from the target in anti-point trials occurred later than the correction towards the target in standard pointing. Subjects were also asked to report their awareness of the motor correction they had just made by immediately reproducing each movement. In normal pointing, subjects showed reduced and delayed awareness, suggesting that the corrections were at least partly automatic. Anti-pointing corrections did not show this dissociation between performance and awareness. We suggest that anti-point corrections, but not standard pointing corrections, involve an additional supervisory system. This system is characterised by its slow operation and its access to conscious awareness.

Adult↗
PubMed2002

When feeling is more important than seeing in sensorimotor adaptation.

Perception and action are based on information from multiple sensory modalities. For instance, both vision and proprioception provide information about hand position, and this information is integrated to generate a single estimate of where the hand is in space. Classically, vision has been thought to dominate this process, with the estimate of hand position relying more on vision than on proprioception. However, an optimal integration model that takes into account the precision of vision and proprioception predicts that the weighting of the two senses varies with direction and that the classical result should only hold for specific spatial directions. Using an adaptation paradigm, we show that, as predicted by this model, the visual-proprioceptive integration varies with direction. Variation with direction was so strong that, in the depth direction, the classical result was reversed: the estimate relies more on proprioception than on vision. These results provide evidence for statistically optimal integration of information from multiple modalities.

Adaptation, Physiological↗
PubMed2002

Vision modulates somatosensory cortical processing.

Over 150 years ago, E.H. Weber declared that experience showed that tactile acuity was not affected by viewing the stimulated body part. However, more recent investigations suggest that cross-modal links do exist between the senses. Viewing the stimulated body site improves performance on tactile discrimination and detection tasks and enhances tactile acuity. Here, we show that vision modulates somatosensory cortex activity, as measured by somatosensory event-related potentials (ERPs). This modulation is greatest when tactile stimulation is task relevant. Visual modulation is not present in the P50 component reflecting the primary afferent input to the cortex but appears in the subsequent N80 component, which has also been localized to SI, the primary somatosensory cortex. Furthermore, we replicate previous findings that noninformative vision improves spatial acuity. These results are consistent with a hypothesis that vision modulates cortical processing of tactile stimuli via back projections from multimodal cortical areas. Several neurophysiological studies suggest that primary and secondary somatosensory cortex (SI and SII, respectively) activity can be modulated by spatial and tactile attention and by visual cues. To our knowledge, this is the first demonstration of direct modulation of somatosensory cortex activity by a noninformative view of the stimulated body site with concomitant enhancement of tactile acuity in normal subjects.

Adult↗
PubMed2002

Voluntary action and conscious awareness.

Humans have the conscious experience of 'free will': we feel we can generate our actions, and thus affect our environment. Here we used the perceived time of intentional actions and of their sensory consequences as a means to study consciousness of action. These perceived times were attracted together in conscious awareness, so that subjects perceived voluntary movements as occurring later and their sensory consequences as occurring earlier than they actually did. Comparable involuntary movements caused by magnetic brain stimulation reversed this attraction effect. We conclude that the CNS applies a specific neural mechanism to produce intentional binding of actions and their effects in conscious awareness.

Adult↗
PubMed2002

rTMS to the supplementary motor area disrupts bimanual coordination.

Bimanual coordination tasks form an essential part of our behaviour. One brain region thought to be involved in bimanual coordination is the supplementary motor area (SMA). We used repetitive transcranial magnetic stimulation (rTMS) at 1 Hz for 5 min to create a temporary virtual lesion of the rostral portion of the human SMA immediately prior to performance of a goal-directed bimanual coordination task. In two control conditions, participants underwent sham stimulation or stimulation over the primary motor cortex (MI). The experimental task was to open a drawer with the left hand, catch a ball with the right hand, and reinsert the ball into the drawer through an aperture just big enough for the ball to pass through, again with the right hand. Hence, the actions of one hand depend upon the actions of the other. We calculated time intervals between the successive component actions of one hand (unimanual intervals) and actions of both hands (bimanual intervals) and analyzed these intervals separately. Interestingly, none of the unimanual intervals were affected by the rTMS, but the variability of a critical bimanual interval--the time between the left hand opening the drawer and the right hand starting to move to catch the ball--was increased by rTMS over the rostral parts of the SMA. No such effect was seen following rTMS over MI or after sham rTMS. Our results suggest that the rostral parts of the SMA play an important role in aspects of functional bimanual tasks, which involve tight temporal coordination between different motor actions of the two hands.

Adult↗
PubMed2001

Look and feel.

It is known that the CNS integrates proprioceptive and visual information to calculate limb position. Recent studies implicate an additional process, which might involve initial visual calibration of limb position, or gaze signals resulting from eye movements towards the felt position.

Journal Article↗
PubMed2001

The psychology of action.

Actions are part of the way that the mind controls the body. Two fundamental psychological questions about actions are 'Where do they come from?' and 'How does the mind produce them?' These may be called the 'internal generation problem' and the 'information expansion problem' respectively. The importance of these questions was appreciated at the birth of the British Psychological Society (BPS) a century ago, though the experimental methods to study them were lacking. This article falls into two halves. The first half discusses some of the major epochs in the psychology of action over the last 100 years; the second half outlines some currently prominent research questions, and considers their historical antecedents. Finally, I offer some speculations regarding where future contributions to the psychology of action will be most fruitful.

Journal Article↗