Solvent-Induced Negative Energetic Elasticity in a Lattice Polymer Chain.

The negative internal energetic contribution to the elastic modulus (negative energetic elasticity) has been recently observed in polymer gels. This finding challenges the conventional notion that the elastic moduli of rubberlike materials are determined mainly by entropic elasticity. However, the microscopic origin of negative energetic elasticity has not yet been clarified. Here, we consider the n-step interacting self-avoiding walk on a cubic lattice as a model of a single polymer chain (a subchain of a network in a polymer gel) in a solvent. We theoretically demonstrate the emergence of negative energetic elasticity based on an exact enumeration up to n=20 and analytic expressions for arbitrary n in special cases. Furthermore, we demonstrate that the negative energetic elasticity of this model originates from the attractive polymer-solvent interaction, which locally stiffens the chain and conversely softens the stiffness of the entire chain. This model qualitatively reproduces the temperature dependence of negative energetic elasticity observed in the polymer-gel experiments, indicating that the analysis of a single chain can explain the properties of negative energetic elasticity in polymer gels.

Perception of the average size of multiple objects in chimpanzees (Pan troglodytes).

Humans can extract statistical information, such as the average size of a group of objects or the general emotion of faces in a crowd without paying attention to any individual object or face. To determine whether summary perception is unique to humans, we investigated the evolutional origins of this ability by assessing whether chimpanzees, which are closely related to humans, can also determine the average size of multiple visual objects. Five chimpanzees and 18 humans were able to choose the array in which the average size was larger, when presented with a pair of arrays, each containing 12 circles of different or the same sizes. Furthermore, both species were more accurate in judging the average size of arrays consisting of 12 circles of different or the same sizes than they were in judging the average size of arrays consisting of a single circle. Our findings could not be explained by the use of a strategy in which the chimpanzee detected the largest or smallest circle among those in the array. Our study provides the first evidence that chimpanzees can perceive the average size of multiple visual objects. This indicates that the ability to compute the statistical properties of a complex visual scene is not unique to humans, but is shared between both species.

The interplay of intrinsic disorder and macromolecular crowding on α-synuclein fibril formation.

α-synuclein (α-syn) is an intrinsically disordered protein which is considered to be one of the causes of Parkinson's disease. This protein forms amyloid fibrils when in a highly concentrated solution. The fibril formation of α-syn is induced not only by increases in α-syn concentration but also by macromolecular crowding. In order to investigate the coupled effect of the intrinsic disorder of α-syn and macromolecular crowding, we construct a lattice gas model of α-syn in contact with a crowding agent reservoir based on statistical mechanics. The main assumption is that α-syn can be expressed as coarse-grained particles with internal states coupled with effective volume; and disordered states are modeled by larger particles with larger internal entropy than other states. Thanks to the simplicity of the model, we can exactly calculate the number of conformations of crowding agents, and this enables us to prove that the original grand canonical ensemble with a crowding agent reservoir is mathematically equivalent to a canonical ensemble without crowding agents. In this expression, the effect of macromolecular crowding is absorbed in the internal entropy of disordered states; it is clearly shown that the crowding effect reduces the internal entropy. Based on Monte Carlo simulation, we provide scenarios of crowding-induced fibril formation. We also discuss the recent controversy over the existence of helically folded tetramers of α-syn, and suggest that macromolecular crowding is the key to resolving the controversy.

Looking away before moving forward: changes in optic-flow perception precede locomotor development.

Voluntary locomotion is one of the most important motor actions performed by animals, including humans, and vision plays an important role in controlling such action. We conducted cross-sectional (Experiment 1) and longitudinal (Experiment 2) investigations and found that the perception of visual motion (optic flow), a critical cue for perceiving and controlling the direction of locomotion, drastically changes just before the emergence of locomotion in infancy. The results suggest that developmental change in particular visual perceptions precedes and potentially promotes the emergence of related motor actions in early development. Our findings offer a new perspective on the development of visuomotor coordination, which has long been thought to derive from the development of motor actions rather than from changes in visual perceptions.

Implied motion perception from a still image in infancy.

Visual motion perception can arise from non-directional visual stimuli, such as still images (implied motion, cf. Kourtzi, Trends Cogn Sci 8:47-49, 2004). We tested 5- to 8-month-old infants' implied motion perception with two experiments using the forced-choice preferential looking method. Our results indicated that a still image of a person running toward either the left or right side significantly enhanced infants' visual preference for a visual target that consistently appeared on the same side as the running direction (the run condition in Experiment 1). Such enhanced visual preference disappeared in response to an image of the same person standing and facing the left/right side (the stand condition in Experiment 1), an image of the running figure covered with a set of opaque rectangles (the block condition in Experiment 2) (Gervais et al. in Atten Percept Psychophys 72:1437-1443, 2010), and an image of the inverted running figure (the inversion condition in Experiment 3). These results suggest that only the figure that implied dynamic body motion shifted the infants' visual preference to the same direction as the implied running action. These findings demonstrate that even infants as young as 5 to 8 months old are sensitive to the implied motion of static figures.

Effects of cluster size on trypophobic discomfort in children aged 4-9 years.

It has been reported that strong discomfort associated with clusters of circles and holes (trypophobia), including lotus pod seeds, manifests in individuals as young as 4 or 5 years old. This study investigated how the size and number of circles within clusters affected discomfort levels in adults and in children aged 4-9 years. In Experiment 1, we confirmed that the remote experimental procedure could evoke discomfort when participants were presented with cluster images. The findings reveal that children as young as 4 or 5 years old consistently experienced discomfort when rating trypophobic images, even printed images rated in real time during video calls. In Experiment 2, we explored the impact of cluster size, considering both the size and number of circles, in a remote experiment. The results indicate that discomfort tended to increase with cluster size in both children and adults, with the effect becoming more pronounced with age.

Structural flexibility of intrinsically disordered proteins induces stepwise target recognition.

An intrinsically disordered protein (IDP) lacks a stable three-dimensional structure, while it folds into a specific structure when it binds to a target molecule. In some IDP-target complexes, not all target binding surfaces are exposed on the outside, and intermediate states are observed in their binding processes. We consider that stepwise target recognition via intermediate states is a characteristic of IDP binding to targets with "hidden" binding sites. To investigate IDP binding to hidden target binding sites, we constructed an IDP lattice model based on the HP model. In our model, the IDP is modeled as a chain and the target is modeled as a highly coarse-grained object. We introduced motion and internal interactions to the target to hide its binding sites. In the case of unhidden binding sites, a two-state transition between the free states and a bound state is observed, and we consider that this represents coupled folding and binding. Introducing hidden binding sites, we found an intermediate bound state in which the IDP forms various structures to temporarily stabilize the complex. The intermediate state provides a scaffold for the IDP to access the hidden binding site. We call this process multiform binding. We conclude that structural flexibility of IDPs enables them to access hidden binding sites and this is a functional advantage of IDPs.

Preschool children aged 4 to 5 years show discomfort with trypophobic images.

The fear or disgust of clustered patterns, such as honeycomb or lotus seed pods, is known as trypophobia. A previous developmental study reported that 4-year-old children prefer neutral images over clustered images. However, whether those results indicated higher rating scores for trypophobic images has been controversial. In this study, we examined discomfort with trypophobic images in adults and children aged 4-9 years using an identical experimental procedure. A modified rating scale applicable for children was used that was based on the established Trypophobia Scale for adults. The participants were required to rate five trypophobic and five neutral images on four rating items (disgusting, fear, feel itchiness, and like) on a 4-point scale ranging from 1 (not at all) to 4 (very much). The participants in all age groups indicated higher rate scores for trypophobic images than for neutral images in terms of 'disgust', 'fear', and 'feeling itchiness', whereas they indicated higher scores for neutral images than for trypophobic images in terms of 'like'. These results suggest that children aged 4-5 years have responses comparable to the responses of adults with respect to trypophobic and neutral images; thus, trypophobia appears to emerge at least by the age of 4-5 years.

Developmental changes in gaze patterns in response to radial optic flow in toddlerhood and childhood.

A large field visual motion pattern (optic flow) with a radial pattern provides a compelling perception of self-motion; a radially expanding/contracting optic flow generates the perception of forward/backward locomotion. Moreover, the focus of a radial optic flow, particularly an expansive flow, is an important visual cue to perceive and control the heading direction during human locomotion. Previous research has shown that human gaze patterns have an "expansion bias": a tendency to be more attracted to the focus of expansive flow than to the focus of contractive flow. We investigated the development of the expansion bias in children (N = 240, 1-12 years) and adults (N = 20). Most children aged ≥ 5 years and adults showed a significant tendency to shift their gaze to the focus of an expansive flow, whereas the youngest group (1-year-old children) showed a significant but opposing tendency; their gaze was more attracted to the focus of contractive flow than to the focus of expansive flow. The relationship between the developmental change from the "contraction bias" in early toddlerhood to the expansion bias in the later developmental stages and possible factors (e.g., global visual motion processing abilities and locomotor experiences) are discussed.

Developmental Changes in the Magnitude of Representational Momentum Among Nursery School Children: A Longitudinal Study.

Representational momentum (RM) is a well-known phenomenon that occurs when a moving object vanishes suddenly and the memory of its final or vanishing position is displaced forward in the direction of its motion. Many studies have shown evidence of various perceptual and cognitive characteristics of RM in various daily aspects, sports, development, and aging. Here we examined the longitudinal developmental changes in the displacement magnitudes of RM among younger (5-year-old) and older (6-year-old) nursery school children for pointing and judging tasks. In our experiments, the children were asked to point at by their finger (pointing task) and judge the spatial location (judging task) of the vanishing point of a moving stimulus. Our results showed that the mean magnitudes of RM significantly decreased from 5- to 6-year-old children for the pointing and judging tasks, although the mean magnitude of RM was significantly greater in the 5-year-old children for the pointing task but not for the judging task. We further examined the developmental changes in RM for a wide range of ages based on data from the present study (5-year-old children) and our previous study (7- and 11-year-old children and 22-year-old adults). This ad hoc examination showed that the magnitude of RM was significantly greater in 5-year-old children than in adults for the pointing and judging tasks. Our findings suggest that the magnitude of RM was significantly greater in young children than in adults and significantly decreased in young children through adults for the pointing and judging tasks.

Influence of Heat Exposure on Motor Control Performance and Learning as Well as Physiological Responses to Visuomotor Accuracy Tracking Task.

This study aimed to determine whether heat exposure attenuates motor control performance and learning, and blunts cardiovascular and thermoregulatory responses to visuomotor accuracy tracking (VAT) tasks. Twenty-nine healthy young adults (22 males) were divided into two groups performing VAT tasks (5 trials × 10 blocks) in thermoneutral (NEUT: 25 °C, 45% RH, n = 14) and hot (HOT: 35 °C, 45% RH, n = 15) environments (acquisition phase). One block of the VAT task was repeated at 1, 2, and 4 h after the acquisition phase (retention phase). Heat exposure elevated skin temperature to ~3 °C with a marginally increased core body temperature. VAT performance (error distance of curve tracking) was more attenuated overall in HOT than in NEUT in the acquisition phase without improvement in magnitude alteration. Heat exposure did not affect VAT performance in the retention phase. The mean arterial blood pressure and heart rate, but not for sweating and cutaneous vascular responses to VAT acquisition trials, were more attenuated in HOT than in NEUT without any retention phase alternations. We conclude that skin temperature elevation exacerbates motor control performance and blunts cardiovascular response during the motor skill acquisition period. However, these alternations are not sustainable thereafter.

Asymmetric perception of radial expansion/contraction in Japanese macaque (Macaca fuscata) infants.

Visual radial expansion/contraction motion provides important visual information that is used to control several adaptive actions. We investigated radial motion perception in infant Japanese macaque monkeys using an experimental procedure previously developed for human infants. We found that the infant monkeys' visual preference for the radial expansion pattern was greater than that for the radial contraction pattern. This trend towards an "expansion bias" is similar to that observed in human infants. These results suggest that asymmetrical radial motion processing is a basic visual function common to primates, and that it emerges early in life.

Effects of visual information presented by augmented reality on children's behavior.

The effects on children's behavior of visual information presented by augmented reality (AR) were investigated. A human-like AR character was presented standing in one of two physical pathways to children aged 5-7 years old and 8-10 years old before they completed a filler task. After the task, the children were required to walk through one of the two pathways to obtain a reward. Both the 5-7- and 8-10-year-olds chose the pathway that was not associated with the AR character more frequently than the pathway that was. Subsequently, adult participants tested in a similar manner showed no significant bias in pathway selection. Taken together, these results suggest that the presentation of an AR character within the present experimental setting affected the behavior of children aged from 5-10 years but not that of adults. The results are discussed in the context of developmental changes in sensitivity to insubstantial agents (e.g., imaginary companion), the reality of information displayed by AR technology, and differences in the methods of AR presentation (e.g., hand-held devices vs. head-mounted devices).

Effects of Body Orientation Relative to Gravity on Vection in Children and Adults.

We investigated the effects of the interaction between the body and gravitational axes on vection (visually induced self-motion perception) in school-age children and adults. Experiment 1 was a pilot study of adults that was conducted to determine the appropriate experimental settings for the main experiment that included children and adults. The adult participants experienced vection in four different directions in the head-centered coordinate (forward, backward, upward, and downward) under two postural conditions: standing (in which the body and gravitational axes were consistent) and supine (in which the body orientation was orthogonally aligned to the gravitational axis). The adults reported more rapid and longer lasting vection when standing than when supine. In the main experiment (Experiment 2), we tested adults and school-age children under conditions similar to those of Experiment 1 and found that the reported vection was more rapid and longer lasting in children than in adults, whereas the reported vection tended to be more rapid and longer lasting under the standing condition than the supine condition for both age groups. Based on the similarities and differences between children and adults found in the present and previous vection studies, child-specific features of vection are discussed.

Asymmetrical cortical processing of radial expansion/contraction in infants and adults.

We report asymmetrical cortical responses (steady-state visual evoked potentials) to radial expansion and contraction in human infants and adults. Forty-four infants (22 3-month-olds and 22 4-month-olds) and nine adults viewed dynamic dot patterns which cyclically (2.1 Hz) alternate between radial expansion (or contraction) and random directional motion. The first harmonic (F1) response in the steady-state VEP response must arise from mechanisms sensitive to the global radial motion structure. We compared F1 amplitudes between expansion-random and contraction-random motion alternations. F1 amplitudes for contraction were significantly larger than those for expansion for the older infants and adults but not for the younger infants. These results suggest that the human cortical motion mechanisms have asymmetrical sensitivity for radial expansion vs. contraction, which develops at around 4 months of age. The relation between development of sensitivity to radial motion and cortical motion mechanisms is discussed.

Sound enhances detection of visual target during infancy: a study using illusory contours.

In adults, a salient tone embedded in a sequence of nonsalient tones improves detection of a synchronously and briefly presented visual target in a rapid, visually distracting sequence. This phenomenon indicates that perception from one sensory modality can be influenced by another one even when the latter modality provides no information about the judged property itself. However, no study has revealed the age-related development of this kind of cross-modal enhancement. Here we tested the effect of concurrent and unique sounds on detection of illusory contours during infancy. We used a preferential looking technique to investigate whether audio-visual enhancement of the detection of illusory contours could be observed at 5, 6, and 7 months of age. A significant enhancement, induced by sound, of the preference for illusory contours was observed only in the 7-month-olds. These results suggest that audio-visual enhancement in visual target detection emerges at 7 months of age.

Infants' sensitivity to shading and line junctions.

We examined the sensitivity to shading and line junction cues in human infants aged 5-8 months using computer-generated displays containing a rectangular-wave grating and a serrated aperture. In Experiment 1, infants were presented with a pair of displays: a two-dimensional to three-dimensional (2D-3D) display, alternating between 2D and 3D images, and a 2D-2D display, alternating between two 2D images. The 3D image consisted of black-and-white borders aligned with the peaks of a serrated aperture, creating the appearance of a 3D folded surface. The 2D image consisted of the black-and-white borders misaligned with the peaks of a serrated aperture, which does not create a 3D impression for adults. Seven- and 8-month-old infants looked longer at the 2D-3D display than the 2D-2D display. In contrast, 5- and 6-month-old infants did not exhibit a looking preference. In Experiment 2, we used images with double-cycle rectangular-wave gratings to impair shading information. These images consisted of black-and-white borders aligned with half of the peaks and misaligned with latter half of the peaks of a serrated aperture, giving the appearance of surface markings. Seven- and 8-month-old infants did not exhibit a significant difference in preference between the two test displays. These results could not be explained by the young infant's failure of discrimination due to the experimental procedure (Experiment 3). These results showed that the sensitivity to shading and line junctions change between 5-6 and 7-8 months of age.

Early development of sensitivity to radial motion at different speeds.

We examined the sensitivity of 2- and 3-month-old infants to radial expansion/contraction at various speeds. The stimuli comprised one radial motion pattern (expansion or contraction) and one translational motion pattern (up, down, left or right; counterbalanced across infants) placed side by side. The two patterns in each stimulus had the same speed. Three-month-old infants could discriminate between radiation and translation, even under relatively low speeds (5.31 and 2.66 degrees /s), whereas discrimination between the two patterns by 2-month-old infants was very limited. Thus, the range of speeds at which infants can detect radial expansion/contraction changes extensively between 2 and 3 months of age. This change in radial motion sensitivity may reflect the development of cortical motion mechanisms in the dorsal pathway, which is specialised to detect radial motion.

Sensitivity to rotational motion in early infancy.

Sensitivity to rotational motion, one of the fundamental components of optic flow, was tested in infants aged 2 and 3 months. The infants in both groups showed significant sensitivity to rotational motion only in the high-speed condition (10.62 degrees/s). There was no significant increase in motion sensitivity between 2 and 3 months of age, indicating that there is not a significant developmental change during this period. A comparison of our results with previous findings that showed a significant increase in radial motion sensitivity between 2 and 3 months suggests that different motion sensitivities have different developmental time courses.

Asymmetry in the perception of motion in depth induced by moving cast shadows.

An expanding object, which may represent an approaching motion, is easier to detect than a contracting one, which may represent a receding object. To confirm the generality of asymmetry in the detection of approaching and receding motions, we focused on the perception of apparent motion in depth created by moving cast shadows. The visual search for an approaching target among receding distractors was more efficient than for the opposite condition (Experiment 1). However, this asymmetry disappeared when a light shadow was added (Experiments 2 and 3). This suggests that the visual system is specialized to detect approaching motion defined by cast shadows, as well as other three-dimensional cues such as expanding motion and shading.