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Saillance et prototypes

rosch_natural_categories.pdf
rosch_principles_categorization.pdf

Eleanor H. [Heider] Rosch,
"Natural Categories",
Cognitive Psychology
,
Vol.4, No.3, (May 1973), pp. 328–350.

Eleanor Rosch,
Principles of Categorization,
in Eleanor Rosch and Barbara B. Lloyd, Eds.,
Cognition and Categorization,
Hillsdale NJ, Lawrence Erlbaum, 1978, pp. 27–48.

Le concept de prototype est introduit par Eleanor Rosch en 1973 dans Natural Categories. Il est défini initialement comme un stimulus en position saillante dans la formation d'une catégorie parce qu'il est le premier stimulus que l'on associera à cette catégorie:

The hypothesis of the study was that the domains of color and form are structured into nonarbitrary, semantic categories which develop around perceptually salient "natural prototypes." Categories which reflected such an organization (where the presumed natural prototypes were central tendencies of the categories) and categories which violated the organization (natural prototypes peripheral) were taught to a total of 162 members of a Stone Age culture which did not initially have hue or geometric-form concepts. In both domains, the presumed "natural" categories were consistently easier to learn than the "distorted" categories. (1973)

Le mot clé est salient, perceptually salient. La saillance, donc une réalité psychologique sinon même psychophysique du prototype. Lequel est ensuite redéfini comme le membre le plus central d'une catégorie, fonctionnant comme un point de référence cognitif. Au lieu d'un modèle définitionnel — par exemple un oiseau peut être défini par les traits [+plumes], [+bec] et [+aptitude à voler] —, la théorie du prototype considère une catégorie «oiseau» comme basée sur différents attributs ayant un statut inégal: par exemple un rouge-gorge (robin) serait un meilleur prototype d'oiseau que, disons, un manchot (penguin).

La saillance est un premier point de départ de la réflexion d'Eleanor Rosch. Un autre point de départ est le pragmatisme qui lui inspire son principe de Cognitive Economy appliqué aux processus de Categorization. Une catégorie a le maximum d'utilité quand le fait de connaître la catégorie à laquelle une chose appartient permet à l'organisme de connaître autant d'attributs de cette chose que possible. L'utilité de la segmentation d'un même domaine en catégories discrètes décroît à mesure que diminue le nombre de propriétés prédictibles à partir de la connaissance de la catégorie. (Toutes les citations qui suivent viennent du texte de 1978.)

To categorize a stimulus means to consider it for purposes. Purposes of that categorization are not only equivalent to other stimuli in the same category but also different from stimuli not in that category. On the one hand, it would appear to the organism's advantage to have as many properties as possible predictable from knowing any one property, a principle that would lead to formation of large numbers of categories with as fine discriminations between categories as possible. On the other hand, one purpose of categorization is to reduce the infinite differences among stimuli to behaviorally and cognitively usable proportions. It is to the organism's advantage not to differentiate one stimulus from others when that differentiation is irrelevant to the purposes at hand.

Les modes de classification occidentaux (the tradition of Western reason) découlent du principe pragmatique d'économie cognitive dans la mesure où des catégories «discrètes», séparées par des frontières claires et nettes, sont plus économiques.

Most, if not all, categories do not have clear-cut boundaries. To argue that basic object categories follow clusters of perceived attributes is not to say that such attribute clusters are necessarily discontinuous. In terms of the principles of categorization proposed earlier, cognitive economy dictates that categories tend to be viewed as being as separate from each other and as clear-cut as possible. One way to achieve this is by means of formal, necessary and sufficient criteria for category membership. The attempt to impose such criteria on categories marks virtual definitions in the tradition of Western reason. The psychological treatment of categories in the standard concept-identification paradigm lies within this tradition. Another way to achieve separateness and clarity of actually continuous categories is by conceiving of each category in terms of its clear cases rather than its boundaries. As Wittgenstein has pointed out, categorical judgments become a problem only if one is concerned with boundaries — in the normal course of life, two neighbors know on whose property they are standing without exact demarcation of the boundary line. Categories can be viewed in terms of their clear cases if the perceiver places emphasis on the correlational structure of perceived attributes such that the categories are represented by their most structured portions.

S'inspirant de Wittgenstein, Rosch considère que la catégorisation n'exige pas que toutes les instances d'une catégorie sémantique partagent un attribut commun. Il suffit qu'elles soient liées entre elles par une ressemblance de famille. Wittgenstein, Investigations Philosophiques, §66-67 sur l'exemple du jeu comme catégorie: «Je ne puis caractériser mieux ces ressemblances que par les mots ressemblance de famille [Familienähnlichkeiten]; car c'est de la sorte que s'entrecroisent et s'enveloppent les unes les autres les différentes ressemblances qui existent entre les différents membres d'une famille; la taille, les traits du visage, la couleur des yeux, la démarche, le tempérament etc. — Et je disais : les jeux constituent une famille.»

By prototypes of categories we have generally meant the clearest cases of category membership defined operationally by people's judgments of goodness of membership in the category. A great deal of confusion in the discussion of prototypes has arisen from two sources. First, the notion of prototypes has tended to become reified as though it meant a specific category member or mental structure. Questions are then asked in an either-or fashion about whether something is or is not the prototype or part of the prototype in exactly the same way in which the question would previously have been asked about the category boundary. Such thinking precisely violates the Wittgensteinian insight that we can judge how clear a case something is and deal with categories on the basis of clear cases in the total absence of information about boundaries. […]

Perception of typicality differences is, in the first place, an empirical fact of people's judgments about category membership. It is by now a well-documented finding that subjects overwhelmingly agree in their judgments of how good an example or clear a case members are of a category, even for categories about whose boundaries they disagree.

Il y a différents moyens de réaliser le consensus sur les "clear cases" qui sont reconnus comme prototypiques, et les Hedges sont l'un de ces moyens.