Face Configuration Research Articles

Vertex Dynamics in Finite Two-Dimensional Square Spin Ices

Local magnetic ordering in artificial spin ices is discussed from the point of view of how geometrical frustration controls dynamics and the approach to steady state. We discuss the possibility of using a particle picture based on vertex configurations to interpret the time evolution of magnetic configurations. Analysis of possible vertex processes allows us to anticipate different behaviors for open and closed edges and the existence of different field regimes. Numerical simulations confirm these results and also demonstrate the importance of correlations and long-range interactions in understanding particle population evolution. We also show that a mean-field model of vertex dynamics gives important insights into finite size effects.

Multi‐Scale Geometry Interpolation

AbstractInterpolating vertex positions among triangle meshes with identical vertex‐edge graphs is a fundamental part of many geometric modelling systems. Linear vertex interpolation is robust but fails to preserve local shape. Most recent approaches identify local affine transformations for parts of the mesh, model desired interpolations of the affine transformations, and then optimize vertex positions to conform with the desired transformations. However, the local interpolation of the rotational part is non‐trivial for more than two input configurations and ambiguous if the meshes are deformed significantly. We propose a solution to the vertex interpolation problem that starts from interpolating the local metric (edge lengths) and mean curvature (dihedral angles) and makes consistent choices of local affine transformations using shape matching applied to successively larger parts of the mesh. The local interpolation can be applied to any number of input vertex configurations and due to the hierarchical scheme for generating consolidated vertex positions, the approach is fast and can be applied to very large meshes.

Residues Contributing to the Na+-binding Pocket of the SLC24 Na+/Ca2+-K+ Exchanger NCKX2

Na(+)/Ca(2+)-K(+) exchangers (NCKX; gene family SLC24) are plasma membrane Ca(2+) transporters that mediate the extrusion of one Ca(2+) ion and one K(+) ion in exchange for four Na(+) ions. NCKX is modeled to have two sets of five transmembrane segments separated by a large cytosolic loop; within each set of transmembrane segments are regions of internal symmetry termed alpha(1) and alpha(2) repeats. The central residues that are important for Ca(2+) and K(+) liganding and transport have been identified in NCKX2, and they comprise three central acidic residues, Glu(188) in alpha(1) and Asp(548) and Asp(575) in alpha(2), as well as Ser/Thr residues one-helical turn away from these residues. In this study, we have scanned through more than 100 single-residue substitutions of NCKX2 for shifts in Na(+) affinity using a fluorescence assay to monitor changes in free Ca(2+) in HEK293 cells treated with gramicidin to control intracellular Na(+). We have identified 31 residues that, when substituted, result in shifts in Na(+) affinity, either toward higher or lower K(m) values when compared with wild type NCKX2 (K(m) for Na(+) 58 mm). These residues include the central acidic residues Glu(188), Asp(548), and Asp(575), and their neighboring residues in alpha(1) and alpha(2), in addition to a number of newly investigated residues in transmembrane segment 3. Our results relate the identification of residues important for Na(+) transport in this study to those previously identified as important in the counter-transport of Ca(2+) and K(+), lending support to the alternating access model of transmembrane transport.

Face-selective adaptation of the M170 is sensitive to face parts, not face configuration

Face-selective adaptation of the M170 is sensitive to face parts, not face configuration

Infants' sensitivity to variability in face configuration

Infants' sensitivity to variability in face configuration

Misaligning face halves increases and delays the N170 specifically for upright faces: Implications for the nature of early face representations

The N170 is an occipito-temporal visual event-related potential that is larger in response to faces than other nonface object categories and has been associated with the early activation of visual face representations in the human brain. It has been recently showed that spatially misaligning the bottom and top halves of a face stimulus–a manipulation used in behavioural studies to disrupt the processing of the whole face configuration (i.e. holistic processing)–increases the latency and the amplitude of the N170, particularly in the right hemisphere. Here we show that these observations cannot be accounted for by a general effect of spatial misalignment of visual patterns. A first experiment showed that the effect of misalignment on the N170 was larger when both top and bottom halves of the stimulus were made of face parts (i.e. a full face) compared to when one of the two halves was made of visual noise. The N170 delay and increase for misaligned faces is similar to the effect of upside-down face inversion, a manipulation thought to disrupt holistic processing. Supporting this view, in a second experiment in which we presented upside-down versions of the stimuli used in the first experiment, we did not observe such a larger effect of misalignment on the N170 for a full face compared to the control conditions. These observations support the view that the early face representation activated in the human brain at the level of the N170, is that of a global upright face pattern. Specifically, when the global configuration of a face is modified by inverting it or spatially misaligning its top and bottom halves, the activation of its representation is delayed in cortical areas coding preferentially for faces. Moreover, when the global face configuration is disrupted, the face stimulus appears to recruit additional neural processes compared to normal face processing, leading to an increase of the N170 amplitude on the scalp.

Perception of Face Parts and Face Configurations: An fMRI Study

fMRI studies have reported three regions in human ventral visual cortex that respond selectively to faces: the occipital face area (OFA), the fusiform face area (FFA), and a face-selective region in the superior temporal sulcus (fSTS). Here, we asked whether these areas respond to two first-order aspects of the face argued to be important for face perception, face parts (eyes, nose, and mouth), and the T-shaped spatial configuration of these parts. Specifically, we measured the magnitude of response in these areas to stimuli that (i) either contained real face parts, or did not, and (ii) either had veridical face configurations, or did not. The OFA and the fSTS were sensitive only to the presence of real face parts, not to the correct configuration of those parts, whereas the FFA was sensitive to both face parts and face configuration. Further, only in the FFA was the response to configuration and part information correlated across voxels, suggesting that the FFA contains a unified representation that includes both kinds of information. In combination with prior results from fMRI, TMS, MEG, and patient studies, our data illuminate the functional division of labor in the OFA, FFA, and fSTS.

Identity modulates short-term memory for facial emotion.

For some time, the relationship between processing of facial expression and facial identity has been in dispute. Using realistic synthetic faces, we reexamined this relationship for both perception and short-term memory. In Experiment 1, subjects tried to identify whether the emotional expression on a probe stimulus face matched the emotional expression on either of two remembered faces that they had just seen. The results showed that identity strongly influenced recognition short-term memory for emotional expression. In Experiment 2, subjects' similarity/dissimilarity judgments were transformed by multidimensional scaling (MDS) into a 2-D description of the faces' perceptual representations. Distances among stimuli in the MDS representation, which showed a strong linkage of emotional expression and facial identity, were good predictors of correct and false recognitions obtained previously in Experiment 1. The convergence of the results from Experiments 1 and 2 suggests that the overall structure and configuration of faces' perceptual representations may parallel their representation in short-term memory and that facial identity modulates the representation of facial emotion, both in perception and in memory. The stimuli from this study may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.

Impaired holistic processing of unfamiliar individual faces in acquired prosopagnosia

Prosopagnosia is an impairment at individualizing faces that classically follows brain damage. Several studies have reported observations supporting an impairment of holistic/configural face processing in acquired prosopagnosia. However, this issue may require more compelling evidence as the cases reported were generally patients suffering from integrative visual agnosia, and the sensitivity of the paradigms used to measure holistic/configural face processing in normal individuals remains unclear. Here we tested a well-characterized case of acquired prosopagnosia (PS) with no object recognition impairment, in five behavioral experiments (whole/part and composite face paradigms with unfamiliar faces). In all experiments, for normal observers we found that processing of a given facial feature was affected by the location and identity of the other features in a whole face configuration. In contrast, the patient's results over these experiments indicate that she encodes local facial information independently of the other features embedded in the whole facial context. These observations and a survey of the literature indicate that abnormal holistic processing of the individual face may be a characteristic hallmark of prosopagnosia following brain damage, perhaps with various degrees of severity.

The Part Task of the Part-Spacing Paradigm Is Not a Pure Measurement of Part-Based Information of Faces

BackgroundFaces are arguably one of the most important object categories encountered by human observers, yet they present one of the most difficult challenges to both the human and artificial visual systems. A variety of experimental paradigms have been developed to study how faces are represented and recognized, among which is the part-spacing paradigm. This paradigm is presumed to characterize the processing of both the featural and configural information of faces, and it has become increasingly popular for testing hypotheses on face specificity and in the diagnosis of face perception in cognitive disorders.Methodology/Principal FindingsIn two experiments we questioned the validity of the part task of this paradigm by showing that, in this task, measuring pure information about face parts is confounded by the effect of face configuration on the perception of those parts. First, we eliminated or reduced contributions from face configuration by either rearranging face parts into a non-face configuration or by removing the low spatial frequencies of face images. We found that face parts were no longer sensitive to inversion, suggesting that the previously reported inversion effect observed in the part task was due in fact to the presence of face configuration. Second, self-reported prosopagnosic patients who were selectively impaired in the holistic processing of faces failed to detect part changes when face configurations were presented. When face configurations were scrambled, however, their performance was as good as that of normal controls.Conclusions/SignificanceIn sum, consistent evidence from testing both normal and prosopagnosic subjects suggests the part task of the part-spacing paradigm is not an appropriate task for either measuring how face parts alone are processed or for providing a valid contrast to the spacing task. Therefore, conclusions from previous studies using the part-spacing paradigm may need re-evaluation with proper paradigms.

A cryo-SEM study of aggregate and floc structure changes during clay settling and raking processes

The destabilization of kaolinite suspension by anionic flocculant addition occurs in three zones; free settling, hindered settling and compression which usually includes a final bed raking process in mineral processing practice. This paper reports changes in the kaolinite aggregate and floc structures in the different settling and raking zones by cryo-vitrification/cryo-SEM techniques with image analysis combining micro- and macro-flocs. Cryo-SEM images indicate that, even during free settling, fine clay particles are bridged predominantly in edge–edge (E–E) with some face–face (F–F) configurations forming single, small flocs and some chain structures. When these small flocs and chains settle into the hindered settling zone, the collision between flocs and chains results in “honeycomb” network structures formed with lateral chain-like extension. The settled bed consists of these honeycomb structures with both inter-aggregate and intra-aggregate trapped water and has relatively low bed density (e.g. < 12 wt.% for a 2 wt.% slurry). The effect of the raking process in dramatically improving thickener underflow solids has been extensively studied but the structural changes in flocs and aggregates in this process are less well defined. Raking the compression zone for 1 h at 3 rpm can release some of the trapped water in the “honeycomb” structure and the bed density for 2 wt.% slurry improves dramatically to more than 36 wt.%. Cryo-SEM illustrates the extensive restructuring of flocs from predominantly E–E to predominantly F–F in many areas. The STructural IMage ANalysis (STIMAN) software is used to combine a series of images at magnifications from 1000× to 8000×, including both macro- and micro-flocs. This structural analysis comparing the un-raked and raked bed samples gives increases in total particle area of 30% and in relative particle area of 6%. The relatively low energy rake action of the shear stress results in the disruption of the E–E chains and the honeycomb structure, partly releasing the trapped water and inducing some E–E to F–F aggregate restructuring are clearly illustrated in these results.

Systematics of High-Genus Fullerenes

In this article, we present a systematic way to classify a family of high-genus fullerenes (HGFs) by decomposing them into two types of necklike structures, which are the negatively curved parts of parent toroidal carbon nanotubes. By replacing the faces of a uniform polyhedron with these necks, an HGF polyhedron corresponding to the vertex configuration of the polyhedron can be obtained. HGF polyhedra including tetrahedron, cube, octahedron, dodecahedron, icosahedron, and truncated icosahedron are proposed under the same construction scheme, which contains nonhexagons other than heptagons. Moreover, simple criteria for determining the stabilities of the proposed HGFs based on four geometric parameters are discussed.

Stationary localized structures and pulsing structures in a cavity soliton laser

A cavity soliton laser is a device able to generate single-peak localized structures, also called cavity solitons, without the injection of an external coherent beam. We realized experimentally a cavity soliton laser by mutually coupling in face to face configuration two broad-area vertical cavity surface emitting lasers, one set to work as amplifier while the second, biased below transparency, plays the role of a saturable absorber. We explore the parameter space, showing the robustness of cavity solitons in this system, and we analyze their switching process. We also report on structures pulsing at the roundtrip time of the compound cavity defined by the two devices. Despite these structures look very similar to cavity solitons in terms of the time-averaged intensity profile, they cannot be interpreted as pulsing cavity solitons since there is no bistability associated with them.

Face inversion disrupts the perception of vertical relations between features in the right human occipito‐temporal cortex

The impact of inversion on the extraction of relational and featural face information was investigated in two fMRI experiments. Unlike previous studies, the contribution of horizontal and vertical spatial relations were considered separately since they have been shown to be differentially vulnerable to face inversion (Goffaux & Rossion, 2007). Hence, inversion largely affects the perception of vertical relations (e.g. eye or mouth height) while the processing of features (e.g. eye shape and surface) and of horizontal relations (e.g. inter-ocular distance) is affected to a far lesser extent. Participants viewed pairs of faces that differed either at the level of one local feature (i.e. the eyes) or of the spatial relations of this feature with adjacent features. Changes of spatial relations were divided into two conditions, depending on the vertical or horizontal axis of the modifications. These stimulus conditions were presented in separate blocks in the first (block) experiment while they were presented in a random order in the second event-related (ER) experiment. Face-preferring voxels located in the right-lateralized middle fusiform gyrus (rMFG) largely decreased their activity with inversion. Inversion-related decreases were more moderate in left-lateralized middle fusiform gyrus (lMFG). ER experiment revealed that inversion affected rMFG and lMFG activity in distinct stimulus conditions. Whereas inversion affected lMFG processing only in featural condition, inversion selectively affected the processing of vertical relations in rMFG. Correlation analyses further indicated that the inversion effect (IE) observed in rMFG and right inferior occipital gyrus (rIOG) reliably predicted the large behavioural IE observed for the processing of vertical relations. In contrast, lMFG IE correlated with the weak behavioural IE observed for the processing of horizontal relations. Our findings suggest that face configuration is mostly encoded in rMFG, whereas more local aspects of face information, such as features and horizontal spatial relations drive lMFG processing. These findings corroborate the view that the vulnerability of face perception to inversion stems mainly from the disrupted processing of vertical face relations in the right-lateralized network of face-preferring regions (rMFG, rIOG).

Morphing polyhedra with parallel faces: Counterexamples

Two simple polyhedra P and Q (not necessarily convex) are parallel if they share the same edge graph G and each face of P has the same outward-facing unit normal as the corresponding face in Q. Parallel polyhedra P and Q admit a parallel morph if the vertices can be moved in a continuous manner taking us from P to Q such that at all times the intermediate polyhedron determined by the vertex configuration and graph G is both simple and parallel with P (and Q). In this note, we show that even for very restrictive classes of orthogonal polyhedra, there exist parallel polyhedra that do not admit a parallel morph.

Restricted square-triangle tilings

Abstract Restricted square-triangle tilings are tilings of regular squares and triangles where the number of vertex types has been limited to a subset of all possible vertex types. Such structures have recently been observed in several places: for example as strip phases in colloidal patterns on laser fields with pentagonal symmetry, and as square-pair-free tilings in patterns formed by dipolar magnetic binary colloidal mixtures. In general there are four vertex configurations: A (4 squares, 44), Z (6 triangles, 36), H (4233), and S (43433). Strip phases belong to type AHZ, square-pair-free phases to SZ, standard inflation generated quasicrystals to HSZ, and unrestricted dodecagonal random tilings to AHSZ. We study several vertex type combinations and describe the properties of the patterns generated. AHZ tilings can be mapped to binary necklaces and classified completely. A similar mapping is possible for many HS tilings. Defect-free SZ tilings can be transformed into a triangle-square-hexagon (TSH) supertiling with matching rules. Monte-Carlo (MC) simulations are used to examine the properties of several classes of restricted tilings.

Identification and Function of a Cytoplasmic K+ Site of the Na+, K+-ATPase

A cytoplasmic nontransport K(+)/Rb(+) site in the P-domain of the Na(+), K(+)-ATPase has been identified by anomalous difference Fourier map analysis of crystals of the [Rb(2)].E(2).MgF(4)(2-) form of the enzyme. The functional roles of this third K(+)/Rb(+) binding site were studied by site-directed mutagenesis, replacing the side chain of Asp(742) donating oxygen ligand(s) to the site with alanine, glutamate, and lysine. Unlike the wild-type Na(+), K(+)-ATPase, the mutants display a biphasic K(+) concentration dependence of E(2)P dephosphorylation, indicating that the cytoplasmic K(+) site is involved in activation of dephosphorylation. The affinity of the site is lowered significantly (30-200-fold) by the mutations, the lysine mutation being most disruptive. Moreover, the mutations accelerate the E(2) to E(1) conformational transition, again with the lysine substitution resulting in the largest effect. Hence, occupation of the cytoplasmic K(+)/Rb(+) site not only enhances E(2)P dephosphorylation but also stabilizes the E(2) dephosphoenzyme. These characteristics of the previously unrecognized nontransport site make it possible to account for the hitherto poorly understood trans-effects of cytoplasmic K(+) by the consecutive transport model, without implicating a simultaneous exposure of the transport sites toward the cytoplasmic and extracellular sides of the membrane. The cytoplasmic K(+)/Rb(+) site appears to be conserved among Na(+), K(+)-ATPases and P-type ATPases in general, and its mode of operation may be associated with stabilizing the loop structure at the C-terminal end of the P6 helix of the P-domain, thereby affecting the function of highly conserved catalytic residues and promoting helix-helix interactions between the P- and A-domains in the E(2) state.

Brief Report: Face Configuration Accuracy and Processing Speed Among Adults with High-Functioning Autism Spectrum Disorders

The present study investigates the accuracy and speed of face processing employed by high-functioning adults with autism spectrum disorders (ASDs). Two behavioral experiments measured sensitivity to distances between features and face recognition when performance depended on holistic versus featural information. Results suggest adults with ASD were less accurate, but responded as quickly as controls for both tasks. In contrast to previous findings with children, adults with ASD demonstrated a holistic advantage only when the eye region was tested. Both groups recognized large manipulations to second-order relations more accurately than no change or small changes, but controls responded more quickly than participants with ASD when recognizing these large manipulations to configural information.

Prosopagnosia associated with a left occipitotemporal lesion

Acquired prosopagnosia is usually associated with bilateral or right-sided lesions of the occipital or temporal lobes. In rare cases of prosopagnosia after left-sided lesions in left-handed subjects, it is attributed to a reversed hemispheric specialization for face processing. This study examines the face-processing functions of a left-handed prosopagnosic patient with a left-sided lesion affecting the region of the occipital face area and possibly the fusiform face area, to contrast his deficits with those of prosopagnosic patients with right-hemispheric lesions. Similar to those patients, he has a moderately severe reduction in familiarity judgments, is impaired in processing face configuration, and shares with some of those patients a greater failure to process eye than mouth information, indicating an altered pattern of facial saliency. He has a mild reduction in the identification of exemplars of non-face objects. Unlike those patients, he has better residual familiarity on a two-alternative forced-choice task and can processing facial configuration if given more time, indicating a reduction in efficiency rather than a severe limitation. He has more difficulty accessing semantic–biographic information from names. He has trouble with facial feature imagery but not imagery for global face shape. Thus this subject's deficits represent a combination of impaired familiarity and configuration processing (normally right-sided functions in right-handed subjects), and impaired feature processing and access to semantic–biographic information (normally left-sided functions). His prosopagnosia likely reflects partially anomalous rather than reversed lateralization of hemispheric perceptual functions.

Inhibition of return for the discrimination of faces

When a target appears unpredictably in the same rather than a different location relative to a preceding onset cue, reaction times (RTs) of participants tasked with responding to the target are slowed. This pattern of results, referred to as inhibition of return (IOR), is believed to reflect the operation of a mechanism that prevents perseverative search of nontarget locations. On the grounds that an evolved mechanism might be sensitive to social stimuli, Taylor and Therrien (2005) examined IOR for localization responses under conditions in which cues and targets could be intact face configurations or nonface configurations; contrary to their predictions, there was no influence of cue or target configuration on the magnitude of IOR, indicating that the mere occurrence of task-irrelevant face and nonface stimuli does not alter IOR. In the present study, we further examined this issue in a task that required a face/nonface target discrimination. When target configuration was thereby made task relevant, we found that IOR differed for face and nonface targets in terms of magnitude (when a single cue-target stimulus onset asynchrony was employed) and time course. We suggest that the RT delay associated with IOR may enable additional processing time and/or response selection when a task-relevant face is presented at the cued location.