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Journal ArticleDOI

Synaesthesia in Phantom Limbs Induced with Mirrors

TL;DR: In this paper, a virtual reality box is used to simulate the feeling of a real arm being touched by a real hand in order to study the inter-sensory effects of visual input on the phantom.
Abstract: Although there is a vast clinical literature on phantom limbs, there have been no experimental studies on the effects of visual input on phantom sensations. We introduce an inexpensive new device--a 'virtual reality box'--to resurrect the phantom visually to study inter-sensory effects. A mirror is placed vertically on the table so that the mirror reflection of the patient's intact had is 'superimposed' on the felt position of the phantom. We used this procedure on ten patients and found the following results. 1. In six patients, when the normal hand was moved, so that the phantom was perceived to move in the mirror, it was also felt to move; i.e. kinesthetic sensations emerged in the phantom. In D.S. this effect occurred even though he had never experienced any movements in the phantom for ten years before we tested him. He found the return of sensations very enjoyable. 2. Repeated practice led to a permanent 'disappearance' of the phantom arm in patient D.S. and the hand became telescoped into the stump near the shoulder. 3. Using an optical trick, impossible postures--e.g. extreme hyperextension of the fingers--could be induced visually in the phantom. In one case this was felt as a transient 'painful tug' in the phantom. 4. Five patients experienced involuntary painful 'clenching spasms' in the phantom hand and in four of them the spasms were relieved when the mirror was used to facilitate 'opening' of the phantom hand; opening was not possible without the mirror. 5. In three patients, touching the normal hand evoked precisely localized touch sensations in the phantom. Interestingly, the referral was especially pronounced when the patients actually 'saw' their phantom being touched in the mirror. Indeed, in a fourth patient (R.L.) the referral occurred only if he saw his phantom being touched: a curious form of synaesthesia. These experiments lend themselves readily to imaging studies using PET and fMRI. Taken collectively, they suggest that there is a considerable amount of latent plasticity even in the adult human brain. For example, precisely organized new pathways, bridging the two cerebral hemispheres, can emerge in less than three weeks. Furthermore, there must be a great deal of back and forth interaction between vision and touch, so that the strictly modular, hierarchical model of the brain that is currently in vogue needs to be replaced with a more dynamic, interactive model, in which 're-entrant' signalling plays the main role.
Citations
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Journal ArticleDOI
TL;DR: A perceptual theory of knowledge can implement a fully functional conceptual system while avoiding problems associated with amodal symbol systems and implications for cognition, neuroscience, evolution, development, and artificial intelligence are explored.
Abstract: Prior to the twentieth century, theories of knowledge were inherently perceptual. Since then, developments in logic, statis- tics, and programming languages have inspired amodal theories that rest on principles fundamentally different from those underlying perception. In addition, perceptual approaches have become widely viewed as untenable because they are assumed to implement record- ing systems, not conceptual systems. A perceptual theory of knowledge is developed here in the context of current cognitive science and neuroscience. During perceptual experience, association areas in the brain capture bottom-up patterns of activation in sensory-motor areas. Later, in a top-down manner, association areas partially reactivate sensory-motor areas to implement perceptual symbols. The stor- age and reactivation of perceptual symbols operates at the level of perceptual components - not at the level of holistic perceptual expe- riences. Through the use of selective attention, schematic representations of perceptual components are extracted from experience and stored in memory (e.g., individual memories of green, purr, hot). As memories of the same component become organized around a com- mon frame, they implement a simulator that produces limitless simulations of the component (e.g., simulations of purr). Not only do such simulators develop for aspects of sensory experience, they also develop for aspects of proprioception (e.g., lift, run) and introspec- tion (e.g., compare, memory, happy, hungry). Once established, these simulators implement a basic conceptual system that represents types, supports categorization, and produces categorical inferences. These simulators further support productivity, propositions, and ab- stract concepts, thereby implementing a fully functional conceptual system. Productivity results from integrating simulators combinato- rially and recursively to produce complex simulations. Propositions result from binding simulators to perceived individuals to represent type-token relations. Abstract concepts are grounded in complex simulations of combined physical and introspective events. Thus, a per- ceptual theory of knowledge can implement a fully functional conceptual system while avoiding problems associated with amodal sym- bol systems. Implications for cognition, neuroscience, evolution, development, and artificial intelligence are explored.

5,259 citations

Book
01 Jan 2002
TL;DR: Wegner as mentioned in this paper argues that the feeling of conscious will is created by the mind and brain and that it serves as a guide to understanding ourselves and to developing a sense of responsibility and morality.
Abstract: Do we consciously cause our actions, or do they happen to us? Philosophers, psychologists, neuroscientists, theologians, and lawyers have long debated the existence of free will versus determinism. In this book Daniel Wegner offers a novel understanding of the issue. Like actions, he argues, the feeling of conscious will is created by the mind and brain. Yet if psychological and neural mechanisms are responsible for all human behavior, how could we have conscious will? The feeling of conscious will, Wegner shows, helps us to appreciate and remember our authorship of the things our minds and bodies do. Yes, we feel that we consciously will our actions, Wegner says, but at the same time, our actions happen to us. Although conscious will is an illusion, it serves as a guide to understanding ourselves and to developing a sense of responsibility and morality. Approaching conscious will as a topic of psychological study, Wegner examines the issue from a variety of angles. He looks at illusions of the will -- those cases where people feel that they are willing an act that they are not doing or, conversely, are not willing an act that they in fact are doing. He explores conscious will in hypnosis, Ouija board spelling, automatic writing, and facilitated communication, as well as in such phenomena as spirit possession, dissociative identity disorder, and trance channeling. The result is a book that sidesteps endless debates to focus, more fruitfully, on the impact on our lives of the illusion of conscious will.

1,814 citations

Journal ArticleDOI
TL;DR: The location of the neural damage associated with these disorders suggests that representations of the current and predicted state of the motor system are in parietal cortex, while representations of intended actions are found in prefrontal and premotor cortex.
Abstract: Much of the functioning of the motor system occurs without awareness. Nevertheless, we are aware of some aspects of the current state of the system and we can prepare and make movements in the imagination. These mental representations of the actual and possible states of the system are based on two sources: sensory signals from skin and muscles, and the stream of motor commands that have been issued to the system. Damage to the neural substrates of the motor system can lead to abnormalities in the awareness of action as well as defects in the control of action. We provide a framework for understanding how these various abnormalities of awareness can arise. Patients with phantom limbs or with anosognosia experience the illusion that they can move their limbs. We suggest that these representations of movement are based on streams of motor commands rather than sensory signals. Patients with utilization behaviour or with delusions of control can no longer properly link their intentions to their actions. In these cases the impairment lies in the representation of intended movements. The location of the neural damage associated with these disorders suggests that representations of the current and predicted state of the motor system are in parietal cortex, while representations of intended actions are found in prefrontal and premotor cortex.

1,004 citations

Journal ArticleDOI
01 Sep 1998-Brain
TL;DR: It is suggested that patients with phantom limbs provide a valuable opportunity not only for exploring neural plasticity in the adult human brain but also for understanding the relationship between the activity of sensory neurons and conscious experience.
Abstract: Almost everyone who has a limb amputated will experience a phantom limb--the vivid impression that the limb is not only still present, but in some cases, painful. There is now a wealth of empirical evidence demonstrating changes in cortical topography in primates following deafferentation or amputation, and this review will attempt to relate these in a systematic way to the clinical phenomenology of phantom limbs. With the advent of non-invasive imaging techniques such as MEG (magnetoencephalogram) and functional MRI, topographical reorganization can also be demonstrated in humans, so that it is now possible to track perceptual changes and changes in cortical topography in individual patients. We suggest, therefore, that these patients provide a valuable opportunity not only for exploring neural plasticity in the adult human brain but also for understanding the relationship between the activity of sensory neurons and conscious experience. We conclude with a theory of phantom limbs, some striking demonstrations of phantoms induced in normal subjects, and some remarks about the relevance of these phenomena to the question of how the brain constructs a 'body image.'

968 citations

Journal Article
TL;DR: In this paper, the authors propose the notion of mind-reading as a way for humans to understand the behaviour of others in terms of their mental states, such as intentions, desires and beliefs.
Abstract: We are social animals. We share this feature with many other species. A complexity and sophistication that we do not observe among ants, bees or wolves, however, characteristically define the social life of primates. This complexity and sophistication is epitomized at its highest level by the social rules our conduct in everyday life is supposed to comply with. Living in a complex society requires individuals to develop cognitive skills enabling them to cope with other individuals’ actions, by recognizing them, understanding them, and reacting appropriately to them. No one doubts that the extant primate ancestors of ours, monkeys and apes, who indeed also live in complex, hierarchically organized societies, are perfectly able to cope with their own social rules. Nevertheless, it is commonly argued that to achieve that goal non-human primates simply rely on behaviour observation. Animals do not represent rules in their minds, and they do not engage in any inference-based reasoning. Accordingly, what non-human primates are lacking would sharply define what is considered to be uniquely human: truly cognitive states, such as intentions, desires and beliefs. In our daily life we are constantly exposed to the actions of the individuals inhabiting our social world. We are not only able to describe these actions, to understand their content, and predict their consequences, but we can also attribute intentions to the agents of the same actions. We can immediately tell whether a given observed act or behaviour is the result of a purposeful attitude or rather the unpredicted consequence of some accidental event, totally unrelated to the agent’s will. In other words, we are able to understand the behaviour of others in terms of their mental states. I will designate this ability as mind-reading. How do we ‘read’ intentions in the mind of other individuals? A common view maintains that all normal humans develop the capacity to represent mental states in others by means of a conceptual system, commonly designated as ‘Theory of Mind’ (TOM, see Premack and Woodruff, 1978). My initial scope will be limited: starting from a neurobiological standpoint, I will analyse how actions are possibly represented and understood. The main aim of my

876 citations

References
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Journal ArticleDOI
28 Jun 1991-Science
TL;DR: The results show the need for a reevaluation of both the upper limit of cortical reorganization in adult primates and the mechanisms responsible for it.
Abstract: After limited sensory deafferentations in adult primates, somatosensory cortical maps reorganize over a distance of 1 to 2 millimeters mediolaterally, that is, in the dimension along which different body parts are represented. This amount of reorganization was considered to be an upper limit imposed by the size of the projection zones of individual thalamocortical axons, which typically also extend a mediolateral distance of 1 to 2 millimeters. However, after extensive long-term deafferentations in adult primates, changes in cortical maps were found to be an order of magnitude greater than those previously described. These results show the need for a reevaluation of both the upper limit of cortical reorganization in adult primates and the mechanisms responsible for it.

1,051 citations

Journal ArticleDOI
TL;DR: This paper found that after the median nerve was transected and ligated in adult owl and squirrel monkeys, the cortical sectors representing it within skin surface representations in Areas 3b and 1 were completely occupied by 'new' and expanded representations of surrounding skin fields.

948 citations

Book
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809 citations

Journal ArticleDOI
11 Nov 1994-Science
TL;DR: In primates, many neurons in ventral premotor cortex respond to visual stimuli in the space adjacent to the hand or arm, and provide a representation of space near the body that may be useful for the visual control of reaching.
Abstract: In primates, the premotor cortex is involved in the sensory guidance of movement. Many neurons in ventral premotor cortex respond to visual stimuli in the space adjacent to the hand or arm. These visual receptive fields were found to move when the arm moved but not when the eye moved; that is, they are in arm-centered, not retinocentric, coordinates. Thus, they provide a representation of space near the body that may be useful for the visual control of reaching.

741 citations