Early changes in muscle activation patterns of toddlers during walking

Early locomotor behavior has been the focus of considerable attention by developmentalists over several decades. Few studies have addressed explicitly patterns of muscle activity that underlie this coordination pattern. Our purposes were to illustrate a method to determine objectively the onset and offset of muscle firings during early walking and to investigate the emergence of patterns of activation of the core locomotor muscles. We tested eight toddlers as they walked overground at walking onset (max. of 3-6 independent steps) and after three months of walking experience. Surface electrodes monitored activity of the gastrocnemius, tibialis anterior, quadriceps, and hamstrings. We reduced EMG signals to a frame-by-frame designation of "on-off," followed by muscle state and co-contraction analyses, and probability distributions for each muscle's activity across multiple cycles. Our results clearly show that at walking onset muscle activity was highly variable with few, if any, muscles showing recurring patterns of behavior, within or among toddlers. Variability and co-activation decreased with walking experience but remained inconsistent, in contrast to the significant increase in stability shown for joint coordination and endpoint (foot placement) parameters. We propose this trend emerges because of the high number of options (muscle combinations) available. Toddlers learn first to marshal sufficient force to balance and make forward progress but slowly discover how to optimize these resources.     

Parasitoid wasps’ exposure to host-infested plant volatiles affects their olfactory cognition of host-infested plants

Using Cotesia vestalis, a parasitoid wasp of diamondback moth larvae and three crucifer plant species (cabbage, komatsuna, and Japanese radish), we examined the effects of exposure to host-infested plant volatiles from one plant species on a newly emerged wasp’s subsequent olfactory cognition of host-infested plant volatiles from the same or different plant species. The preference of C. vestalis between infested and uninfested plant volatiles was tested in a choice chamber. Volatile-inexperienced wasps significantly preferred infested cabbage and infested radish volatiles, but not infested komatsuna volatiles. After exposure to infested cabbage volatiles, wasps showed a significant preference for infested cabbage volatiles, while the significant preference for infested radish volatiles that had been observed in inexperienced wasps was no longer observed. After exposure to infested komatsuna volatiles, wasps significantly preferred infested komatsuna volatiles, and the pre-exposure significant preferences for infested cabbage volatiles and infested radish volatiles remained. After exposure to infested radish volatiles, the significant preferences for infested cabbage and infested radish volatiles did not change. Furthermore, wasps showed a significant preference for infested komatsuna volatiles. The compound compositions of the volatile blends from the three infested plant species were grouped separately in a principal coordinates analysis. The experience-based cognition of C. vestalis for host-infested plant volatiles of three plant species is discussed.     

Discovery of the pendulum and spring dynamics in the early stages of walking

The authors investigated the self-selected, overground walking patterns of 7 children (aged 11 months to 1 year, 5 months) at the initiation of walking (brand-new walkers [BNWs]) and for the next 6 months at 1-month intervals. Walking speed, stride length, and stride frequency increased significantly between the first 2 visits without significant changes in height and weight. The authors calculated sagittal plane angular accelerations of the center of mass over the foot for each step as an indicator of the escapement pulse. Results for the acceleration profiles changed after the 1st visit to positive, single-peaked accelerations that occurred < 0.20 s after initial foot contact. Increases in sagittal plane hip angular displacement and decreases in frontal plane pelvic angular displacement were observed. The pattern changes suggest that children quickly discover appropriately timed and directed escapements that initiate and support the conservative sagittal plane pendulum and spring dynamics observed in older children.     

Positive mood enhances divergent but not convergent thinking

A positive mood enhances creative performance. We examined which type of creativity, divergent or convergent thinking, was enhanced by a positive mood. Half of the participants listened to happy music and thought about happy events (positive group). The other half listened to the Japanese Constitution (neutral group). Participants' emotional valence and arousal were measured before and after mood induction. All participants then engaged in a creative activity involving the generation of new names for rice. The results indicated that the positive group produced more divergent ideas than did the neutral group. On the other hand, the two groups did not differ with respect to the number of convergent ideas that were generated. We suggest that being in a positive mood facilitates flexible thinking and consequently leads to production of unconventional and atypical ideas.     

Embodiment and sexual experiences of some latin American PLWHA men in Japan

In this paper, we present the third part of our ethnographic investigation including HIV-positive Latin Americans living in Japan. In order to investigate the relationship between psychological well-being and sexual activity among our informants, we interviewed 20 male HIV-positive Latin Americans living in Japan. From April to September, 2002 and August 2003, and 2004, we conducted a set of six 60-minute interviews with twenty 28- to 37-year-old HIV-positive males. Three of them were illegal aliens and seven of them claimed to be homosexual. Participants were contacted through a hospital, a NGO, (non-governmental organization) and by snowball sampling. Our analysis of the interviews indicates that concurrent with a negative attitude towards life informants feel disembodied and asexual after seroconversion. However, after resuming their sex life they experience a positive attitudinal change and emotional release. Drug side-effects on libido make them use stimulants and Viagra. Phallocentrism, fears of infection, and discrimination are obstacles to a full sex life. Informants look for casual sex and engage in prostitution in big cities. These findings have several implications for sex education practice.     

Impaired discrimination learning in mice lacking the NMDA receptor NR2A subunit

N-Methyl-D-aspartate receptors (NMDARs) mediate certain forms of synaptic plasticity and learning. We used a touchscreen system to assess NR2A subunit knockout mice (KO) for (1) pairwise visual discrimination and reversal learning and (2) acquisition and extinction of an instrumental response requiring no pairwise discrimination. NR2A KO mice exhibited significantly retarded discrimination learning. Performance on reversal was impaired in NR2A KO mice during the learning phase of the task; with no evidence of heightened perseverative responses. Acquisition and extinction of an instrumental behavior requiring no pairwise discrimination was normal in NR2A KO mice. The present findings demonstrate a significant and selective deficit in discrimination learning following loss of NR2A.     

A biomechanical analysis of the 'high guard' position of arms during walking in toddlers

In this study, we investigated biomechanical contributions of the high guard position of the arms observed only in a subgroup of toddlers at very early stages of gait development. Six healthy toddlers who showed this peculiar arm posture were involved in this study. They participated in two data collection sessions (1 month apart). We used three-dimensional analysis of arm posture during gait to estimate the changes in forces and torques generated by the arms and acting on the upper trunk segment. Across visits, toddlers’ increase in walking speeds coincided with lowering arm postures. Despite the apparent trend of changes in arm posture in this group of toddlers, the interaction between arm posture and upper trunk position created a variety of changes in forces and torques among individuals. Findings of this study exhibited an example of the exploration of dynamics by toddlers in the early stage of gait development.     

Illusory motion and representational momentum

When a moving target vanishes abruptly, participants judge its final position as being ahead of its actual final position, in the direction of motion (representational momentum; Freyd & Finke, 1984). In the present study, we presented illusory motion and examined whether or not forward displacement was affected by the perceived direction and speed of the target. Experiments 1A and 1B showed that an illusory direction of movement of a target was perceived, and Experiment 2 showed that an illusory speed of a moving target was observed. However, neither the direction nor the magnitude of forward displacement was affected by these illusions. Therefore, it was suggested that the mechanism underlying forward displacement (or some extrapolation processing) uses different motion signals than does the perceptual mechanism.     

Spontaneous Interpersonal Coordination in Stepping and Autistic-Like Traits1

Spontaneous behavior, matching that of others, is influenced by various social factors. Mimicking and synchronizing with others' behaviors can facilitate the development of harmonious relationships. This study examined whether the level of autistic-like traits in a non-clinical population influences the spontaneous-behavioral coordination of a dyad's stepping-on-the-spot movements. The strength of spontaneous stepping synchronization was negatively correlated with levels of autistic-like traits when participants faced one another, and no synchronization was observed for individuals with high levels of autistic-like traits. The deficit in spontaneous interpersonal behaviour-matching among individuals with high levels of autistic-like traits is discussed as a potential source of their poor social-communication abilities.