Bodywide fluctuations support manual exploration: Fractal fluctuations in posture predict perception of heaviness and length via effortful touch by the hand

The human haptic perceptual system respects a bodywide organization that responds to local stimulation through full-bodied coordination of nested tensions and compressions across multiple nonoverlapping scales. Under such an organization, the suprapostural task of manually hefting objects to perceive their heaviness and length should depend on roots extending into the postural control for maintaining upright balance on the ground surface. Postural sway of the whole body should thus carry signatures predicting what the hand can extract by hefting an object. We found that fractal fluctuations in Euclidean displacement in the participants' center of pressure (CoP) contributed to perceptual judgments by moderating how the participants' hand picked up the informational variable of the moment of inertia. The role of fractality in CoP displacement in supporting heaviness and length judgments increased across trials, indicating that the participants progressively implicate their fractal scaling in their perception of heaviness and length. Traditionally, we had to measure fractality in hand movements to predict perceptual judgments by manual hefting. However, our findings suggest that we can observe what is happening at hand in the relatively distant-from-hand measure of CoP. Our findings reveal the complex relationship through which posture supports manual exploration, entailing perception of the intended properties of hefted objects (heaviness or length) putatively through the redistribution of forces throughout the body.     

Comparison of dynamic (effortful) touch by hand and foot

Spatial perception by dynamic touch is a well-documented capability of the hand and arm. Morphological and physiological characteristics of the foot and leg suggest that such a capability may not generalize to that putatively less dexterous limb. The authors examined length perception by dynamic touch in a task in which weighted aluminum rods were grasped by the hand and wielded about the wrist or secured to the foot and wielded about the ankle. Participants' (N = 10) upper and lower extremities were comparable in terms of (a) the accuracy and consistency of length perception and (b) their sensitivity to manipulations of the moments of the mass distribution of the rods. The authors discuss those results in terms of the field-like structure of the haptic perceptual system, an organization that may underlie what appears to be functional, rather than anatomical, specificity.     

Selective perception by dynamic touch

Perceiving the length of a rod by dynamic touch is tied to the inertia tensorIij, a quantification of its resistance to rotational acceleration. Perception of the portion extending in front of the grasp has previously been ascribed to decomposing one component ofIij by attention. The tensorial nature of dynamic touch suggests that this ability must be anchored wholly in the tensor. Three experiments show that perceived partial length is a function of two components of the tensor, one tied primarily to magnitude and the other tied primarily to direction, whereas perceived whole length is a function of a magnitude component alone. Dynamic touch is characterized in terms of a haptic perceptual instrument that softly assembles to exploitIij differently depending on the intention, producing 1:1 maps that are appropriately scaled for each intention.     

The perception of complex patterns by touch

Two experiments are reported on matching Braille characters in dot pattern and outline shape formats by congenitally blind subjects. In a third experiment subjects' drawings of Braille shapes were analysed. Experiment 1 showed that normal and retarded readers differed significantly when outline shapes 'cued' identical dot patterns, but did not differ when the dot patterns preceded outlines. However, normal as well as retarded readers were faster and more accurate in judging identical pairs in dot-pattern format than in any other condition. In experiment 2 dot patterns and outline shapes were matched at three levels of reading proficiency. Faster readers made fewer errors in matching identical pairs, but all subjects were more accurate and faster with dot patterns than with outline shapes. Experiment 3 showed that blind subjects' drawing of outline shapes is not affected by reading proficiency. Most common were errors of alignment, including 'rotation' from vertical to horizontal axes, suggesting that sources of confusion were spatial position of dots and major axes of alignment rather than mirror-image reversals. It is argued that the results are not compatible with the hypothesis that Braille letters are perceived as global outline shapes by faster readers.     

Exploration styles modulate length perception through dynamic touch

One of the most surprising capacities of the haptic system is the ability to estimate different properties of objects, like weight or length, through invariants of rotational mechanics that are accessible via the proprioceptive system. This field of research is called Dynamic Touch. In its classical experimental paradigm, the participant firmly grasps a rod that can be wielded but not seen, and he or she tries to match the hand-held rod's length using another rod that can be seen but not wielded. In the experiment reported here, we focus on the role of the exploratory behavior, restricting the wielding in six conditions that vary both the amplitude and the frequency of movements. Increments in the speed of the movement are shown to increase the accuracy in the haptic estimation. It is argued that these results support the moment of inertia as the best informational candidate, given that it is an invariant property that only emerges when rotational torques are applied. Alternative candidates such as static moment or mass are discarded because they do not depend on differential movements.     

Preparing for perception and action (II): Automatic and effortful processes in response cueing

In this paper we tested the automatic-effortful processing assumption of the Grouping Model. According to the Grouping Model, left-right cues are pull cues and inner-outer cues are push cues, evoking exogenous and endogenous control, respectively. In a series of four experiments we manipulated the characteristics of the cues: Onset vs. no-onset cues, spatial vs. symbolic cues, valid vs. invalid cues. The results consistently showed a dissociation between left-right and inner-outer cues. Together, the present findings provide converging evidence for the notion that left-right cues induce a fast, automatic selection of the cued responses, whereas inner-outer cues need slower, effortful processes to establish a selective preparatory set.     

Stroke me for longer this touch feels too short: The effect of pleasant touch on temporal perception

Negative, painful, somatosensory stimulation lengthens the perceived duration of time. However, to date, no research has explored the influence of positive, pleasant, somatosensory stimulation on temporal perception. Here we asked whether gentle stroking touch influences perceptions of duration. Pleasant (gentle) and mildly unpleasant (rough) tactile stimulation was delivered whilst participants estimated the duration of a neutral visual stimulus. Pleasant touch resulted in shorter estimates of duration than unpleasant touch. There was no difference in duration perception in the unpleasant and control conditions. Taken together with the results of previous research (Ogden, Moore, Redfern, & McGlone, 2015), the results of this study suggest that pleasant and painful somatosensory stimulation have opposing effects on temporal perception, and additionally that pleasant touch can alter aspects of perceptual and attentional processing outside the purely affective domain.     

Transfer of calibration in length perception by dynamic touch

Earlier studies suggested that the calibration of actions is functionally, rather than anatomically, specific; thus, calibration of an action ought to transfer to actions that serve the same goal (Rieser, Pick, Ashmead, & Garing, 1995). In the present study, we investigated whether the calibration of perception also follows a functional organization: If one means of detecting an information variable is recalibrated, are other means of detection recalibrated as well? In two experiments, visual feedback was used to recalibrate perceived length of a rod wielded by the right hand; the recalibration was found to transfer to length perception with the left hand. This implies that calibration in perception is organized functionally rather than anatomically, and supports the general view that calibration applies to functional systems.     

Cortical coordination dynamics and cognition

New imaging techniques in cognitive neuroscience have produced a deluge of information correlating cognitive and neural phenomena. Yet our understanding of the inter-relationship between brain and mind remains hampered by the lack of a theoretical language for expressing cognitive functions in neural terms. We propose an approach to understanding operational laws in cognition based on principles of coordination dynamics that are derived from a simple and experimentally verified theoretical model. When applied to the dynamical properties of cortical areas and their coordination, these principles support a mechanism of adaptive inter-area pattern constraint that we postulate underlies cognitive operations generally.     

Categorizing coordination from the perception of joint actions

The ability to perceive others’ actions and coordinate our own body movements accordingly is essential for humans to interact with the social world. However, it is still unclear how the visual system achieves the remarkable feat of identifying temporally coordinated joint actions between individuals. Specifically, do humans rely on certain visual features of coordinated movements to facilitate the detection of meaningful interactivity? To address this question, participants viewed short video sequences of two actors performing different joint actions, such as handshakes, high fives, etc. Temporal misalignments were introduced to shift one actor’s movements forward or backward in time relative to the partner actor. Participants rated the degree of interactivity for the temporally shifted joint actions. The impact of temporal offsets on human interactivity ratings varied for different types of joint actions. Based on human rating distributions, we used a probabilistic cluster model to infer latent categories, each revealing shared characteristics of coordinated movements among sets of joint actions. Further analysis on the clustered structure suggested that global motion synchrony, spatial proximity between actors, and highly salient moments of interpersonal coordination are critical features that impact judgments of interactivity.     

Social cognition in simple action coordination: A case for direct perception

In this paper we sketch the outlines of an account of the kind of social cognition involved in simple action coordination that is based on direct social perception (DSP) rather than recursive mindreading. While we recognize the viability of a mindreading-based account such as e.g. Michael Tomasello’s, we present an alternative DSP account that (i) explains simple action coordination in a less cognitively demanding manner, (ii) is better able to explain flexibility and strategy-switching in coordination and crucially (iii) allows for formal modeling. This account of action coordination is based on the notion of an agent’s field of affordances. Coordination ensues, we argue, when, given a shared intention, the actions of and/or affordances for one agent shape the field of affordances for another agent. This a form of social perception since in particular perceiving affordances for another person involves seeing that person as an agent. It is a form of social perception since it involves perceiving affordances for another person and registering how another person’s actions influence one’s own perceived field of affordances.     

Interpersonal coordination tendencies and perception of visual information for decision-making in futsal

This study investigated how futsal players visually perceived information on angular interpersonal coordination relations, between available sources such as nearest defender, goalkeeper position and ball, when deciding to shoot at goal. Experienced players (n = 180) participated in eighteen, video-recorded futsal matches, during which 32 participants wore an eye tracking device. Forty-five sequences of play were selected and edited from the moment a teammate passed the ball to the shooter, until the moment a shot was undertaken. Independent variables included the angle connecting the shooter to their closest defender and goalkeeper, and it’s rate of change (velocity and variability) during performance. Then eye tracking system (TOBII PRO) was used to examine gaze patterns of shooters during task performance. Findings revealed that: (i) futsal players adapted their gaze patterns differently between key information sources when shooting confirmed as: their closest defender, goalkeeper, ball, and court floor; and (ii), the ball was the information source which was most fixated on, regardless of the characteristics of interpersonal coordination tendencies that emerged when shooting. These findings can be interpreted as evidence of functional perceptual behaviours used to regulate actions needed to ensure precise contact with the ball when shooting at goal. Further, adaptations of fixation patterns, varied between marking defender, goalkeeper, and ball, may provide functional postural orientation to facilitate a successful shot at goal.     

Evaluating the coordination dynamics of handwriting

This study aims to test the hypothesis that handwriting is governed by the dynamics of non-linear coupled oscillators. Accordingly, its first goal is to identify preferred, basic graphic shapes corresponding to spontaneously stable combinations of the two frequency-locked oscillatory x-y components of the trajectories. Six participants were required to produce 26 ellipsoids of varying eccentricities and orientations presented consecutively on a graphic tablet. These shapes corresponded to a systematic manipulation of the relative phase and the relative amplitude of the oscillators by a constant step. Results showed that among those, only eight ellipsoids were produced in a spontaneous and stable fashion. They were characterized by attraction of nearby shapes, and by a higher accuracy and velocity. Alike all periodic motion, graphic skills, hence handwriting, exhibit preferred coordination patterns, which can be ascribed to the non-linear coupling of two oscillators.     

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.     

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.