Limit cycle properties of rhythmic forearm movements.

The kinematics of 1- and 2-armed rhythmic forearm movements were examined using the methodology and limit cycle modeling strategy of B. A. Kay, J. A. S. Kelso, E. L. Saltzman, and G. Schoner (see record 1987-23926-001). As frequency was paced from 1 to 6 Hz (in steps of 1 Hz), amplitude decreased in all 7 participants, whereas peak velocity showed different trends for different participants. The data of 2 of the 7 participants could be described with Kay et al.'s model. To account for the data of the remaining 5 participants, a new model was proposed with a dissipative structure involving a frequency-dependent Rayleigh term and a standard Van der Pol term. For 2 of these 5 participants, the coefficient of the Van der Pol term was not significantly different from zero. Contrary to Kay et al.'s model, the new model suggests that the energy bookkeeping of rhythmic forearm oscillations is affected by the frequency of movement. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Body orientation and control of coordinated movements in microgravity

DNA sequencing by SPEL-6 (Sequential Primer Elongation by Ligation of 6-mers) primer walking is based on the rapid assembly of true primers by ligation of several (three to 10) contiguous hexamers complementary to a DNA template saturated with Escherichia coli single-stranded DNA-binding protein. To prove the usefulness and to check the reliability of this method, a 3-kb DNA fragment carrying the genes encoding the EcoVIII restriction-modification (RM) system was sequenced with low redundancy (2.8). The use of both single-stranded (ss) and double-stranded (ds) DNA templates was compared. For this project, 27 primers were assembled by hexamer ligation to form 18-30-nt strings of three to five hexamers. Each primer was designed based on nucleotide sequence determined in a previous run, and was produced in a matter of minutes. The overall length of the easily readable sequencing ladders was about 300-450nt. We found that strong secondary structures in the ss DNA tend to interfere with its template function for the primer assembly by hexamer ligation, especially when they overlap the 3'-end of such a primer. This was easily overcome either by avoiding such hairpin regions or by using longer strings of hexamers, since we show that their ligation is highly cooperative, and ligation efficiency increases with the length of the string (). Some general rules for successful primer assembly and prospects for using the SPEL-6 method for large-scale, fully automated fluorescent sequencing of large genomes are discussed.     

Phase transitions and critical fluctuations in the visual coordination of rhythmic movements between people.

By watching each other's lower oscillating leg, 2 seated Ss kept a common tempo and a particular phase relation of either 0° (symmetric mode) or 180° (alternate mode). This study investigated the differential stability of the 2 phase modes. In Experiment 1, in which Ss were instructed to remain in the initial phase mode, the alternate phase mode was found to be less stable as the frequency of oscillation increased. In addition, analysis of the nonsteady state cycles revealed evidence of a switching to the symmetric phase mode for the initial alternate phase mode trials. In Experiments 2 and 3, Ss were instructed to remain at a noninitial phase angle if it was found to be more comfortable. The transition observed between the 2 phase modes satisfies the criteria of a physical bifurcation (hysteresis, critical fluctuations, and divergence) and is consonant with previous findings on transitions in limb coordination within a person. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatiotemporal symmetry and multifractal structure of head movements during dyadic conversation.

This study examined the influence of sex, social dominance, and context on motion-tracked head movements during dyadic conversations. Windowed cross-correlation analyses found high peak correlation between conversants’ head movements over short (≈2-s) intervals and a high degree of nonstationarity. Nonstationarity in head movements was found to be positively related to the number of men in a conversation. Surrogate data analysis offsetting the conversants’ time series by a large lag was unable to reject the null hypothesis that the observed high peak correlations were unrelated to short-term coordination between conversants. One way that high peak correlations could be observed when 2 time series are offset by a large time lag is for each time series to exhibit self-similarity over a range of scales. Multifractal analysis found small-scale fluctuations to be persistent, τ(q) 0.5. These results are consistent with a view that symmetry is formed between conversants over short intervals and that this symmetry is broken at longer, irregular intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of the microstructure of the rhythmic tongue movements of rats ingesting maltose and sucrose solutions.

Analyzed interlick interval distribution of rats ingesting maltose under real and sham feeding conditions and while ingesting 7 concentrations of sucrose under real feeding conditions. The analysis revealed that the licking behavior of rats is organized into bursts of licking at a high rate. These bursts occurred in clusters that were separated by brief (250–500 msec) interruptions. The clusters were separated by intervals that ranged from 500 msec to many hundreds of seconds. Sham feeding increased the length of the meal by increasing the number but not the size of the clusters. Increasing the concentration of sucrose increased monotonically the size of the clusters but varied the number of clusters as an inverted-V-shaped function. Analysis revealed the details of the central nervous system's (CNS) control over ingestive behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ab initio phase determination and phase extension using non-crystallographic symmetry

Non-crystallographic symmetry (NCS) can be used to improve, extend or find ab initio phases to be associated with a set of observed structure amplitudes, resulting in an interpretable electron-density map. The simplest application is merely to improve the accuracy of the phases by cyclically averaging the electron density, Fourier back-transformation of the modified map, and recomputing a new map with the newly found phases. The first sophistication of this procedure is to phase extend, in successive small steps, the currently available phase information to higher resolution, where only observed amplitudes were previously available. A further sophistication is to initiate the phase extension from very low resolution where a simple geometric model, or an electron microscope image, would be consistent with the chosen resolution. A number of recent examples of virus structure determination exist where such ab initio phasing was successful. The ultimate ab initio phase determination would be to extend phases given only an estimate of the F(000) term.     

Comment: gating effects and constraints on the central pattern generators for rhythmic movements

Respiration, mastication, and locomotion are compared in terms of the contributions of events occurring at the motoneuron membrane and at premotoneuronal levels for the production of phasic gain changes of afferent effects. Data are presented which suggest that an inhibitory mechanism operating on limb motoneurons can prevent disruption of the locomotor pattern by proprioceptive input and that Ia inhibitory interneurons contribute to this rhythmic inhibition of both flexor and extensor motoneurons. Renshaw cell rhythmic activity during locomotion is described and discussed in terms of its possible role in gating of inputs to motoneurons.     

Age-specific problems in rhythmic timing.

The authors investigated performance in 2 rhythm tasks in young (M?=?23.8 years) and older (M?=?71.4 years) amateur pianists to test whether slowing of a central clock can explain age-related changes in timing variability. Successive keystrokes in the rhythm tasks were separated by either identical (isochronous) time intervals or varying (anisochronous) intervals. Variability was comparable for young and older adults in the isochronous task; pronounced age effects were found for the anisochronous rhythm. Analyses of covariances between intervals rule out slowing of a central clock as an explanation of the findings, which instead support the distinction between target specification, timekeeper execution, and motor implementation proposed by the rhythm program hypothesis (D. Vorberg & A. M. Wing, 1996). Age stability was found at the level of motor implementation, but there were age-related deficits for processes related to target-duration specification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of the mandibular stretch reflex sensitivity during various phases of rhythmic open-close movements in humans

Enzymatically formed peptides show positional variations as well as highly conserved amino acids. In the cases of gramicidin S, tyrocidine, linear gramicidins, enniatins, echinocandins and viridogrisein in vivo and in vitro studies indicate substrate selection at the level of amino acid activation as a major control step. Evidence for proof-reading steps beyond activation has been obtained in penicillin and cyclosporin biosynthesis. Activated substrate analogues may promote the formation of side products such as dipeptides and cyclodipeptides. Modifications of intermediates, such as N-methylation, influence the rates of peptide synthesis. These control steps pose limitations for the application of such enzyme systems in the production of peptide libraries. They may originate from a target oriented evolution of these synthetases.     

Resonance constraints on rhythmic movement.

The component frequencies of rhythmic patterns forming rational ratios, either simple (e.g., 1:2, 1:3) or complex (e.g., 2:3, 2:5), are known as mode locks or resonances. A general theory of resonances is provided by the circle map, the Farey series, and continued fractions. Predictions were evaluated in which rhythms (simple and poly) were established implicitly; the S neither intended them nor knew their ratios. In Exp 1, a prescribed unimanual frequency was performed as the primary task while hearing another frequency irrelevant to the task. In Exps 2 and 3, a hand-held pendulum was oscillated at its natural frequency, while the other hand performed the primary task of following a metronome. The frequency ratio at the outset of a trial often changed during the trial. Consistent with the general theory, shifts were toward unimodular ratios of the Farey tree, and Fibonacci ratios tended to shift more than non-Fibonacci ratios. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Task-effector asymmetries in a rhythmic continuation task.

Variability in rhythmic movements has been interpreted as a signature of internal or peripheral noise processes. Grounded in an oscillator interpretation, this study hypothesized that period variability and drift arises from the asymmetry between target period and the limb's intrinsic dynamics. Participants synchronized to 7 target periods, swinging 1 of 3 pendulums in a continuation paradigm; 3 periods were longer, 3 shorter, and 1 identical to the preferred period. Results supported 5 predictions: Drift toward the preferred period was observed that scaled with the asymmetry. Variability was lowest for symmetry conditions and increased with the asymmetry. Variability decreased concomitant with the approach toward the preferred period. Periods exponentially approached the preferred period with positive autocorrelations up to 10 cycles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Daily Fluctuations in Self-Control Demands and Alcohol Intake.

Predictions made by the self-control strength model were tested in a sample of underage social drinkers using ecological momentary assessment methodology. On days that participants experienced more self-control demands than average, they were more likely to violate their self-imposed drinking limit after controlling for mood and urge to drink. There was no relationship between self-control demands and urge or intention to drink, nor were self-control demands related to plans to limit drinking. When individuals planned to limit their alcohol intake, they were more affected by self-control demands than when they did not plan to limit their alcohol intake. Trait self-control moderated these relationships. Consistent with the self-control strength model, it appears that exerting self-control in nondrinking areas undermines individuals' capacity to exert self-control of drinking in daily life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Compensatory movements of horses with a stance phase lameness

In order to study the mechanism of lameness transfer from fore- and hindlimb lamenesses 2 hypotheses were investigated. Hypothesis 1: Horses with a true supporting limb lameness in one hindlimb show a false supporting limb lameness in the ipsilateral forelimb. Hypothesis 2: Horses with a true supporting limb lameness in one forelimb show a false supporting limb lameness in the contralateral hindlimb. Fourteen horses with fore- or hindlimb lameness were used for this study. Each horse was measured at the trot on a treadmill with standardised speed, before and after diagnostic blocks (9 horses), or with and without induced lameness (5 horses). The head acceleration asymmetry (HAAS) and the sacrum acceleration asymmetry (SAAS) were used for quantification of fore- and hindlimb lameness respectively. Changes were documented by changes of the HAAS or the SAAS. In all 4 horses with a true hindlimb lameness a synchronous false lameness of the ipsilateral forelimb was documented. In 6 of 10 horses with a forelimb lameness a lameness transfer could be assessed according to hypothesis 2. The results of this study show, that horses with a true severe lameness in the forelimb show a false lameness in the contralateral hindlimb, and horses with a true hindlimb lameness show a false lameness in the ipsilateral forelimb. This indicates that the location of the truly lame limb can be deduced from the distribution of 2 lamenesses on a sagittal or diagonal axis.     

Segmentation and coupling in complex movements.

Two experiments in which the authors and an adult female served as Ss, examined the structure of complex sequences of drawing movements. In these movements, a single parameter—the velocity gain factor—was shown to relate the geometrical and kinematic aspects of the movement trajectory via a two-thirds power law. Exp I investigated the relation between the velocity gain factor and the linear extent of the trajectory, while Exp II demonstrated that the gain factor provided criterion for segmenting the movement into distinct units of motor action and investigated the effects of the speed of execution on this segmentation. A theoretical analysis showed that the results of both experiments can be given a unitary interpretation by assuming a coupling function of variable strength between segments. The general problem of representing motor programs is discussed within this theoretical framework. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)