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.     

Material properties determine how force and position signals combine in haptic shape perception

When integrating estimates from redundant sensory signals, humans seem to weight these estimates according to their reliabilities. In the present study, human observers used active touch to judge the curvature of a shape. The curvature was specified by positional and force signals: When a finger slides across a surface, the finger's position follows the surface geometry (position signal). At the same time, it is exposed to patterns of forces depending on the gradient of the surface (force signal; Robles-de-la-Torre, G., & Hayward, V. (2001). Force can overcome object geometry in the perception of shape through active touch. Nature, 412, 445-448). We show that variations in the surface's material properties (compliance, friction) influence the sensorily available position and force signals, as well as the noise associated with these signals. Along with this, material properties affect the weights given to the position and force signals for curvature judgements. Our findings are consistent with the notion of an observer who weights signal estimates according to their reliabilities. That is, signal weights shifted with the signal noise, which in the present case resulted from active exploration.     

The contributions of egocentric and allocentric reference frames in haptic spatial tasks

The influence of egocentric and allocentric reference frames on performance in haptic spatial tasks, was tested in three conditions. Blindfolded subjects had to make two bars haptically parallel, perpendicular or mirrored in the midsagittal plane. The hypothesis is that the contributions of egocentric and allocentric reference frames are combined, resulting in settings that lie in between the allo-representation and the ego-representation. This leads to different predictions for the outcome of different conditions. All findings were consistent with the hypothesis. In addition, for subjects with large deviations a reversal of the oblique effect was found once again, which provides extra support for the hypothesis.     

The use of proprioception and tactile information in haptic search

To investigate how tactile and proprioceptive information are used in haptic object discrimination we conducted a haptic search task in which participants had to search for either a cylinder, a bar or a rotated cube within a grid of aligned cubes. Tactile information from one finger is enough to detect a cylinder amongst the cubes. For detecting a bar or a rotated cube amongst cubes touch alone is not enough. For the rotated cube this is evident because its shape is identical to that of the non-targets, so proprioception must provide information about the orientation of the fingers and hand when touching it. For the bar one either needs proprioceptive information about the distance and direction of a single finger’s movements along the surfaces, or proprioceptive information from several fingers when they touch it simultaneously. When using only one finger, search times for the bar were much longer than those for the other two targets. When the whole hand or both hands were used the search times were similar for all shapes. Most errors were made when searching for the rotated cube, probably due to systematic posture-related biases in judging orientation on the basis of proprioception. The results suggest that tactile and proprioceptive information are readily combined for shape discrimination.     

Parallel processing of shape and texture in haptic search

In a haptic search task, one has to determine the presence of a target among distractors. It has been shown that if the target differs from the distractors in two properties, shape and texture, performance is better than in both single-property conditions (Van Polanen, Bergmann Tiest, & Kappers, 2013). The search for a smooth sphere among rough cubical distractors was faster than both the searches for a rough sphere (shape information only) and for a smooth cube (texture information only). This effect was replicated in this study as a baseline. The main focus here was to further investigate the nature of this integration. It was shown that performance is better when the two properties are combined in a single target (smooth sphere), than when located in two separate targets (rough sphere and smooth cube) that are simultaneously present. A race model that assumes independent parallel processing of the two properties could explain the enhanced performance with two properties, but this could only take place effectively when the two properties were located in a single target.     

The effects of sex, age, and interval duration on the perception of time

The present experiment examined the interactive effects of sex, age, and interval duration on individual’s time perception accuracy. Participants engaged in the duration production task and subsequently completed questionnaires designed to elicit their temporal attitudes. The overall group of 100 individuals was divided evenly between the sexes. Five groups, each composed of 10 males and 10 females, were divided by decades of age ranging from 20 to 69 years old. The specific time estimation task was an empty interval production procedure composed of 50 trials on each of four different intervals of 1, 3, 7, and 20 s, respectively. The presentation orders of these intervals were randomized across participants but yoked across the sexes within each of the respective age groups. Analysis of the production results indicated significant influences for the sex of the participant while age did not appear to affect estimates of these short durations. Temporal attitudes, as reflected in responses to time questionnaire inquiries, did however exhibit significant differences across age. The contending theoretical accounts of such sex and age differences are considered and explanatory accounts that present a synthesis of endogenous and exogenous causal factors are discussed in light of the present pattern of findings.     

Seeing and feeling volumes: The influence of shape on volume perception

The volume of common objects can be perceived visually, haptically or by a combination of both senses. The present study shows large effects of the object's shape on volume perception within all these modalities, with an average bias of 36%. In all conditions, the volume of a tetrahedron was overestimated compared to that of a cube or a sphere, and the volume of a cube was overestimated compared to that of a sphere. Additional analyses revealed that the biases could be explained by the dependence of the volume judgment on different geometric properties. During visual volume perception, the strategies depended on the objects that were compared and they were also subject-dependent. However, analysis of the haptic and bimodal data showed more consistent results and revealed that surface area of the stimuli influenced haptic as well as bimodal volume perception. This suggests that bimodal volume perception is more influenced by haptic input than by visual information.     

Categorical perception of facial expressions of emotion: Evidence from multidimensional scaling

Recent studies have shown that the perception of facial expressions of emotion fits the criteria of categorical perception (CP). The present paper tests whether a pattern of categories emerges when facial expressions are examined within the framework of multidimensional scaling. Blends of five “pure” expressions (Angry, Sad, Surprised, Happy, Neutral) were created using computerised “morphing”, providing the stimuli for four experiments. Instead of attempting to identify these stimuli, subjects described the proximities between them, using two quite different forms of data: similarity comparisons, and sorting partitions. Multidimensional scaling techniques were applied to integrate the resulting ordinal-level data into models which represent the interstimulus similarities at ratio level. All four experiments yielded strong evidence that the expressions were perceived in distinct categories. Adjacent pairs in the models were not spaced at equal intervals, but were clustered together as if drawn towards a “perceptual magnet”; within each category. We argue that spatial representations are compatible with CP effects, and indeed are a useful tool for investigating them.     

A comparison of AME and CR100 for scaling perceived exertion

In psychophysical studies of the relation between perceived magnitude and physical stimulus, interest has focused on the preciseness of growth functions. Very little interest has been devoted to natural levels of an "absolute" character and to the validity of direct measurements. In this article, the Category (C)-Ratio (R) (CR) scaling methodology, developed by Borg (1973, 1977, 1982) is presented together with a new CR scale: the CR100 scale. In an experiment on perceived exertion, CR100 was compared with Absolute Magnitude Estimation (AME). Perceived exertion has the advantage of having easily measured physiological variables that can function as validity criteria. 32 persons (16 men and 16 women) participated as subjects on two different occasions, and the presentation order was counterbalanced. Results from CR100 and AME could be described equally well with psychophysical functions. The exponents obtained with CR100 were n = 1.60 for women and n = 1.69 for men, and the corresponding exponents for AME were n = 1.60 for women and n = 1.46 for men (with a "noise" constant included in the function). ANOVA showed that CR100 could make the predicted differentiation between sexes, whereas AME could not. This drawback with AME was also found when using the methods to predict working capacity.     

A multidimensional scaling and semantic differential technique study of the perception of environmental settings

Abstract.— Multidimensional scaling is compared with the semantic differential technique (SDT) as methods for dimensional analysis of the perception of environmental settings. In one experiment employing as stimuli SDT scales used in previous experiments a General Evaluation , a Social Status , a Potency , a Closedness , and an Affection factor were found for both methods. A Unity and a Complexity factor merged into a single factor, an O riginality factor was only found for multidimensional scaling. In a second experiment employing as stimuli perspective drawings of urban and suburban settings, the results differed in that the General Evaluation , the Social Status , the Closedness , and the Unity/Complexity factors were found for the SDT, and only the first two for multidimensional scaling. Further experiments with other stimuli and methods of representation are needed in order to draw firm conclusions regarding the correspondence between SDT and multidimensional scaling results within the area under consideration.     

Visual and haptic perception of the horizontal-vertical illusion

The horizontal-vertical illusion consists of two lines of the same length (one horizontal and the other vertical) at a 90 degree angle from one another forming either an inverted-T or an L-shape. The illusion occurs when the length of a vertical line is perceived as longer than the horizontal line even though they are the same physical length. The illusion has been shown both visually and haptically. The present purpose was to assess differences between the visual or haptic perception of the illusions and also whether differences occur between the inverted-T and the L-shape illusions. The current study showed a greater effect in the haptic perception of the horizontal-vertical illusion than in visual perception. There is also greater illusory susceptibility of the inverted-T than the L-shape.     

Discrimination and memory experiments on haptic perception of softness

This paper described a pilot study and two follow-up experiments, using a device developed in the laboratory to study the human fingertip's discrimination and memory for softness perception. According to the pilot study, soft objects were easier to identify than hard ones. When subjects touched objects, the number of times seemed to be from 2 to 6. For most, the touch frequency ranged from 0.3 to 1.3 Hz. In Exp. 1, the method of constant stimuli was used to study the human fingertip's stiffness difference threshold for haptic perception. The estimated difference threshold averaged over 24 subjects was 33 N/m. And, the stiffness difference thresholds for most people were in the range of 20 N/m to 40 N/m. In Exp. 2, the haptic memory span was discussed according to the recall experiment. Human haptic memory span lay between three and four items.     

The visual and haptic perception of natural object shape

In this study, we evaluated observers' ability to compare naturally shaped three-dimensional (3-D) objects, using their senses of vision and touch. In one experiment, the observers haptically manipulated 1 object and then indicated which of 12 visible objects possessed the same shape. In the second experiment, pairs of objects were presented, and the observers indicated whether their 3-D shape was the same or different. The 2 objects were presented either unimodally (vision-vision or haptic-haptic) or cross-modally (vision-haptic or haptic-vision). In both experiments, the observers were able to compare 3-D shape across modalities with reasonably high levels of accuracy. In Experiment 1, for example, the observers' matching performance rose to 72% correct (chance performance was 8.3%) after five experimental sessions. In Experiment 2, small (but significant) differences in performance were obtained between the unimodal vision-vision condition and the two cross-modal conditions. Taken together, the results suggest that vision and touch have functionally overlapping, but not necessarily equivalent, representations of 3-D shape.     

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.