The Mirror Neuron System and Imitation--论文代写范文精选

其次,需要提取什么信息才能模仿他的行为?它足以理解观察到行为的目的，最后,感觉和运动系统通常被认为是独立的系统。因此,视觉事件的描述如何复制观察到的事件。下面的paper代写范文进一步叙述。

Introduction 
‘‘Every one knows what attention is.’’ This famous sentence by William James (1890, p. 403) appears to be appropriate also for imitation. Everyone knows what imitation is. Yet, as soon as imitation is more closely examined, this concept loses its simplicity; it appears to include different behaviors, some learned, some innate. In this chapter, unless specified otherwise, I adopt Thorndike’s definition of imitation. Imitation is learning to do an act from seeing it done (Thorndike, 1898). This definition includes two basic ideas: (1) imitation implies learning; and (2) during imitation the observer transforms an observed action into an executed action that is similar or even identical to the observed one. 

How does imitation occur? The response to this question is obviously not easy. In the first place, why should an individual copy an action made by another individual? In everyday life, copying an action is typically useless and frequently dangerous. If an animal observing a conspecific eating some food imitates its movements, it will never get food. It will only aimlessly move its mouth. Imitation implies an understanding of what another individual is doing as well as the capacity to use this knowledge only in particular conditions. Second, what information must the observer extract from an acting conspecific in order to imitate his behavior? Is it sufficient to understand the goal of the observed actions or must its details also be coded? Finally, there is the so-called ‘‘translation’’ problem. Sensory and motor systems are classically considered to be separate systems. Thus, how can the description of a visual event become a muscle excitation that faithfully replicates the observed event? 

In this chapter, the following theoretical positions are defended: 1. Imitation is composed of two strictly related cognitive phenomena. The first is the capacity to make sense of others’ actions. The second is the capacity, once the action is understood, to replicate it. According to the task and external contingencies, the imitated action can be structured differently. In some cases the observer replicates the goal of the observed action; in others the goal and the means used for achieving the goal are replicated. 2. 

The fundamental neurophysiological mechanism that underlies understanding of an action is a direct matching of the observed action with the motor representation of that action. This matching is made by the mirror neuron system. The matching of the observed action with its motor representation is a necessary prerequisite for imitation. 3. The matching mechanism by itself is not sufficient. It must be complemented by the activity of other mechanisms that modify and organize the mirror neuron system. Here I summarize the properties of mirror neurons in monkeys, describe the properties of the mirror neuron system in humans, and finish by discussing the mechanisms that are necessary to achieve imitation.

The Monkey Mirror Neuron System: Motor and Visual Properties of F5 Neurons 
Mirror neurons were originally discovered in area F5 of the monkey premotor cortex (di Pellegrino et al., 1992; Gallese et al., 1996; Rizzolatti et al., 1996a). This is a motor area that controls hand and mouth movements. A fundamental characteristic of this area is that many of its neurons discharge during specific goal-directed action (Rizzolatti et al., 1988). These neurons become active regardless of the effector (the right hand or the left hand or the mouth) used to achieve a specific goal (e.g., grasping an object). Conversely, they do not fire when a monkey uses the same effectors, but for another purpose (e.g., pushing objects away). According to the action effective in triggering them, F5 neurons have been subdivided into various classes. Among them, the most represented are grasping, holding, tearing, and manipulating neurons. A second fundamental characteristic of area F5 is that many of its neurons specify how a goal can be achieved. For example, the majority of grasping neurons discharge only if grasping is made using a particular type of prehension, such as a precision grip, finger prehension, and, more rarely, whole-hand prehension.

About 20% of F5 neurons respond to visual stimuli (Rizzolatti et al., 1988). One class of these visuomotor neurons is made up of canonical neurons, which discharge when a monkey sees an object that is congruent with the type of grip coded by the neuron (Murata et al., 1997). Visuomotor neurons in a second class do not discharge in response to the presentation of 3-D objects. The visual stimuli effective in triggering them are actions in which the experimenter (or a monkey) interacts with objects. Neurons with these properties are called mirror neurons (Gallese et al., 1996; Rizzolatti et al., 1996a). Typically, in order to be triggered F5 mirror neurons require an interaction between hand and object. The sight of the object alone or of an agent mimicking an action is ineffective. The object’s significance for the animal has no influence on mirror neuron response. Grasping a piece of food or a geometric solid produces responses of the same intensity. A functional property of mirror neurons that is important for the issue of imitation is the relationship between their visual and motor properties. 

Most mirror neurons (93%) show a clear congruence between the visual actions they respond to and the motor response they code. According to the type of congruence they exhibit, mirror neurons were subdivided into strictly congruent and broadly congruent neurons (Gallese et al., 1996). We labeled as strictly congruent those mirror neurons in which the effective observed and effective executed actions correspond both in terms of goal (e.g., grasping) and means, that is, the way the action is executed (e.g., precision grip). They represent about 30% of F5 mirror neurons. We labeled as broadly congruent those mirror neurons that in order to be triggered do not require the observation of exactly the same action they code for motorically. Some of them discharge during the execution of a particular type of action (e.g., grasping) when executed using a particular grip type (e.g., precision grip). However, they respond to the observation of grasping made by another individual, regardless of the type of grip used (figure 1.1). Other broadly congruent neurons discharge in association with a single motor action (e.g., holding), but also respond to the observation of two actions (e.g., grasping and holding). Broadly congruent neurons are the largest class of mirror neurons (about 60%).

Action Coding in the Temporal and Parietal Lobes of the Monkey
Neurons responding to the observation of actions made by others are not located only in area F5. In a brilliant series of studies, Perrett and his coworkers (Perrett et al., 1989; see for review Jellema & Perrett, 2002; Jellema et al., 2002) showed that neurons selectively responding to biological actions are present in the region of the superior temporal sulcus (STS). Actions effective in eliciting STS neuron responses are walking, turning the head, bending the torso, moving the arms, and facial movements, as well as gaze direction. A small set of neurons discharge during the observation of goal-directed hand movements (Perrett et al., 1990b). The motor properties of STS neurons have not been specifically investigated. Motor-related activity, however, if present, should involve only a limited number of STS neurons. Another cortical area where there are neurons that respond to action observation is area PF (Fogassi et al., 1998; Gallese et al., 2002). This area forms the rostral part of the inferior parietal lobule. 

PF receives input from STS and sends output to area F5. Conversely, F5 sends output to PF, which in turn sends projections to STS. Information is flowing, therefore, not only from STS to F5, but also from F5 to STS. Direct connections between STS and F5 have not been described. Neurons in area PF are functionally heterogeneous. Most of them (about 90%) respond to sensory stimuli (Hyvarinen, 1982; Leinonen & Nyman, 1979; Fogassi et al., 1998; Gallese et al., 2002). About 50% of them also discharge in association with a monkey’s active movements. 

PF neurons responding to sensory stimuli can be subdivided into three categories: somatosensory neurons (33%); visual neurons (11%); and bimodal neurons, which respond to somatosensory and visual stimuli (56%). Among the neurons with visual responses (visual neurons and bimodal neurons), 41% respond to the observations of actions made by another individual. The effective actions most represented are grasping, holding, manipulating, and bimanual interactions. One third of PF neurons triggered by action observation do not appear to have motor-related activity. The other two-thirds discharge also during a monkey’s movement and, in most cases, show the visuomotor congruence typical of mirror neurons (PF mirror neurons) (Gallese et al., 2002). From these findings the following picture emerges. Visually described actions are first stored in STS. In this area many neurons ‘‘resonate’’ in response to the sight of specific actions. STS action description is then transferred to PF. In PF, some neurons are exclusively visual, but most of them also discharge during action execution.

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