Multiplicative-cascade dynamics supports whole-body coordination for perception via effortful touch

Effortful touch by the hand is essential to engaging with and perceiving properties of objects. The temporal structure of whole-body coordination must reflect the prospective control that provides for both the engagement with and perception of properties of the hefted objects. In the present study, we found signatures of multifractality in the time series of fluctuations in Euclidean displacement in the participants' center of pressure (CoP) as they hefted weighted objects to perceive their heaviness and length. Comparisons of widths of the multifractal spectrums of CoP series with 32 Iterative Amplitude Adjusted Fourier Transform (IAAFT) surrogates provided evidence for multiplicative-cascade dynamics and interactivity across scales, through the continuous t-statistic comparing the original and surrogate widths (t_MF). After controlling for the linear properties of CoP series and their interactions with the informational variable (i.e., the moment of inertia of the hefted objects), regression modeling of unsigned error in judgments of heaviness and length revealed that the multifractal evidence for nonlinearity (t_MF) significantly influenced unsigned error. The two indicators showed opposite, task-specific effects on accuracy: accuracy in judgments of heaviness and length decreased and increased, respectively, with greater t_MF. These findings suggest that multiplicative-cascade dynamics in posture play a role in prospective coordination during the engagement with objects and perception of their properties via effortful touch by the hand. Future work may elucidate how constraint(s) on exploratory kinematics influence the multifractal behavior in such suprapostural perceptual tasks as effortful touch.     

Transfer of calibration between hand and foot: Functional equivalence and fractal fluctuations

Transfer of competency in a perceptual task often depends on shared information between anatomically different perceptual subsystems. The problem of studying transfer involves isolating conditions of similarity and then trying to account for any resulting differences in transfer. To respect this twofold aspect, this article takes a two-pronged approach to transfer in dynamic touch. The present research first tests the hypothesis that functional equivalence supports the transfer of dynamic touch. Participants were trained to wield unseen objects with the hand or foot and were then tested on anatomically disparate limbs (i.e., the foot or hand, respectively). Next, we examined motion capture of these wielding behaviors for predictors of any asymmetry in transfer. Temporally fractal fluctuations of exploratory behavior can modulate information detection, and we tested whether the fractality of wielding might predict asymmetries in transfer across disparate limbs. Results suggest that transfer of training to anatomically disparate limbs respects functional conditions of similarity and also that the degree of temporally fractal fluctuations predicted limb differences in transfer.     

Fractal fluctuations in gaze speed visual search

Visual search involves a subtle coordination of visual memory and lower-order perceptual mechanisms. Specifically, the fluctuations in gaze may provide support for visual search above and beyond what may be attributed to memory. Prior research indicates that gaze during search exhibits fractal fluctuations, which allow for a wide sampling of the field of view. Fractal fluctuations constitute a case of fast diffusion that may provide an advantage in exploration. We present reanalyses of eye-tracking data collected by Stephen and Mirman (Cognition, 115, 154-165, 2010) for single-feature and conjunction search tasks. Fluctuations in gaze during these search tasks were indeed fractal. Furthermore, the degree of fractality predicted decreases in reaction time on a trial-by-trial basis. We propose that fractality may play a key role in explaining the efficacy of perceptual exploration.     

Metamers in the haptic perception of heaviness and moveableness

It is hypothesized that heaviness perception for a freely wielded nonvisible object can be mapped to a point in a three-dimensional heaviness space. The three dimensions are mass, the volume of the inertia ellipsoid, and the symmetry of the inertia ellipsoid. Within this space, particular combinations yield heaviness metamers (objects of different mass that feel equally heavy), whereas other combinations yield analogues to the size-weight illusion (objects of the same mass that feel unequally heavy). Evidence for the two types of combinations was provided by experiments in which participants wielded occluded hand-held objects and estimated the heaviness of the objects relative to a standard. Further experiments with similar procedures showed that metamers of heaviness were metamers of moveableness but not metamers of length. A promising conjecture is that the haptic perceptual system maps the combination of an object's inertia for translation and inertia for rotation to a perception of the object's maneuverability.     

Hefting for a maximum distance throw: a smart perceptual mechanism

Objects for throwing to a maximum distance were selected by hefting objects varying in size and weight. Preferred weights increased with size reproducing size-weight illusion scaling between weight and volume. In maximum distance throws, preferred objects were thrown the farthest. Throwing was related to hefting as a smart perceptual mechanism. Two strategies for conveying high kinetic energy to projectiles were investigated by studying the kinematics of hefting light, preferred, and heavy objects. Changes in tendon lengths occurring when objects of varying size were grasped corresponded to changes in stiffness at the wrist. Hefting with preferred objects produced an invariant phase between the wrist and elbow. This result corresponded to an optimal relation at peak kinetic energy for the hefting. A paradigm for the study of perceptual properties was compared to size-weight illusion methodology.     

"Ratio" and "difference" judgments for length, area, and volume: are there two classes of sensory continua?

Subjects were required to judge ratios and differences of (a) line length for pairs of lines, (b) area for pairs of squares, and (c) volume for pairs of cubes. Nonmetric analyses of these judgments indicated that all subjects were able to make consistent ratio judgments for all three continua. Many of the subjects, when asked to judge subjective differences, however, performed as if they were judging subjective ratios rather than differences. The data for the few subjects who appeared to be judging subjective differences were not consistent across subjects and conditions. Previous studies of ratio and difference judgments of loudness and heaviness, on the other hand, showed the opposite pattern, in that subjects most often behaved as if they were judging sensory differences when asked to judge sensory ratios. We propose that ratio judgments are more natural to perceptual continua along which stimuli are easily "decomposed" into a number of smaller perceptual units.     

Mapping the tip of the tongue--deprivation, sensory sensitisation, and oral haptics

We investigated the impact of food deprivation on oral and manual haptic size perception of food and non-food objects. From relevant theories (need-proportional perception, motivated perception, frustrative nonreward, perceptual defence, and sensory sensitisation) at least four completely different competing predictions can be derived. Testing these predictions, we found across four experiments that participants estimated the length of both non-food and food objects to be larger when hungry than when satiated, which was true only for oral haptic perception, while manual haptic perception was not influenced by hunger state. Subjectively reported hunger correlated positively with estimated object size in oral, but not in manual, haptic perception. The impact of food deprivation on oral perception vanished after oral stimulations even for hungry individuals. These results favour a sensory sensitisation account maintaining that hunger itself does not alter oral perception but the accompanying lack of sensory stimulation of the oral mucosa. Both oral and manual haptic perception tended to underestimate actual object size. Finally, an enhancing effect of domain-target matching was found, ie food objects were perceived larger by oral than by manual haptics, while non-food objects were perceived larger by manual than by oral haptics.     

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.     

Dynamic (Kinesthetic) Touch Perception in Preschool Children

The preschool years are an important time during which children gain proficiency using the hands for both performatory and perceptual functions that involve dynamic (kinesthetic) touch. We evaluated dynamic touch perception of object extent and found that preschool children are able to discriminate length by dynamic touch early, but perception is not very fine-tuned and perceptual attunement to inertial characteristics increased with age. An analysis comparing the performatory and perceptual functions of the hands showed links between performance and perception in dynamic touch tasks that did not require haptic–visual correspondence. We concluded that whereas dynamic touch is functional early in the preschool years, perceptual acuity is not very precise and haptic–visual correspondence remains immature. In addition, reliance on inertial properties as information to make judgments of length emerges between 3 and 5 years and attunement to inertial properties likely continues to develop throughout childhood because perceptual judgments of 5-year-olds did not reach adult levels. Tight links between the performatory and the perceptual functions of the hand suggest this is an important avenue for future research.     

Perceptually Equivalent Judgments Made Visually and via Haptic Sensory-Substitution Devices

ABSTRACT

According to the ecological theory of perception–action, perception is primarily of affordances, which are directly perceivable opportunities for behavior. The current study evaluated participants’ ability to use vision and haptic sensory-substitution devices to support perceptual judgments of affordances involving the task of passing through apertures. Sighted participants made perceptual judgments about whether they could walk through apertures of various widths and their level of confidence in each judgment, using unrestricted vision and, when blindfolded, using two haptic sensory-substitution instruments: a cane-like wooden rod and the Enactive Torch, a device that converts distance information into vibrotactile stimuli. The boundary between aperture widths that were judged as pass-through-able versus non-pass-through-able was statistically equivalent across sensory modalities. However, participants were not as confident in their judgments using the rod or Enactive Torch as they were using vision. Additionally, participants’ judgments with the haptic instruments were significantly more accurate than with vision. The results underscore the need to assess sensory-substitution devices in the context of functional behaviors.     

The time course of perception and retrieval in matching and recognition

A four-part experiment was carried out to study the relationship between the time course of object-feature perception and the time course of retrieval of object information from memory. The experiment consisted of 2 perceptual matching tasks, and 2 perceptual recognition tasks. In all 4 tasks, participants provided speeded judgments of the identity of 2 objects. A stochastic feature-sampling model was used to estimate the time needed for feature perception and the time needed for retrieval of feature information. No evidence was found for a systematic relationship between perception times and retrieval times for individual features. Indeed, the model applications indicated that retrieval times were constant for different features, whereas perception rates varied across the features.     

Infants’ perception of object–surface interplays

Twelve‐ and 18‐month‐old infants participated in a study designed to investigate the quality of their manual action when relating an object to the surface on which it is explored. Specifically, infants’ perception‐action routines were observed when they were presented with multiple objects (wooden scoop, Velcro block, and crayon) on surfaces of varying properties (paper, sand, and Velcro) to determine if sensory feedback or perceptual awareness steered their exploration of the available materials. Infants were observed to selectively tailor their manual actions across conditions, apparently guided by a perceived awareness of the fit between their manual dexterity and the environmental arrangement.     

Using direct and indirect measures to study perception without awareness

Many studies directed at demonstrating perception without awareness have relied on the dissociation paradigm. Although the logic underlying this paradigm is relatively straightforward, definitive results have been elusive in the absence of any general consensus as to what constitutes an adequate measure of awareness. We propose an alternative approach that involves comparisons of the relative sensitivity of comparable direct and indirect indexes of perception. The only assumption required by the proposed approach is that the sensitivity of direct discriminations to relevant conscious information is greater than or equal to the sensitivity of comparable indirect discriminations. The proposed approach is illustrated through an evaluation of Avant and Thieman’s (1985) recent claim that an indirect measure of perception based on judgments of apparent visual duration provides a more sensitive indicator of perception than does a direct measure based on forced-choice recognition. Contrary to this claim, when direct and indirect indexes are measured under comparable conditions, an indirect measure based on judgments of perceived duration provides a less sensitive index of perceptual processing than do comparable direct measures. The proposed approach provides a general conceptual/methodological framework for using the dissociation paradigm in studies directed at establishing unconscious processes.     

The effect of a prior presentation on temporal judgments in a perceptual identification task

Subjects read aloud words presented once at the rate of one per second. A perceptual identification task, involving 30- or 50-msec presentations, followed. Some of the words presented for identification had been read previously; others were new. After each presentation, in addition to identifying the word, the subjects judged its duration. The data indicate that a single presentation of a word affects its later perception, as revealed by enhanced perceptual identification, longer duration judgments, and better temporal discrimination. A second experiment showed that a single presentation influenced duration judgments even when identification was not required. The final experiment addressed the issue of what is preserved in memory from a prior presentation. The results from the three experiments indicate that duration judgments provide a valuable dependent measure of memory in the perceptual identification task and support the misattribution hypothesis: A prior presentation enhances perceptual identification, and this increase in relative perceptual fluency is incorrectly attributed to a longer presentation duration.     

Making features similar: comparison processes affect perception

In this paper, the constructive nature of comparison processes (both similarity- and differenceoriented judgments) is examined through their effects on visual perception. Previous research has shown that comparison processes enhance the tendency to interpret ambiguous objects in the light of the unambiguous objects with which they are compared (Medin, Goldstone, & Gentner, 1993). In the present paper, it is argued that comparison processes affect not only the interpretation of objects, but also their perception. In addition, it is argued that the perceptual effects of similarity-oriented comparison processes differ from those of difference-oriented comparison processes. Accordingly, it is demonstrated that when estimation of an object’s size is preceded by similarity-oriented comparisons, the Ebbinghaus illusion practically disappears, whereas prior difference-oriented comparisons tend to enhance the illusion.     

Of holes and wholes: the perception of surrounded regions.

Fully enclosed regions in a two-dimensional image can often be perceived either as an object in front of a surface or as a hole through a surface. Several experiments were conducted to determine what factors affect perception of holes versus objects. Three types of factors were tested and found to influence this outcome. First, depth factors directly indicate that the enclosed region lies behind its surrounding surface. Second, grouping factors relate the enclosed region to an outer region that is generally perceived as a continuation of the surface seen through the hole. Finally, figural factors indicate whether the enclosed region is to be perceived as figure or ground. Relations among these factors and their implications for perceptual organization are discussed.     

Neurobiological tensegrity: The basis for understanding inter-individual variations in task performance?

Bernstein's (1996) levels of movement organization includes tonus, the muscular-contraction level that primes individual movement systems for (re)organizing coordination patterns. The hypothesis advanced is that the tonus architecture is a multi-fractal tensegrity system, deeply reliant on haptic perception for regulating movement of an individual actor in a specific environment. Further arguments have been proposed that the tensegrity-haptic system is implied in all neurobiological perception and -action. In this position statement we consider whether the musculoskeletal system can be conceptualized as a neurobiological tensegrity system, supporting each individual in co-adapting to many varied contexts of dynamic performance. Evidence for this position, revealed in investigations of judgments of object properties, perceived during manual hefting, is based on each participant's tensegrity. The implication is that the background organizational state of every individual is unique, given that no neurobiological architecture (musculo-skeletal components) is identical. The unique tensegrity of every organism is intimately related to individual differences, channeling individualized adaptations to constraints (task, environment, organismic), which change over different timescales. This neurobiological property assists transitions from one stable state of coordination to another which is needed in skill adaptation during performance. We conclude by discussing how tensegrity changes over time according to skill acquisition and learning.     

Individual differences in learning to perceive length by dynamic touch: Evidence for variation in perceptual learning capacities

Recent studies of perceptual learning have explored and commented on variation in learning trajectories. Although several factors have been suggested to account for this variation, thus far the idea that humans vary in their perceptual learning capacities has received scant attention. In the present experiment, we aimed at providing a detailed picture of the variation in this capacity by investigating the perceptual learning trajectories of a considerable number of participants. The learning process was studied using the paradigm of length perception by dynamic touch. The results showed that there are substantial individual differences in the way perceivers respond to feedback. Indeed, after feedback, the participants' perceptual performances diverged. We conclude that humans vary in their perceptual learning capacities. The implications of this finding for recent discussions on variation in perception are explored.     

Multimodal Perception of Reachability Expressed Through Locomotion

We investigated the information that supports perception of whether an object is within reach using a locomotor task. Participants adjusted their own position relative to a fixed target by stepping or by propelling a wheelchair until they judged it to be within reach. The to-be-reached object was presented in virtual reality. The display of the target was driven in real time as a function of the observer's movement, thus depicting a stationary virtual object at a definite distance only through the relation across optical and nonoptical patterns of stimulation. We asked participants to judge the distance they could reach with their unaided hand or when holding a rod that extended their effective reach. They could see neither their body nor the rod thereby limiting available visual information about “reachability.” As expected, our results showed that despite the limited information that was available, participants' locomotor adjustments were influenced by (a) their simulated distance from the target, (b) their arm length, and (c) the presence or absence of the rod. The type of motion (stepping or wheelchair) had little influence. However, judgment accuracy was influenced by participants' initial simulated distance from the target. We compare the performance obtained in our locomotor judgment task with previous studies that have used different methods for measuring perceived reaching-ability. We discuss perceptual information that could have supported performance within the framework of the global array.