Showing papers by "School for Advanced Studies in the Social Sciences published in 1986"

Sunspots and Cycles

Abstract: Because sunspot equilibria seem to be of central importance for an understanding of rational expectations, we seek here to characterize completely a limited class of sunspot equilibria (stationary ones with two possible natural events) in the simplest overlapping generations model of production. We present a sufficient condition for the existence of stationary sunspot equilibria, examine how these are related to strictly periodic equilibria of the same order, and investigate how deterministic stationary equilibria bifurcate to stationary sunspot equilibria. A concluding section examines how our results survive in more general settings.

Partially Verifiable Information and Mechanism Design

Abstract: In a principal-agent model with adverse selection, we study the implementation of social choice functions when the agent's message space is a correspondence which depends on this true characteristic. We characterize such correspondence for which the Revelation Principle is valid. returns must not contradict easily observable elements of the taxpayer's lifestyle. In this paper we present a model of two-person organizations in which these considerations are important. We ask whether the restrictions on fallacious statements inherent in the system are sufficient to achieve the goals of the organization. We show that the optimal way of eliciting the agent's response may not be to establish incentives for truthtelling in all instances. In our model there is one player, the "agent", who observes the state of the economic system. Another player, the "principal", takes an action based on the information presented to him by the agent. This class of models is often referred to as the principal-agent problem. In the extensive and growing literature on this problem, it has always been assumed that the agent could lie to the principal, and therefore that he had to be properly motivated to act at least partially in the principal's interest. Our formal way of modelling the partial verifiability of information is to introduce the restriction that the agent's responses must lie in a set M(O) that varies with the true state 0. It is assumed that this set always admits the possibility of responding with the true state. The way in which the allowable response set varies with the true state is known to the principal. In other respects we retain the usual principal-agent formalization. In particular, the principal is the Stackelberg leader in this game. He can commit himself to choose a collective action as a function of the message transmitted by the agent. Whether the variation of the message space with the true observation is purely technological, or whether it is induced by the severity of potential actions of the principal,

Eye-movement control in visual search: How direct is visual span control?

Abstract: In order to distinguish between the effects of low-level sensory mechanisms and those of higher level factors on eye-movement control processes, a simple letter search task was used in which cognitive load was reduced to the very minimum. The special purpose of this study was to test the visual span control hypothesis, which considers that, in such a task, eye movements are controlled as a direct function of spatial visibility limits (O’Regan, Levy-Schoen, & Jacobs, 1983). In a first psychophysical experiment, three methods were used to manipulate the spatial visibility limits (visual span), as measured by a psychophysical procedure: changing viewing distance, interletter spacing, and target-background similarity. The results of this experiment then were used as a reference for predicting mean saccade sizes and fixation durations in a visual search task in which the same visibility changes were made. About 80% of the variance of mean saccade sizes could be accounted for by adjustment of saccades to changes in visual span, so the visual span control hypothesis was confirmed. As to the temporal characteristics of scanning behavior, less than 50% of fixation duration variance seemed to be determined by visual span changes. Other, higher level factors, possibly related to decisional processes intervening in the triggering of saccades and the computation of their spatial parameters, might play an important role in determining fixation durations in a simple search task. The results are interpreted in relation to recent models of eye-movement control by two largely independent subsystems functioning in parallel.

The Cultural Context of Motor Development: Postural Manipulations in the Daily Life of Bambara Babies (Mali):

Abstract: The present study is the first exploratory step of a larger investigation focusing on the influence of culturally-related caretaking practices on motor development. Four Bambara infants between 4 a...

Les problèmes cognitifs rencontrés par des elèves de l’enseignement secondaire dans l’apprentissage de l’informatique

Abstract: Cet article de synthese developpe des elements theoriques et methodologiques dans une problematique d’analyse des difficultes cognitives rencontrees par des eleves de l’enseignement secondaire dans l’apprentissage de l’informatique L’accent est mis d’une part sur les representations que les eleves construisent sur le fonctionnement du systeme et sur la structuration de l’information (representation des donnees) et, d’autre part, sur l’acquisition des concepts cles de variable et d’iteration