Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. Mar-Jun 2007;24(1-2):53-70.
doi: 10.1080/08990220701318163.

Texture Perception Through Direct and Indirect Touch: An Analysis of Perceptual Space for Tactile Textures in Two Modes of Exploration

Affiliations
Free PMC article

Texture Perception Through Direct and Indirect Touch: An Analysis of Perceptual Space for Tactile Textures in Two Modes of Exploration

T Yoshioka et al. Somatosens Mot Res. .
Free PMC article

Abstract

Considerable information about the texture of objects can be perceived remotely through a probe. It is not clear, however, how texture perception with a probe compares with texture perception with the bare finger. Here we investigate the perception of a variety of textured surfaces encountered daily (e.g., corduroy, paper, and rubber) using the two scanning modes - direct touch through the finger and indirect touch through a probe held in the hand - in two tasks. In the first task, subjects rated the overall pair-wise dissimilarity of the textures. In the second task, subjects rated each texture along three continua, namely, perceived roughness, hardness, and stickiness of the surfaces, shown previously as the primary dimensions of texture perception in direct touch. From the dissimilarity judgment experiment, we found that the texture percept is similar though not identical in the two scanning modes. From the adjective rating experiments, we found that while roughness ratings are similar, hardness and stickiness ratings tend to differ between scanning conditions. These differences between the two modes of scanning are apparent in perceptual space for tactile textures based on multidimensional scaling (MDS) analysis. Finally, we demonstrate that three physical quantities, vibratory power, compliance, and friction carry roughness, hardness, and stickiness information, predicting perceived dissimilarity of texture pairs with indirect touch. Given that different types of texture information are processed by separate groups of neurons across direct and indirect touch, we propose that the neural mechanisms underlying texture perception differ between scanning modes.

Figures

Figure 1.
Figure 1.
Subject’s (left) and experimenter’s (right) view of the experimental setup. The green circle signaled the beginning of the trial. The subject placed the finger or probe on the leftmost platform of the stimulus assembly and waited for the circle to disappear, at which time the subject began moving the finger or probe to their right. As the subjects scanned the finger/probe to the right, they reached the first aperture (i.e., the first stimulus). The subjects explored the first stimulus by scanning it in a back and forth motion with the finger/probe for as long as they wished. The subjects then slid the finger/probe up the rightmost edge of the aperture, across a short platform on the stimulus assembly, to the second aperture. Again, the subjects explored the stimulus by scanning back and forth until they were satisfied, and then slid the finger/probe out of the second aperture. When the finger/probe was on the rightmost platform, the subjects removed the finger/probe from the assembly and provided the experimenter with their dissimilarity rating. In the adjective rating task, subjects explored only the first texture, then produced their rating.
Figure 2.
Figure 2.
Vibrations recorded from scanning corduroy when the texture surface was moved at 40 mm/s against a Delrin probe (diameter = 3mm) held by a stationary hand. A tri-axial accelerometer attached to the top of the probe monitored accelerations along the x- (scanning direction), y- (orthogonal to x in the horizontal plane), and z-(vertical) axes. The corresponding Fourier spectra are shown on the right. Notice that the amplitudes of Fourier components along the scanning direction (x) are the largest, and that the same frequency peaks (13.5, 27, 40 Hz) are present in the y- and z-axes.
Figure 3.
Figure 3.
Vibration (acceleration) signals recorded in the scanning direction (left panels) and their corresponding Fourier spectra (right panels; logarithmic) for five sample textures. (See figure 2 for details).
Figure 4.
Figure 4.
Normalized dissimilarity ratings for the 120 texture pairs obtained in the finger-scanning condition vs. ratings obtained in the probe-scanning condition. Dissimilarity ratings were first normalized within block by dividing each dissimilarity rating by the mean rating for that block. Ratings were then averaged over eight subjects and five repeats. The solid line is the least-squares regression line, and error bars show the standard error of the mean. The perceived dissimilarity of textures was similar but not identical in the two scanning conditions.
Figure 5.
Figure 5.
Results from the adjective scaling experiment. Perceived roughness (top panel), hardness (middle panel), and stickiness (bottom panel), normalized within block then averaged over eight subjects. Solid bars show the results obtained in the finger-scanning condition, and open bars represent the results obtained in the probe-scanning condition. For many textures, ratings are similar between finger- and probe-scanning conditions. Some textures, however, yielded considerably different ratings in the two conditions along some textural continua (e.g., the perceived stickiness of glass was high in the finger-scanning condition and low in the probe-scanning condition). Textures are ordered from the left to the right in increasing order of perceived roughness in the finger-scanning condition. Error bars show standard error of the mean.
Figure 6.
Figure 6.
Normalized perceived roughness (left panel), hardness (middle panel), and stickiness (right panel) ratings obtained in the finger-scanning condition vs. ratings obtained in the probe-scanning condition. Data are the same as those presented in Figure 5. Roughness ratings obtained in the two scanning conditions are highly correlated whereas hardness and stickiness ratings are less so. Error bars show the standard error of the mean.
Figure 7.
Figure 7.
Predicted vs. measured dissimilarity in the finger-scanning (left panel) and probe-scanning (right panel) conditions. To obtain the predicted dissimilarity ratings, we first regressed pair-wise differences in the subjects’ ratings along the three texture continua on predicted dissimilarity, then used the resulting regression coefficients to generate the estimates (see text for details). The match between predicted and measured dissimilarity suggests that, in both scanning conditions, perceived dissimilarity can be reliably predicted from differences in roughness, hardness, and stickiness.
Figure 8.
Figure 8.
Relative locations of 16 textures are shown in the multidimensional scaling (MDS) space model based on perceived dissimilarity ratings (dark blue dots with vertical gray lines) and their relation to perceived roughness (red line), hardness (green line), and stickiness (dark blue line). Left panel shows a plot in the finger-scanning condition and right panel shows probe-scanning condition. The radii of the spheres represent the overall mean of adjective ratings, and angle values provide the degree of orthogonality between the two adjective axes. These angles were measured between the high ends of the two adjective axes (where the words “Rough”, “Hard”, or “Sticky” are placed). MDS solutions of dissimilarity ratings are based on 3D models in which each axis (Dimensions 1–3) is chosen arbitrarily to attain best fit between the model and normalized ratings. Averaged data over eight subjects in each scanning condition were used. Note a large difference in angle between the hardness and stickiness axes across two modes of scanning (47°: finger scanning, 150°: probe scanning), demonstrating that the correlations of the ratings along these two continua are different across two modes of scanning (Table III).
Figure 9.
Figure 9.
Cluster plots (dendrograms) of inter-texture distances in perceptual space based on the 3D multidimensional scaling (MDS) models using perceived dissimilarity of texture pairs. Different colors are used to categorize different clusters at the thresholded at, two standard deviations above the mean perceptual distance.
Figure 10.
Figure 10.
Scree plots illustrating the coefficient of determination R² achieved by an n-dimensional MDS model as a function of the dimensionality of the model for dissimilarity ratings obtained in the finger-scanning (circles) and probe-scanning (squares) conditions. Two or more dimensions are necessary to achieve a good fit in the finger-scanning and probe-scanning conditions at the level above R² = 0.9.
Figure 11.
Figure 11.
Physical quantities associated with perceived roughness, hardness, and stickiness when exploring textures through probes. (A) Log power of texture-elicited vibrations vs. subjective roughness magnitude. Correlation coefficients between log vibratory power and perceived roughness, hardness, and stickiness were 0.92, 0.04, and 0.23, respectively. (B) Perceived hardness vs. log relative compliance. Relative compliance was given by the ratio between the displacement of a Delrin 3-mm diameter probe into a textured surface and the weight that produced it (in cm/g). Correlation coefficients between log relative compliance and perceived roughness, hardness, and stickiness were 0.43, −0.93, and 0.59, respectively. (C) Perceived stickiness vs. the log coefficient of friction. Correlation coefficients between log coefficient of friction and perceived roughness, hardness, and stickiness were 0.57, −0.54, and 0.82, respectively. Thus, perceived roughness is associated with vibratory information, perceived hardness with relative compliance, and perceived stickiness with friction.

Similar articles

See all similar articles

Cited by 32 articles

See all "Cited by" articles

Publication types

Feedback