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.

An archer's perceived form scales the "hitableness" of archery targets.

For skills that involve hitting a target, subsequent judgments of target size correlate with prior success in hitting that target. We used an archery context to examine the judgment-success relationship with varied target sizes in the absence of explicit knowledge of results. Competitive archers shot at targets 50 m away that varied in size among five diameters. Immediately after the arrow's release, its flight and landing were occluded and archers chose which of 18 miniature targets looked most like the distal target. Greater apparent size correlated with higher accuracy. In a second experiment, nonarchers merely aimed the bow (without an arrow) at varied targets. Apparent size was larger when the bow arm was stabilized than when it was not. Archery is seemingly an instance of affordance-based control: For an archer, the affordance of the target is the "hitableness" of its central regions, a property inclusive of his or her momentary, and perceptible, archery form.

Human odometry verifies the symmetry perspective on bipedal gaits.

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 gaits are characterized by dihedral symmetry, whereas secondary gaits are characterized by a lower, cyclic symmetry. This fact was used in a test of human odometry. 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. Lessons are drawn from modeling the dynamics of behaviors executed in parallel (e.g., interlimb coordination) to model the dynamics of human odometry, in which the behaviors are executed sequentially. The major observations are characterized in terms of 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 that dynamic.

Equivalence of human odometry by walk and run is indifferent to self-selected speed.

Humans and other animals can measure distances nonvisually by legged locomotion. Experiments typically employ an outbound measure (M) and an inbound report (R) phase. Previous research has found distance reproduction to be maximally accurate, when gait symmetry and speed of M and R are of like kind: Successful human odometry manifests at the level of the M-R system. In the present work, M was an experimenter-set distance produced by a blindfolded participant using a primary gait (walk, run). R was always by walk. Fast and slow versions of walk and run were adopted by participants, such that when M was fast R was slow, and vice versa. Distance was underestimated when M was slower than R and overestimated when M was faster than R. However, the pattern of participant-adopted velocities indicated that it was the instructions, not the speed as such, that yielded the pattern of results. The results are interpretable through a dynamical perspective and indicate speed is an imperfection parameter acting on the attractors of the M-R system.

Obtaining information by dynamic (effortful) touching.

Dynamic touching is effortful touching. It entails deformation of muscles and fascia and activation of the embedded mechanoreceptors, as when an object is supported and moved by the body. It is realized as exploratory activities that can vary widely in spatial and temporal extents (a momentary heft, an extended walk). Research has revealed the potential of dynamic touching for obtaining non-visual information about the body (e.g. limb orientation), attachments to the body (e.g. an object's height and width) and the relation of the body both to attachments (e.g. hand's location on a grasped object) and surrounding surfaces (e.g. places and their distances). Invariants over the exploratory activity (e.g. moments of a wielded object's mass distribution) seem to ground this 'information about'. The conception of a haptic medium as a nested tensegrity structure has been proposed to express the obtained information realized by myofascia deformation, by its invariants and transformations. The tensegrity proposal rationalizes the relative indifference of dynamic touch to the site of mechanical contact (hand, foot, torso or probe) and the overtness of exploratory activity. It also provides a framework for dynamic touching's fractal nature, and the finding that its degree of fractality may matter to its accomplishments.

Interleg coordination in quiet standing: influence of age and visual environment on noise and stability.

The authors reexamined reported effects of age, illumination, and stationary visible structure on the net center of pressure (COP) derived from dual, side-by-side force plates (J. Kinsella-Shaw, S. Harrison, C. Colon-Semenza, & M. Turvey, 2006 ) from the perspective of axial postural control. They questioned how left and right COP(x)(t), COP(y)(t), and vertically oriented ground reactive force, GRF(z)(t), coordinated during quiet standing. The Cross-recurrence Quantification (CRQ) revealed that coordination was primarily between fluctuations of similar direction, with coordination of left and right COP(y) (t) (anteroposterior fluctuations) dominant. CRQ also revealed that (a) illumination and structure affected the interlimb dynamics of older (M age = 72.2 ± 4.90 years) participants more than their younger (M age = 22.8 ± 0.83 years) counterparts, and (b) older participants exhibited greater interlimb entrainment (dynamical stability) in the presence of greater interlimb noise.

Principles of part-whole selective perception by dynamic touch extend to the torso.

The haptic subsystem of dynamic touch expresses a novel form of part-whole selective perception. When wielding a nonvisible rod grasped at some intermediate point along its length, an individual can attend to and report the length of a part of the rod (e.g., the segment forward of the hand) or the length of the whole rod. Both perceptions relate to the rod's mass moments about the point of grasp but in systematically different ways. Previous demonstrations of this part-whole selectivity have been in respect to rods grasped by hand or attached to a foot. The authors demonstrated the part-whole selectivity for nonvisible rods attached to the shoulder girdle and wielded primarily by movements of the trunk with benchmark performance provided by the same rods grasped and wielded by hand. Their results suggest that part-whole selectivity is a haptic capability general to the body.

Whole body lexical decision.

When a person standing upright raises an arm on cue, muscles of the left and right sides of the body exhibit changes prior to and specific to the responding arm. We had standing participants perform a visual lexical decision task ("is this letter string a word?"), responding yes by raising one arm and no by raising the other arm. We recorded onset of the arm movement and onset of electromyographic activity in thigh, trunk, and shoulder muscles. We observed the expected responding arm specificity and found that the onset difference favoring word decisions was evident in similar magnitude at all measurement sites, with the difference at the levels of thigh, trunk and shoulder muscles available 225, 189, and 120 ms, respectively, prior to its manifestation at the level of arm movement. We discuss including (a) whole body reaction time along with event-related potentials in determining the decision-response, brain-body temporal relation and (b) response execution along with response initiation in investigating mental chronometry.

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".

Effects of intention and learning on attention to information in dynamic touch.

The current research distinguishes two types of attention shifts: those entailed by perceptual learning and those entailed by changing intention. In perceptual learning, participants given feedback have been shown to gradually shift attention toward the optimal (i.e., specifying) information variable for the task. A shift in variable use is also expected when intention changes, because an intention to perceive some property entails attunement to information about that property. We compared the effects of feedback and intention in a dynamic (kinesthetic) touch task by representing both as changes of locus in an information space of inertial variables. Participants wielded variously sized, unseen, rectangular parallelepipeds and made length or width judgments about them. When given feedback, participants made gradual attentional shifts toward the optimal variable, which demonstrates the education of attention. When asked to report a new property, participants made large attentional jumps to the ballpark of the optimal variable for the new property. Exploratory movements were measured on 6 participants and were found to differ as a function of intention and to change with learning.

Deterministic and stochastic postural processes: effects of task, environment, and age.

Upright standing is always environmentally embedded and typically co-occurs with another (suprapostural) activity. In the present study, the authors investigate how these facts affect postural dynamics in an experiment in which younger (M age = 20.23 years, SD = 2.02 years) and older (M age = 75.26 years, SD = 4.87 years) participants performed a task of detecting letters in text or maintaining gaze within a target while standing upright in a structured or nonstructured stationary environment. They extracted the coefficients of drift (indexing attractor strength) and diffusion (indexing noise strength) from the center of pressure (COP) time series in anteroposterior (AP) and mediolateral (ML) axes. COP standard deviation decreased with drift and increased with diffusion. The authors found that structure reduced AP diffusion for both groups and that letter detection reduced younger SDAP (primarily by diffusion decrease) and increased older SDML (primarily by drift decrease). For older and younger participants, ML drift was lower during letter detection. Further, in older letter detection, larger visual contrast sensitivity was associated with larger ML drift and smaller SDML, raising the hypotheses that ML sway helps information detection and reflects neurophysiological age.

Order parameter dynamics of body-scaled hysteresis and mode transitions in grasping behavior.

Several experimental studies have shown that human grasping behavior exhibits a transition from one-handed to two-handed grasping when to-be-grasped objects become larger and larger. The transition point depends on the relative size of objects measured in terms of human body-scales. Most strikingly, the transitions between the two different behavioral 'modes' of grasping exhibit hysteresis. That is, one-to-two hand transitions and two-to-one hand transitions occur at different relative object sizes when objects are scaled up or down in size. In our study we approach body-scaled hysteresis and mode transitions in grasping by exploiting the notion that human behavior in general results from self-organization and satisfies appropriately-defined order parameter equations. To this end, grasping transitions and grasping hysteresis are discussed from a theoretical perspective in analogy to cognitive processes defined by Haken's neural network model for pattern recognition. In doing so, issues such as the exclusivity of grasping modes, biomechanical constraints, mode-mode interactions, single subject behavior and population behavior are explored.

Load affects human odometry for travelled distance but not straight-line distance.

In a simple homing task with human participants, we disassociated the outbound distance travelled from the straight-line distance between home and target. Prior to the outbound journey, which involved a detour, participants were given one of two instructions concerning the inbound journey, which did not involve a detour: to walk the distance travelled or to walk to home. The inbound journey under each intention, made with eyes closed at a self-selected pace, was the measure of the perceived distance. We conducted two experiments that differed in whether or not the detour and target were visible during the outbound journey. In both experiments, we manipulated the load carried in the outbound journey (0% or 20% body weight) and the speed (fast or slow) of the outbound journey. The outcome of both experiments was that, indifferent to speed, participants perceived the distance travelled with load to be longer than that travelled without load, but perceived home's straight-line distance from target to be the same for both load conditions. Perceptions of travel distance and straight-line distance seem to be based on different information kinds and to refer to different animal-environment relations. In identifying neural mechanisms supportive of navigation, straight-line distance versus travelled distance may prove to be a productive distinction.

Prism adaptation of underhand throwing: rotational inertia and the primary and latent aftereffects.

The effect of prism adaptation on movement is typically reduced when movement at test (with prisms removed) is different from movement at training. Previous research [J. Fernández-Ruiz, C. Hall-Haro, R. Díaz, J. Mischner, P. Vergara, J. C. Lopez-Garcia, Learning motor synergies makes use of information on muscular load, Learning & Memory 7 (2000) 193-198] suggests, however, that some adaptation is latent and only revealed through further testing in which the movement at training is fully reinstated. Movement in their training trials was throwing overhand to a vertical target with a mass attached to the arm. The critical test trials involved the same act initially without the attached mass and then with the attached mass. In replication, we studied throwing underhand to a horizontal target with left shifting prisms and a dissociation of the throwing arm's mass and moment of inertia. The two main results were that the observed latent aftereffect (a) depended on the similarity of training and test moments of inertia, and (b) combined with the primary aftereffect to yield a condition-independent sum. Discussion focused on a parallel between prism adaptation and principles governing recall highlighted in investigations of implicit memory: whether given training (study) conditions lead to good or poor persistence of adaptation (memory performance) at test depends on the conditions at test relative to the conditions at training (study).

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.

Muscle-based perception: theory, research and implications for rehabilitation: [review] / Percepção baseada nos músculos: teoria, pesquisa e implicações na reabilitação: [revisão]

BACKGROUND: Muscle-based perception of the spatial properties of limbs constrains the patterning, timing and magnitude of muscle forces while performing motor activities. The centrality of muscle-based perception to both ordinary and skilled actions warrants attention from the rehabilitation community, since deficits in its functioning would be related to important functional limitations. In this overview, we summarize a body of research that may be used to guide the development of effective assessment tools and rehabilitation programs that are specifically directed towards such deficits. OBJECTIVES: There were four specific aims: first, to present an information-based approach to muscle-based perception that is grounded in physical laws; second to identify central principles underlying muscle-based perception that have been revealed and supported by empirical work; third, to summarize reports that have investigated whether the principles identified can be generalized to muscle-based perception in individuals with sensory-motor impairments; and fourth to provide a preliminary discussion of the potential implications of the research presented here for issues relating to rehabilitation.

INTRODUÇÃO: A percepção muscular das propriedades espaciais dos membros restringe o padrão, período e magnitude das forças exercidas durante a execução de atividades motoras. A importância central da percepção muscular, tanto para ações rotineiras quanto para ações especializadas, merece atenção da comunidade envolvida na área de reabilitação, uma vez que alterações em suas funções podem estar relacionadas a importantes limitações funcionais. Nesta revisão, os autores apresentam um resumo da pesquisa que pode ser utilizada para guiar o desenvolvimento de ferramentas de avaliação eficazes bem como programas de reabilitação que sejam especificamente direcionados para estas disfunções. OBJETIVOS: Quatro pontos específicos foram incluídos: primeiro, a apresentação da abordagem com base em informações relativas à percepção muscular de acordo com as leis da física; segundo, a identificação dos princípios centrais determinantes da percepção muscular que vem sendo revelada e apoiada por trabalhos empíricos; terceiro, um resumo dos relatos que investigaram e se os princípios identificados poderiam ser generalizados para a percepção muscular dos indivíduos com alterações motoras e sensitivas; e quarto, uma discussão preliminar sobre as implicações potenciais da pesquisa aqui apresentada, no tocante aos assuntos relacionados à reabilitação.

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.

Equivalent inter- and intramodality long-term priming: evidence for a common lexicon for words seen and words heard.

Weaker inter- than intramodality long-term priming of words has promoted two hypotheses: (1) separate visual and auditory lexicons and (2) modality dependence of implicit memory. In five experiments, we employed manipulations aimed to minimize study-test asymmetries between the two priming conditions. Activities at visual and auditory study were matched, words were phonologically consistent, and study modality was manipulated between subjects. Equal magnitudes of inter- and intramodality priming were found in experiments with visual and auditory stem completion at test, with visual fragment completion at test, and with visual and auditory perceptual identification at test. A within-subjects experiment yielded the conventional intramodality advantage. The results point to a single amodal lexicon and to modality-independent phonological processing as the basis of implicit word memory.