Advantages of Rhythmic Movements at Resonance: Minimal Active Degrees of Freedom,Minimal Noise,and Maximal Predictability

Using time delay embedding, the authors applied phase space reconstruction to the time series of rhythmic movements of a hand-held pendulum. Subjects (N = 6) produced the manual oscillations about the wrist at the pendulum's resonant frequency and at a higher and a lower frequency. The number of active degrees of freedom required to capture the dynamics of the rhythmic behavior was 3 for the resonant frequency and 4 for each of the nonresonant frequencies. The residual high-dimensional noise was similarly lowest for the resonant frequency. Whereas 33% and 20%, respectively, of the vectors in the phase spaces of the dynamics higher and lower than resonance were unpredictable, only 12% were unpredictable at resonance. Finally, the predictability of the evolving dynamics extended farther into the future for oscillations at the resonant frequency. At resonance, the prediction horizon was 5 times farther than the prediction horizon for the higher than resonance behavior and 2.5 times farther than that for the lower than resonance behavior. The results suggest that, in pendular oscillations of a limb or limb segment, attunement of the central nervous system to the resonant frequency minimizes the variables to be controlled and maximizes the predictability of the rhythmic movement's chaotic dynamics.     

Visual and haptic feedback contribute to tuning and online control during object manipulation

The authors employed a virtual environment to investigate how humans use haptic and visual feedback in a simple, rhythmic object-manipulation task. The authors hypothesized that feedback would help participants identify the appropriate resonant frequency and perform online control adjustments. The 1st test was whether sensory feedback is needed at all; the 2nd was whether the motor system combines visual and haptic feedback to improve performance. Task performance was quantified in terms of work performed on the virtual inertia, ability to identify the correct rhythm, and variability of movement. Strict feedforward control was found to be ineffective for this task, even when participants had previous knowledge of the rhythm. Participants (N = 11) performed far better when feedback was available (11 times more work, 2.2 times more precise frequency, 30% less variability; p < .05 for all 3 performance measures). Using sensory feedback, participants were able to rapidly identify 4 different spring-inertia systems without foreknowledge of the corresponding resonant frequencies. They performed over 20% more work with 24% less variability when provided with both visual and haptic feedback than they did with either feedback channel alone (p < .05), providing evidence that they integrated online sensory channels. Whereas feedforward control alone led to poor performance, feedback control led to fast tuning or calibration of control according to the resonant frequency of the object, and to better control of the rhythmic movement itself.     

Resonance Tuning in Rhythmic Arm Movements

The hypothesis was tested that the preferred frequency of rhythmic movement corresponds to the resonant frequency of the muscle-limb system, as proposed by the hybrid spring-pendulum model (Kugler Turvey, 1987). In contrast to previous studies, the resonant frequency and stiffness of the system were estimated independently, which permitted quantitative predictions of the preferred frequency to be made. Human subjects (N = 5) were asked to oscillate their forearms in the vertical plane at their preferred frequency under conditions of added mass and external spring loading. Subjects also oscillated their arms at frequencies below and above the preferred frequency, which enabled the investigators to estimate the resonant frequency and stiffness of the elbow joint by using the phase transfer method (Viviani, Soechting, Terzuolo, 1976). The preferred frequency corresponded to the resonant frequency of the muscle-limb system under each condition, as predicted. The oscillation amplitude varied inversely with the preferred frequency, which was also predicted. Finally, the internal joint stiffness was modulated so that it matched the impedance of the external springs but was unaffected by added mass. The results are consistent with an autonomous oscillator model that incorporates proprioception about the dynamics of the periphery.     

Coordination Dynamics of the Bipedal Galloping Pattern

A motion equation in relative phase was developed that incorporates the spatial-temporal pattern of the bipedal gallop along with the more commonplace patterns of the bipedal jump and walk-run. In 3 experiments, human participants (N = 6 per experiment) simulated the bipedal gait patterns through the rhythmic motions of hand-held pendulums. Predictions of the motion equation for coordination equilibria and their respective degrees of stability were confirmed. In particular, the gallop pattern was less stable than the fundamental in-phase and antiphase patterns but changed in qualitatively similar ways to those gaits as a function of limb asymmetry and movement frequency. The relation between the modeled coordination dynamics and the kinematic characteristics of real bipedal galloping is discussed     

Coordination Dynamics of the Bipedal Galloping Pattern

A motion equation in relative phase was developed that incorporates the spatial-temporal pattern of the bipedal gallop along with the more commonplace patterns of the bipedal jump and walk-run. In 3 experiments, human participants (N = 6 per experiment) simulated the bipedal gait patterns through the rhythmic motions of hand-held pendulums. Predictions of the motion equation for coordination equilibria and their respective degrees of stability were confirmed. In particular, the gallop pattern was less stable than the fundamental in-phase and antiphase patterns but changed in qualitatively similar ways to those gaits as a function of limb asymmetry and movement frequency. The relation between the modeled coordination dynamics and the kinematic characteristics of real bipedal galloping is discussed.     

Interference effects in bimanual coordination are independent of movement type

Simultaneously executed limb movements interfere with each other. Whereas the interference between discrete movements is examined mostly from a cognitive perspective, that between rhythmic movements is studied mainly from a dynamical systems perspective. As the tools and concepts developed by both communities are limited in their applicability to the other domain, it remains unclear if a common cause underlies motor interference in both domains. We investigated the interference between simultaneously executed discrete and rhythmic wrist movements. The discrete movements' reaction time and movement time decreased with increasing rhythmic movement frequency. The discrete movements accelerated or decelerated the rhythmic movements in a manner that depended on movement frequency and the discrete movement's initiation phase. The acceleration/deceleration profile was bimodal at low frequencies and unimodal at high frequencies, mimicking the hallmark feature of rhythmic-rhythmic coordination, thus suggesting that interference between movements may be invariant across different movement types.     

Simulation of surface effects on the intrinsic dissipation of nanooscillators

The rapid increase of surface area-volume ratio (SVR) with shrinking structure size has a great impact on surface-related intrinsic dissipation, which usually leads to low quality factors for the devices composed of nanoelectromechanical systems. In the present study, the flexural oscillations of nanocantilevers with varying thicknesses and lengths were simulated using the molecular dynamics method, in which the surface effects on the energy dissipation was evaluated when SVR was increased to extremely large values (between 0.4 and 2.0 nm^?1). And, it is also interesting to note that the prediction of the size-dependent Young's modulus by means of resonant frequency of the underdamped oscillation showed good agreement with previous findings.     

注意过程中的行为振荡现象

行为振荡是个体心理加工过程的周期性动态变化在行为上的表现。通过高时间分辨率的行为采样方法, 行为振荡研究为探索视觉注意的时间动态结构提供了一个新的视角。各种不同的注意任务中都发现存在行为振荡现象。大量行为振荡证据表明, 注意过程存在两种主要的节律成分：反映注意抑制的α节律(8~13 Hz)和反映注意转移的θ节律(4~8 Hz)。这些结果有助于揭示注意的时间动态结构, 也为序列搜索理论和平行搜索理论之间的争论提供了新的分析思路。行为振荡的节律特征会受到一些潜在因素(如任务难度、线索有效性)的影响。行为振荡和神经振荡在某些任务中表现出相同的节律成分, 提示两者涉及了相似的心理过程。后续研究应进一步关注各种不同的注意控制过程以及多模态交互任务, 深入探索其行为振荡特点, 以更好地揭示注意的动态加工过程。     

Tracking simple and complex sequences

We address issues of synchronization to rhythms of musical complexity. In two experiments, synchronization to simple and more complex rhythmic sequences was investigated. Experiment 1 examined responses to phase and tempo perturbations within simple, structurally isochronous sequences, presented at different base rates. Experiment 2 investigated responses to similar perturbations embedded within more complex, metrically structured sequences; participants were explicitly instructed to synchronize at different metrical levels (i.e., tap at different rates to the same rhythmic patterns) on different trials. We found evidence that (1) the intrinsic tapping frequency adapts in response to temporal perturbations in both simple (isochronous) and complex (metrically structured) rhythms, (2) people can synchronize with unpredictable, metrically structured rhythms at different metrical levels, with qualitatively different patterns of synchronization seen at higher versus lower levels of metrical structure, and (3) synchronization at each tapping level reflects information from other metrical levels. The latter finding provides evidence for a dynamic and flexible internal representation of the sequence's metrical structure.     

Dynamics of 1:2 Coordination: Generalizing Relative Phase to n:m Rhythms

Interlimb rhythmic movements can be modeled as coupled oscillators, with stable performance characterized by the relative phase between the limbs. In the present study, that modeling strategy, verified previously for 1:1 coordination, was generalized to 1:2 coordination with a view to n:m coordination. The generalized model predicted interactions between coordination (specifically, 1:1 vs. 1:2) and the frequency asymmetry between the limbs determining mean relative phase and its variability. The predicted interactions were evaluated with bimanual 1:2 and 1:1 rhythmic tasks in which participants (N = 8) oscillated hand-held pendulums whose uncoupled frequencies could be adjusted so that different interlimb asymmetries were produced. The authors needed new analytic procedures to verify stable 1:2 coordination and to resolve stochastic and deterministic sources of variability in the component oscillations. The major expectations from the generalized model were confirmed, and the implications of additional but unpredicted findings for the modeling of multifrequency behavior are discussed.     

Spontaneous transitions and symmetry: Pattern dynamics in human four-limb coordination

Transitions between the coordinative patterns of rhythmically moving human arms and legs were studied to test the predictions of a four-component model (Schöner, Jiang and Kelso, 1990). Based upon results from previous two-component experiments (Kelso and Jeka, 1992), three assumptions were made about the four-limb system: (1) all limb pairs produce stable in-phase and anti-phase patterns; (2) the coupling between homologous limbs (i.e., right and left arms or right and left legs) is appreciably stronger than the coupling between nonhomologous limbs (i.e., arm and leg); and (3) right-left symmetry. An analysis of a four-component model (Jeka, Kelso and Kiemel, 1993) led to the prediction of four attracting invariant circles, each with two stable patterns in the state space of four-limb dynamics. In an experiment to test this prediction, subjects were required to cycle all four limbs in one of the eight patterns to the beat of an auditory metronome whose frequency was systematically increased. All subjects demonstrated spontaneous transitions corresponding to pathways along the invariant circles. Pre-transition relative phase variability increased with required frequency up to the transition, suggesting that loss of pattern stability induced the observed transitions. Thus, despite a large number of potential transitions, differential coupling between limb pairs and symmetry of the pattern dynamics restricts the behavior of the human four-limb system to a limited area of its state space.     

Dependence of Finger Flexion Force on the Posture of the Nonperforming Fingers During Key Pressing Tasks

In visuomotor tasks that involve accuracy demands, small directional changes in the trajectories have been taken as evidence of feedback-based error corrections. In the present study variability, or intermittency, in visuomanual tracking of sinusoidal targets was investigated. Two lines of analyses were pursued: First, the hypothesis that humans fundamentally act as intermittent servo-controllers was re-examined, probing the question of whether discontinuities in the movement trajectory directly imply intermittent control. Second, an alternative hypothesis was evaluated: that rhythmic tracking movements are generated by entrainment between the oscillations of the target and the actor, such that intermittency expresses the degree of stability. In 2 experiments, participants (N = 6 in each experiment) swung 1 of 2 different hand-held pendulums, tracking a rhythmic target that oscillated at different frequencies with a constant amplitude. In 1 line of analyses, the authors tested the intermittency hypothesis by using the typical kinematic error measures and spectral analysis. In a 2nd line, they examined relative phase and its variability, following analyses of rhythmic interlimb coordination. The results showed that visually guided corrective processes play a role, especially for slow movements. Intermittency, assessed as frequency and power components of the movement trajectory, was found to change as a function of both target frequency and the manipulandum's inertia. Support for entrainment was found in conditions in which task frequency was identical to or higher than the effector's eigenfrequency. The results suggest that it is the symmetry between task and effector that determines which behavioral regime is dominant.     

Panic-relevant predictability preferences: a laboratory test

In the present investigation the authors evaluated the role of verbally instructed safety periods as they relate to predictability preference within a single-session challenge paradigm involving recurrent administrations of 20% carbon dioxide (CO-sub-2) enriched air. Participants included 160 nonclinical young adults (91 women, 69 men) between the ages of 18 and 59 (M=21.6 years; SD=7.23). Results indicated that equivalent levels of anxiety were experienced during predictable and unpredictable administrations of 20% CO-sub-2, yet participants preferred predictable compared with unpredictable trials, with women showing a stronger predictability preference than men. Lower anxiety was reported during known safety periods (predictable room air trials) but not during predictable compared with unpredictable administrations of 20% CO-sub-2. Findings are discussed in relation to theoretical and applied implications for the role of predictability in the nature of anxiety and its disorders.     

Order and chaos in fixed-interval schedules of reinforcement

Fixed-interval schedule performance is characterized by high levels of variability. Responding is absent at the onset of the interval and gradually increases in frequency until reinforcer delivery. Measures of behavior also vary drastically and unpredictably between successive intervals. Recent advances in the study of nonlinear dynamics have allowed researchers to study irregular and unpredictable behavior in a number of fields. This paper reviews several concepts and techniques from nonlinear dynamics and examines their utility in predicting the behavior of pigeons responding to a fixed-interval schedule of reinforcement. The analysis provided fairly accurate a priori accounts of response rates, accounting for 92.8% of the variance when predicting response rate 1 second in the future and 64% of the variance when predicting response rates for each second over the entire next interreinforcer interval. The nonlinear dynamics account suggests that even the “noisiest” behavior might be the product of purely deterministic mechanisms.     

Lexical access of function versus content words

There has been a simmering debate as to whether evidence exists for differential processes of lexical access for function and content words. This has centered around the frequency effect (higher word frequency reducing access times for content words but not function words). Previous work has used the lexical decision paradigm, which has been shown to reflect more than lexical access times. We measured naming times for words in sentences read for meaning. Our findings confirm that lexical access for function words is indeed faster than for content words as predicted by neurolinguistic theory and electrophysiological evidence, but that this difference can be attributed to word predictability (Cloze value) and word familiarity (log frequency). We also show that differences in frequency effect for the two word types holds only for the lower frequency words and not at all for the higher frequency words. We discuss the implications of the results for neurolinguistic theory.     

Chaos in Human Rhythmic Movement

Rhythmic movements typical of locomotory actions are usually modeled as limit cycle dynamics, and their deviations from pure periodicity are attributed to stochastic physiological noise. In the present study, the dynamics of human rhythmic movements were found to contain more than the 2 dynamically active variables expected from limit cycle dynamics; the number depended upon the size of the limb oscillator. Observed positive Lyapunov exponents and fractal attractor dimensions indicated that the gross variability of human rhythmic movements may stem largely from low-dimensional chaotic motion on strange attractors.     

Kinematic adaptations to perturbations as a function of practice in rhythmic drawing movements

Kinematic adaptations in multijoint rhythmic drawing movements were investigated under unexpected perturbations in friction levels between stylus and writing surface. Changes in coupling and stability properties were assessed as a function of practice level by applying perturbations to subjects' dominant and nondominant limbs. Under nonperturbation and perturbation conditions, joint motions of right-handed subjects were highly coupled in the nondominant limb and uncoupled in the dominant limb. Stability analyses of the kinematic responses in the phase plane showed a relatively higher intrajoint resistance to perturbations in the nondominant limb as compared to the dominant limb for the elbow joint. indicating a decrease in global joint stiffness with practice. These changes in joint coupling and stiffness with practice were not observed for left-handed subjects. In addition, the stability to perturbations in the end-effector (stylus) kinematics was related to the amount of joint coupling in the nondominant limb, whereas in the dominant limb there existed no such coupling. It was concluded that (a) practice changes the responses to perturbations from anatomically specific early in practice to task-specific late in practice, and (b) this shift is related to the stability in the joint phase-plane dynamics, degree of coupling between joint angles, and the decoupling of the dynamics in the intrinsic and extrinsic control spaces.     

Concurrent cognitive task modulates coordination dynamics

Does a concurrent cognitive task affect the dynamics of bimanual rhythmic coordination? In‐phase coordination was performed under manipulations of phase detuning and movement frequency and either singly or in combination with an arithmetic task. Predicted direction‐specific shifts in stable relative phase from 0° due to detuning and movement frequency were amplified by the cognitive task. Nonlinear cross‐recurrence analysis suggested that this cognitive influence on the locations of the stable points or attractors of coordination entailed a magnification of attractor noise without a reduction in attractor strength. An approximation to these findings was achieved through parameter changes in a motion equation in relative phase. Results are discussed in terms of dual‐task performance as limited resources, dynamics rather than chronometrics, and reparameterization rather than degradation.     

The beat goes on: rhythmic modulation of cortical potentials by imagined tapping

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180 degrees out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions.     

词汇预测性对中文高、低阅读技能儿童眼动行为的影响

操纵目标词的预测性、词频和阅读技能水平,考察句子阅读中词汇预测性对高、低阅读技能儿童眼动行为的影响,揭示其在儿童阅读发展中的作用。结果显示：儿童对高预测词的跳读率更高、注视时间更短,且预测性与词频交互影响跳读率和注视时间;预测性对高阅读技能儿童早期的跳读率影响更大,而对低阅读技能儿童晚期的再阅读时间具有更大影响。结果表明：词汇预测性影响儿童阅读的眼动行为和词汇加工,且作用大小和发生时程受阅读技能调节。