Papers by Jean-Pierre Nadal
arXiv (Cornell University), Nov 26, 2001
We present a model of opinion dynamics in which agents adjust continuous opinions as a result of ... more We present a model of opinion dynamics in which agents adjust continuous opinions as a result of random binary encounters whenever their difference in opinion is below a given threshold. High thresholds yield convergence of opinions towards an average opinion, whereas low thresholds result in several opinion clusters. The model is further generalised to network interactions, threshold heterogeneity, adaptive thresholds and binary strings of opinions.
Author response: Cerebellar learning using perturbations
Annuaire de l’EHESS. Comptes rendus des cours et conférences, 2008
Neural networks that learn temporal sequences
Springer eBooks, Apr 6, 2008
arXiv (Cornell University), May 22, 2023
We analyse the income distributions of cities in France and the scaling of the income of differen... more We analyse the income distributions of cities in France and the scaling of the income of different deciles as a function of the population. We find a significant difference in the scaling exponents for the richer and poorer parts of the population, implying an unequivocal rise in inequalities in larger cities, made worse by living costs that are disproportionately higher for the poor. We find that the distribution of revenues of cities in France has a universal, Gumbel-like form, with mean and variance growing with the logarithm of population. We show how this result directly implies different income scaling exponents as a function of decile. We also study the spatial correlations of income and population, which decay exponentially with distance. We find that large cities are not more income-segregated than small cities. Finally, we search for couplings between social and economic factors, like age and income, and propose a toy model that reproduces some of our observations.
arXiv (Cornell University), Dec 12, 2010
Addressing issues of social diversity, we introduce a model of housing transactions between agent... more Addressing issues of social diversity, we introduce a model of housing transactions between agents who are heterogeneous in their willingness to pay. A key assumption is that agents' preferences for a location depend on both an intrinsic attractiveness and on the social characteristics of the neighborhood. The stationary space distribution of income is analytically and numerically characterized. The main results are that socio-spatial segregation occurs if -and only if -the social influence is strong enough, but even so, some social diversity is preserved at most locations. Comparison with data on the Paris housing market shows that the results reproduce general trends of price distribution and spatial income segregation.
bioRxiv (Cold Spring Harbor Laboratory), May 23, 2019
Electrophysiological recordings during perceptual decision tasks in monkeys suggest that the degr... more Electrophysiological recordings during perceptual decision tasks in monkeys suggest that the degree of confidence in a decision is based on a simple neural signal produced by the neural decision process. Attractor neural networks provide an appropriate biophysical modeling framework, and account for the experimental results very well. However, it remains unclear whether attractor neural networks can account for confidence reports in humans. We present the results from an experiment in which participants are asked to perform an orientation discrimination task, followed by a confidence judgment. Here we show that an attractor neural network model quantitatively reproduces, for each participant, the relations between accuracy, response times and confidence, as well as sequential effects. Our results suggest that a metacognitive process such as confidence in one's decision is linked to the intrinsically nonlinear dynamics of the decision-making neural network.
arXiv (Cornell University), Jun 1, 2016
We represent the functioning of the housing market and study the relation between income segregat... more We represent the functioning of the housing market and study the relation between income segregation, income inequality and house prices by introducing a spatial Agent-Based Model (ABM). Differently from traditional models in urban economics, we explicitly specify the behavior of buyers and sellers and the price formation mechanism. Buyers who differ by income select among heterogeneous neighborhoods using a probabilistic model of residential choice; sellers employ an aspiration level heuristic to set their reservation offer price; prices are determined through a continuous double auction. We first provide an approximate analytical solution of the ABM, shedding light on the structure of the model and on the effect of the parameters. We then simulate the ABM and find that: (i) a more unequal income distribution lowers the prices globally, but implies stronger segregation; (ii) a spike of the demand in one part of the city increases the prices all over the city; (iii) subsidies are more efficient than taxes in fostering social mixing.
arXiv (Cornell University), Jun 1, 2016
We represent the functioning of the housing market and study the relation between income segregat... more We represent the functioning of the housing market and study the relation between income segregation, income inequality and house prices by introducing a spatial Agent-Based Model (ABM). Differently from traditional models in urban economics, we explicitly specify the behavior of buyers and sellers and the price formation mechanism. Buyers who differ by income select among heterogeneous neighborhoods using a probabilistic model of residential choice; sellers employ an aspiration level heuristic to set their reservation offer price; prices are determined through a continuous double auction. We first provide an approximate analytical solution of the ABM, shedding light on the structure of the model and on the effect of the parameters. We then simulate the ABM and find that: (i) a more unequal income distribution lowers the prices globally, but implies stronger segregation; (ii) a spike of the demand in one part of the city increases the prices all over the city; (iii) subsidies are more efficient than taxes in fostering social mixing.
Neural Computation, Nov 4, 2021
HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific r... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
eLife, Nov 12, 2018
The cerebellum aids the learning of fast, coordinated movements. According to current consensus, ... more The cerebellum aids the learning of fast, coordinated movements. According to current consensus, erroneously active parallel fibre synapses are depressed by complex spikes signalling movement errors. However, this theory cannot solve the credit assignment problem of processing a global movement evaluation into multiple cell-specific error signals. We identify a possible implementation of an algorithm solving this problem, whereby spontaneous complex spikes perturb ongoing movements, create eligibility traces and signal error changes guiding plasticity. Error changes are extracted by adaptively cancelling the average error. This framework, stochastic gradient descent with estimated global errors (SGDEGE), predicts synaptic plasticity rules that apparently contradict the current consensus but were supported by plasticity experiments in slices from mice under conditions designed to be physiological, highlighting the sensitivity of plasticity studies to experimental conditions. We analyse the algorithm's convergence and capacity. Finally, we suggest SGDEGE may also operate in the basal ganglia.
arXiv (Cornell University), Jun 28, 2023
Contribution to the edited volume "Spin Glass Theory & Far Beyond -Replica Symmetry Breaking afte... more Contribution to the edited volume "Spin Glass Theory & Far Beyond -Replica Symmetry Breaking after 40 Years", World Scientific, 2023 (to appear).
Basins of Attraction in a Perception-like Neural Network
Complex Systems, 1988
We st udy the perfor mance of a neu ral net work of the per cept ron typ e. We isolate two impor... more We st udy the perfor mance of a neu ral net work of the per cept ron typ e. We isolate two important set s of pa rameters which ren der t he network fau lt tolerant (existence of large basins of attraction ) in both hetero-as sociative and auto-associative systems and study t he size of the bas ins of attraction (the maximal allowable noise level still ens uring recognition ) for sets of random patterns. The releva nce of ou r result s to t he pe rcept ron's ability t o gene ralize are pointed out, as is t he role of diagonal couplings in t he fully connected Hopfield model.
Manifesto da ciência social computacional
DOAJ (DOAJ: Directory of Open Access Journals), Mar 1, 2013
Background: The CRASH-3 trial provides a high level of evidence on the question whether to admini... more Background: The CRASH-3 trial provides a high level of evidence on the question whether to administer Tranexamic Acid (TXA) for Traumatic brain injury (TBI). For numerous other research questions, the available evidence will not correspond to such a level of evidence and will rely on observational evidence only. The development of methodological alternatives to analyze observational data is necessary. The Crash-3trial provided the opportunity to explore the effect of TXA on TBI mortality with two distinct causal inference methods using incomplete observational data. Methods: Two causal inference techniques, inverse propensity weighting (IPW) and doubly robust method (DR), associated with machine learning method techniques to handle missing data, explored the effect of TXA administration on 30-day head injury related death expressed in registry data. The effect was expressed as Average Treatment Effect (ATE). TBI was defined as a head Abbreviated Injury Score >2. The hypothesis ex...
Modeling Language Change
Language evolution is the subject of various theoretical studies, following two main paths: one, ... more Language evolution is the subject of various theoretical studies, following two main paths: one, where language is viewed as a code between meanings and forms to express them, with a focus on language as a social convention; and the other defining language as a set of grammatical rules governing the production of utterances, evolution being the outcome of mistakes in the acquisition process. We claim that none of the current models provides a satisfactory account of the grammaticalization phenomenon, a linguistic process by which words acquire a grammatical status. We argue that this limitation is mainly due to the way these models represent language and communication mechanisms. We therefore introduce a new framework, the " grammatheme, " as a tool which formalizes in an unambiguous way different concepts and mechanisms involved in grammaticalization. The model especially includes an inference mechanism triggering new grammaticalization processes. We present promising preliminary results of a numerical implementation and discuss a possible research program based on this framework.
The Journal of Neuroscience, 2018
Perceptual decision-making is the subject of many experimental and theoretical studies. Most mode... more Perceptual decision-making is the subject of many experimental and theoretical studies. Most modeling analyses are based on statistical processes of accumulation of evidence. In contrast, very few works confront attractor network models' predictions with empirical data from continuous sequences of trials. Recently however, numerical simulations of a biophysical competitive attractor network model have shown that such a network can describe sequences of decision trials and reproduce repetition biases observed in perceptual decision experiments. Here we get more insights into such effects by considering an extension of the reduced attractor network model of Wong and Wang (2006), taking into account an inhibitory current delivered to the network once a decision has been made. We make explicit the conditions on this inhibitory input for which the network can perform a succession of trials, without being either trapped in the first reached attractor, or losing all memory of the past ...
Between
dilemma due to social interactions
Bioinformatics Original Paper
Identifying genes from up–down properties of microarray expression series Vol. 21 no. 20 2005, pa... more Identifying genes from up–down properties of microarray expression series Vol. 21 no. 20 2005, pages 3859–3864 doi:10.1093/bioinformatics/bti549
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Papers by Jean-Pierre Nadal