Mirror Symmetric Patterns Research Articles

Variability of visual field maps in human early extrastriate cortex challenges the canonical model of organization of V2 and V3.

Visual field maps in human early extrastriate areas (V2 and V3) are traditionally thought to form mirror-image representations which surround the primary visual cortex (V1). According to this scheme, V2 and V3 form nearly symmetrical halves with respect to the calcarine sulcus, with the dorsal halves representing lower contralateral quadrants, and the ventral halves representing upper contralateral quadrants. This arrangement is considered to be consistent across individuals, and thus predictable with reasonable accuracy using templates. However, data that deviate from this expected pattern have been observed, but mainly treated as artifactual. Here, we systematically investigate individual variability in the visual field maps of human early visual cortex using the 7T Human Connectome Project (HCP) retinotopy dataset. Our results demonstrate substantial and principled inter-individual variability. Visual field representation in the dorsal portions of V2 and V3 was more variable than in their ventral counterparts, including substantial departures from the expected mirror-symmetrical patterns. In addition, left hemisphere retinotopic maps were more variable than those in the right hemisphere. Surprisingly, only one-third of individuals had maps that conformed to the expected pattern in the left hemisphere. Visual field sign analysis further revealed that in many individuals the area conventionally identified as dorsal V3 shows a discontinuity in the mirror-image representation of the retina, associated with a Y-shaped lower vertical representation. Our findings challenge the current view that inter-individual variability in early extrastriate cortex is negligible, and that the dorsal portions of V2 and V3 are roughly mirror images of their ventral counterparts.

Spatial transcriptomics reveals a cnidarian segment polarity program in Nematostella vectensis

During early animal evolution, the emergence of axially polarized segments was central to the diversification of complex bilaterian body plans. Nevertheless, precisely how and when segment polarity pathways arose remains obscure. Here, we demonstrate the molecular basis for segment polarization in developing larvae of the sea anemone Nematostella vectensis. Utilizing spatial transcriptomics, we first constructed a 3D gene expression atlas of developing larval segments. Capitalizing on accurate in silico predictions, we identified Lbx and Uncx, conserved homeodomain-containing genes that occupy opposing subsegmental domains under the control of both bone morphogenetic protein (BMP) signaling and the Hox-Gbx cascade. Functionally, Lbx mutagenesis eliminated all molecular evidence of segment polarization at the larval stage and caused an aberrant mirror-symmetric pattern of retractor muscles (RMs) in primary polyps. These results demonstrate the molecular basis for segment polarity in a non-bilaterian animal, suggesting that polarized metameric structures were present in the Cnidaria-Bilateria common ancestor over 600 million years ago.

Ultrafine Nickel Sulfide-Based Bipolar Resistive Switching Device as Artificial Synapses for Neuromorphic Application

Biologically inspired systems, particularly those that mimic the nervous system of living beings, are becoming more demanded due to their ability to solve ill-posed problems such as pattern recognition or communication with the external environment. Memristors are essential components to replicate high-density networks of biological synapses that control the effectiveness of communication among neurons and implement learning capability because of their tunable conductance. In this study, an organic–inorganic hybrid system of hexamethylenediamine-stabilized ultrafine nickel sulfide particles was synthesized by employing a complexation-mediated route. Here, we propose a nickel sulfide-based memristor as an artificial synapse for neuromorphic application. The current–voltage behavior of the device exhibited bipolar resistive switching with a stable ON and OFF state with an ON/OFF ratio value of 2.5 × 101. The high-conductance state of the device showed the Ohmic conduction mechanism, and the low-conductance state of the device exhibited the Fowler–Nordheim tunneling mechanism. Using identical and nonidentical pulses, the synaptic plasticity behavior of the device was investigated, which revealed the inverse-symmetric and mirror-symmetric patterns, respectively. The device mimicked the spike-time-dependent plasticity properties for Hebbian learning with a conductance value change from −86 to 91%. We also designed the spiking neural network, consisting of 18 synapses and 11 integrated firing neurons, based on the winner-take-all strategy for unsupervised feature learning.

Notch-dependent Abl signaling regulates cell motility during ommatidial rotation in Drosophila.

A collective cell motility event that occurs during Drosophila eye development, ommatidial rotation (OR), serves as a paradigm for signaling-pathway-regulated directed movement of cell clusters. OR is instructed by the EGFR and Notch pathways and Frizzled/planar cell polarity (Fz/PCP) signaling, all of which are associated with photoreceptor R3 and R4 specification. Here, we show that Abl kinase negatively regulates OR through its activity in the R3/R4 pair. Abl is localized to apical junctional regions in R4, but not in R3, during OR, and this apical localization requires Notch signaling. We demonstrate that Abl and Notch interact genetically during OR, and Abl co-immunoprecipitates in complexes with Notch in eye discs. Perturbations of Abl interfere with adherens junctional organization of ommatidial preclusters, which mediate the OR process. Together, our data suggest that Abl kinase acts directly downstream of Notch in R4 to fine-tune OR via its effect on adherens junctions.

Twinned Martensitic Substructure in a Water Quenched Fe-1.0 Wt.% C Alloy

A Fe-1.0wt.%C alloy was quenched into water from 1100 o C, leading to lath martensite and plate martensite of body centered tetragonal structure. Both these two martensites have the twinned substructure that generates mirror symmetric diffraction patterns with extra diffraction spots around n /3 of (112). The twinned substructure has the origin from twinned martensitic variants, namely twin-related crystals separated by {110}, rather than {112} deformation twins. Tetragonality effect on the electron double diffraction of twinned variants was discussed.

Electric-field-driven exciton vortices in transition metal dichalcogenide monolayers

We predict electric-field-driven exciton vortices in transition metal dichalcogenide monolayers in the Bose-Einstein condensation regime. The Rashba spin-orbit coupling created by perpendicular electric fields couples the bright and dark excitons, behaves like an emerging SU(2) gauge field for excitons, and induces spatially asymmetric distribution of exciton density. We find the interplay between the dipole-dipole interaction among excitons and Rashba spin-orbit coupling leads to the phase transitions containing different vortices, from a single pair of vortices to numerous satellite vortices appearing at the edge of the sample. The exciton condensation at the $K$ and ${K}^{\ensuremath{'}}$ valleys shows mirror-symmetric patterns composed of exciton vortices rotating oppositely, which are protected topologically by the winding numbers.

Penerapan Semitic Rhetorical Analysis (SRA) Pada Surah Al-Qiyamah

Nicolai Sinai has criticized the method of Qur’anic structural analysis offered by Michel Cuypers due to his arbitrary mode of cutting verses and neglecting rhyme of the Qur’an. This paper, then, attempts to apply the method, which is called as Semitic Rhetorical Analysis (SRA), into surah al-Qiyamah by concerning the waqf of the verses. The purpose of this study is to determine whether the structure of surah al-Qiyamah is coherent and consistent to the pattern of text composition in Semitic Rhetoric analysis. This paper argues that there are parallel, concentric, or mirror symmetrical composition patterns at various levels of text based on Semitic Rhetoric principles. The structure of the surah, then, shows its coherence and thus, opposes to the notion of the existing of some irrelevant verses in this surah.

Effects of bilateral priming on motor cortex function in healthy adults.

Bilateral priming is a rehabilitation adjuvant that can improve upper limb motor recovery poststroke. It uses a table-top device to couple the upper limbs together such that active flexion and extension of one wrist leads to passive movement of the opposite wrist in a mirror symmetric pattern. Bilateral priming increases corticomotor excitability (CME) in the primary motor cortex (M1) of the passively driven wrist; however, the neurophysiological mechanisms underlying this increase remain unclear. This study explored these mechanisms by using transcranial magnetic stimulation over the right M1 and recording motor-evoked potentials from the passively driven left extensor carpi radialis of healthy adults. Intracortical measures were recorded before and 5 and 35 min after a single 15-min session of priming. One-millisecond short-interval intracortical inhibition, long-interval intracortical inhibition, late cortical disinhibition (LCD), and intracortical facilitation were recorded with a posterior-anterior (PA) intracortical current, whereas CME and short-interval intracortical facilitation (SICF) were recorded with both PA and anterior-posterior (AP) currents. CME with PA stimulation was also recorded ~1 h postpriming. PA CME was elevated 35 min postpriming and remained elevated ~1 h postpriming. LCD decreased, and AP SICF increased at both 5 and 35 min postpriming. However, these changes in LCD and AP SICF are unlikely to be the cause of the increased PA CME because of the differing timelines of their effects and AP and PA currents activating separate interneuron circuits. These results suggest that bilateral priming does not increase CME through alterations of the intracortical circuits investigated here. NEW & NOTEWORTHY This is the first study to measure how bilateral priming modulates corticomotor excitability with posterior-anterior and anterior-posterior intracortical currents, 1-ms short-interval intracortical inhibition, late cortical disinhibition, intracortical facilitation, and short-interval intracortical facilitation. We found corticomotor excitability with a posterior-anterior current increased by 35 min until ~1 h postpriming. Short-interval intracortical facilitation with an anterior-posterior current was greater for at least 35 min postpriming. This provides further insight into the neurophysiological mechanisms underlying bilateral priming.

Hyper-vision of mirror symmetry in patients with macular degenerationreflects parafoveal cortical reorganization.

This study aims at comparing participants with juvenile macular degeneration (MD) and normally sighted observers in their sensitivity to mirror and translational symmetry. We measured in 25 normal sighted and 9 MD participants sensitivity (d') to detect the symmetry of two dot patterns presented at the opposite sides of their central scotoma. At a large dot patterns separation (13.3 deg), at which detection failed in normally sighted observers, MD patients had high sensitivity to mirror symmetry, whereas translational symmetry was undetected. The mirror-translational dissociation is not predicted by the well-known phenomenon of shrinking the location of images surrounding the scotoma. Our results indicate higher capacity of MD with respect to normally sighted observers to organize mirror symmetric dot patterns far apart into a unique percept. Our results suggest that MD have acquired the capability to use information only present in mirror symmetry, i.e., the co-aligned position of the centre of low-frequency filters connecting symmetric dot pairs on opposite sides of the scotoma. This relevant functional change in vision of MD patients may find its explanation in a functionally acquired high-level cortical representation of visual input.

Effects of coupled upper limbs movements on postural stabilisation

The preference for in-phase association of coupled cyclic limbs movements is well described (mirror-symmetrical patterns) and this is demonstrated by the ease of performing in-phase movements compared to anti-phase ones. The hypothesis of this study is that the easiest movement patterns are those with minor postural activity. The aim of this study was to describe postural activity in standing subjects in the sagittal and frontal planes during the execution of three upper limbs tasks (single arm, in-phase, anti-phase) at four different frequencies (from 0.6 to 1.2Hz).We employed six infrared cameras for recording kinematics information, a force platform for measuring forces exerted on the ground, and a system for surface electromyography (SEMG). Outcome measures were: upper limb range of movement and relative-phase, centre of pressure displacement (COP), screw torque (Tz) exerted on the ground, and SEMG recordings of postural muscles (adductor longus, gluteus medius, rectus femoris, and biceps femoris).Our results show that in both the planes the in-phase task resulted in less COP displacement, torque production, and postural muscles involvement than the anti-phase and single arm tasks. This reduced need of postural control could explain the ease of performing in-phase coupled limb movements compared with anti-phase movements.

Symmetry in context: Salience of mirror symmetry in natural patterns

Symmetry is a biologically relevant, mathematically involving, and aesthetically compelling visual phenomenon. Mirror symmetry detection is considered particularly rapid and efficient, based on experiments with random noise. Symmetry detection in natural settings, however, is often accomplished against structured backgrounds. To measure salience of symmetry in diverse contexts, we assembled mirror symmetric patterns from 101 natural textures. Temporal thresholds for detecting the symmetry axis ranged from 28 to 568 ms indicating a wide range of salience (1/Threshold). We built a model for estimating symmetry-energy by connecting pairs of mirror-symmetric filters that simulated cortical receptive fields. The model easily identified the axis of symmetry for all patterns. However, symmetry-energy quantified at this axis correlated weakly with salience. To examine context effects on symmetry detection, we used the same model to estimate approximate symmetry resulting from the underlying texture throughout the image. Magnitudes of approximate symmetry at flanking and orthogonal axes showed strong negative correlations with salience, revealing context interference with symmetry detection. A regression model that included the context-based measures explained the salience results, and revealed why perceptual symmetry can differ from mathematical characterizations. Using natural patterns thus produces new insights into symmetry perception and its possible neural circuits.

Biases in rhythmic sensorimotor coordination: Effects of modality and intentionality

Sensorimotor biases were examined for intentional (tracking task) and unintentional (distractor task) rhythmic coordination. The tracking task involved unimanual tracking of either an oscillating visual signal or the passive movements of the contralateral hand (proprioceptive signal). In both conditions the required coordination patterns (isodirectional and mirror-symmetric) were defined relative to the body midline and the hands were not visible. For proprioceptive tracking the two patterns did not differ in stability, whereas for visual tracking the isodirectional pattern was performed more stably than the mirror-symmetric pattern. However, when visual feedback about the unimanual hand movements was provided during visual tracking, the isodirectional pattern ceased to be dominant. Together these results indicated that the stability of the coordination patterns did not depend on the modality of the target signal per se, but on the combination of sensory signals that needed to be processed (unimodal vs. cross-modal). The distractor task entailed rhythmic unimanual movements during which a rhythmic visual or proprioceptive distractor signal had to be ignored. The observed biases were similar as for intentional coordination, suggesting that intentionality did not affect the underlying sensorimotor processes qualitatively. Intentional tracking was characterized by active sensory pursuit, through muscle activity in the passively moved arm (proprioceptive tracking task) and rhythmic eye movements (visual tracking task). Presumably this pursuit afforded predictive information serving the coordination process.

Asymmetrical representation of body orientation

The perceived orientation of objects, gravity, and the body are biased to the left. Whether this leftward bias is attributable to biases in sensing or processing vestibular, visual, and body sense cues has never been assessed directly. The orientation in which characters are most easily recognized--the perceived upright (PU)--can be well predicted from a weighted vector sum of these sensory cues. A simple form of this model assumes that the directions of the contributing inputs are coded accurately and as a consequence participants tilted left- or right-side-down relative to gravity should exhibit mirror symmetric patterns of responses. If a left/right asymmetry were present then varying these sensory cues could be used to assess in which sensory modality or modalities a PU bias may have arisen. Participants completed the Oriented Character Recognition Test (OCHART) while manipulating body posture and visual orientation cues relative to gravity. The response patterns showed systematic differences depending on which side they were tilted. An asymmetry of the PU was found to be best modeled by adding a leftward bias of 5.6° to the perceived orientation of the body relative to its actual orientation relative to the head. The asymmetry in the effect of body orientation is reminiscent of the body-defined left-leaning asymmetry in the perceived direction of light coming from above and reports that people tend to adopt a right-leaning posture.

Mirror Symmetric Bimanual Movement Priming Can Increase Corticomotor Excitability and Enhance Motor Learning

Repetitive mirror symmetric bilateral upper limb may be a suitable priming technique for upper limb rehabilitation after stroke. Here we demonstrate neurophysiological and behavioural after-effects in healthy participants after priming with 20 minutes of repetitive active-passive bimanual wrist flexion and extension in a mirror symmetric pattern with respect to the body midline (MIR) compared to an control priming condition with alternating flexion-extension (ALT). Transcranial magnetic stimulation (TMS) indicated that corticomotor excitability (CME) of the passive hemisphere remained elevated compared to baseline for at least 30 minutes after MIR but not ALT, evidenced by an increase in the size of motor evoked potentials in ECR and FCR. Short and long-latency intracortical inhibition (SICI, LICI), short afferent inhibition (SAI) and interhemispheric inhibition (IHI) were also examined using pairs of stimuli. LICI differed between patterns, with less LICI after MIR compared with ALT, and an effect of pattern on IHI, with reduced IHI in passive FCR 15 minutes after MIR compared with ALT and baseline. There was no effect of pattern on SAI or FCR H-reflex. Similarly, SICI remained unchanged after 20 minutes of MIR. We then had participants complete a timed manual dexterity motor learning task with the passive hand during, immediately after, and 24 hours after MIR or control priming. The rate of task completion was faster with MIR priming compared to control conditions. Finally, ECR and FCR MEPs were examined within a pre-movement facilitation paradigm of wrist extension before and after MIR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation. In summary, mirror symmetric active-passive bimanual movement increases CME and can enhance motor learning without degradation of muscle selectivity. These findings rationalise the use of mirror symmetric bimanual movement as a priming modality in post-stroke upper limb rehabilitation.

THE PRECESSION OF THE HERBIG-HARO 111 FLOW IN THE INFRARED

We present Spitzer IRAC images of the HH 111 outflow, that show a wealth of condensations/knots in both jet and counterjet. Studying the positional distribution of these knots, we find very suggestive evidence of a mirror symmetric pattern in the jet/counterjet flow. We model this pattern as the result of an orbital motion of the jet source around a binary companion. From a fit of an analytic, ballistic model to the observed path of the HH 111 system, we find that the motion in a binary with two approx. 1 Msolar stars (one of them being the HH 111 source), in a circular orbit with a separation of approx. 186 AU would produce the mirror symmetric pattern seen in the outflow.

Limitations on Coupling of Bimanual Movements Caused by Arm Dominance: When the Muscle Homology Principle Fails

Studies of bimanual movements typically report interference between motions of the two arms and preference to perform mirror-symmetrical patterns. However, recent studies have demonstrated that the two arms differ in the ability to control interaction torque (INT). This predicts limitations in the capability to perform mirror-symmetrical movements. Here, two experiments were performed to test this prediction. The first experiment included bimanual symmetrical and asymmetrical circle drawing at two frequency levels. Unimanual circle drawing was also recorded. The increases in cycling frequency caused differences between the two arms in movement trajectories in both bimanual modes, although the differences were more pronounced in the asymmetrical compared with the symmetrical mode. Based on torque analysis, the differences were attributed to the nondominant arm's decreased capability to control INT. The intraarm differences during the symmetrical pattern of bimanual movements were similar (although more pronounced) to those during unimanual movements. This finding was verified in the second experiment for symmetrical bimanual oval drawing. Four oval orientations were used to provide variations in INT. Similar to the first experiment, increases in cycling frequency caused spontaneous deviations from perfect bimanual symmetry associated with inefficient INT control in the nondominant arm. This finding supports the limitations in performing mirror-symmetrical bimanual movements due to differences in joint control between the arms. Based on our results and previous research, we argue that bimanual interference occurs during specification of characteristics of required motion, whereas lower-level generation of muscle forces is independent between the arms. A hierarchical model of bimanual control is proposed.

Steering Organizational and Conformational Surface Chirality by Controlling Molecular Chemical Functionality

Molecular chirality on surfaces has been widely explored, both for intrinsically chiral molecules and for prochiral molecules that become chiral upon adsorption due to the reduced symmetry which follows from surface confinement. However, little attention has been devoted to chiral effects that originate from conformational degrees of freedom for adsorbed molecules. Here we have used scanning tunneling microscopy to investigate the self-assembled structures formed when a class of six linear, organic molecules (oligo-phenylene-ethynylenes) are adsorbed on a Au(111) surface under ultrahigh vacuum conditions. All of the investigated compounds are intrinsically achiral, but most display conformational chirality in the sense that the molecules can adsorb on the surface in different conformations giving rise to either one of two chiral surface enantiomers or a mirror-symmetric achiral meso form. A total of eleven observed adsorption structures are systematically investigated with respect to conformational chirality as well as point chirality (arising where molecular adsorption locally breaks the substrate symmetry) and organizational chirality (arising from the tiling pattern of the molecular backbones). A number of interesting correlations are identified between these different levels of chirality. Most importantly, we demonstrate that it is possible through control of the terminal group functionalization to steer the oligo(phenylene-ethynylene) molecular backbones into surface assemblies that either display pronounced organizational chirality or have mirror symmetric tiling patterns, and that it is furthermore possible to control the conformational surface chirality so the compounds preferentially assume either chiral or achiral surface conformers.

‘Rules for Design’: Beauty and Grace in Caroso's Choreographies

This article examines the changes Fabritio Caroso made to his choreographies from his first treatise Il ballarino (1581) to those from his second, Nobiltà di dame (1600), as well as the terms Caroso used to refer to these changes and the significance that these terms had for him. While modern scholars have discussed these changes as evincing an increased interest in symmetry by Caroso, the dance master did not employ this term in his treatises at all. The terms he did use were closer to the earlier concepts of Vitruvius's symmetria and of Leon Battista Alberti's concinnitas. The analysis of his choreographic changes demonstrate that Caroso was not particularly focused on symmetry in the modern sense, that is, in increasing the number of mirror or rotational symmetrical spatial patterns in his revised choreographies. What we do see in Caroso's revised choreographies is an increased interest in balance and repetition, the arrangement and number of elements, and a concern to provide a theory or rules for designing choreographies that were articulated and written down, and conformed to the prevailing theory of beauty in the other arts, in order that his choreographies would also be judged to be perfect and to epitomise grace and beauty.

Generation of Bilateral Symmetry in the Ectoderm of the Tubifex Embryo: Involvement of Cell–cell Interactions

In embryos of the oligochaete annelid Tubifex, most ectodermal tissues are derived from four bilateral pairs of embryonic stem cells called teloblasts (ectoteloblasts N, O, P and Q). Ectoteloblasts are generated on both left and right sides of the embryo through an invariable sequence of cell divisions of a proteloblast, NOPQ, and they are positioned in a mirror symmetric pattern relative to the embryonic midline. This mirror symmetry of ectoteloblast arrangement gives rise to the generation of bilateral symmetry in the ectoderm. Here we review results of our recent experiments on Tubifex tubifex that were designed to gain an insight into the mechanisms underlying the generation of the bilaterally symmetric organization of ectoteloblasts. Cell transplantation experiments have shown that nascent NOPQ cells can be polarized according to positional information residing in the embryo. If a left NOPQ cell is transplanted to the right side of a host embryo, it exhibits polarity comparable to that of right NOPQ cells. It has also been shown that contact between NOPQ cells serves as an external cue for their polarization. Another series of cell transplantation experiments have suggested that the competence of NOPQ cells to respond to external cues becomes undetectable shortly before the production of the first teloblast (N) from the NOPQ cell. Another series of experiments utilizing cell ablation techniques have shown that teloblasts N, P and Q are specified to express the N, P and Q fates, respectively, as early as their birth. In contrast, the O teloblast and its progeny are initially pluripotent and their fate becomes restricted through inductive signals emanating from its sister P lineage. On the basis of these findings, we have proposed a model for polarization of ectodermal teloblastogenesis in the Tubifex embryo.

Effects of surface pre‐presentation on symmetry detection on a 3‐D bumpy surface

Abstract: The aim of this study was to investigate the visual detection mechanism of mirror symmetrical dot patterns drawn on a 3‐D bumpy surface (i.e., 3‐D noisy curved surface). The focus of this investigation was whether symmetry detection on the bumpy surface is associated with structure recovery of the surface. In Experiment 1, we confirmed that the human visual system can distinguish the bumpy surface from a distorted dot pattern on a transparent bumpy surface. In Experiment 2, we required participants to discriminate between a symmetrical pattern on a transparent (non‐visible) bumpy surface and an opaque (visible) bumpy surface for the same stimuli as in Experiment 1. Finally, in Experiment 3, we examined the effect of pre‐presentation of the opaque bumpy surface on pattern discrimination. The results showed that pre‐presentation of the opaque surface facilitated the detection of a diagonal symmetry, but not in the case of the detection of a cardinal symmetry. These results suggested that diagonal symmetry involves the process of surface recovery, whereas cardinal symmetry does not.