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As light travels through a disordered medium such as biological tissues, it undergoes multiple scattering events. This phenomenon is detrimental to in-depth optical microscopy, as it causes a drastic degradation of contrast, resolution and brightness of the resulting image beyond a few scattering mean free paths. However, the information about the inner reflectivity of the sample is not lost; only scrambled. To recover this information, a matrix approach of optical imaging can be fruitful. Here we report on the compressed measurement of a high-dimension reflection matrix R via low coherence interferometry. Then, we show how the inner transmission matrix linking each camera sensor and each medium voxel can be extracted through an iterative multi-scale analysis of wave distortions contained in R. This transmission matrix is the Holy Grail for volumetric imaging since it enables an optimal compensation of forward multiple scattering paths and provides a three-dimensional confocal image of the sample as the latter one had become digitally transparent. The proof-of-concept experiment is performed on a human opaque cornea and an extension of the penetration depth by a factor five is demonstrated compared to the state-of-the-art., Comment: 39 page, 10 figures

The last decade has seen the development of a wide set of tools, such as wavefront shaping, computational or fundamental methods, that allow to understand and control light propagation in a complex medium, such as biological tissues or multimode fibers. A vibrant and diverse community is now working on this field, that has revolutionized the prospect of diffraction-limited imaging at depth in tissues. This roadmap highlights several key aspects of this fast developing field, and some of the challenges and opportunities ahead., submitted to J.Phys Photonics (IOP), 116 pages, 23 sections

Improvisational theatre (improv) is supposed to have an impact on cognitive processes (divergent thinking, flexibility, language, memory, problem solving, and co-construction), academic performance, and everyday life in many ways. However, little research studied on the psychological impact of improv, with some results highlighting a divergent thinking enhancement in children and adults, but not with teenagers, one of the most important age groups to practice improv. Therefore, this study aims to assess divergent thinking for middle school students before and after an 11-week session compared to a control group with a sport practice. The Alternative Uses Task was used before and after the session for both groups to evaluate divergent thinking. The improv group had better performance in originality, flexibility and gave less prototypical items after the improv sessions compared to before, while the control group performance was similar before and after. Our results suggest that improv helps teenagers’ divergent thinking to improve, not only with experimental games in the lab context but also after ecological sessions. We urge scientists to study in depth psychological impacts of improvisational theatre and applied improvisation, for a better understanding of improv and as a model to study embodied cognition.

We report on anomalous light transport in the strong scattering regime. Using low-coherence interferometry, we measure the reflection matrix of titanium dioxide powders, revealing crucial features of strong optical scattering which can not be observed with transmission measurements: (i) a subdiffusive regime of transport at early times of flight that is a direct consequence of predominant recurrent scattering loops, and (ii) a crossover to a conventional, but extremely slow, diffusive regime at long times. These observations support previous predictions that near-field coupling between scatterers prohibits Anderson localization of light in three-dimensional disordered media., 13 pages, 7 figures

13 pages, 9 figures; We report on anomalous light transport in the strong scattering regime. Using low-coherence interferometry, we measure the reflection matrix of titanium dioxide powders, revealing crucial features of strong optical scattering which can not be observed with transmission measurements: (i) a subdiffusive regime of transport at early times of flight that is a direct consequence of predominant recurrent scattering loops, and (ii) a transition to a conventional, but extremely slow, diffusive regime at long times. These observations support previous predictions that near-field coupling between scatterers prohibits Anderson localization of light in three-dimensional disordered media.

Introduction Intellectually gifted children have higher performance in many domains of attention than intellectually average children. However, these empirical findings are not consistent in the literature. Few studies investigated the characteristics of alerting, orienting, and executive control networks in intellectually gifted children. The aim of our study was to investigate their characteristics of attentional abilities compared to intellectually average children. Method Fifty‐five intellectually gifted children (age range 8–14 years old) were compared to 55 intellectually average children (age range 8–14 years old) using the Attention Network Test (ANT) to assess these three attentional constructs. Results Intellectually gifted children made fewer errors than intellectually average children in the processing of the ANT. In terms of attention network scores, they also outperformed intellectually average children in executive control only. Conclusion Intellectually gifted children do not differ from intellectual average children in terms of the speed of processing in a speeded task such as ANT, but they stand out in terms of accuracy of processing. Intellectually gifted children have better ability to focus volitionally in order to solve a simple perceptual conflict than intellectually average children., The aim of this study was to investigate the characteristics of three attentional networks in intellectually gifted children. The findings show the intellectually gifted children have better ability to focus volitionally in order to solve a simple perceptual conflict than intellectually average children.

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This is the first article in a series of two dealing with a matrix approach \alex{for} aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a raw ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A focusing criterion can then be built, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the standard coherence factor used in the literature, this new indicator is robust to multiple scattering and electronic noise, thereby providing a highly contrasted map of the focusing quality. As a proof-of-concept, UMI is applied here to the in-vivo study of a human calf, but it can be extended to any kind of ultrasound diagnosis or non-destructive evaluation.

We report on experimental and numerical implementations of devices based on the negative refraction of elastic guided waves, the so-called Lamb waves. Consisting in plates of varying thickness, these devices rely on the concept of complementary media, where a particular layout of negative index media can cloak an object with its anti-object or trap waves around a negative corner. The diffraction cancellation operated by negative refraction is investigated by means of laser ultrasound experiments. However, unlike original theoretical predictions, these intriguing wave phenomena remain, nevertheless, limited to the propagating component of the wave-field. To go beyond the diffraction limit, negative refraction is combined with the concept of metalens, a device converting the evanescent components of an object into propagating waves. The transport of an evanescent wave-field is then possible from an object plane to a far-field imaging plane. Twenty years after Pendry's initial proposal, this work thus paves the way towards an elastic superlens.

International audience; We present a physically intuitive matrix approach for wave imaging and characterization in scattering media. The experimental proof-of-concept is performed with ultrasonic waves, but this approach can be applied to any field of wave physics for which multi-element technology is available. The concept is that focused beamforming enables the synthesis, in transmit and receive, of an array of virtual transducers which map the entire medium to be imaged. The inter-element responses of this virtual array form a focused reflection matrix from which spatial maps of various characteristics of the propagating wave can be retrieved. Here we demonstrate: (i) a local focusing criterion that enables the imaging quality to be evaluated everywhere inside the medium, including in random speckle; (ii) a tomographic measurement of wave velocity, which allows for aberration corrections in the original image; (iii) an highly resolved spatial mapping of the prevalence of multiple scattering, which constitutes a new and unique contrast for ultrasonic imaging. More generally, this matrix approach opens an original and powerful route for quantitative imaging in wave physics.

International audience; Ultrasonic inspection of forged metal alloys is made difficult by multiple scattering due to strong heterogeneities of the microstructure: the echo of a defect is harder to distinguish from structural noise. An estimation of the proportion of multiple scattering would be a valuable indicator to assess the quality of ultrasonic inspection. In order to understand the contribution of multiple scattering in the multi- element reflection matrix, a simple model is built. Our simulation is an acoustic adaptation of the coupled-dipole method, also called Multiple Scattering Theory, with a medium thickness ranging from one half to several scattering mean-free paths and considering longitudinal waves only. Reflection matrices generated by each order of scattering are independently calculated and the temporal evolution of their average intensity is compared to a Monte-Carlo simulation of the Radiative Transfer Equation. A good agreement is found between the two approaches when the Born series converges. Two indicators for the proportion of single versus multiple scattering are compared. The first one, introduced by Aubry and Derode [1] and rearranged by Baelde & al.[2] consists in projecting the data matrix onto a theoretical subspace of single scattering. The second method, built by Lambert & al.[3], projects the data matrix in a focused basis to extract the local scattering parameters. Single scattering proportions estimated on the numerical array response matrix will be discussed and compared to those obtained in titanium alloys billets. References: [1] A. Aubry, A. Derode, Phys. Rev. Lett., 102, 2009, 084301 [2] A. Baelde, & al., Ultrasonics, 82, 2018, 379?389 [3] W. Lambert & al., ArXiv, 2019, 1911.03147

International audience; L’investigation de la qualité des relations sociales des adolescent.e.s à haut potentiel intellectuel (HPI) montre des spécificités de cette population à besoins particuliers (Coleman, Micko & Cross, 2015). Par exemple, les adolescent.e.s HPI peuvent faire état du sentiment de se sentir différents des autres jeunes. Ce ressenti serait en partie dû au fait qu’ils sont désignés comme « haut potentiel », ce qui a tendance à les stigmatiser et à biaiser la nature de leurs relations sociales (Manor-Bullock et al., 1995). Cependant, ces résultats reposent essentiellement sur des données qualitatives recueillies auprès d’adolescent.e.s HPI. Par ailleurs, les adolescent.e.s HPI ne diffèrent pas de leur pairs concernant le nombre d’amis, mais ils évalueraient leurs relations amicales comme étant de moins bonne qualité (Masden et al., 2015). La qualité perçue de l’amitié peut être influencée par le concept de soi, le genre et l’âge (Masden et al., 2015). Toutefois, il n’existe que peu d’études dans ce domaine. C’est pourquoi l’objectif de cette recherche est d’investiguer : (1) les attentes des relations amicales des adolescent.e.s HPI en lien avec leur estime de soi, et (2) leur perception des caractéristiques spécifiques de leur meilleur.e. ami.e. Nous avons ainsi comparé 73 adolescent.e.s HPI et 73 adolescent.e.s tout-venant (mâge = 13.3, ety= 1.73) appariés sur l’âge et le sexe. Ils étaient scolarisés en 6ème, 4ème et 2nde dans des établissements accueillant des élèves à HPI. Nous avons évalué les attendus des relations amicales avec le questionnaire Friendship Expectation (Hall, 2012), la qualité de la relation avec leur.e meilleur.e ami.e avec le questionnaire élaboré par Mallet et al. (2018), et l'estime de soi avec l'échlle de mesure de l'estime de soi pour adolescents (EMESA, Kindelberger & Picherit, 2016). Les résultats confirment que les adolescent.e.s HPI n’ont pas moins d’ami.e.s que leurs pairs, t(109.7) = 1.474, p = 0.215. Cependant, les adolescent.e.s HPI ont moins d’attendus vis-à-vis de leurs relations amicales que leurs pairs, t(143.66) = 2.46, p = .007. Ils montrent particulièrement une moindre exigence de la demande de protection de la part de leur meilleur.e ami.e en cas de besoin, F(1, 142) = 5.59, p = .019. Ces résultats montrent que les adolescent.e.s HPI auraient une tendance à être plus indépendant vis-à-vis de leurs ami.e.s., et seront discutées en regard des recherches antérieures et de l’intérêt de prendre en compte en pratique leurs expériences des relations amicales.

We present a physically intuitive matrix approach for wave imaging and characterization in scattering media. The experimental proof-of-concept is performed with ultrasonic waves, but this approach can be applied to any field of wave physics for which multi-element technology is available. The concept is that focused beamforming enables the synthesis, in transmit and receive, of an array of virtual transducers which map the entire medium to be imaged. The inter-element responses of this virtual array form a focused reflection matrix from which spatial maps of various characteristics of the propagating wave can be retrieved. Here we demonstrate: (i) a local focusing criterion that enables the image quality and the wave velocity to be evaluated everywhere inside the medium, including in random speckle, and (ii) an highly resolved spatial mapping of the prevalence of multiple scattering, which constitutes a new and unique contrast for ultrasonic imaging. The approach is demonstrated for a controllable phantom system, and for in vivo imaging of the human abdomen. More generally, this matrix approach opens an original and powerful route for quantitative imaging in wave physics., Comment: 18 pages, 6 figures

International audience; Focusing waves inside inhomogeneous media is a fundamental problem for imaging. Spatial variations of wave velocity can strongly distort propagating wavefronts and degrade image quality. Adaptive focusing can compensate for such aberration, but is only effective over a restricted field of view. Here, we introduce a full-field approach to wave imaging based on the concept of the distortion matrix. This operator essentially connects any focal point inside the medium with the distortion that a wavefront, emitted from that point, experiences due to heterogeneities. A time-reversal analysis of the distortion matrix enables the estimation of the transmission matrix that links each sensor and image voxel. Phase aberrations can then be unscrambled for any point, providing a full-field image of the medium with diffraction-limited resolution. Importantly, this process is particularly efficient in random scattering media, where traditional approaches such as adaptive focusing fail. Here, we present a proof of concept based on an ultrasound imaging experiment, but this approach can also be extended to optical microscopy, radar or seismic imaging.

33 pages, 8 figures; In optical imaging, light propagation is affected by the inhomogeneities of the medium. Sample-induced aberrations and multiple scattering can strongly degrade the image resolution and contrast. Based on a dynamic correction of the incident and/or reflected wave-fronts, adaptive optics has been employed to compensate for those aberrations. However, it mainly applies to spatially-invariant aberrations or to thin aberrating layers. Here, we propose a global and non-invasive approach based on the distortion matrix concept. This matrix basically connects any focusing point of the image with the distorted part of its wave-front in reflection. A time-reversal and entropy analysis of the distortion matrix allows to correct for high-order aberrations and forward multiple scattering over multiple isoplanatic areas. Proof-of-concept experiments are performed through biological tissues and an opaque cornea. We demonstrate a Strehl ratio enhancement up to 2500 and recover a diffraction-limited resolution until a depth of ten scattering mean free paths.

International audience; Multiple scattering and phase distortions of seismic waves are often seen as a nightmare for conventional migration techniques that generally rely on a ballistic or a single-scattering assumption. In heterogeneous areas such as volcanoes or fault zones, the multiple-scattering contribution limits the imaging-depth to one scattering mean free path, the mean distance between two successive scattering events for body waves. Moreover, large-scale wave speed inhomogeneities induce phase distortions that tend to deteriorate the resolution and contrast of the subsoil image. Inspired by previous works in ultrasound imaging, we propose a reflection matrix approach of passive seismic imaging that allows to overcome those two fundamental issues by making an efficient use of scattered body waves drowned into a noisy seismic coda. Our method is based on the projection of the reflection matrix recorded at the surface to depth by applying focusing operations at emission and reception. Iterative time reversal is then applied in order to: (i) remove the predominant multiple scattering background; (ii) compensate for phase distortions in order to recover an image resolution only limited by diffraction. Although seismic noise is dominated by surface waves, these adaptive focusing operations allow to extract the body wave components and take advantage of them to build a constrasted image of in-depth structures. As proofs-of-concept, the matrix approach is applied to the in-depth imaging of two particularly heterogeneous areas : the Erebus volcano in Antarctica (Blondel et al., J. Geophys. Res.: Solid Earth, 2018-see figure below) and the San Jacynto Fault zone in California (Ben-Zion et al., Geophys. J. Int., 2015). This matrix approach paves the way towards a greatly improved monitoring of volcanic or tectonic structures in depth. Beyond these specific cases, this matrix method can generally be applied to all scales and areas where wave aberrations and multiple scattering prevent from an in-depth imaging of the Earth's crust.

International audience