Coherence optimization model of suicide--论文代写范文精选

陀思妥耶夫斯基的小说中，阿列克谢认为人类有绝对的自由意志,超越了所有的心理动机能够表达它。尽管其哲学的魅力,但科学家宁愿喜欢寻找自杀的原因和机制。下面的essay代写范文进行详述。

Abstract
This article describes a model that approaches both individual and social dimensions of suicide. At the individual level, the model construes suicidal thoughts as optimization of coherence between relevant cognitive unit sets (i.e. collections of interrelated cognitive units that focus on a particular external or internal object). It assumes that suicidal thoughts are mostly affected by the manner individuals construe their egos, their economic, relational, professional, and health situations, as well as life, death, and suicide.  At the social level, the model argues that suicide rates depend on the distributions of these cognitive unit sets and of the connections between them. The model has been implemented in a computer program that simulates important characteristics of suicide rates. 
  
INTRODUCTION
In Dostoyevsky's novel, The Possessed, one of the characters, Aleksei Kirillov, maintains that humans have an absolutely free will and that only a gratuitous suicide, which transcends all psychological motivations, would be able to express it. In spite of its philosophical attractiveness, extremely few scientists would favor the idea of a gratuitous suicide act and would rather prefer to search for suicides causes and mechanisms. Many of them would say that suicide is determined by individual factors. Psychologists, whether they construe suicide as escape from psychological conflict or focus on the beliefs, expectations, problem solving skills, developmental factors or other psychological variables that affect suicide, usually adhere to this conception. Durkheim, the author of the most influential theory of suicide (Atkinson, 1978), did not. According to his counterintuitive theory, although suicide seems the most personal act a human being can do, it is exclusively determined by social factors (Durkheim, 1897/1993).

The split between approaches centered on individual factors and approaches centered on external factors (mostly on social factors) is one of the most important in suicidology. Usually, researches that focus on the individual dimension of suicidal behavior are not concerned with and are of no use to researches that focus on the social dimension of suicide and vice versa. However, there are researches concerned with both individual and social aspects of suicide. The classic theory elaborated by Henri and Short (1954) provides a nice example. Its basic psychological assumptions are simple: frustration is positively related to aggression and people attribute the responsibility for their frustration externally or internally, external attributions determining aggressive acts oriented toward others (homicide) and internal attributions determining self aggressive acts (suicide). A negative economical evolution of the society increases frustration among individuals and, consequently, the number of aggressive acts. However, suicide and homicide rates do not rise uniformly. Suicide will be more frequent among those with high status and homicide will be more frequent among those with low status because high status is associated with weak external restraints that determine  internal attributions of responsibility, and low status is associated with strong external restraints that determine external attributions of responsibility.

Like Henri and Shorts theory, the present work addresses both psychological and social dimensions of suicide. Unlike Henri and Shorts theory, the theoretical frame used here is different. At the individual level, the model focuses on the optimization of coherence among relevant cognitive unit sets. At the social level, it assumes that suicidal rates depend on the relevant cognitive unit set distributions of a population. 

  Coherence optimization and constraint satisfaction
In a coherence optimization problem, one has to divide a set of elements that constrain one another into an accepted set and a rejected set, in a way that maximizes the satisfaction of constraints. The satisfaction is not uniform, constraints that are more important being preferred. A constraint between two elements is positive if they fit together (i.e. the relation between them can be of positive association, consistency, facilitation, explanation etc.) and negative if they conflict (i.e. the relation between them can be of negative association, inconsistency, incompatibility). If the constraint between two elements is positive, they are accepted or rejected together, if the constraint is negative one is accepted and the other rejected (Thagard and Verbeurgt, 1998; Thagard and Kunda, 1998).

Constraint satisfaction networks are used in order to approximate coherence optimization. They have been successfully used in psychology to model various cognitive (Thagard and Millgram, 1995; Holyoak and Thagard, 1997 etc.) and social psychological processes (Shultz and Lepper, 1996; Kunda and Thagard, 1996 etc.). In a parallel constraint satisfaction network, the basic unit is an oversimplified analogue of the biological neuron. It is defined by three characteristics: input set (the activation coming from other units, weighted with the connection importance), activation function (how is processed the input set), and activation (the result obtained after the activation function has been applied to the input set). The connection between two units represents a constraint. Negative connection weights correspond to negative constraints and positive connection weights correspond to positive constraints.

Cognitive unit sets

Some psychological and psychiatric studies of suicide focus on variables such as personality or temperament traits (e.g. Engstrom, Persson, and Levander S, 1999), hopelessness and depression (e.g. Uncapher, Gallagher-Thompson, Osgood, and Bongar, 1998) or self-esteem (e.g. Overholser, Adams, Lehnert, and Brinkman, 1995). Other studies are concerned with interpersonal interactions (e.g. Zhang and Jin, 1998), psychoanalytic processes (e.g. Goldberg, 1999), life events (e.g. Cavanagh, Owens, and Johnstone, 1999), developmental factors (e.g. Van der Kolk, Perry, and Herman, 1991) etc. In the coherence model of suicide, the basic elements are the cognitive unit sets.

A cognitive unit set (CUS) is a collection of interrelated constructs, evaluations, beliefs, affects, or other cognitive units that focus on the same external or internal object or situational domain and can usefully be regarded as a whole. The meaning of a CUS depends on the associations between its component cognitive units and on the associations with other CUSs. A CUS has a positive pole or cognitive unit subset and a negative pole or cognitive unit subset. The direction of a CUS depends on the difference between the strength of its poles: the bigger the difference, the less ambiguous the direction. The cognitive units forming the positive pole and the cognitive units forming the negative pole negatively constrain one another. For example, in the case of ego CUS, cognitive units such as "I am a good person", "I am a successful person" etc. (positive pole) are negatively associated with cognitive units such as "I am a bad person", "I am a loser" etc. (negative pole). 

Two CUSs can be positively or negatively associated. If positively associated, the constraint between their positive poles and the constraint between their negative poles are positive, whereas the positive pole-negative pole constraints are negative. For instance, economic CUS is positively associated with ego CUS: positive cognitive units focused on the personal economic situation ("Im richer than most people I know", "I have a decent financial situation" etc.) activate ego positive cognitive units and deactivate ego negative cognitive units. Economic negative cognitive units ("Im poorer than most people I know", "My financial situation is very constraining" etc.) deactivate ego positive cognitive units and activate ego negative cognitive units. If two CUSs are negatively associated, the constraints between their positive poles and between their negative poles are negative, while the positive pole-negative pole constraints are positive.

The cognitive unit sets are represented by sets of units in a connectionist network. Two negatively connected nodes  - excitatory and inhibitory - represent a cognitive unit subset. A CUS is represented by two negatively connected cognitive unit subsets - one standing for the positive pole, the other for the negative pole. The excitatory and the inhibitory nodes of a subset are construed according to the rules specified by Shultz and Lepper (1996): inhibitory nodes have smaller maximum activation values (0.5) compared with excitatory nodes (1.0). However, in the coherence model of suicide two negatively connected nodes represents a subset of cognitions and not a particular cognition.

This representational schema tends to be more sensitive to the complexity and the ambiguity of human cognition. The fact that a person can hold simultaneously contradictory beliefs about the same object can be easily represented in the coherence model, by assigning similar initial activation values for the two poles of the CUS that focus on the respective object. Ambiguity plays an important role in suicide (Cosman, 1999; Firestone, 1997).

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