Symmetry and order parameter dynamics of the human odometer.

Bipedal gaits have been classified on the basis of the group symmetry of the minimal network of identical differential equations (alias cells) required to model them. Primary bipedal gaits (e.g., walk, run) are characterized by dihedral symmetry, whereas secondary bipedal gaits (e.g., gallop-walk, gallop- run) are characterized by a lower, cyclic symmetry. This fact has been used in tests of human odometry (e.g., Turvey et al. in P Roy Soc Lond B Biol 276:4309-4314, 2009, J Exp Psychol Hum Percept Perform 38:1014-1025, 2012). Results suggest that when distance is measured and reported by gaits from the same symmetry class, primary and secondary gaits are comparable. Switching symmetry classes at report compresses (primary to secondary) or inflates (secondary to primary) measured distance, with the compression and inflation equal in magnitude. The present research (a) extends these findings from overground locomotion to treadmill locomotion and (b) assesses a dynamics of sequentially coupled measure and report phases, with relative velocity as an order parameter, or equilibrium state, and difference in symmetry class as an imperfection parameter, or detuning, of those dynamics. The results suggest that the symmetries and dynamics of distance measurement by the human odometer are the same whether the odometer is in motion relative to a stationary ground or stationary relative to a moving ground.

Laterality of quiet standing in old and young.

"Quiet standing" is standing without intended movement. To the naked eye, a person "quiet standing" on a rigid surface of support is stationary. In the laboratory quiet standing is indexed by behavior (at the millimeter scale) of the center of pressure (COP), the point location of the vertical ground reaction force vector (GRF). We asked whether quiet standing is lateralized and whether the COP dynamics of the right and left legs differ. In answer, we reexamined a previous quiet standing experiment (Kinsella-Shaw et al. in J Mot Behav 38:251-264, 2006) that used dual, side-by-side, force plates to investigate effects of age and embedding environment. All participants, old (M age = 72.2 ± 4.90 years) and young (M age = 22.8 ± 0.83 years), were right handed and right footed. Cross-recurrence quantification of the anterior-posterior and mediolateral coordinates of each COP revealed that, independent of age, and with no right GRF bias, right-leg coordination was (1) more dynamically stable and less noisy than left-leg coordination and (2) more responsive to changes in degree of visible structure. The results are considered in the context of theories of laterality inclusive of lateralized differences in postural dynamics.

Do phonological constraints on the spoken word affect visual lexical decision?

Reading a word may involve the spoken language in two ways: in the conversion of letters to phonemes according to the conventions of the language's writing system and the assimilation of phonemes according to the language's constraints on speaking. If so, then words that require assimilation when uttered would require a change in the phonemes produced by grapheme-phoneme conversion when read. In two experiments, each involving 40 fluent readers, we compared visual lexical decision on Korean orthographic forms that would require such a change (C stimuli) or not (NC stimuli). We found that NC words were accepted faster than C words, and C nonwords were rejected faster than NC nonwords. The results suggest that phoneme-to-phoneme transformations involved in uttering a word may also be involved in visually identifying the word.

On Strong Anticipation.

We examine Dubois's (2003) distinction between weak anticipation and strong anticipation. Anticipation is weak if it arises from a model of the system via internal simulations. Anticipation is strong if it arises from the system itself via lawful regularities embedded in the system's ordinary mode of functioning. The assumption of weak anticipation dominates cognitive science and neuroscience and in particular the study of perception and action. The assumption of strong anticipation, however, seems to be required by anticipation's ubiquity. It is, for example, characteristic of homeostatic processes at the level of the organism, organs, and cells. We develop the formal distinction between strong and weak anticipation by elaboration of anticipating synchronization, a phenomenon arising from time delays in appropriately coupled dynamical systems. The elaboration is conducted in respect to (a) strictly physical systems, (b) the defining features of circadian rhythms, often viewed as paradigmatic of biological behavior based in internal models, (c) Pavlovian learning, and (d) forward models in motor control. We identify the common thread of strongly anticipatory systems and argue for its significance in furthering understanding of notions such as "internal", "model" and "prediction".

Diabetes and postural stability: review and hypotheses.

Among the complications associated with diabetes mellitus is postural control. The authors reviewed 28 studies in the literature that focused on the magnitudes of postural sway that people with and without diabetes exhibit. The general observation is that postural sway is greater for people with diabetes, especially if their condition includes neuropathy. Peripheral sensory neuropathy seems to be the primary factor, but the available evidence does not rule out diabetes per se, other neuropathies (central, autonomic, motor), or an inability to exploit fully optical and inertial information about posture. The authors' review raises the issue of foot disorders and the possibility of increased sway as a useful adaptation; it also calls for better neuropathy assessments, postural tasks, and measures.

Steady-state stress at one hand magnifies the amplitude, stiffness, and non-linearity of oscillatory behavior at the other hand.

Stress at one body segment can influence rhythmic movements of non-neighboring body segments. The nervous, circulatory, and fascia (connective tissue) systems are potential mediators of such remote effects. Assessing them begins with a detailed description of the remote effects. Precisely, how do the rhythmic movements change? In our experiment with seven participants, left-hand oscillations of held pendulums at self-selected frequencies were examined as a function of right-hand tonic forces of 0, 10 or 20% of the maximum voluntary contraction. We evaluated the effect of the right hand's tonic force on the amplitude and frequency, and the stiffness and friction functions of the left hand's oscillations. Our results suggest that (a) amplitude and stiffness (both linear and non-linear) increased with tonic force but frequency and friction (both linear and non-linear) did not, and (b) the stiffness increases due to right hand 10 and 20% stress were indifferent to the initial (0%) left-hand stiffness values. Discussion took note of how the nervous system and architectural features of the body (e.g., its network of connective tissue) may produce such effects.

Haptic selective attention by foot and by hand.

Nonvisual perceptions of a wielded object's spatial properties are based on the quantities expressing the object's mass distribution, quantities that are invariant during the wielding. The mechanoreceptors underlying the kind of haptic perception involved in wielding - referred to as effortful, kinesthetic, or dynamic touch - are those embedded in the muscles, tendons, and ligaments. The present experiment's focus was the selectivity of this muscle-based form of haptic perception. For an occluded rod grasped by the hand at some intermediate position along its length, participants can attend to and report selectively the rod's full length, its partial lengths (fore or aft of the hand), and the position of the grip. The present experiment evaluated whether participants could similarly attend selectively when wielding by foot. For a given rod attached to and wielded by foot or attached to (i.e. grasped) and wielded by hand, participants reported (by magnitude production) the rod's whole length or fractional length leftward of the point of attachment. On measures of mean perceived length, accuracy, and reliability, the degree of differentiation of partial from full extent achieved by means of the foot matched that achieved by means of the hand. Despite their neural, anatomical, and experiential differences, the lower and upper limbs seem to abide by the same principles of selective muscle-based perception and seem to express this perceptual function with equal facility.

Action and perception at the level of synergies.

Meeting the challenge of assembling coherent organizations of very many muscles characterizes a functional level of biological movement systems referred to as the level of muscular-articular links or synergies. The present article examines the issues confronting the forming, regulating, and ordering of synergies and the hypothesized principles, both classical and contemporary, which resolve them. A primary goal of the article is to highlight the abstractness of the concepts and tools required to understand the level's action-perception competence. Coverage is given to symmetry groups, task space, order parameters, metastability, biotensegrity, allometric scaling, and impredicative definitions.

Peripheral neuropathy and object length perception by effortful (dynamic) touch: a case study.

The spatial extents of hand-held objects can be perceived nonvisually by wielding them. This ability of effortful or dynamic touch to exploit the mass moments of an object to perceive its length was evaluated with a 40-years old right-handed woman with surgically treated Arnold-Chiari Type 1 Malformation and cervical syrinx. At the time of the experiment she presented with loss of discriminative touch in the left arm but no comparable sensory deficits in the right arm or the lower extremities. She could neither identify objects in her left hand nor tell that they were in the hand while manipulating them. She could, however, grasp an object tightly and wield it on request. In the experiment she wielded weighted rods of 45, 60, and 80cm length about the wrist. There were two main results. First, her nonvisual perception of rod length by the insensate left arm scaled systematically with rod moment of inertia. The scaling matched that of the intact right arm and the nondominant arm of haptically unimpaired controls tested with rods of similar dimensions. Second, her right arm was superior in accuracy and reliability than her insensate left arm and was equal to or better than the dominant arm of the control group on key measures of nonvisual length perception. The first result was evaluated in respect to the notions of numb touch and differences in the neural bases of discriminative and effortful touch. The second result was discussed in terms of contralateral cortical enhancement by deafferentation.

Environmental coupling modulates the attractors of rhythmic coordination.

A simple instance of coupling behavior to the environment is oscillating the hands in pace with metronome beats. This environmental coupling can be weaker (1 beat per cycle) or stronger (2 beats per cycle). The authors examined whether strength of environmental coupling enhanced the stability of in-phase bimanual coordination. Detuning by manipulanda that produced different left and right eigenfrequencies shifted the relative phase angle from 0 degrees, with the size of the shift larger for higher movement frequencies. Stronger environmental coupling was found to decrease this relative-phase shift, with accompanying increase and reduction, respectively, in recurrence quantification measures related to coordination stability and coordination noise. Stronger environmental coupling also increased oscillation amplitude. Results are considered from the perspective of parametric stabilization.

Dual-task influences on retrieval from semantic memory and coordination dynamics.

Bimanual 1:1 rhythmic coordination was performed while retrieving words from a specified category. The effects of divided attention (DA) on coordination were indexed by changes in mean relative phase and recurrence measures of shared activity between the two limbs. Effects of DA on memory were indexed by deficits in exemplars retrieved relative to the baseline. Shifts in relative phase were found, accompanied by a recall deficit for DA during the retrieval task. DA also reduced the degree of shared activity between left and right rhythmic motions. Our discussion focuses on DA-induced parameter changes in retrieval and coordination dynamics, as well as on the hypothesis that stability is the general factor mediating dual-task performance.

The motor theory of speech perception reviewed.

More than 50 years after the appearance of the motor theory of speech perception, it is timely to evaluate its three main claims that (1) speech processing is special, (2) perceiving speech is perceiving gestures, and (3) the motor system is recruited for perceiving speech. We argue that to the extent that it can be evaluated, the first claim is likely false. As for the second claim, we review findings that support it and argue that although each of these findings may be explained by alternative accounts, the claim provides a single coherent account. As for the third claim, we review findings in the literature that support it at different levels of generality and argue that the claim anticipated a theme that has become widespread in cognitive science.

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.

Hemispheric asymmetries in phonological processing.

In Serbo-Croat, lexical decision to phonologically bivalent letter strings is slowed relative to their phonologically unique counterparts. This feature was exploited in order to assess the linguistic capacity of the two hemispheres. Lexical decision to laterally presented words and pseudowords revealed a right visual field advantage for both males and females in words and pseudowords. But the demands of phonological processing were not met in the same way by the two hemispheres, the two hemispheres did not respond in the same way in the two sexes, and the pattern of these differences was opposite for words and pseudowords.

Maintenance tendency in co-ordinated rhythmic movements: relative fluctuations and phase.

Evidence from the oscillatory behavior of fish fins and the crayfish swimmeret system suggests that local rhythmic-pattern generators preserve their characteristic properties over the various locomotory co-ordinations in which they participate. This maintenance tendency, as von Holst termed it, was investigated in an experiment in which human subjects swung, through motions at the wrists, hand-held pendulums of variable mass and length. In the experiment (comprising six sessions over 21 months with the same three subjects) the context for the maintenance tendency was steady-state absolute co-ordination: two rhythmic units oscillating at a single, common period and at a bounded phase relation. The experimental methodology permitted systematic control of (a) the characteristic periods of the individual rhythmic units and (b) the deviations from these periods. Relative fluctuations in periodic timing and amplitude were least when a rhythmic unit's period in absolute co-ordination approximated its characteristic period and increased with departures from the characteristic period. Rates of increase in timing fluctuations were approximately the same for deviations on either side of the characteristic period; the rate of increase in spacing fluctuations was substantially greater for the range in which periods were less than the characteristic period. The phase relation between two co-ordinated rhythmic movement units in absolute co-ordination depended on the difference between their characteristic periods. The intended phase relation of 180 degrees was attained only when the characteristic periods were identical. When the characteristic periods differed, the departure from 180 degrees increased systematically with the difference. The fluctuation results are discussed in terms of the relation between relaxation and harmonic dynamics in producing rhythmic movements, with particular emphasis on the harmonic tuning of relaxation oscillations. The phase results are discussed in terms of whether or not the very many stable phase relations in absolute co-ordination are reflective of the nervous system or of differences in response latencies in left and right muscle systems induced by different degrees of inertial compensation.

Eigenvalues of the inertia tensor and exteroception by the "muscular sense".

Muscle spindles and Golgi tendon organs constitute the receptor foundation to the "muscle sense." Muscle sensitivity has long been assumed relevant to the non-visual perception of the positions and motions of the body's segments and of the properties of hand-held objects. Dynamic touch is the label given to the particular kind of tactile exteroperception that involves a non-spatial input from muscles and tendons. When a hand-held object is wielded, hefted, carried and so on, the hand movements, together with the physical properties of the object, produce torques and angular motions that change in time with the movement. There is, however, an unchanging quantity that relates the variable torques and angular motions, namely, the object's inertia for rotation about a fixed point in the wrist. Our research revealed that the non-visual perception of the length of a wielded object by dynamic touch is a function of muscular sensitivity to the principal moments or eigenvalues of the inertia tensor. Across four experiments, variations in object length were accompanied by variations in width, spatial and material heterogeneity, the relation of the tensorial components to mass, and geometric shape. Subjects had no foreknowledge of the variations in object dimensions. Perceived lengths of occluded objects were reported by adjusting a visible marker so that its position corresponded to the position of the felt end of the object. In each experiment, perceived length was closely related to actual length and uniquely constrained by the major and minor eigenvalues of the inertia tensor. The present results, in conjunction with previous research, suggest that the inertia tensor provides the domains for two sets of functions realized by the "muscular sense," one consisting of the principal moments of inertia or eigenvalues, which map on to perceived object magnitudes (e.g. length, weight), and one consisting of the principal directions or eigenvectors, which map on to perceived relations between hand and object (e.g. position of grasp). The significance of information-perception specificity over cognitive mechanisms is underlined and perspectives on dynamic touch and its underlying muscular sensitivity, including a general tensorial analysis, are discussed.

'Clock' and 'motor' components in absolute coordination of rhythmic movements.

Human subjects swung, through motions at the two wrists, hand-held pendulums of variable mass and length. Within a pair, the two pendulums could be of the same or different magnitude. The subjects were required to produce a coordinated state in which the two rhythmic units oscillated at a single common period. Fifty-four conditions of absolute coordination, that is, 54 different pairs of wrist-pendulum systems, were investigated for each of three subjects in the course of six sessions. Each condition of absolute coordination was conducted in the out of phase mode and at the single most comfortable period. The period variances of the right and left systems in the 162 instances of absolute coordination were analysed according to a method that assumes that a timekeeper function and a motor implementation function contribute independently to the variance in the periodic timing of a rhythmic movement. The major findings were that in absolute coordination: (a) a system's 'motor' variance, but not its 'clock' variance, depended on the deviation of the period of absolute coordination tau from the system's characteristic period; (b) right and left 'clock' variances were related and (c) neither the 'motor' variances nor the 'clock' variances were affected by deviations in the mean phase relation from 180 degrees. The results were discussed in terms of their implications for interpreting von Holst's notions of maintenance tendency and magnetic effect and, more generally, the neural and dynamical basis of absolute coordination.

Affordance, proper function, and the physical basis of perceived heaviness.

The physical basis of perceived heaviness requires consideration of the haptic perceptual system's role in controlling actions (the system's proper function) and the relation of an object's inertial properties to properties of the human movement system (the object's affordance). We show that the mass of a wielded object and particular scalar variables calculated from the object's inertia tensor combine linearly in determining perceived heaviness. The tensor-derived scalars reflect the symmetry and volume of the corresponding inertia ellipsoid. These measures bear directly on the object's wieldability, that is, on the patterning and level of muscular forces required to move the object in a controlled fashion.

Does visual word identification involve a sub-phonemic level?

The phonological codes activated in visual word recognition can be thought of minimally as strings of discrete and unstructured phoneme-like units. We asked whether these codes might additionally express a letter string's phonological form at a featural or gestural level. Specifically, we asked whether the priming of a word (e.g. sea, film, basic) by a rhyming non-word would depend on the non-word's phonemic-feature similarity to the word. The question was asked within a mask--prime--target--mask sequence with both brief (57 ms in Experiments 1 and 2) and long (486 ms in Experiment 1) prime durations. Non-word primes that differed from their targets by a single phonemic feature (initial voicing as in ZEA, VILM, PASIC) led to faster target lexical decisions than non-word primes that differed by more than a single phonemic feature (e.g. VEA, JILM, SASIC). Visual word recognition seems to involve a sub-phonemic level of processing.

When nonwords activate semantics better than words.

We conducted a strong test of the idea that visual word processing and the activation of a printed word's meaning proceeds at a rate scaled by the temporal evolution of a unique and stable phonological code. Using the lexical decision task, and readers fluent in the two alphabets of Serbo-Croatian, we compared the priming of a target word such as automat by the semantically related word ROBOT and by the nonword ROBOT. Whereas the Serbo-Croatian word ROBOT can support two phonological codes, /robot/ and /rovot/, the nonword ROBOT composed by illegally mixing Roman and Cyrillic letters can support only the phonological code /robot/, that corresponding to the word whose meaning is related to automat's. At a prime duration of 35 ms, the lexical decision on the target automat was facilitated by ROBOT but not by ROBOT. At a prime duration of 125 ms, the word ROBOT was the more effective prime. One consequence of phonology's leading role in visual word recognition is that a nonword can sometimes activate a given word's meaning better than the word itself.