Tactile roughness of grooved surfaces: The touching process and effects of macro- and microsurface structure

Ss made magnitude estimates of the perceived roughness of grooved aluminum plates. Two aspects of the touching process were altered and their effects upon roughness examined. Roughness increased with increasing finger force, regardless of whether the S or the E chose the values. Rate of hand motion had a negligible effect on perceived roughness, indicating a roughness constancy and providing further evidence of the relative unimportance of vibratory frequency. The effects of these components of the touching process were discussed in terms of an active-passive continuum rather than a dichotomy. Perceived roughness declined with increasing land width (with narrow grooves), although only over the widest half of the land range; there was no land effect when the grooves were wide. In addition to these macrostructural parameters, the effects of two stimulus production techniques were compared. The discrepancies between the two sets of data were interpreted in terms of the microscopic irregularities of the plate surfaces. The findings were briefly related to an analysis of perceived roughness of grooved surfaces in terms of static deformation of the skin.     

Tactile roughness of grooved surfaces: A model and the effect of friction

Previous experimental data on the roughness of grooved aluminum tiles provide a data base against which to test theories of roughness perception. A model based on the static deformation of the skin touching the stimulus tile is developed, and 11 parameters of the deformation are individually compared with the experimental data. All parameters were tested first in an approximate way, and then the better parameters were recalculated in a more exact manner. Three parameters, the depth to which the finger penetrates the groove, the cross-sectional area of the finger within the groove, and the cross-sectional area of the deviation of the skin from its resting position, all predict the roughness well as a function of finger force and groove width. The last of the three predicts roughness best as a function of land width, and is tentatively preferred as “the stimulus for roughness.” All predictions from the static model indicate that variation of the coefficient of friction between skin and tile should have little or no effect. This counterintuitive prediction was confirmed by an experiment.     

Perceived roughness as a function of body locus

Twenty subjects made magnitude estimates of the roughness of grooved metallic surfaces applied to 10 body loci. To a first approximation, perceived roughness grew as a power function of groove width, in accordance with earlier studies. The exponents and intercepts (up-down position in log-log coordinates) of the power function turn out to depend strongly on body locus. The straight lines in log-log coordinates tend to diverge with groove width so that differences among body loci are especially pronounced at large groove widths. Sensitivity to roughness was greatest for the lips, fingers, and forearm, and least for the heel, back, and thigh. The rank order of the body loci in terms of roughness sensitivity closely parallels the rank order for punctate pressure sensitivity, as reported by von Frey in 1894, but apparently not for other measures of tactile sensitivity, such as vibration thresholds to various frequencies, two-point thresholds, and error of point localization.     

Roughness perception in haptic virtual reality for sighted and blind people

Psychophysical functions for perceived roughness, relating ln (magnitude estimate of roughness) to ln (groove width), were obtained for blind and sighted participants in virtual reality using the PHANToM force feedback device. The stimuli were sinusoidal surfaces with groove widths between 0.675 mm and 20.700 mm. Group functions showed a similar nonlinearity to those obtained in physical reality using rigid probes (Klatzky, Lederman, Hamilton, Grindley, & Swendsen, 2003; Lederman, Klatzky, Hamilton, & Ramsay, 1999). Individual functions gave a different picture. Of 23 total participants, there were 13 with wholly descending linear psychometric functions, 7 with quadratic functions similar to the group function, and 3 with anomalous functions. Individual power law exponents showed no significant effects of visual status. All analyses gave a power law exponent close to -0.80. The implications for theories of roughness, methodologies of data analysis, and the design of haptic virtual reality interfaces are considered.     

Fingertip force,surface geometry,and the perception of roughness by active touch

Ss made magnitude estimates of the perceived roughness of grooved metal plates under conditions of active touch with controlled finger force. The wider the grooves in the plate, the narrower the lands between the grooves, or the greater the finger force, the greater was the perceived roughness. Increase in finger force also slightly increased the slope of the magnitude estimation function, suggesting not only that the roughness of a uniform surface but also the contrasts in the roughness of differing parts of a patterned surface would be altered by changes in the manner of feeling the surface. An analogous effect has been reported in vision, in that increases in illumination increase the apparent contrast of a surface.     

Tactile perception of nonpainful unpleasantness in relation to perceived roughness: effects of inter-element spacing and speed of relative motion of rigid 2-D raised-dot patterns at two body loci

Rigid surfaces consisting of spatially jittered 2-D raised-dot patterns with different inter-element spacings were moved back and forth across the skin at three different speeds (10-fold range). Within each psychophysical experiment, participants numerically estimated the perceived magnitude of either unpleasantness (nonpainful) or roughness of 2-D raised-dot surfaces applied to two stationary body sites (experiment 1: fingers; experiment 2: forearm). The psychophysical functions for the two types of perceptual judgment were highly similar at both body loci; more specifically, the perceived magnitude of unpleasantness and roughness both increased monotonically as a power function of increasing inter-element spacing, with the rate of growth declining at the upper end of the continuum. These results suggest that inter-element spacing is a critical determinant of the perceived magnitude of unpleasantness (nonpainful), as well as of roughness. Each perceptual judgment also increased as a function of increasing relative speed at both body loci. However, the magnitude of this effect was significantly greater for perceived unpleasantness than for perceived roughness; conversely, the speed effect was significantly greater on the forearm than on the fingers. Several possible explanations for these findings are considered.     

Tactile roughness perception with a rigid link interposed between skin and surface.

Subjects made roughness judgments of textured surfaces made of raised elements, while holding stick-like probes or through a rigid sheath mounted on the fingertip. These rigid links, which impose vibratory coding of roughness, were compared with the finger (bare or covered with a compliant glove), using magnitude-estimation and roughness differentiation tasks. All end effectors led to an increasing function relating subjective roughness magnitude to surface interelement spacing, and all produced above-chance roughness discrimination. Although discrimination was best with the finger, rigid links produced greater perceived roughness for the smoothest stimuli. A peak in the magnitude-estimation functions for the small probe and a transition from calling more sparsely spaced surfaces rougher to calling them smoother were predictable from the size of the contact area. The results indicate the potential viability of vibratory coding of roughness through a rigid link and have implications for teleoperation and virtual-reality systems.     

Tactile roughness perception with a rigid link interposed between skin and surface

Subjects made roughness judgments of textured surfaces made of raised elements, while holding stick-like probes or through a rigid sheath mounted on the fingertip. These rigid links, which impose vibratory coding of roughness, were compared with the finger (bare or covered with a compliant glove), using magnitude-estimation and roughness differentiation tasks. All end effectors led to an increasing function relating subjective roughness magnitude to surface interelement spacing, and all produced above-chance roughness discrimination. Although discrimination was best with the finger, rigid links produced greater perceived roughness for the smoothest stimuli. A peak in the magnitude-estimation functions for the small probe and a transition from calling more sparsely spaced surfaces rougher to calling them smoother were predictable from the size of the contact area. The results indicate the potential viability of vibratory coding of roughness through a rigid link and have implications for teleoperation and virtual-reality systems.     

Feeling textures through a probe: effects of probe and surface geometry and exploratory factors

Vibratory roughness perception occurs when people feel a surface with a rigid probe. Accordingly, perceived roughness should reflect probe and surface geometry, exploratory speed, and force. Experiments 1 and 2 compared magnitude estimation of roughness with the bare finger and two types of probes, one designed to eliminate force moments, under the subject's active control. Experiments 3 and 4 varied speed under passive control. Log magnitude was consistently a quadratic function of log spacing between elements in the surface. The location of the function's peak was related to the drop point--that is, the spacing at which the probe can just drop between elements--which is affected by probe tip diameter, element height, and speed. Other parameters of the quadratic were affected by probe type and speed.     

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.     

Processing of tactile spatial information with crossed fingers

The erroneous perception of two objects when one object is touched with crossed fingers has been explained as an inability of the brain to correctly perceive the crossed fingers' positions. This account is examined in Experiment 1, in which the perceived position of stimuli touching the crossed fingers is mapped. Crossing the third finger over the fourth displaced the perceived stimulus position counter-clockwise; crossing the third under the fourth displaced perceptions clockwise. In Experiment 2, perceived positions were found to fit a model of tactile saturation past the point of the functional range of action of the fingers. Two major conclusions are drawn: (a) Tactile stimuli are always perceived as if fingers were uncrossed, and (b) spatial mapping is present only within the functional range of finger excursion.     

Cross-modality matches of finger span and line length

Perceived finger span—the perceived spatial separation between the tip of the thumb and the tip of the index finger—was measured by using cross-modal matching to line length. In the first experiment, subjects adjusted finger span to match the length of line segments presented on a video monitor, and conversely, with both hands. Subjects also made estimates of finger span in physical units (“dead reckoning”). Finger spans were measured by using infrared LEDs mounted on the tip of the thumb and the finger tip, so the hand made no contact with any object during the experiment. Unlike in previous studies, the results suggest that perceived finger span is proportional to line length and slightly shorter than the actual span, provided that corrections are made for regression bias. The effect of finger contact was assessed in a second experiment by matching line length both to free span and to spans constrained by the pinching of blocks in the same session. The matching function when subjects were pinching blocks was accelerating, consistent with previous reports. In contrast, matched line length was a decelerating function of free span. The exponent of the free span matching function in the second experiment was slightly smaller than in the first experiment, probably due to uncorrected matching biases in the second experiment.     

Psychological analyses of haptic and haptic-visual judgements of extent

Magnitude estimates of haptic extent resulted in positively accelerated psychophysical power function with an exponent of 1.18. However, in two further experiments right-handed male subjects made rating-scale judgements of the combined width of two stimulus blocks. Six widths were used and five replications of the 36 factorial combinations were presented to each subject. In Experiment II both stimuli were out of view and one was held between the thumb and index finger of each hand. In Experiment III one stimulus was held out of view between thumb and finger of the right hand and the second was shown to the subject. Mean ratings in both experiments were fit by a model which assumes that responses are a weighted average of the scale values of the two stimuli (Anderson, 1974a).     

Neutral vs ego-orienting instructions: Effects on judgments of magnitude estimation

Three experiments were performed to examine the relative constancy of the exponent in the psychophysical power law under varying motivating conditions. The method of magnitude estimation was used to obtain judgments of apparent tactual roughness or of apparent area size of squares. Patterns of the qualitative observations of the three Es and of the various exponents for the six groups of Ss indicated that neutral instructions and “ego-orienting” instructions, which were perceived as unbelievable coming from an equal fellow student, both yielded exponents identical to those reported in the literature. Believable ego-orienting instructions given by an E of clearly perceived higher social status produced a statistically significantly lower exponent than neutral. Intermediate conditions, wherein Ss apparently disbelieved both types of instructions, but assumed that the superior-status E was “analyzing” them, yielded exponents of intermediate size. Results and supplementary trend analyses are discussed as possible, highly sensitive indicators of motivational impacts on sensory judgments.     

Effects of steady-state exercise on perceived pain: comparison of sedentary students and cyclists

In this study, the effect of fitness level on perceived pain before and after a steady state exercise was investigated. Ten trained cyclists (M age=25.2 yr., SD=4.9) and 10 sedentary men (Mage=24.5 yr., SD=2.2) performed a maximal graded test on a cycle ergometer. At least 48 hr. later the participants of both groups performed a 30-min. steady-state cycling test at 75% of VO2 max. Before the steady-state exercise and 5- and 30-min. postexercise, a pressure pain stimulation test was applied on the finger of each participant. Perceived pain was measured with Borg's CR10 scale at the end of each pain stimulation. The results indicated no significant changes in perceived pain between the pre-exercise and 5- and 30-min. postexercise values (effect sizes=.07 and .19, respectively). Moreover, no significant difference in perceived pain was found between the groups for pre-exercise (ES=.02) and 5- and 30-min. postexercise (ES=.16 and .21, respectively) values. These results do not confirm the analgesic effects usually observed after steady state exercise. Therefore, it is not possible to compare the analgesic effect of this exercise mode between participants characterized by different fitness levels.     

Perception of depth: Processing of simple positional disparity as a function of viewing distance

Dependency of perceived depth (relative to the fixation point) on disparity, viewing distance, and the type of the stereoscopic stimulus was investigated. Nearly complete constancy of depth, as required for a veridically matched perception, was observed only at small disparity values and with the larger square-formed stimulus; under these conditions, perceived depth corresponded well with real depth intervals for close viewing distances. Additionally, a model for perceptual processing of both variables, disparity and viewing distance, was applied to the data.     

The kinesthetic fusion effect: Perceptual elimination of spatial discordance in the kinesthetic modality

Three experiments in intrasensory kinesthetic discordance are reported. The treatment required both arms to be outstretched in the midsagittal plane. In the absence of vision, a finger of one hand depressed a button that caused a probe to touch the other arm 12.7 cm closer to the body than the position of the finger. This difference was at first clearly sensed, but very rapidly the disparate positions were perceived to be identical: We have called this “the kinesthetic fusion effect.” It was also shown that a delay of up to 4 sec in probe onset after the finger depressed the button did not diminish the extent of fusion. The phenomenon gave rise to a predictable aftereffect, in which a probe directly opposite to the active finger was sensed to be farther away than the finger. The results were not due either to joint adaptation or to postural aftereffects.     

Cultural Values,Counseling Stigma,and Intentions to Seek Counseling Among Asian American College Women

The authors explored the extent to which Asian American college women's perceived stigma about counseling mediated the relationship between their adherence to Asian cultural values and intentions to seek counseling. Participants, 201 Asian American college women (age range = 18–24 years), completed measures of Asian cultural values, perceived stigma regarding counseling, and intentions to seek counseling, along with a demographic questionnaire. Asian cultural values were positively correlated with perceived counseling stigma; both Asian cultural values and social stigma were negatively correlated with intentions to seek counseling. The main analysis showed that perceived counseling stigma partially mediated the relationship between participants' Asian cultural values and intentions to seek counseling.     

Perceived distributions of the characteristics of in-group and out-group members: empirical evidence and a computer simulation

This research studied 2 properties of perceived distributions of the characteristics of social category members: the probability of differentiating (making distinctions) among category members and the perceived variability (variance) of category members. The results of 4 experiments supported the hypothesis that greater familiarity with a social group leads to greater perceived differentiation and variability regarding that group. In-group members formed more differentiated and variable distributions for groups defined by age and more differentiated distributions for groups defined by nationality. For gender (where students were roughly equally familiar with people of both genders), no in-group--out-group differences occurred. Also, students perceived greater differentiation and variability among classmates over the course of a semester. To explain these results, we developed PDIST, a multiple exemplar model that assumes that people form perceived distributions by activating a set of category exemplars and then judging the relative likelihoods of different feature values on the basis of the relative activation strengths of these feature values. The results of a computer simulation experiment indicated that PDIST is sufficient to explain the results of our 4 experiments. According to the perceived distributions formed by PDIST, increasing familiarity leads to greater differentiation and variability, has a concave impact, and has greater impact on differentiation than on variability.     

Roughness perception across the hands

It has previously been shown that the perceived roughness of a surface touched by one digit is influenced by the roughness of a different surface touched simultaneously by another digit on the same hand. The present study was designed to examine whether this is the case when surfaces of varying roughness are touched using digits on separate hands. Participants touched pairs of sandpaper surfaces, in sequence, using the same digit, and identified which of the two was rougher. Roughness discrimination was measured in the presence of distractor surfaces touched simultaneously with the target surface, but using a different digit either on the same or on the other hand. The overall perception of roughness of the attended surfaces was better on the left than on the right hand. Perceived roughness also varied systematically with the roughness of the distractor surfaces. Attended surfaces were more likely to be perceived as smoother when they were paired with smooth rather than rough distractors. Likewise, attended surfaces tended to be perceived as rougher with rough distractors. This pattern of results occurred whether the attended and distractor digits were on the same hand or different hands. These data confirm that it is difficult to restrict tactile attention for roughness to a single digit and show that this difficulty extends to restricting attention to a single hand. Furthermore, the effect of a stimulus at an unattended body location was not simply to impair perception in general, but to bias it in the roughness direction of the distractor surface.