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.     

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.     

Direct Learning in Auditory Perception: An Information-Space Analysis of Auditory Perceptual Learning of Object Length

The theory of direct learning characterizes perception of a given property as occupying a locus in an information space and characterizes perceptual learning as continuous movement in that information space toward a more optimal locus. Three experiments investigated whether such an information-based account of learning could be applied to perceptual learning in audition. The results of Experiment 1 showed that perception of length by audition could be characterized as occupying a locus in an information space consisting of inertial variables that constrain perception of length by dynamic or effortful touch. Experiments 2 and 3 showed that feedback about length led to predictable movements across the information space from less optimal to more optimal loci. Such results provide additional support for the theory of direct learning and suggest that convergence information may be modality independent.     

Transfer of recalibration from audition to touch: modality independence as a special case of anatomical independence

An important step in developing a theory of calibration is establishing what it is that participants become calibrated to as a result of feedback. Three experiments used a transfer of calibration paradigm to investigate this issue. In particular, these experiments investigated whether recalibration of perception of length transferred from audition to dynamic (i.e., kinesthetic) touch when objects were grasped at one end (Experiment 1), when objects were grasped at one end and when they were grasped at a different location (i.e., the middle) (Experiment 2), and when false (i.e., inflated) feedback was provided about object length (Experiment 3). In all three experiments, there was a transfer of recalibration of perception of length from audition to dynamic touch when feedback was provided on perception by audition. Such results suggest that calibration is not specific to a particular perceptual modality and are also consistent with previous research that perception of object length by audition and dynamic touch are each constrained by the object's mechanical properties.     

How mechanical context and feedback jointly determine the use of mechanical variables in length perception by dynamic touch

Earlier studies have revealed that both mechanical context and feedback determine what mechanical invariant is used to perceive length by dynamic touch. In the present article, the authors examined how these two factors jointly constrain the informational variable that is relied upon. Participants were to judge length while wielding a rod or while holding it stationary. In two experiments, it was tested whether perceptual learning effects in the wielding condition transferred to the holding condition and vice versa. There was an asymmetry in transfer across mechanical conditions: Improvements in the holding context transferred to the wielding condition, but not vice versa. Examining the individuals’ exploitation of mechanical variables, we found that, after feedback, participants changed in information usage in both mechanical conditions. For many participants, these changes were not confined to the mechanical context in which the feedback was provided. Indeed, feedback in one mechanical context brought about changes in information usage that often manifested themselves in the other mechanical condition. The authors explore the implications of these findings for research on perceptual learning in dynamic touch and the salience hypothesis.     

The role of feedback information for calibration and attunement in perceiving length by dynamic touch

Two processes have been hypothesized to underlie improvement in perception: attunement and calibration. These processes were examined in a dynamic touch paradigm in which participants were asked to report the lengths of unseen, wielded rods differing in length, diameter, and material. Two experiments addressed whether feedback informs about the need for reattunement and recalibration. Feedback indicating actual length induced both recalibration and reattunement. Recalibration did not occur when feedback indicated only whether 2 rods were of the same length or of different lengths. Such feedback, however, did induce reattunement. These results suggest that attunement and calibration are dissociable processes and that feedback informs which is needed. The observed change in variable use has implications also for research on what mechanical variables underlie length perception by dynamic touch.     

A feedback model of perceptual learning and categorization

Top-down, feedback, influences are known to have significant effects on visual information processing. Such influences are also likely to affect perceptual learning. This paper employs a computational model of the cortical region inter-actions underlying visual perception to investigate possible influences of top-down information on learning. The results suggest that feedback could bias the way in which perceptual stimuli are categorized and could also facilitate the learning of subordinate level representations suitable for object identification and perceptual expertise.     

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.     

Perceptual Learning of Tooling Affordances of a Jointed Object via Dynamic Touch

We investigated whether perceptual learning via dynamic touch can facilitate the discovery of tooling affordances. Twelve blindfolded participants manipulated two structurally identical aluminum objects consisting of a blade and a shaft; one object was seven and a half times heavier than and twice as large as the other object. Flexions/extensions at two joints in the shaft changed the configuration and functionality of each object. A rigid shaft (one of four possible configurations) rendered each object a functional hoe. The number of changes in the configuration produced prior to determining that the grasped object had been rendered a functional hoe greatly exceeded the number of possible configurations and declined with experience, whereas the rate of change in configuration increased with experience. Inertial properties specifically support perception via dynamic touch and explained the observed differences in actions with the two objects. These findings demonstrate that perceptual learning via dynamic touch can facilitate the discovery of tooling affordances.     

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.     

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.     

Visual movement perception: A comparison of absolute and relative movement discrimination

It is proposed that there are two types of visual movement perception, absolute and relative. The former occurs when an object is seen to move in an otherwise homogeneous (or at least locally homogeneous) visual field. Relative judgments occur when one object is seen to move with respect to another, i.e., the separation between them is seen to change. Quantitative models for both processes are developed, and an experiment reported for which the models seem appropriate. The results appear relevant to a theory of size of length perception as well as to the general perceptual issue of absolute and relative judgments.     

Somatosensory processes subserving perception and action

The functions of the somatosensory system are multiple. We use tactile input to localize and experience the various qualities of touch, and proprioceptive information to determine the position of different parts of the body with respect to each other, which provides fundamental information for action. Further, tactile exploration of the characteristics of external objects can result in conscious perceptual experience and stimulus or object recognition. Neuroanatomical studies suggest parallel processing as well as serial processing within the cerebral somatosensory system that reflect these separate functions, with one processing stream terminating in the posterior parietal cortex (PPC), and the other terminating in the insula. We suggest that, analogously to the organisation of the visual system, somatosensory processing for the guidance of action can be dissociated from the processing that leads to perception and memory. In addition, we find a second division between tactile information processing about external targets in service of object recognition and tactile information processing related to the body itself. We suggest the posterior parietal cortex subserves both perception and action, whereas the insula principally subserves perceptual recognition and learning.     

An ecological analysis of knowing by wielding.

The ecological approach to perception, as developed by James Gibson, is described and applied to how one knows, by means of the haptic perceptual system, various properties of hand-held objects. Four sets of experiments are reviewed in which subjects reported on the extent, orientation, shape, and fractional components of unseen objects wielded freely. For each task, an invariant specific to the object property in question is identified in the structured arrays of rotational moments and strains produced by the act of wielding. Results are discussed in relation to the concepts of attention and stimulation, as reformulated by the ecological approach, and the general theory of perception as information pickup.     

The experience of force: the role of haptic experience of forces in visual perception of object motion and interactions, mental simulation, and motion-related judgments

Forces are experienced in actions on objects. The mechanoreceptor system is stimulated by proximal forces in interactions with objects, and experiences of force occur in a context of information yielded by other sensory modalities, principally vision. These experiences are registered and stored as episodic traces in the brain. These stored representations are involved in generating visual impressions of forces and causality in object motion and interactions. Kinematic information provided by vision is matched to kinematic features of stored representations, and the information about forces and causality in those representations then forms part of the perceptual interpretation. I apply this account to the perception of interactions between objects and to motions of objects that do not have perceived external causes, in which motion tends to be perceptually interpreted as biological or internally caused. I also apply it to internal simulations of events involving mental imagery, such as mental rotation, trajectory extrapolation and judgment, visual memory for the location of moving objects, and the learning of perceptual judgments and motor skills. Simulations support more accurate judgments when they represent the underlying dynamics of the event simulated. Mechanoreception gives us whatever limited ability we have to perceive interactions and object motions in terms of forces and resistances; it supports our practical interventions on objects by enabling us to generate simulations that are guided by inferences about forces and resistances, and it helps us learn novel, visually based judgments about object behavior.     

Generating complex three-dimensional stimuli (Greebles) for haptic expertise training

An apparatus is described that accurately measures response times and video records hand movements during haptic object recognition using complex three-dimensional (3-D) forms. The apparatus was used for training participants to become expert at perceptual judgments of 3-D objects (Greebles) using only their sense of touch. Inspiration came from previous visual experiments, and therefore training and testing protocols that were similar to the earlier visual procedures were used. Two sets of Greebles were created. One set (clay Greebles) was hand crafted from clay, and the other (plastic Greebles) was machine created using rapid prototyping technology. Differences between these object creation techniques and their impact on perceptual expertise training are discussed. The full set of these stimuli may be downloaded from www.psychonomic.org/archive/.     

Perception of the length of an object through dynamic touch is invariant across changes in the medium

Rotational inertia—a mechanical quantity that describes the differential resistance of an object to angular acceleration in different directions—has been shown to support perception of the properties of that object through dynamic touch (wielding). The goal of the present study was to examine if perception of the length of an object through dynamic touch depends on its rotational inertia, independent of the medium in which it is wielded. The participants (n = 14) wielded 12 different objects held in air or completely immersed in water and reported perceived lengths of those objects. Each object consisted of a rod of a particular density with a particular number of stacked steel rings attached at a particular location along its length. Perceived length was invariant across medium. In addition, a single-valued function of the major eigenvalue, I ₁, and the minor eigenvalue, I ₃, of the rotational inertia, I, of the 12 objects predicted the perceived lengths of those objects in both air and water, and the perceived lengths were invariant across the two media. These results support the hypothesis that the informational support for perception of the length of an object through dynamic touch is invariant across changes in the medium.     

What aspects of vision facilitate haptic processing?

We investigate how vision affects haptic performance when task-relevant visual cues are reduced or excluded. The task was to remember the spatial location of six landmarks that were explored by touch in a tactile map. Here, we use specially designed spectacles that simulate residual peripheral vision, tunnel vision, diffuse light perception, and total blindness. Results for target locations differed, suggesting additional effects from adjacent touch cues. These are discussed. Touch with full vision was most accurate, as expected. Peripheral and tunnel vision, which reduce visuo-spatial cues, differed in error pattern. Both were less accurate than full vision, and significantly more accurate than touch with diffuse light perception, and touch alone. The important finding was that touch with diffuse light perception, which excludes spatial cues, did not differ from touch without vision in performance accuracy, nor in location error pattern. The contrast between spatially relevant versus spatially irrelevant vision provides new, rather decisive, evidence against the hypothesis that vision affects haptic processing even if it does not add task-relevant information. The results support optimal integration theories, and suggest that spatial and non-spatial aspects of vision need explicit distinction in bimodal studies and theories of spatial integration.     

Similarity and categorization: from vision to touch

Even though human perceptual development relies on combining multiple modalities, most categorization studies so far have focused on the visual modality. To better understand the mechanisms underlying multisensory categorization, we analyzed visual and haptic perceptual spaces and compared them with human categorization behavior. As stimuli we used a three-dimensional object space of complex, parametrically-defined objects. First, we gathered similarity ratings for all objects and analyzed the perceptual spaces of both modalities using multidimensional scaling analysis. Next, we performed three different categorization tasks which are representative of every-day learning scenarios: in a fully unconstrained task, objects were freely categorized, in a semi-constrained task, exactly three groups had to be created, whereas in a constrained task, participants received three prototype objects and had to assign all other objects accordingly. We found that the haptic modality was on par with the visual modality both in recovering the topology of the physical space and in solving the categorization tasks. We also found that within-category similarity was consistently higher than across-category similarity for all categorization tasks and thus show how perceptual spaces based on similarity can explain visual and haptic object categorization. Our results suggest that both modalities employ similar processes in forming categories of complex objects.