ENS

To maintain a coherent and continuous percept over time, the brain relies on past sensory information to predict forthcoming stimuli. Combining novel behavioural methods with advanced neuroimaging techniques, the present research project aims to determine the neural mechanisms by which the auditory system uses information from the recent past to overcome signal noise and ambiguity. Specifically, we test the hypothesis that sensory predictions involve neural oscillations at alpha rhythm, ~9-10 Hz, that mediate the propagation of perceptual priors. The first part of this research project investigates the neural structures underlying such predictive oscillatory mechanism. To this end, we adapt a novel time-resolved sampling technique used to examine rhythmic fluctuations in perceptual performance for functional magnetic resonance imaging (fMRI). We hypothesise that cortical and subcortical activation, especially in the auditory cortex and thalamus, will exhibit rhythmic modulations that correlate with oscillations in decision bias during the detection of a brief auditory signal masked by white noise. The second part of this project examines whether the resolution of perceptual ambiguities by prior contextual information involves similar oscillatory mechanisms. For this purpose, we combine the time-resolved sampling technique with a classic paradigm (involving Shepard tones) for inducing ambiguous pitch shifts. By presenting a single tone before the ambiguous stimulus, listeners can be biased toward a perceived upward or downward pitch shift. If resolving perceptual ambiguities involves oscillatory mechanisms, we expect to observe periodic fluctuations of decision bias (that is, the tendency to make certain responses) at alpha rhythm over time. The results of this research project will shed light on a potentially crucial and yet unknown core process of perception, useful in every interaction we have with the world.

Phylogenetic trees represent the evolutionary relationships among individuals, populations, or species. These trees also contain information on the evolutionary dynamics in the underlying population, and can be used in a wide range of applications, from studying the dynamics of an epidemic to analyzing the speciation and extinction dynamics of groups of species. Reconstructing phylogenetic trees from sequence data requires specifying a "tree prior", i.e. a model that represents a prior idea about the evolutionary dynamics. The adequacy of the tree prior influences the quality of the phylogenetic reconstruction, and consequently the quality of the inferred evolutionary dynamics. Unfortunately, the currently used priors are over-simplistic; in particular, they assume that evolutionary rates are constant in time and identical across lineages. These homogeneous tree priors are most often inconsistent with the model subsequently used to infer evolutionary dynamics, which is statistically problematic and likely to bias inferences. Several factors contribute to this issue: i) the computational challenges of carrying out "full phylogenetic inferences", that is analyses that co-estimate trees and dynamics, ii) the under-recognized influence of tree priors on phylogenetic reconstruction and subsequent analyses of evolutionary dynamics and iii) the lack of empirical guidance on the use and interpretation of rate-heterogeneous tree priors. PHYLOBD will address this issue and significantly improve full Bayesian phylogenetic inference by: i) providing efficient implementations of tree priors that account for rate heterogeneity across lineages ii) evaluating the importance of using such tree priors iii) providing tools for an accurate representation of rate-heterogeneous Bayesian posteriors, and iv) providing efficient implementations of full Bayesian phylogenetic inference when data are sampled through time.

The economic history of early Rome has been mainly investigated as a local phenomenon and often only on the basis of literary evidence. We propose a long-term and regional approach: the early Roman economy as part of the economic history of central Tyrrhenian Italy from the 8th to the 4th century BC, and its interactions with the wider Mediterranean networks of exchange. This aim will be achieved by means of the following objectives and methods. Objective 1: Systematic and critical review of the literary sources and of the scientific literature on the archaeological evidence of settlements, land use, production and importation in the Low Tiber Valley between the 10th and the 4th century BC. Objective 2: Intensive surveys in the Roman hinterland of three productive extra-urban Archaic settlements within their natural context: a farmhouse, a rural village and a coastal settlement. Objective 3: Archaeometric analysis of amphoras dating back to the 8th – 6th centuries BC and of Greek Geometric (or Greek Geometric style) pottery dating back to the 8th century BC found in Ancient Latium. Objective 5: Historical reconstruction of production, trade and consumption in Rome between the 8th and the 4th century BC; theorisation of new models for Iron Age and pre-monetary economies.

The discovery of molecules in the early universe is a challenging providence. Molecules unveil the truly cold universe in which stars form and their rich versatility provides unique diagnostics to unravel the ”relative importance of purely gravitational effects and gas dynamical effects involving dissipation and radiative cooling”, recognized 40 years ago by White and Rees to be a central issue in theories of galaxy formation. Molecules also reveal that cosmic turbulence is far less dissipative than predicted by cosmological simulations, with a broad equipartition in a vast variety of media between the thermal energy of the hottest phases and the turbulent energy of the coldest. Our project focuses on the physics of turbulent dissipation, and its link to the emergence of molecules, in the magnetized compressible medium where gravitational instability develops to form stars and seed galaxies in the early universe. It builds on a fundamental property of turbulence, its space-time intermittency: dissipation occurs in bursts. Our team will foster strong interactions between three main research axes: (1) observations of the chemical and thermal markers of turbulent dissipation in the high-redshift and local universe, (2) statistical analyses of the magnetic and velocity fields in samples of unprecedented size and sensitivity to study the non-Gaussian signatures of turbulent dissipation, and (3) numerical experiments dedicated to (a) the space-time structures of turbulent dissipation and the formation of molecules in their wake, and (b) the split of the energy trails between hot/thermal and cold/turbulent phases. This project will benefit from the prodigious capabilities of the ALMA and NOEMA interferometers, the launch of the JWST in 2018, and the Planck satellite data on polarized Galactic foregrounds. The ENS Physics Department, with its strong theoretical and experimental expertise on turbulence, is an ideal place to house such a project.