Biomedical subjects

J A Kelso

Publications and source records attributed to J A Kelso.

At least 37 records · Page 2Linked to original sources

PubMed1997

Temporal patterning in an auditory illusion: the verbal transformation effect.

When the same syllable is presented repeatedly to a human subject, it undergoes perceptual changes known as verbal transformations. However, the dynamics of such perceptual changes is poorly understood. In the present work we show that the main organization of the perceptual transitions is into pairs. This pairwise coupling is pronounced in the frequency of switching to pair members, but not in their dwell times (the time spent perceiving a given phonemic form before switching to another form). We show that the paircoupled transforms of perception have a faster and more stable dynamic than the nonpaircoupled transforms. We also demonstrate that the pairwise coupling is stronger than would be expected from random arrangement of small numbers of transforms. These characteristic patterns of verbal transforms have been predicted by a mathematical model, first proposed as a model of perceptual alternations of ambiguous visual figures.

Adult↗

PubMed1997

A synergetic model for the verbal transformation effect.

We describe a nonlinear dynamical model based on synergetics for the auditory perceptual illusion known as the verbal transformation effect. The model is an extension of a synergetic model of perceptual oscillations of visual ambiguous figures. The main extension is connected to the number of reported alternative phonemic structures, which is typically much greater than the two or three alternatives usually reported in experiments with visual ambiguous figures. The properties of the model, which are derived using basic psychophysical principles, are presented and evaluated on the basis of the fit to earlier empirical work. It will be shown that there is very good agreement between the empirically observed properties of the verbal transformation effect and the properties detected by the model.

Attention↗

PubMed1997

Coordination dynamics of learning and transfer: collective and component levels.

The dynamics of learning a new coordinated behavior was examined by requiring participants to perform a visually specified phase relationship between the hands. Results showed that learning may involve qualitative or quantitative alterations in the layout of the coordination dynamics depending on whether such dynamics are bistable or multistable before exposure to the learning task. In both cases, the process stabilized the to-be-learned behavior and its symmetry partner, even though the latter had not actually been practiced. Kinematic analyses of hand motion showed that previously existing coordination tendencies were exploited during learning in order to match visual requirements. These findings and the concepts presented here provide a framework for understanding how learning occurs in the context of previous experience and allow individual differences in learning to be tackled explicitly.

Adult↗

PubMed1997

Fractal timing of verbal transforms.

The paper deals with the timing pattern of perceptual change elicited by multiple repetitions of a syllable (the verbal-transformation effect). We show that the distribution of the dwell time, the time spent perceiving a given phonemic form before switching to another form, obeys a power law with an exponent valued between 1 and 2. This result is robust, occurring for meaningless syllables and for English words of different initial phonemic salience. Experiment 2 demonstrates that subjects are aware of the temporal dynamics of perceptual change. On the basis of these results, it is argued that within this paradigm the notion of a mean dwell time is ill defined and there is apparently no characteristic time scale for perceptual change.

Adolescent↗

PubMed1996

Extending the HKB model of coordinated movement to oscillators with different eigenfrequencies.

We study the dynamics of a system of coupled nonlinear oscillators that has been used to model coordinated human movement behavior. In contrast to earlier work we examine the case where the two component oscillators have different eigenfrequencies. Problems related to the decomposition of a time series (from an experiment) into amplitude and phase are discussed. We show that oscillations at multiples of the main frequency of the oscillator system may occur in the phase and amplitude due to the choice of a coordinate system and how these oscillations can be eliminated. We derive an explicit equation for the dynamics of the relative phase of the oscillator system in phase space that enables a direct comparison between theory and experiment.

Cybernetics↗

PubMed1996

Coordination dynamics of trajectory formation.

The present study aims to understand the neurally based coordination dynamics (multistability, loss of stability, transitions, etc.) of trajectory formation in a simple task. Six subjects produced two spatial patterns of coordination in the xy plane by alternating the abduction-adduction and flexion-extension motions of their right index finger. Each pattern was characterized by a unique temporal ratio between the x and y directions of motion: (1) a figure zero, a 1:1 temporal pattern; and (2) a figure eight, a 2:1 temporal pattern. The patterns were produced rhythmically and movement frequency was scaled across ten frequency plateaus, with ten cycles of motion per step. As movement frequency increased, switching from a figure eight to a figure zero was observed at critical cycling frequencies. The switch from pattern (2) to pattern (1) was identified in the spatial trajectory and power spectra of x(t) and y(t). En route to the transition, enhancement of fluctuations was observed in the Fourier amplitudes of x(t) and y(t), specifically at f0 (the metronome frequency) and 2f0 (the first harmonic of f0). Interestingly, there was no difference in the spatial variability of the two patterns. Overall, the data demonstrate that spatial patterns of coordination can be characterized in terms of the temporal relationship between the spatial components of the trajectory itself. We discuss the experimental findings in relation to other end-point planning and multijoint control strategies, as well as the much more general problem of temporal synchronization in many interlimb and intralimb coordination tasks.

Adult↗

PubMed1995

Frequency and phase characteristics of slow cortical potentials preceding bimanual coordination.

The aim of the present study was to derive quantities which relate behavioral and neurophysiological levels of observation during a bimanual coordination task. We recorded the scalp electroencephalographic (EEG) signal preceding a sequence of 4 bimanual finger flexions of varying response rates in 12 subjects. A slow negative-going Bereitschaftspotential (BP) displayed larger mean amplitudes and earlier onset times for the faster required response rates. The amplitude of the BP was also larger for electrode locations contralateral to the side initiating the behavioral response. A Fourier transform showed two predominant frequencies (0.5 and 2.0 Hz) to be amplitude modulated as a function of the required response rate in addition to increased power on the contralateral side of the finger initiating the response. A measure of the phase relationship between the left (C3) and right (C4) hemispheres of the fronto-central cortex at each of these spectral frequencies was calculated as well as the variance in this measure and found to correspond closely to the variance in inter-response times derived from the subjects' movements. These findings indicate that changes in the stability and rate of a patterned movement are generally preceded by similar changes in the stability and amplitude of components observed on the neurophysiological level.

Acoustic Stimulation↗

PubMed1995

Manipulating symmetry in the coordination dynamics of human movement.

J. A. S. Kelso and J. J. Jeka (1992) demonstrated that symmetry is a useful conceptual tool to distinguish the coordination between components with similar versus different anatomical properties. The present experiments studied human arm-leg patterns to test whether their coordinative asymmetry was changed by manipulating the inertial properties of a single limb. The results showed that (a) consistent with model predictions, adding weight to the arm or the leg minimized or enhanced coordinative asymmetry, respectively and (b) the response to a perturbation slowed as movement frequency increased but in a fashion that reflected the underlying coordinative asymmetry. The observed coordinative effects suggest the influence of neural phase relationships and emphasize that symmetry plays an important role in understanding coordination in systems in which control cannot be traced unequivocally to a single end-effector or a neurophysiological substrate.

Adolescent↗

PubMed1995

Evaluation of a dynamical model of speech perception.

Previous work (Tuller, Case, Ding, & Kelso, 1994) has revealed signature properties of nonlinear dynamical systems in how people categorize speech sounds. The data were modeled by using a two-well potential function that deformed with stimulus properties and was sensitive to context. Here we evaluate one prediction of the model--namely, that the rate of change of the potential's slope should increase when the category is repeatedly perceived. Judged goodness of category membership was used as an index of the slope of the potential. Stimuli from a "say"-"stay" continuum were presented with gap duration changing sequentially throughout the range from 0 to 76 to 0 msec, or from 76 to 0 to 76 msec. Subjects identified each token as either "say" or "stay" and rated how good an exemplar it was of the identified category. As predicted, the same physical stimulus presented at the end of a sequence was judged a better exemplar of the category than was the identical stimulus presented at the beginning of the sequence. In contrast, stimuli presented twice near the middle of a sequence with few (or no) stimuli between them, as well as stimuli presented with an intervening random set, showed no such differences. These results confirm the hypothesis of a context-sensitive dynamical representation underlying speech.

Humans↗

PubMed1994

A theoretical model of phase transitions in the human brain.

An experiment using a multisensor SQUID (superconducting quantum interference device) array was performed by Kelso and colleagues (1992) which combined information from three different sources: perception, motor response, and brain signals. When an acoustic stimulus frequency is changed systematically, a spontaneous transition in coordination occurs at a critical frequency in both motor behavior and brain signals. Qualitatively analogous transitions are known for physical and biological systems such as changes in the coordination of human hand movements (Kelso 1981, 1984). In this paper we develop a theoretical model based on methods from the interdisciplinary field of synergetics (Haken 1983, 1987) and nonlinear oscillator theory that reproduces the main experimental features very well and suggests a formulation of a fundamental biophysical coupling.

Acoustic Stimulation↗

PubMed1994

The nonlinear dynamics of speech categorization.

Little is known about the processes underlying the nonlinear relationship between acoustics and speech perception. In Experiment 1, we explored the effects of systematic variation of a single acoustic parameter (silent gap duration between a natural utterance of s and a synthetic vowel ay) on judgements of speech category. The resulting shifts in category boundary between say and stay showed rich dynamics, including hysteresis, contrast, and critical boundary effects. We propose a dynamical model to account for the observed patterns. Experiment 2 evaluated one prediction of the model, that changing the relative stability of the two percepts allows categorical switching. In agreement with the model; an increase in the number of stimulus repetitions maximized the frequency of judgments of category change near the boundary. Thus, a dynamical approach affords the rudiments for a theory of the effects of temporal context on speech categorization.

Acoustic Stimulation↗

PubMed1994

A theoretical note on models of interlimb coordination.

This article clarifies some points about models of interlimb coordination. The authors discuss in detail the predictions and extensions of the H. Haken, J.A.S. Kelso, and H. Bunz (1985) model and compare these to a truncated version used by R.C. Schmidt and colleagues. It is demonstrated that procedures commonly used to fit experimental data to model parameters require the fulfillment of certain assumptions. Finally, the authors show how recent experimental findings can be modeled straightforwardly using a system of coupled nonlinear oscillators.

Extremities↗

PubMed1994

Lip-larynx coordination in speech: effects of mechanical perturbations to the lower lip.

This experiment investigates the coordination between the larynx and the lips and jaw in voiceless consonant production using an experimental paradigm where a mechanical perturbation is applied to an articulator. Three subjects received unexpected perturbations to the lower lip during the transition between the first vowel and the first stop in /i'pip/. Movements of the upper articulators (lips and jaw) were recorded using an optoelectronic technique. Laryngeal responses were monitored using transillumination; intraoral pressure and the acoustic signal were also recorded. Results showed that laryngeal abduction was delayed following lip perturbation and that the duration of the laryngeal adduction gesture was lengthened. The oral movements toward closure of two of the subjects were modified and all subjects showed modification of the oral release movements in the perturbed conditions. All subjects showed an increased movement velocity and displacement of the upper lip, lower lip, and jaw in the oral opening phase. First trial compensation, however, was not observed in two of the three subjects. The results are discussed with respect to the speech perturbation literature and the notion of coordinative structures.

Biomechanical Phenomena↗

PubMed1993

Posturally induced transitions in rhythmic multijoint limb movements.

The coordination dynamics (e.g., stability, loss of stability, switching) of multijoint arm movements are studied as a function of forearm rotation. Rhythmical coordination of flexion and extension of the right elbow and wrist was examined under the following conditions: (1) forearm supine (forearm angle 0 degrees), simultaneous coordination of wrist flexion/elbow flexion and wrist extension/elbow extension (termed in-phase); and (2) forearm prone (forearm angle 160 degrees), simultaneous coordination of wrist flexion/elbow extension and wrist extension/elbow flexion (termed anti-phase). Starting in either pattern, subjects rotated the forearm in nine 20 degrees steps, producing 15 cycles of motion per step at a frequency of 1.25 Hz. Spontaneous transitions from pattern 1 to pattern 2 and from pattern 2 to pattern 1 were observed at a critical forearm angle. The critical angle depended on the direction of forearm rotational change, thus revealing the hysteretic nature of the switching process. En route to the transition, regardless of direction of forearm rotation, enhancement of phase fluctuations and an increase in perturbation response times (critical slowing down) were observed in the relative phasing between the joints. Such observations support loss of stability as a central, self-organizing process underlying coordinative change. Neurophysiological mechanisms supporting multijoint coordinative dynamics are discussed.

Adolescent↗

PubMed1993

Pattern switching in human multilimb coordination dynamics.

A relative phase model of four coupled oscillators is used to interpret experiments on the coordination between rhythmically moving human limbs. The pairwise coupling functions in the model are motivated by experiments on two-limb coordination. Stable patterns of coordination between the limbs are represented by fixed points in relative phase coordinates. Four invariant circles exist in the model, each containing two patterns of coordination seen experimentally. The direction of switches between two four-limb patterns on the same circle can be understood in terms of two-limb coordination. Transitions between patterns in the human four-limb system are theoretically interpreted as bifurcations in a nonlinear dynamical system.

Animals↗

PubMed1993

Bistability and hysteresis in the organization of apparent motion patterns.

In a paradigm for which 2 distinct patterns are perceived for the same stimulus, perceptual hysteresis (persistence of a percept despite parameter change to values favoring the alternative pattern) and temporal stability (persistence despite intrinsic propensities toward spontaneous change) are interdependent. Greater persistence during parameter change reduces temporal stability, slowing the rate of parameter change reduces hysteresis by increasing opportunity for spontaneous change, and increasing temporal stability (by enlarging the stimulus) increases hysteresis. Hysteresis results in the perception of parametrically disfavored patterns; a parameter can influence a percept without specifying it. The visual system thus exhibits time-dependent behavior analogous to dynamical behavior observed in other systems, both physical and biological, for which there is competition among alternative patterns that vary in relative stability.

Adult↗

PubMed1992

Evolution of behavioral attractors with learning: nonequilibrium phase transitions.

Learning a bimanual coordination task (synchronization to a visually specified phasing relation) was studied as a dynamical process over 5 days of practicing a required phasing pattern. Systematic probes of the attractor layout of the 5 Ss' coordination dynamics (expressed through a collective variable, relative phase) were conducted before, during, and after practice. Depending on the relationship between the initial coordination dynamics (so-called intrinsic dynamics) and the pattern to be learned (termed behavioral information, which acts as an attractor of the coordination dynamics toward the required phasing), qualitative changes in the phase diagram occurred with learning, accompanied by quantitative evidence for loss of stability (phase transitions). Such effects persisted beyond 1 week. The nature of change due to learning (e.g., abrupt vs. gradual) is shown to arise from the cooperative or competitive interplay between behavioral information and the intrinsic dynamics.

Adult↗

PubMed1992

Symmetry breaking dynamics of human multilimb coordination.

The dynamics of pattern formation and change are studied in a complex multicomponent system, specifically the arms and legs of human Ss. Among the novel features observed are differential stability of coordinative modes produced by limbs moving in the same versus different directions (Experiment 1); transitions between coordinative modes preceded by a slow drift in relative phase (Experiments 1 and 2); bifurcations or phase transitions from 1 four-limb pattern to another (Experiment 2); and spontaneous emergence of non-1:1-frequency- and phase-locked patterns, in addition to periods of relative coordination (Experiment 3). All observed relative phasing patterns and their dynamics (stability, loss of stability, intermittency) are shown to arise from the same underlying nonlinear dynamical structure, an important feature of which is broken symmetry.

Acceleration↗