Rationality | EPFL Graph Search

Rationality is the quality of being guided by or based on reasons. In this regard, a person acts rationally if they have a good reason for what they do or a belief is rational if it is based on strong evidence. This quality can apply to an ability, as in rational animal, to a psychological process, like reasoning, to mental states, such as beliefs and intentions, or to persons who possess these other forms of rationality. A thing that lacks rationality is either arational, if it is outside the domain of rational evaluation, or irrational, if it belongs to this domain but does not fulfill its standards. There are many discussions about the essential features shared by all forms of rationality. According to reason-responsiveness accounts, to be rational is to be responsive to reasons. For example, dark clouds are a reason for taking an umbrella, which is why it is rational for an agent to do so in response. An important rival to this approach are coherence-based accounts, which define

Essays on individual decision making under uncertainty

Elise Le Nestour

This research project is an experimental study of decision-making in very difficult contexts resembling those encountered in financial markets. The starting point was the empirical observation that financial assets are objects of a very complex kind. Specifically, financial assets generate rewards in an unpredictable way (stochastic processes), and they jump regularly (unstable processes). What's more, they are covert: finance practitioners lack information about their nature, and may well be unable to uncover it. After all, can humans really learn the nature of unstable stochastic processes? To address this question, I designed an investment task, the "Boardgame," characterized by assets – in the form of locations displayed on a board – which are, like the financial assets in the real world, unpredictable, unstable, and (initially) unknown. Specifically, the game consists of choosing between six locations of initially unknown probability of winning or losing. Each trial, the player selects one location and immediately receives the outcome returned by the chosen location (a reward, a loss, or 0 CHF). She accumulates gains and losses throughout the game, with the goal of maximizing the cumulative earnings. One essential characteristic of the Boardgame is that outcome probabilities – at all locations – jump regularly. An ideal player accounts for jump occurrence and re-learns outcome probabilities once a jump has occurred. Such two-stage mental process – consisting of jump detection and subsequent reappraisal of the probabilities – is extremely demanding. I invited 62 subjects – all undergraduate or graduate students at the EPFL – to play the Boardgame during 30 minutes, and recorded their action in each trial (namely, which location they chose). From their choices, I attempted to infer the nature of their learning in the game. To do so, I followed an inter-disciplinary approach, at the intersection of economics, machine learning, and neurobiology. I first formalized normative learning in the game (how ideal players learn), as well as bounded rational learning (how adaptive – intelligent – agents, albeit of limited cognitive capabilities, are expected to learn). I then examined whether my subjects did a good job of learning in the Boardgame, by comparing the fits of the normative and bounded rational models. I eventually studied the neural implementation of the behavior at work. It appears that for the majority of my subjects, the normative learning model did a much better job of explaining actual behavior than the alternative, bounded rational model. In other words, subjects were apt at learning the outcome probabilities of the locations, despite the difficulty of the enterprise. This suggests that people may be better fit to cope with the instability of financial markets than previously thought. Beyond being of interest for the finance field, this result has actually a broader scope. For it demonstrates the human ability to adapt behavior to suit an uncertain changing environment. This cognitive flexibility, which some eminent neuroscientists have been taken to be the most relevant definition of human intelligence, is essential in many domains beyond the one studied here (reward learning) – in particular, the same neuroscientists have suggested that it is chief in contexts of social interaction. The finding that my subjects were very good at learning the nature of the locations is also important from an epistemological point of view. For one message drawn from this study is that people can be very sophisticated in the face of very complex problems. This message should prompt a reevaluation of the scope of the dominant paradigm in decision making – namely, the limited cognition paradigm. The limited cognition paradigm has led either to a hyperemphasis on cognitive biases as sources of human mistakes (irrationality), or to the idea that complexity in a cognitive task precludes the emergence of optimal behavior (bounded rationality). In contrast, the present work highlights human adaptation, and further suggests that complexity is not necessarily an obstacle for full rationality to emerge. One reason that my subjects could fare so well in my complex task is that the human brain is fit to cope with the Boardgame, which is reminiscent of the living conditions of the early man. For Homo has long had to deal with an uncertain unstable environment. As a result, the hominoid brain was geared to cope with instability. The finding that optimal behavior prevailed in my experiment prompted me to flesh out the neural implementation of this behavior. In the final stage of this project, I conjectured a neural system that is fit to cope with unforeseen and ever-changing conditions. I attempted to describe this neural system rigorously, in the vein of a recent computational trend in decision neuroscience. This computational approach aims to reveal the neural substrates of subjective states that the behavioral models purport to estimate – e.g., how much reward a subject expected on each trial, how much surprise a subject experienced on each trial, how much uncertainty a subject perceived in her environment on each trial. Likewise, I estimated subjective variables that are essential to implement the optimal Bayesian rule in my task. In particular, I estimated how much credit a subject assigned to the belief that a jump occurred on each trial. This estimation enabled me to make precise predictions as to the neural mechanisms involved in the Boardgame. The incoming step shall be to put these predictions to a test in an imaging study of the Boardgame. As such, the present research has laid the basis for a larger research program to be pursued. It is hoped that it shows the utility of bringing the modeling tools from economics to bear on neurobiological questions. I think that such scientific exchanges carry the possibility of insights useful to build an adequate model of individual decision-making.

EPFL2009

Transfer Design and Incentives for Nationally Appropriate Mitigation Actions in Developing Countries

Juan Carlos Altamirano Cabrera, Ronal Gainza Carmenates, Philippe Thalmann

Transfers would play a key role in the implementation of Nationally Appropriate Mitigation Actions (NAMAs) in developing countries. In this paper, we analyze the desirable features of such transfers - i.e., individually rational, budget-balanced, anti-incentives for free-riding and misrepresentation. We model NAMAs as a non-cooperative, one shot game. We consider NAMAs under two alternative transfer schemes: a horizontal equity-based transfer and an “optimal” transfer scheme that we call à la Weikard. Our analysis is further refined by the inclusion of the notion of pivotal countries. We find, firstly, that both transfer schemes may allow the implementation of an individually rational and budget-balanced NAMAs portfolio; secondly, that the transfer à la Weikard is more effective in avoiding free-riding. Thirdly, both transfer schemes fail to avoid misrepresentation of costs and benefits from reductions in greenhouse gas emissions. Finally, pivotal countries for NAMAs are the most interested in its implementation even if they are the largest transfer contributors.

Climate Economics at the NCCR Climate2010

Stabilizing Unusual Oxidation States of Lanthanides in Molecular Complexes: Synthesis, Properties, and Reactivity

Aurélien René Willauer

The chemistry of divalent lanthanides has generated increasing interest in the past years due to their redox properties and unique reaction pathways. Notably, molecular complexes of low-valent lanthanides have been shown to be suitable one-electron reductants that are able to activate inert small molecules such as heteroallenes and dinitrogen in mild conditions. Lanthanide(II) complexes usually undergo mono-electron transfer, but multi-electron transfer can be achieved through multiple one-electron processes in polymetallic complexes. The first part of this thesis describes attempts to expand the redox chemistry of lanthanide complexes and lays the basis for a wider understanding of the chemical and reductive properties of low-valent polynuclear lanthanide complexes. Thus, Chapter 2, 3, and 4, reports the synthesis and characterization of different polynuclear lanthanides(II) complexes of various siloxide ligands. In Chapter 2, the outcome of carbon dioxide reduction (oxalate versus carbonate) by dinuclear Ln(II) tris(tert-butoxy)siloxide complexes, depending on the solvent polarity and on the nature of the Ln ions, was investigated. Furthermore, unprecedented reduction products could be isolated from the reaction with CS2, providing the first example of acetylenedithiolate ligand formation from metal reduction of carbon disulphide. In all cases, it has been shown that cooperative binding of the substrate plays an important role in the outcome of the reaction. Chapter 3 describes a rational route to the first metallasilsesquioxane of a dinuclear divalent lanthanide which can selectively effect the reductive disproportionation of CO2 and the two-electron reduction of azobenzene. In an attempt to confer increased reductive reactivity to Eu(II) ions, Chapter 4 describes the use of the tetraphenyldisiloxanediolate ligand to form polynuclear complexes of Eu(II) that can initiate for the first time carbon dioxide activation by Eu(II) ions in an isolated complex.Differently, until 2019, the +IV oxidation state of lanthanide in molecular complexes remained limited to a single lanthanide ion, cerium. It is only recently that the terbium ion was shown to be able to access the +IV oxidation state in molecular complexes. However, given the broad applications of cerium(IV), the discovery of other molecular complexes of Ln(IV) is of great interest for chemists. Chapter 5 describes the synthesis of the third example of a Tb(IV) complex displaying an open coordination sphere and the very first report of a molecular complex of praseodymium in the +IV oxidation state. The novel Ln(IV) complexes were characterized by UV-Visible, NMR, EPR and IR spectroscopy, magnetometry, single-crystal X-ray diffraction analysis, cyclic voltammetry, and computational studies. In particular, this provided an opportunity to measure and study the luminescent spectra of Pr(IV) for the first time, which upon binding to the siloxide ligand results in a large shift of the ligand triplet state. Furthermore, these complexes have been shown to be appropriate starting materials for the synthesis of Ln(IV) phosphine oxide adducts. Preliminary studies directed towards the isolation of Nd(IV) molecular complexes are discussed.

EPFL2022