Biomedical subjects

M T Turvey

Publications and source records attributed to M T Turvey.

At least 55 records · Page 3Linked to original sources

PubMed1998

Spatial and physical frames of reference in positioning a limb.

Splints attached to the right forearm were used to rotate the forearm's physical reference frame, as defined by the eigenvectors of its inertia tensor, relative to its spatial reference frame. In two experiments, when subjects were required to orient the forearm parallel to, or at 45 degrees to, the environmental horizontal, they produced limb orientations that were systematically deflected from the forearm's longitudinal spatial axis in the direction of the forearm's physical axes. The position sense seems to be based on inertial eigenvectors rather than on joint angles or gravitational torques.

Data Collection↗

PubMed1998

Inertial eigenvalues, rod density, and rod diameter in length perception by dynamic touch.

Four experiments addressed the relevance of the eigenvalues Ik of the inertia tensor for perceiving length by dynamic touch. Experiments 1-2 focused on the consequences of limiting variation in the minimum eigenvalue I3. Both revealed that perceived length is a function of Ik. Whether the contribution of I3 is detected, however, depends on the range of values that characterize a particular object set. Experiments 3-4 considered the relationship between an independent index of a rod's diameter, which does not affect Ik, and actual manipulation of a rod's diameter, which does affect Ik. Whereas the former appeared as satisfaction of implicit instructions to alter reports of perceived length, the latter entailed actual differences in perceived length in accordance with Ik. Results are discussed with respect to the links among actual length, perceived length, and Ik, as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.

Adult↗

PubMed1997

Common effects of touch and vision on postural parameters.

Subjects stood upright with the index finger of the right hand either touching a nearby surface gently or not touching it at all and with the eyes either open or closed. Trajectories of the center of pressure (COP) were analyzed as fractional Brownian motion. The extracted parameters were the effective diffusion (D) coefficients and Hurst (H) exponents for short-term time intervals (corresponding to positively correlated random walks) and long-term time intervals (corresponding to negatively correlated random walks). Gentle tactile contact reduced the effective stochastic activity measured by D to the same extent as the availability of vision. Further, touch interacted with time interval in the same way as vision, with the correlated activity closer to H = 0.5 at both time scales when the finger contacted the nearby surface. The results corroborate and extend major features of recent investigations of haptic influences on posture and recent analyses of vision's influence on the fractional Brownian motions of the COP. Discussion focused on (a) the equivalence of expropriospecific information (about the body's orientation to the environment) registered haptically and visually and (b) the possibility that postural sway may reflect exploratory motions in the short term (obtaining information about the postural system) and performatory motions in the long term (using this information).

Adolescent↗

PubMed1997

Intrinsic and required dynamics of a simple bat-ball skill.

Three experiments investigated the coordination dynamics of a simple bat-and-ball skill: cyclically striking a ball suspended by a string with a pendular bat. The relative phase phi between the bat and ball is dictated by the potential function V(phi) = k sin phi and the difference delta omega in their uncoupled frequencies. For various delta omega, phi and its standard deviation were measured in the absence of any environmental restraints (intrinsic dynamics) and when the ball had to reach resistive or nonresistive targets at set distances (required dynamics). Results support the dynamical theory of coordination patterns (G. Schöner & J.A.S. Kelso, 1988a, 1988c), particularly the hypothesis that required dynamics are understandable as the addition of terms to the potential governing the intrinsic dynamics.

Biomechanical Phenomena↗

PubMed1997

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.

coupling↗

PubMed1997

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.

degrees of freedom↗

PubMed1996

Adiabatic transformability hypothesis of human locomotion.

It is hypothesized that metabolic and mechanical changes in human locomotion associated with changes in speed v are constrained by two attractive strategies: Qmetab = 1 and delta Qmetab/delta v = a positive definite constant. Qmetab = delta Eks-1/ml O2s-1 where delta Eks-1 is the summed increments and decrements per unit time in the translational and rotational kinetic energies of the body's segments and ml O2s-1 is the rate at which chemical energy is dissipated. The expected constancy of delta Qmetab/delta v was derived from an extension of Ehrenfest's adiabatic hypothesis by which transformations (increases, decreases) in locomotion v can be considered as adiabatic, even though the biological conditions are nonconservative and non-rate-limited. The expected significance of Qmetab = 1 was derived from stability considerations of the symmetry per stride of stored and dissipated energy. An experimental evaluation was provided by collecting metabolic and mechanical measures on walking (10 subjects) and running (9 subjects) at progressively greater treadmill speeds but within the aerobic limit. Results revealed that walking was restricted to Qmetab < or = 1, with a nonlinear trajectory in v x Qmetab coordinates shaped by Qmetab = 1 (primarily) and the constancy of delta Qmetab/delta v. Running satisfied Qmetab > 1, with a linear trajectory in v x Qmetab coordinates conforming to delta Qmetab/delta v = a constant, with the constant predicted from invariants in the mechanical space v x delta Eks-1. Results also suggested that the metabolic costs of running might be predictable from measures made in the v x delta Eks-1 space.

Adult↗

PubMed1996

Symmetry, broken symmetry, and handedness in bimanual coordination dynamics.

The symmetrical dynamics of 1:1 rhythmic bimanual coordination may be specified by an order parameter equation involving the relative phase between rhythmic components, and an interlimb coupling which determines the relative attractiveness of in-phase and anti-phase patterns. Symmetry breaking of these dynamics can occur via the difference in the natural frequencies, delta omega, of the left and right rhythmic components, or by the intrinsic asymmetrical dynamics of the body. The latter is captured by additional terms that render the symmetrical coupling slightly anisotropic. A major prediction resulting from this step is that although delta omega = 0, as the frequency of coordination is increased, the asymmetrical coupling will increase and the symmetrical coupling will decrease. This results in a greater left-limb bias in left-handers and right-limb bias in right-handers. This "increased handedness" prediction was confirmed in an experiment in which 20 left-handed and 20 right-handed individuals performed 1:1 coordination with hand-held rigid pendulums. Manipulations of left and right pendulum lengths controlled delta omega, and the coupled frequency was determined by a metronome. Also confirmed was the prediction that the small shift in equilibria from in-phase and anti-phase due to the intrinsic asymmetry should be amplified in left-handers when delta omega > 0 and in right-handers when delta omega < 0. Further, the bias in left-handers was more consistent than the bias in right-handers, and a subgroup of right-handers was identified who performed similarly to left-handers. The coordination dynamics of functional asymmetry provides insights into the elementary synergy between the limbs, the dynamical mechanism that modulates it, and the nature of the asymmetry in left-handed and right-handed individuals.

Adult↗

PubMed1996

Dynamic touch.

People can perceive a number of spatial and other properties of objects, without the benefit of vision, simply by wielding and hefting the objects. A variety of recent experiments are reported, showing that in this kind of touching, which is closely connected with the states of muscles, the nervous system cleverly exploits the physics of rotations.

Discrimination Learning↗

PubMed1996

Weight perception and the haptic size-weight illusion are functions of the inertia tensor.

The complex effects of mass and volume on weight perception (e.g., the size-weight illusion) were hypothesized to follow simply from invariants of rotational dynamics. In Experiments 1-3, the rotational inertia of wielded, occluded objects was varied independently of mass, size, and torque. Perceived heaviness depended only on rotational intertia. Reanalysis of J. C. Stevens and L. L. Rubin's (1970) study revealed that size's influence on weight perception depends on specific patterns of the eigenvalues of the inertia tensor. These patterns were simulated in Experiments 4-6 with objects of fixed mass, volume, and visible size. Perceived heaviness decreased and increased, respectively, over object sets with the eigenvalue patterns of (a) constant mass, increasing volume and (b) increasing mass, constant volume. Weight perception and the size-weight illusion depend on stimulus invariants, not inference.

Female↗

PubMed1996

An experimental note on defining frequency competition in intersegmental coordination dynamics.

Synchronous coordination between two body segments departs from phase locking at 0 or pi radians when the segments are asymmetrical. In models of coordination dynamics, this detuning is typically quantified by Deltaomega = (omega1 - omega2), where omega1 and omega2 are the uncoupled frequencies of the two segments. An experiment is reported in which the magnitude of Deltaomega not equal 0 was satisfied by different ratios Omega of omega1 and omega2. The degree of detuning was found to vary systematically with Omega and Deltaomega. This result corroborates previous research using the complementary manipulation of varying Deltaomega for a fixed Omega. A challenge for future dynamical modeling is identifying precisely how the detuning quantity incorporates both the absolute and relative differences in the. uncoupled segmental frequencies.

Journal Article↗

PubMed1996

Inhibition of naming by rhyming primes.

The priming effects of graphemically similar (e.g., HOSE) and graphemically dissimilar (e.g., ROWS) rhymes on the naming of target words (NOSE) were examined at prime-target stimulus onset asynchronies (SOA) of 36, 70, and 250 msec. A four-field presentation procedure was used of mask-prime-mask-target. The effects of rhyme primes were measured relative to those of nonrhyming control primes (CHEF, DISH) that matched the rhymes in frequency and length and shared no letters in the same positions. At SOAs of 36 and 70 msec, rhyme priming was inhibitory and equal for graphemically similar and graphemically dissimilar rhymes. At SOA = 250 msec, rhyme priming was insignificant with a tendency toward facilitation. The results are discussed in the context of (1) contrasting effects of complete versus partial phonological overlap within a prime-target pair, and (2) the hypothesis that phonological codes stabilize fastest and provide, therefore, the earliest and major constraint on word recognition.

Adult↗

PubMed1996

Exteroception and exproprioception by dynamic touch are different functions of the inertia tensor.

When an object is held and wielded, a time-invariant quantity of the wielding dynamics is the inertia tensor Iij. The 3 x 3 quantity Iij is composed of moments of inertia (on the diagonal) and products of inertia (off the diagonal). Examination of Iij as a function of different locations at which a cylindrical object is grasped revealed that the products related systematically to grip position (a direction), and both the products and moments taken together related systematically to the extent of the rod to one side of the hand (a magnitude in a direction). In two experiments, observers wielded an occluded rod that was held at an intermediate point along its length and reproduced both the felt grip position and partial rod length. In both experiments, perceived grip position was a function of the rod's products of inertia and perceived partial rod length was a function of the moments and products. Discussion focuses on the specificity of exteroception and exproprioception to Iij.

Adult↗

PubMed1995

The detuning factor in the dynamics of interlimb rhythmic coordination.

Dynamical models of two coupled biological oscillators interpret the detuning term as an arithmetic difference between the uncoupled frequencies, delta omega = (omega 1-omega 2). This delta omega interpretation of detuning was addressed in four experiments in which human subjects oscillated pendulums in their right and left hands in 1:1 frequency locking in antiphase (Experiments 1-3) or inphase (Experiment 4). Differences between the uncoupled frequencies were manipulated through differences in the equivalent simple pendulum lengths, and the effects of this manipulation on the detuning of relative phase from pi or O and the standard deviation of relative phase SD phi were measured. In Experiment 1, the same values of omega i were satisfied by several different physical configurations. The experiment confirmed that the detuning term is related strictly to the uncoupled frequencies rather than to other physical characteristics of the oscillators. Experiments 2, 3 and 4 showed, however, that the particular dependency of fixed point drift and SD phi on delta omega depends on the particulars of omega 1 and omega 2. With variations in delta omega brought about by different omega 1 and omega 2 that always formed a constant ratio, fixed point drift related inversely to delta omega, and SD phi varied with delta omega in ways that depended on the magnitude of the constant ratio. These outcomes do not conform to expectations from models of coordination dynamics that interpret detuning as (omega 1-omega 2).

Adult↗

PubMed1995

Linear and nonlinear stiffness and friction in biological rhythmic movements.

Biological rhythmic movements can be viewed as instances of self-sustained oscillators. Auto-oscillatory phenomena must involve a nonlinear friction function, and usually involve a nonlinear elastic function. With respect to rhythmic movements, the question is: What kinds of nonlinear friction and elastic functions are involved? The nonlinear friction functions of the kind identified by Rayleigh (involving terms such as theta3) and van der Pol (involving terms such as theta2theta), and the nonlinear elastic functions identified by Duffing (involving terms such as theta3), constitute elementary nonlinear components for the assembling of self-sustained oscillators, Recently, additional elementary nonlinear friction and stiffness functions expressed, respectively, through terms such as theta2theta3 and thetatheta2, and a methodology for evaluating the contribution of the elementary components to any given cyclic activity have been identified. The methodology uses a quantification of the continuous deviation of oscillatory motion from ideal (harmonic) motion. Multiple regression of this quantity on the elementary linear and nonlinear terms reveals the individual contribution of each term to the oscillator's non-harmonic behavior. In the present article the methodology was applied to the data from three experiments in which human subjects produced pendular rhythmic movements under manipulations of rotational inertia (experiment 1), rotational inertia and frequency (experiment 2), and rotational inertia and amplitude (experiment 3). The analysis revealed that the pendular oscillators assembled in the three experiments were compositionally rich, braiding linear and nonlinear friction and elastic functions in a manner that depended on the nature of the task.

Adult↗

PubMed1995

Frequency detuning of the phase entrainment dynamics of visually coupled rhythmic movements.

An order parameter equation for correlated limb movements was applied to rhythmic coordination between the limbs of two people. The interlimb coordination was established and maintained through vision. Manipulations of frequency competition, coupled frequency, and intended mode (in-phase or anti-phase) produced equilibria and fluctuations in relative phase predicted by the order parameter equation and confirmed originally in within-person coordination. It was concluded that there is an elementary coordination dynamics governing the rhythmic coordination between organisms as well as between components of a single organism.

Adult↗

PubMed1995

Models of interlimb coordination--equilibria, local analyses, and spectral patterning: comment on Fuchs and Kelso (1994).

This article is a comment on A. Fuchs and J. A. S. Kelso's (1994) theoretical note on models of interlimb coordination. The generality of the order parameter equation derived by H. Haken, J. A. S. Kelso, and H. Bunz (HKB; 1985) for correlated limb movements is underscored through the correct and nonintuitive predictions it makes about steady state behavior. Local and global dynamical models are contrasted, and experimental situations in which local models are pragmatic alternatives to global models, like the HKB equation, are described. Questions are raised about the basis for interpreting detuning in HKB as a simple frequency difference and about the ability of the system of coupled nonlinear oscillators proposed by A. Fuchs and J. A. S. Kelso (1994) to model fully the experimental findings on the spectrum of relative phase.

Extremities↗

PubMed1995

The inertia tensor as a basis for the perception of limb orientation.

The ability of humans to perceive the spatial orientation of an occluded arm was investigated. It was hypothesized that this ability is tied to the arm's inertial eigenvectors, invariant mechanical parameters corresponding to a limb's axes of rotational symmetry. By breaking the coincidence between the eigenvectors of the arm and its longitudinal axis, 3 experiments were directed at the possibility that the perceived orientation of an occluded arm would vary as a function of the eigenvectors. Overall, the angles in which the arm was positioned were affected by the direction in which the eigenvectors of the limb were oriented by small appended masses. Discussion focused on the importance of physical invariants for proprioception.

Adult↗