Expérience comportementale et modélisation par réseau neuronal des différences entre les processus de catégorisation par règles logiques et par ressemblance familiale

Notre étude est bipartite. En premier lieu nous avons effectué une étude empirique des différences entre les processus de catégorisation explicite (verbalisable) et implicite (non-verbalisable). Nous avons examiné la difficulté et le temps nécessaire pour apprendre trois tâches de catégorisation dites par air de famille, par règle logique conjonctive et par règle logique disjonctive. Nous avons ensuite utilisé un réseau neuronal pour modéliser la catégorisation en lui faisant compléter les mêmes tâches. La comparaison entre les deux nous permet de juger de l’adéquation du modèle. Les données empiriques ont montré un effet de la typicité et de la familiarité en accord avec la documentation et nous trouvons que la tâche de catégorisation par règle disjonctive est la plus difficile alors que la tâche de catégorisation par air de famille est la plus facile. La modélisation par le réseau est une réussite partielle mais nous présentons des solutions afin qu’un réseau futur puisse modéliser le processus catégoriel humain efficacement

Auditory perceptual decision-making based on semantic categorization of environmental sounds.

Discriminating complex sounds relies on multiple stages of differential brain activity. The specific roles of these stages and their links to perception were the focus of the present study. We presented 250ms duration sounds of living and man-made objects while recording 160-channel electroencephalography (EEG). Subjects categorized each sound as that of a living, man-made or unknown item. We tested whether/when the brain discriminates between sound categories even when not transpiring behaviorally. We applied a single-trial classifier that identified voltage topographies and latencies at which brain responses are most discriminative. For sounds that the subjects could not categorize, we could successfully decode the semantic category based on differences in voltage topographies during the 116-174ms post-stimulus period. Sounds that were correctly categorized as that of a living or man-made item by the same subjects exhibited two periods of differences in voltage topographies at the single-trial level. Subjects exhibited differential activity before the sound ended (starting at 112ms) and on a separate period at ~270ms post-stimulus onset. Because each of these periods could be used to reliably decode semantic categories, we interpreted the first as being related to an implicit tuning for sound representations and the second as being linked to perceptual decision-making processes. Collectively, our results show that the brain discriminates environmental sounds during early stages and independently of behavioral proficiency and that explicit sound categorization requires a subsequent processing stage.

Cognitive inertia and the implicit association test

The authors review the implicit association test (IAT), its use in marketing, and the methodology and validity issues that surround it. They focus on a validity problem that has not been investigated previously, namely, the impact of cognitive inertia on IAT effects. Cognitive inertia refers to the difficulty in switching from one categorization rule to another, which causes IAT effects to depend on the order of administration of the two IAT blocks. In Study 1, the authors observe an IAT effect when the compatible block precedes the incompatible block but not when it follows the incompatible block. In Studies 2 and 3, the IAT effect changes its sign when the order of the blocks reverses. Cognitive inertia distorts individual IAT scores and diminishes the correlations between IAT scores and predictor variables when the block order is counterbalanced between subjects. Study 4 shows that counterbalancing the block order repeatedly within subjects can eliminate cognitive inertia effects on the individual level. The authors conclude that researchers should either interpret IAT scores at the aggregate level or, if individual IAT scores are of interest, counterbalance the block order repeatedly within subjects.

Categorization skills and recall in brain damaged children: a multiple case study

During development, children become capable of categorically associating stimuli and of using these relationships for memory recall. Brain damage in childhood can interfere with this development. This study investigated categorical association of stimuli and recall in four children with brain damages. The etiology, topography and timing of the lesions were diverse. Tasks included naming and immediate recall of 30 perceptually and semantically related figures, free sorting, delayed recall, and cued recall of the same material. Traditional neuropsychological tests were also employed. Two children with brain damage sustained in middle childhood relied on perceptual rather than on categorical associations in making associations between figures and showed deficits in delayed or cued recall, in contrast to those with perinatal lesions. One child exhibited normal performance in recall despite categorical association deficits. The present results suggest that brain damaged children show deficits in categorization and recall that are not usually identified in traditional neuropsychological tests.

MEMORY TRAINING FOR OLDER ADULTS WITH LOW EDUCATION: MENTAL IMAGES VERSUS CATEGORIZATION

This study aimed to describe the benefits of memory training for older adults with low education. Twenty-nine healthy older adults with zero to two years of formal education participated. Sixteen participants received training based on categorization (categorization group = CATG) and 13 received training based on mental images (imagery group = IMG). One group served as control for the other because they trained with different strategies. Training was offered in eight sessions of 90 minutes. The participants were evaluated pre- and posttraining. IMG improved performance in episodic memory tests and had reduced depressive symptoms. CATG increased the use of categorization but did not increase performance in episodic memory tests. Results suggest that the strategy based on the creation of mental images was more effective for older adults with low formal education.

On state representations of nonlinear implicit systems

This work considers a semi-implicit system A, that is, a pair (S, y), where S is an explicit system described by a state representation (x)over dot(t) = f(t, x(t), u(t)), where x(t) is an element of R(n) and u(t) is an element of R(m), which is subject to a set of algebraic constraints y(t) = h(t, x(t), u(t)) = 0, where y(t) is an element of R(l). An input candidate is a set of functions v = (v(1),.... v(s)), which may depend on time t, on x, and on u and its derivatives up to a Finite order. The problem of finding a (local) proper state representation (z)over dot = g(t, z, v) with input v for the implicit system Delta is studied in this article. The main result shows necessary and sufficient conditions for the solution of this problem, under mild assumptions on the class of admissible state representations of Delta. These solvability conditions rely on an integrability test that is computed from the explicit system S. The approach of this article is the infinite-dimensional differential geometric setting of Fliess, Levine, Martin, and Rouchon (1999) (`A Lie-Backlund Approach to Equivalence and Flatness of Nonlinear Systems`, IEEE Transactions on Automatic Control, 44(5), (922-937)).

Distinct conformational properties determined by implicit and explicit representation of protein-solvent interactions. An analytical and computer simulation study

In the protein folding problem, solvent-mediated forces are commonly represented by intra-chain pairwise contact energy. Although this approximation has proven to be useful in several circumstances, it is limited in some other aspects of the problem. Here we show that it is possible to achieve two models to represent the chain-solvent system. one of them with implicit and other with explicit solvent, such that both reproduce the same thermodynamic results. Firstly, lattice models treated by analytical methods, were used to show that the implicit and explicitly representation of solvent effects can be energetically equivalent only if local solvent properties are time and spatially invariant. Following, applying the same reasoning Used for the lattice models, two inter-consistent Monte Carlo off-lattice models for implicit and explicit solvent are constructed, being that now in the latter the solvent properties are allowed to fluctuate. Then, it is shown that the chain configurational evolution as well as the globule equilibrium conformation are significantly distinct for implicit and explicit solvent systems. Actually, strongly contrasting with the implicit solvent version, the explicit solvent model predicts: (i) a malleable globule, in agreement with the estimated large protein-volume fluctuations; (ii) thermal conformational stability, resembling the conformational hear resistance of globular proteins, in which radii of gyration are practically insensitive to thermal effects over a relatively wide range of temperatures; and (iii) smaller radii of gyration at higher temperatures, indicating that the chain conformational entropy in the unfolded state is significantly smaller than that estimated from random coil configurations. Finally, we comment on the meaning of these results with respect to the understanding of the folding process. (C) 2009 Elsevier B.V. All rights reserved.

The cost of life expectancy and the implicit social valuation of life

A new method of estimating the economic value of life is proposed. Using cross-country data, an equation is estimated to explain life expectancy as a function of real consumption of goods and services. The associated cost function for life expectancy in terms of the prices of specific goods and services is used to estimate the cost of a reduction in age-specific mortality rates sufficient to save the life of one person. The cost of saving a life in OECD countries is as much as 1000 times that in the poorest countries. Ethical implications are discussed.

Social identity and self-categorization processes in organizational contexts

Although aspects of social identity theory are familiar to organizational psychologists, its elaboration, through self-categorization theory, of how social categorization and prototype-based depersonalization actually produce social identity effects is less well known. We describe these processes, relate self-categorization theory to social identity theory, describe new theoretical developments in detail, and show how these developments can address a: range of organizational phenomena. We discuss cohesion and deviance, leadership, subgroup and sociodemographic structure, and mergers and acquisitions.

Stereotypic explanatory bias: Implicit stereotyping as a predictor of discrimination

Two experiments examined whether a measure of implicit stereotyping based on the tendency to explain Black stereotype-incongruent events more often than Black stereotype-congruent events (Stereotypic Explanatory Bias or SEB) is predictive of behavior toward a partner in an interracial interaction. In Experiment I SEB predicted White males' choice to ask stereotypic questions of a Black female (but not a White male or White female) in an interview. In Experiment 2 the type of explanation (internal or external attribution) made for stereotype-inconsistency was examined. Results showed that White participants who made internal attributions for Black stereotype-incongruent behavior were rated more positively and those who made external attributions were rated more negatively by a Black male confederate. These results point to the potential of implicit stereotyping as an important predictor of behavior in an interracial interaction. (C) 2002 Elsevier Science (USA). All rights reserved.

Approximate controllability of second-order distributed implicit functional systems

In this paper we study the approximate controllability of control systems with states and controls in Hilbert spaces, and described by a second-order semilinear abstract functional differential equation with infinite delay. Initially we establish a characterization for the approximate controllability of a second-order abstract linear system and, in the last section, we compare the approximate controllability of a semilinear abstract functional system with the approximate controllability of the associated linear system. (C) 2008 Elsevier Ltd. All rights reserved.