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.     

Reaction-anticipation transitions in human perception-action patterns

We investigated the hypothesis that reaction and anticipation in human perceptual-motor performance are two coordinative modes of a single pattern-forming dynamical system, rather than separate behaviors. Subjects coordinated the onset of finger flexions with visual metronome flashes in each of three patterns: reactive, synchronized, or syncopated. The stimulus frequency was progressively increased (0.125–1.375 Hz) or decreased (1.375-0.125 Hz) in small steps (0.125 Hz) every 10 cycles. We observed qualitative transitions in both the time interval between stimulus and corresponding action (Δt) and their relative phase (ø) at critical values of the stimulus frequency, corresponding to changes from ‘reactive-to-anticipatory’ and ‘anticipatory-to-reactive’ performance. Such transitions provide evidence of a single, multifunctional system, which can be adequately described by the dynamics of collective variables characterizing the respective perception-action patterns.     

The role of proprioception in the perception and control of human movement: Toward a theoretical reassessment

The theoretical role of proprioception in the perception and control of human movement is elusive because of the obvious inability to manipulate experimentally the various receptive systems. Individuals who have had the metacarpophalangeal joint and joint capsule removed and replaced with silastic inserts afford a unique opportunity to evaluate a principal source of proprioception, namely, slowly adapting joint afferents. In a set of experiments, we show that such individuals show no deficits in finger localization following joint replacement. We take this and other complementary findings as a preliminary basis for proposing a dynamic rather than kinematic account of movement production. In addition, we provide a reconceptualization of the function of proprioceptive information in the CNS. Our arguments focus on proprioceptive inputs as tuning or modulating interneuronal pools rather than providing dimension-pecific information to the brain, as is commonly assumed.     

An Essay on Understanding the Mind

Several conjectures by A. S. Iberall on life and mind are used as a backdrop to sketch a theory of mental activity that respects both the contents of thought and the dynamics of thinking. The dynamics, in this case, refers fundamentally to animated, meaningfully coupled self-organizing processes (coordination dynamics) and exhibit multistability, switching, and, because of symmetry breaking, metastability. The interplay of 2 simultaneously acting forces underlies the metastable mind: the tendency for the coordinating elements to couple together (integration) and the tendency for the elements to express their individual autonomy (segregation). Metrics for metastability are introduced that enable these cooperative and competitive tendencies to be quantified. Whereas bistability is the basis for polarized, either/or thinking, the metastable régime—which contains neither stable nor unstable states, no states at all, in fact—gives rise to a far more fluid, complementary mode of operation in which it is possible for apparent contraries to coexist in the mind at the same time.     

The Role of Similarity Analysis in Understanding Movement

Primates have evolved separately from other mammals since the late Cretaceous, and during this time the two major extant primate groups, prosimians (lorises, lemurs, and tarsiers) and anthropoids (monkeys, apes, and humans) arose. Concurrently, structures within the central nervous system acquired primate characteristics. Not all of the uniquely primate features have been identified in the brain, but several are well known. The pyramidal system, the best studied motor system, shows a distinct primate pattern in its terminal connections in the spinal cord. Other descending systems are less well known, but primate specializations in the vestibular system and red nucleus have been observed. The primary and secondary motor cortices are topographically separated in primates, suggesting one basis for increased complexity. Given the size of the brain, structures in the basal ganglia are relatively enlarged in primates as compared with other mammals, whereas the cerebellum has the same relative size.     

Patterns of Human Interlimb Coordination Emerge from the Properties of Non-Linear,Limit Cycle Oscillatory Processes

The present article represents an initial attempt to offer a principled solution to a fundamental problem of movement identified by Bernstein (1967), namely, how the degrees of freedom of the motor system are regulated. Conventional views of movement control focus on motor programs or closed-loop devices and have little or nothing to say on this matter. As an appropriate conceptual framework we offer Iberall and his colleagues’ physical theory of homeokinetics first elaborated for movement by Kugler, Kelso, and Turvey (1980). Homeokinetic theory characterizes biological systems as ensembles of non-linear, limit cycle oscillatory processes coupled and mutually entrained at all levels of organization. Patterns of interlimb coordination may be predicted from the properties of non-linear, limit cycle oscillators. In a set of experiments and formal demonstrations we show that cyclical, two-handed movements maintain fixed amplitude and frequency (a stable limit cycle organization) under the following conditions: (a) when brief and constantly applied load perturbations are imposed on one hand or the other, (b) regardless of the presence or absence of fixed mechanical constraints, and (c) in the face of a range of external driving frequencies from a visual source. In addition, we observe a tight phasic relationship between the hands before and after perturbations (quantified by cross-correlation techniques), a tendency of one limb to entrain the other (mutual entrainment) and that limbs cycling at different frequencies reveal non-arbitrary, sub-harmonic relationships (small integer, subharmonic entrainment). In short, all the above patterns of interlimb coordination fall out of a non-linear oscillatory design. Discussion focuses on the compatibility of these results with past and present neurobiological work, and the theoretical insights into problems of movement offered by homeokinetic physics. Among these are, we think, the beginnings of a principled solution to the degrees of freedom problem, and the tentative claim that coordination and control are emergent consequences of dynamical interactions among non-linear, limit cycle oscillatory processes.     

The relation of self-reported competencies to aptitude test scores

The scales of the Self-Directed Search were correlated with the scales of the Armed Forces Vocational Aptitude Battery for a sample of 192 high school girls. The two devices have small to moderate correlations that indicate that self-reported abilities and competencies have some concurrent validity.     

On the space-time structure of human interlimb co-ordination

In three experiments we show, using behavioural measures of movement outcome, as well as movement trajectory information and resultant kinematic profiles, that there is a strong tendency for the limbs to be co-ordinated as a unitary structure even under conditions where the movements are of disparate difficulty. Environmental constraints (an obstacle placed in the path of one limb, but not in the other) are shown to modulate the space-time behaviour of both limbs (Experiment II). Our results obtain for symmetrical (Experiment I) as well as asymmetrical movements that involve non-homologous muscle groups (Experiment III). These findings suggest that in multi-joint limb movements, the many degrees of freedom are organised to function temporarily as a single coherent unit that is uniquely specific to the task demands placed on it. For movements in general, and two-handed movements in particular, such units are revealed in a partitioning of the relevant force demands for each component (a force scaling characteristic) and a preservation of the internal “topology” of the action, as indexed by the relative timing among components. These features, as well as systematic deviations from perfect synchrony between the limbs can be rationalised by a model that assumes the limbs behave qualitatively like non-linear oscillators.     

Peer tutoring to prevent firearm play acquisition, generalization, and long-term maintenance of safety skills

Hundreds of accidental injuries and deaths to children occur annually in the United States as a result of firearm play. Behavioral skills training (BST) and in situ training have been found to be effective in teaching children the skills to use if they find a firearm, but training requires substantial time and effort. The current study examined the use of peers as tutors as a potential way to decrease the time and resources needed to teach these safety skills to youngsters. Peer trainers conducted BST and in situ training with other children. Children taught by the peer trainers acquired the safety skills and demonstrated them in naturalistic situations in which the skills were needed. Furthermore, all of the peer trainers acquired and maintained the skills. These results support the use of peer tutoring for teaching safety skills to other children.