Elucidating the Neural Representation and the Processing Dynamics of Face Ensembles.

Extensive behavioral work has documented the ability of the human visual system to extract summary representations from face ensembles (e.g., the average identity of a crowd of faces). Yet, the nature of such representations, their underlying neural mechanisms, and their temporal dynamics await elucidation. Here, we examine summary representations of facial identity in human adults (of both sexes) with the aid of pattern analyses, as applied to EEG data, along with behavioral testing. Our findings confirm the ability of the visual system to form such representations both explicitly and implicitly (i.e., with or without the use of specific instructions). We show that summary representations, rather than individual ensemble constituents, can be decoded from neural signals elicited by ensemble perception, we describe the properties of such representations by appeal to multidimensional face space constructs, and we visualize their content through neural-based image reconstruction. Further, we show that the temporal profile of ensemble processing diverges systematically from that of single faces consistent with a slower, more gradual accumulation of perceptual information. Thus, our findings reveal the representational basis of ensemble processing, its fine-grained visual content, and its neural dynamics.SIGNIFICANCE STATEMENT Humans encounter groups of faces, or ensembles, in a variety of environments. Previous behavioral research has investigated how humans process face ensembles as well as the types of summary representations that can be derived from them, such as average emotion, gender, and identity. However, the neural mechanisms mediating these processes are unclear. Here, we demonstrate that ensemble representations, with different facial identity summaries, can be decoded and even visualized from neural data through multivariate analyses. These results provide, to our knowledge, the first detailed investigation into the status and the visual content of neural ensemble representations of faces. Further, the current findings shed light on the temporal dynamics of face ensembles and its relationship with single-face processing.

Nanoparticle self-assembly at the interface of liquid crystal droplets.

Nanoparticles adsorbed at the interface of nematic liquid crystals are known to form ordered structures whose morphology depends on the orientation of the underlying nematic field. The origin of such structures is believed to result from an interplay between the liquid crystal orientation at the particles' surface, the orientation at the liquid crystal's air interface, and the bulk elasticity of the underlying liquid crystal. In this work, we consider nanoparticle assembly at the interface of nematic droplets. We present a systematic study of the free energy of nanoparticle-laden droplets in terms of experiments and a Landau-de Gennes formalism. The results of that study indicate that, even for conditions under which particles interact only weakly at flat interfaces, particles aggregate at the poles of bipolar droplets and assemble into robust, quantized arrangements that can be mapped onto hexagonal lattices. The contributions of elasticity and interfacial energy corresponding to different arrangements are used to explain the resulting morphologies, and the predictions of the model are shown to be consistent with experimental observations. The findings presented here suggest that particle-laden liquid crystal droplets could provide a unique and versatile route toward building blocks for hierarchical materials assembly.

Spherical nematic shells with a prolate ellipsoidal core.

Liquid crystal shells have attracted considerable attention in recent years. In such systems, a combination of confinement and curvature generates topological defect structures that do not exist in the bulk. Past studies, however, have largely focused on perfectly spherical shells, and little attention has been devoted to the impact of core geometry on the configuration and arrangement of topological defects. In this work, a microfluidic glass capillary device is used to encapsulate spherical and prolate ellipsoidal particles in nematic liquid crystal (LC) droplets dispersed in aqueous media. Our experimental studies show that, when trapped inside a radial LC droplet, spherical particles with both homeotropic and planar anchoring are highly localized at the droplet's center. While the radial configuration of the LC droplets is not altered by a homeotropic particle, polystyrene particles with strong planar anchoring disturb the radial ordering, leading to a twisted structure. Experiments indicate that off-center particle positions can also arise, in which defects are displaced towards the vicinity of the droplet's surface. In contrast, when prolate ellipsoidal particles are encapsulated in a thick radial LC shell, the minimum free energy corresponds to configurations where the particle is positioned at the droplet center. In this case, defects arise at the two ends of the prolate ellipsoid, where the curvature of the particle is maximal, leading to the formation of peculiar hybrid and twisted structures.

Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring.

Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices.

A Novel Inhibitor of Protease-activated Receptor 1: A Review of Chemical Structure and Mode of Action.

Limitations of current antiplatelet therapies have led to the discovery of new antiplatelet agents with new modes of action. Vorapaxar has been developed as a thrombin receptor antagonist. This drug works against the protease-activated receptor 1 (PAR1) and inhibits platelet aggregation mediated by PAR1. This article reviews this new class of antiplatelet therapy in detail with an acute focus on the TRACER (Thrombin Receptor Antagonist for Clinical Event Reduction in Acute Coronary Syndrome) and TRA 2°P-TIMI 50 (Trial to Assess the Effects of Vorapaxar in Preventing Heart Attack and Stroke in Patients With Atherosclerosis-Thrombolysis In Myocardial Infarction 50) trials. Vorapaxar has proven to be beneficial when administered to stable atherosclerotic patients. However, it has been shown to increase risk of intracranial hemorrhage in patients with known, previous history of cerebrovascular incidence. Despite these limitations, TRA 2°P-TIMI 50 results showed that vorapaxar appears to have a definitive therapeutic benefit when administered alongside aspirin or when it is used as an addition to dual antiplatelet therapy for patients with stable atherosclerosis.

The Effect of Age and Sex on Early Postoperative Outcomes after Surgical Treatment of Distal Radius Fractures.

Background: We aim to evaluate the impact of advanced age and sex on postoperative complications and radiographic outcomes after open reduction with internal fixation of distal radius fractures (DRF). Methods: We conducted a retrospective chart review, including all patients who underwent open reduction with internal fixation of a DRF between 2012 and 2018 at a single level 1 trauma centre. We recorded patient age, sex, fracture classification (Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association [AO/OTA]), time from injury to surgical date, surgical duration, diabetes status, tobacco use, illicit drug use, history of osteoporosis, use of adjuvants, fixation type, postoperative radiographic restoration of normal parameters and early complications including loss of reduction within 30 days postoperatively. Advanced age was defined as age greater than 60 years. Results: A total of 521 patients underwent operative treatment - 264 males and 257 females. Males were twice as likely (23.5% vs. 10.1%; p < 0.0001) to sustain a type C3 fracture and be treated with a wrist spanning plate (5.3% vs. 0; p < 0.0001). A larger percentage of elderly patients undergoing operative treatment of DRF were female (20.2% vs. 5.7%; p < 0.0001) and females were more likely to carry a pre-injury diagnosis of osteoporosis (9.3% vs. 0%; p < 0.0001). And 100% of the elderly patients received were treated with a volar plate. The overall early loss of reduction was 7.5%. The overall complication rate was 8.2%. No differences in early postoperative complications were identified between sexes or age groups. Neither female sex nor advanced age was found to have increased risk of postoperative complications or early loss of reduction. Similar postoperative radiographic parameter measurements were obtained across groups as well. Conclusions: Our results support the idea that operative treatment of unstable DRF in elderly patients and women is a reasonable treatment option without significant increases in early postoperative complications. Level of Evidence: Level III (Therapeutic III).

Exploring the Use of the Picture Exchange Communication System (PECS) in Special Education Settings.

The Picture Exchange Communication System (PECS) is an Augmentative and Alternative Communication (AAC) system which is widely used to support children with developmental disabilities. In the present study, we surveyed individuals responsible for implementing PECS in special educational settings in the United Kingdom (N=283). We explored knowledge of and adherence to the  intervention, with a view to identifying training and support needs. Specifically, we examined participants' knowledge, implementation accuracy, training experiences, access to resources, and attitudes towards PECS. We developed hierarchical logistic regression models to explore the association between training experience and both knowledge and use of PECS. We pre-registered our methods, predictions and the analysis plan on the Open Science Framework (OSF).We found considerable variation in practitioner knowledge and implementation of PECS. Formal training predicted greater knowledge and more accurate implementation when practitioner role and the degree of setting support were accounted for. While PECS was rated by a large majority to be effective and practical, many participants identified that time and the availability of resources were barriers to implementation. We also found that the purpose of PECS was not always fully understood by practitioners, and we identified some consistent gaps in knowledge and implementation.  This study contributes new information regarding the real-world  use of PECS in educational settings and offers new insights for supporting practitioners.

Liquid-crystal mediated nanoparticle interactions and gel formation.

Colloidal particles embedded within nematic liquid crystals exhibit strong anisotropic interactions arising from preferential orientation of nematogens near the particle surface. Such interactions are conducive to forming branched, gel-like aggregates. Anchoring effects also induce interactions between colloids dispersed in the isotropic liquid phase, through the interactions of the pre-nematic wetting layers. Here we utilize computer simulation using coarse-grained mesogens to perform a molecular-level calculation of the potential of mean force between two embedded nanoparticles as a function of anchoring for a set of solvent conditions straddling the isotropic-nematic transition. We observe that strong, nontrivial interactions can be induced between particles dispersed in mesogenic solvent, and explore how such interactions might be utilized to induce a gel state in the isotropic and nematic phases.

New information triggers prospective codes to adapt for flexible navigation.

Navigating a dynamic world requires rapidly updating choices by integrating past experiences with new information. In hippocampus and prefrontal cortex, neural activity representing future goals is theorized to support planning. However, it remains unknown how prospective goal representations incorporate new, pivotal information. Accordingly, we designed a novel task that precisely introduces new information using virtual reality, and we recorded neural activity as mice flexibly adapted their planned destinations. We found that new information triggered increased hippocampal prospective representations of both possible goals; while in prefrontal cortex, new information caused prospective representations of choices to rapidly shift to the new choice. When mice did not flexibly adapt, prefrontal choice codes failed to switch, despite relatively intact hippocampal goal representations. Prospective code updating depended on the commitment to the initial choice and degree of adaptation needed. Thus, we show how prospective codes update with new information to flexibly adapt ongoing navigational plans.

Designing Interfacial Reactions for Nanometer-Scale Surface Patterning of PDMS with Controlled Elastic Modulus.

Control over the surface chemistry of elastomers such as polydimethylsiloxane (PDMS) is important for many applications. However, achieving nanostructured chemical control on amorphous material interfaces below the length scale of substrate heterogeneity is not straightforward, and can be particularly difficult to decouple from changes in network structure that are required for certain applications (e.g., variation of elastic modulus for cell culture). We have recently reported a new method for precisely structured surface functionalization of PDMS and other soft materials, which displays high densities of ligands directly on the material surface, maximizing steric accessibility. Here, we systematically examine structural factors in the PDMS components (e.g., base and cross-linker structures) that impact efficiency of the interfacial reaction that leads to surface functionalization. Applying this understanding, we demonstrate routes for generating equivalent nanometer-scale functional patterns on PDMS with elastic moduli from 0.013 to 1.4 MPa, establishing a foundation for use in applications such as cell culture.

Isotropic-nematic phase transition in the Lebwohl-Lasher model from density of states simulations.

Density of states Monte Carlo simulations have been performed to study the isotropic-nematic (IN) transition of the Lebwohl-Lasher model for liquid crystals. The IN transition temperature was calculated as a function of system size using expanded ensemble density of states simulations with histogram reweighting. The IN temperature for infinite system size was obtained by extrapolation of three independent measures. A subsequent analysis of the kinetics in the model showed that the transition occurs via spinodal decomposition through aggregation of clusters of liquid crystal molecules.

A multivariate investigation of visual word, face, and ensemble processing: Perspectives from EEG-based decoding and feature selection.

Recent investigations have focused on the spatiotemporal dynamics of visual recognition by appealing to pattern analysis of EEG signals. While this work has established the ability to decode identity-level information (such as the identity of a face or of a word) from neural signals, much less is known about the precise nature of the signals that support such feats, their robustness across visual categories, or their consistency across human participants. Here, we address these questions through the use of EEG-based decoding and multivariate feature selection as applied to three visual categories: words, faces and face ensembles (i.e., crowds of faces). Specifically, we use recursive feature elimination to estimate the diagnosticity of time and frequency-based EEG features for identity-level decoding across three datasets targeting each of the three categories. We then relate feature diagnosticity across categories and across participants while, also, aiming to increase decoding performance and reliability. Our investigation shows that word and face processing are similar in their reliance on spatiotemporal information provided by occipitotemporal channels. In contrast, ensemble processing appears to also rely on central channels and exhibits a similar profile with word processing in the frequency domain. Further, we find that feature diagnosticity is stable across participants and is even capable of supporting cross-participant feature selection, as demonstrated by systematic boosts in decoding accuracy and feature reduction. Thus, our investigation sheds new light on the nature and the structure of the information underlying identity-level visual processing as well as on its generality across categories and participants.

Neurophysiological effects of prediction on head reassignment in German compounds.

Recent research on noun-noun compounds has suggested that the parser may commit to the first noun (N1) as the head and then have to revise that commitment when the second noun (N2) is encountered. However, it remains unclear under what circumstances head commitment at N1 occurs, and whether it involves both semantic and syntactic revisions at N2. In two event-related potential experiments in German, we explored these questions by manipulating gender matches between a determiner and N1/N2 in compounds. In Experiment 1, a determiner-noun match in gender at N1 compared with a mismatch yielded an effect at N2 for the matching condition (increased negativity at 480-550 ms, strongest in the left hemisphere); there was a similar effect for the gender violation at N2. The observed negativity could have been due to either semantic or syntactic head revision, or both. Experiment 2 increased expectations that an N2 was imminent, which attenuated syntactic, but not semantic, effects at N2. We found N400-like effects, often associated with semantic integration, suggesting that, in Experiment 1, the syntactic effects had masked the semantic costs. Taken together, these results support the idea that both semantic and syntactic head commitment and revision occur during compound processing.

Structural Transitions in Cholesteric Liquid Crystal Droplets.

Confinement of cholesteric liquid crystals (ChLC) into droplets leads to a delicate interplay between elasticity, chirality, and surface energy. In this work, we rely on a combination of theory and experiments to understand the rich morphological behavior that arises from that balance. More specifically, a systematic study of micrometer-sized ChLC droplets is presented as a function of chirality and surface energy (or anchoring). With increasing chirality, a continuous transition is observed from a twisted bipolar structure to a radial spherical structure, all within a narrow range of chirality. During such a transition, a bent structure is predicted by simulations and confirmed by experimental observations. Simulations are also able to capture the dynamics of the quenching process observed in experiments. Consistent with published work, it is found that nanoparticles are attracted to defect regions on the surface of the droplets. For weak anchoring conditions at the nanoparticle surface, ChLC droplets adopt a morphology similar to that of the equilibrium helical phase observed for ChLCs in the bulk. As the anchoring strength increases, a planar bipolar structure arises, followed by a morphological transition to a bent structure. The influence of chirality and surface interactions are discussed in the context of the potential use of ChLC droplets as stimuli-responsive materials for reporting molecular adsorbates.

Modeling the polydomain-monodomain transition of liquid crystal elastomers.

We study the mechanism of the polydomain-monodomain transition in liquid crystalline elastomers at the molecular scale. A coarse-grained model is proposed in which mesogens are described as ellipsoidal particles. Molecular dynamics simulations are used to examine the transition from a polydomain state to a monodomain state in the presence of uniaxial strain. Our model demonstrates soft elasticity, similar to that exhibited by side-chain elastomers in the literature. By analyzing the growth dynamics of nematic domains during uniaxial extension, we provide direct evidence that at a molecular level the polydomain-monodomain transition proceeds through cluster rotation and domain growth.