Haptic perception of wetness

In daily life, people interact with textiles of different degrees of wetness, but little is known about the mechanics of wetness perception. This paper describes an experiment with six conditions regarding haptic discrimination of the wetness of fabrics. Three materials were used: cotton wool, sponge-structured viscose and thin viscose. Two ways of touching were investigated: static touching, in which only thermal cues were available, and dynamic touching, in which additional mechanical cues were available. For dynamic touching, average Weber fractions for discrimination were around 0.3, whereas for static touching, they ranged from 0.34 to 0.63. The results show that people can make use of the additional mechanical cues to significantly improve their discrimination performance. There was no significant difference between Weber fractions for the three materials, showing that wetness can be judged as a separate perceptual quantity, independent of the material.     

Haptic perception in newborns

Two experiments using different procedures were performed in which newborns’ ability to process information about object shape with their hands was explored. In the first experiment, a haptic fixed‐trial procedure was used and a decrease in holding times was found for both right and left hands. In the second experiment, discrimination between objects was studied in which a shifted procedure associated to an infant‐control procedure followed by a dishabituation procedure was used. Habituation to an object and a reaction to the novelty of a new object were shown for both right and left hands, showing that neonates are able to process and encode some information about object shape and then to discriminate between different shapes. It is the first evidence of such an ability in neonates. Methodological procedure and haptic cognition with regard to sensory symmetry are discussed and some developmental perspectives are proposed.     

Haptic distal spatial perception mediated by strings: haptic "looming"

Five experiments tested a haptic analog of optical looming, demonstrating string-mediated haptic distal spatial perception. Horizontally collinear hooks supported a weighted string held taut by a blindfolded participant's finger midway between the hooks. At the finger, the angle between string segments increased as the finger approached collinearity with the hooks, just as the optical angle subtended by an approaching object increases. The vertical force component at the finger is potentially informative for perception, approaching zero at finger-hook collinearity. In Experiment 1, participants judged hook height reasonably accurately. To retain force relationships but eliminate immediate skin contact, Experiment 2 employed a hand-held rod; results replicated those of Experiment 1. Experiment 3 replicated Experiment 2 using a ring instead of a rod. In all three experiments, estimated hook height closely paralleled actual height, r > .9. Experiments 4 and 5 showed that participants could project impending finger-hook collinearity when finger contact with the string was interrupted during its traverse. Perceivers' estimate errors were nearly perfectly predicted by height-force ratio relationships (Rs > .96). Outcomes are related to optical and acoustic looming, dynamic touch, tau theory, and Gibsonian perceptual theory.     

Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem concerning tactile pictorial perception by the blind. The aim of the experiments reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute values of 3-D properties from 2-D patterns read by the finger pads, the abilities of participants to perceive gradients lying between known maxima and minima were assessed. Experiment 1 involved blindfolded sighted participants making verbal magnitude estimations of texture-gradient magnitudes corresponding to plane surfaces at different slants. In experiment 2 the participants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind participants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for learning. Texture gradients appear as informative to the blind as they do to the sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigated.     

Haptic perception of linear extent

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.     

Haptic perception: A tutorial

This tutorial focuses on the sense of touch within the context of a fully active human observer. It is intended for graduate students and researchers outside the discipline who seek an introduction to the rapidly evolving field of human haptics. The tutorial begins with a review of peripheral sensory receptors in skin, muscles, tendons, and joints. We then describe an extensive body of research on “what” and “where” channels, the former dealing with haptic perception of objects, surfaces, and their properties, and the latter with perception of spatial layout on the skin and in external space relative to the perceiver. We conclude with a brief discussion of other significant issues in the field, including vision-touch interactions, affective touch, neural plasticity, and applications.     

Haptic perception of linear extent.

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.     

Haptic and visual perception of roughness

In this study, we are interested in the following two questions: (1) how does perceived roughness correlate with physical roughness, and (2) how do visually and haptically perceived roughness compare? We used 96 samples of everyday materials, such as wood, paper, glass, sandpaper, ceramics, foams, textiles, etc. The samples were characterized by various different physical roughness measures, all determined from accurately measured roughness profiles. These measures consisted of spectral densities measured at different spatial scales and industrial roughness standards (R(a), R(q) and R(z)). In separate haptic and visual conditions, 12 na?ve subjects were instructed to order the 96 samples according to perceived roughness. The rank orders of both conditions were correlated with the various physical roughness measures. With most physical roughness measures, haptic and visual correspondence with the physical ordering was about equal. With others, haptic correspondence was slightly better. It turned out that different subjects ordered the samples using different criteria; for some subjects the correlation was better with roughness measures that were based on higher spatial frequencies, while others seemed to be paying more attention to the lower spatial frequencies. Also, physical roughness was not found to be the same as perceived roughness.     

Haptic distal spatial perception mediated by strings: Point of closest approach and bypass distance

Four experiments examined haptic perception of two distal spatial properties in a bypass event. A hook suspended a string held taut between the participant's finger and a weight. Moving their fingers laterally beneath the hook, participants estimated the finger's point of closest approach (PCA) to the hook and bypass distance (BPD; i.e., hook height above the finger's track at PCA). Experiment 1 yielded near perfect PCA estimates (group average r > .99), independent of BPD and traverse distance. Experiment 2 replicated PCA results, and showed good BPD estimates (group r = .74). BPD estimates depended on lateral movement distance to PCA, but not weight. In Experiment 3, feedback on accuracy improved BPD estimates (maximum group average R = .91). Magnitude estimation of BPD in Experiment 4 yielded a power law relationship (group average r = .90; exponent, .30). Results show that human perceivers can make effective judgments of PCA and BPD using haptically available force relationships. Results are interpreted in terms of haptics as a telemodality, the Gibsonian perceptual research program, and dynamic touch. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Language, perception, and the schematic representation of spatial relations

Schemas are abstract nonverbal representations that parsimoniously depict spatial relations. Despite their ubiquitous use in maps and diagrams, little is known about their neural instantiation. We sought to determine the extent to which schematic representations are neurally distinguished from language on the one hand, and from rich perceptual representations on the other. In patients with either left hemisphere damage or right hemisphere damage, a battery of matching tasks depicting categorical spatial relations was used to probe for the comprehension of basic spatial concepts across distinct representational formats (words, pictures, and schemas). Left hemisphere patients underperformed right hemisphere patients across all tasks. However, focused residual analyses using voxel-based lesion-symptom mapping (VLSM) suggest that (1) left hemisphere deficits in the representation of categorical spatial relations are difficult to distinguish from deficits in naming these relations and (2) the right hemisphere plays a special role in extracting schematic representations from richly textured pictures.     

Haptic perception of parallelity in the midsagittal plane.

Previous studies [Perception 28 (1999) 1001; Perception 28 (1999) 781] on the haptic perception of parallelity on a horizontal plane showed that what subjects haptically perceive as being parallel deviates considerably from what is physically parallel. The deviations could be described with a subject-dependent orientation gradient in the left-right direction. The gradients found in the bimanual conditions were significantly larger (about 70%) than those in the unimanual conditions. The questions to be answered in the present study are the following: (1) Does the haptic perception of parallelity in the midsagittal plane also show systematic deviations from veridicality? (2) Are the unimanual and bimanual performances again quantitatively but not qualitatively different? The set-up consisted of a plate positioned in the midsagittal plane of the subject. The subject touched the right side of the plate with his/her right hand and the left side with the left hand. The results show again large systematic deviations. The major part of the deviations can be described by means of a subject-dependent orientation gradient in the vertical direction. The quantitative (but not qualitative) difference between the unimanual and the bimanual conditions is much larger in the midsagittal plane than in the horizontal plane.     

Curve tracing: A possible basic operation in the perception of spatial relations

The two experiments in this study suggest that fast internal tracing of curves is employed by the visual system in the perception of certain shape properties and spatial relations. The experimental task in the first experiment was to determine, as rapidly as possible, whether two Xs lay on the same curve or on different curves in a visual display. Mean response time for “same” responses increased monotonically with increasing distance along the curve between the Xs. The task in the second experiment was to decide either that a curve joining two Xs was unbroken or that the curve had a gap. Decision times again increased as the length of the curve joining the Xs was increased. The results of both experiments suggest that people can trace curves in a visual display internally at high speed (the average rate of tracing was about 40° of visual angle per second). Curve tracing may be an important visual process used to integrate information from different parts of a visual display.     

Haptic perception of the distance walked when blindfolded.

The ability to detect the distance walked when blindfolded using only haptic information generated by the walking activity was investigated. Participants walked a straight path until told to stop, turned, and attempted to return to their starting point. The path was completely featureless. Counting was prevented. Blindfolded, sighted participants traveled with a long cane or a trained sighted guide. Gait was varied or distorted. In all experiments the return distance was a linear function of the set distance, with some participants giving and some conditions resulting in remarkably sensitive performances. The magnitude of errors was a linear function of step length.     

Haptic distal spatial perception mediated by strings: Size at a distance and egocentric localization based on ellipse geometry

Participants explored ellipse perimeters defined by fixed-length strings, held taut by their moving finger, with ends attached to two fixed hooks (foci). Participants haptically judged ellipse interfocal distance (IFD; in effect, exocentric separation, or size at a distance) or location of ellipse major axes (i.e., egocentric localization relative to the moving finger). In Experiment 1A, perceivers made reliable and accurate multialternative forced choice IFD judgments. Experiment 1B showed similar reliability for direct estimations but showed greater scaling error. In Experiment 2, perceivers reliably localized ellipse major axes. Both experiments derived from a priori geometrical analysis, consistent with the Gibsonian perceptual research program and previous string-mediated haptic distal spatial studies. Results are discussed with respect to haptic perception as a telemodality and to dynamic touch.     

Haptic perception of object distance in a single-strand vibratory web

Can humans, like other animals, perceive distance by mechanical vibrations transmitted in a solid medium? In seven experiments, subjects perceived the distances from the hand of occluded metal disks attached to a taut nylon strand. Mechanical waves were initiated at the hand by the subject or at the disk by the experimenter. The results of Experiments 1 and 2 showed that perceived distance was linearly dependent on object distance with or without practice. The results of Experiments 3 and 4 revealed an inverse dependency of perceived distance on strand tension. In Experiment 5, a constant difference in perceived distance between vertical and horizontal strand manipulations was found. The results of Experiments 6 and 7 showed that distance was perceptible when the mechanical wave was not initiated by the subject. The informational basis for this haptic spatial ability was sought in the dynamics expressed by the one-dimensional wave equation, specifically, in the constants relating strand forces to strand motions.