Angle Discrimination in Raised-Line Drawings

Touching and hearing the shapes: How auditory angular and curved sounds influence proficiency in recognising tactile angle and curve shapes when experienced and inexperienced in using haptic touch

This study investigated whether adding auditory angular and curved sounds to tactile angle and curve shapes – one unspecified sound to one unspecified shape – positively influences the accuracy and exploration time in recognising tactile angles and curves when experienced and inexperienced in using haptic touch. A within-participant experiment was conducted, with two groups of participants: experienced and inexperienced in using haptic touch, and with two conditions: congruous (e.g., angle shape and angular sound) and incongruous (e.g., angle shape and curved sound) tactile and auditory shape information. Adding congruous auditory angular and curved sounds to tactile angle and curve shapes positively influences the accuracy in recognising tactile angles and curves both when experienced and inexperienced in using haptic touch, and the exploration time on correct recognitions when experienced. People integrate tactile and auditory (angle; curve) shape information and this improves their proficiency in recognising tactile angles and curves.

Improved access to museum collections without vision: How museum visitors with very low or no vision perceive and process tactile–auditory pictures

This study investigated how museum visitors with very low or no vision perceived and processed tactile pictures and/or audio-descriptions of visual paintings. Two visual paintings were selected and a focus group was established ( N = 8). Qualitative interview and observation data were collected. This study found two types of museum visitors: those who explored the tactile picture first and those who rather listened to the audio-description. When exploring each element in the tactile picture, they all started by exploring the element’s global (shape) outline and, when struggling to recognise it, turned to the audio-description. They preferred the audio-description to start describing where their fingers were. Tactile texture attracted their attention, sparked their curiosity, and enabled them to create a mental image of the tactile picture, but also confused them. They preferred the global (element shape) outline to be straightened out, so that curves become angular, and texture only for targeting certain elements.

Proximal-distal, not medial-lateral, movement across an edge increases discrimination of edge sharpness

Edges are fundamental properties of our environment and the objects we interact with. There is a lack of research on the haptic perception of edges, especially the sharpness of an edge. Skinner et al. [2013 PLoS ONE, 8(9): e73283] found that haptic discriminability of sharpness was clearly superior when using a relatively unrestrained, free exploration strategy compared with a static single touch strategy. In the free exploration condition two distinct movement patterns were frequently used by participants: a proximal-distal movement of the fingerpad across the test edge and a medial-lateral movement of the fingerpad along the test edge. Here, using the same stimuli and two-alternative forced-choice method of constant stimuli as Skinner et al. (2013), we demonstrate that a proximal-distal movement results in substantially lower sharpness discrimination thresholds than a medial-lateral movement. The underlying neurophysiology and implications for the design of haptic displays are considered.

Path integration in tactile perception of shapes

Whenever we move the hand across a surface, tactile signals provide information about the relative velocity between the skin and the surface. If the system were able to integrate the tactile velocity information over time, cutaneous touch may provide an estimate of the relative displacement between the hand and the surface. Here, we asked whether humans are able to form a reliable representation of the motion path from tactile cues only, integrating motion information over time. In order to address this issue, we conducted three experiments using tactile motion and asked participants (1) to estimate the length of a simulated triangle, (2) to reproduce the shape of a simulated triangular path, and (3) to estimate the angle between two-line segments. Participants were able to accurately indicate the length of the path, whereas the perceived direction was affected by a direction bias (inward bias). The response pattern was thus qualitatively similar to the ones reported in classical path integration studies involving locomotion. However, we explain the directional biases as the result of a tactile motion aftereffect.

On the edge: haptic discrimination of edge sharpness

The increasing ubiquity of haptic displays (e.g., smart phones and tablets) necessitates a better understanding of the perceptual capabilities of the human haptic system. Haptic displays will soon be capable of locally deforming to create simple 3D shapes. This study investigated the sensitivity of our haptic system to a fundamental component of shapes: edges. A novel set of eight high quality shape stimuli with test edges that varied in sharpness were fabricated in a 3D printer. In a two alternative, forced choice task, blindfolded participants were presented with two of these shapes side by side (one the reference, the other selected randomly from the remaining set of seven) and after actively exploring the test edge of each shape with the tip of their index finger, reported which shape had the sharper edge. We used a model selection approach to fit optimal psychometric functions to performance data, and from these obtained just noticeable differences and Weber fractions. In Experiment 1, participants performed the task with four different references. With sharpness defined as the angle at which one surface meets the horizontal plane, the four JNDs closely followed Weber's Law, giving a Weber fraction of 0.11. Comparisons to previously reported Weber fractions from other haptic manipulations (e.g. amplitude of vibration) suggests we are sufficiently sensitive to changes in edge sharpness for this to be of potential utility in the design of future haptic displays. In Experiment 2, two groups of participants performed the task with a single reference but different exploration strategies; one was limited to a single touch, the other unconstrained and free to explore as they wished. As predicted, the JND in the free exploration condition was lower than that in the single touch condition, indicating exploration strategy affects sensitivity to edge sharpness.

Haptic perception

Fueled by novel applications, interest in haptic perception is growing. This paper provides an overview of the state of the art of a number of important aspects of haptic perception. By means of touch we can not only perceive quite different material properties, such as roughness, compliance, friction, coldness and slipperiness, but we can also perceive spatial properties, such as shape, curvature, size and orientation. Moreover, the number of objects we have in our hand can be determined, either by counting or subitizing. All these aspects will be presented and discussed in this paper. Although our intuition tells us that touch provides us with veridical information about our environment, the existence of prominent haptic illusions will show otherwise. Knowledge about haptic perception is interesting from a fundamental viewpoint, but it also is of eminent importance in the technological development of haptic devices. At the end of this paper, a few recent applications will be presented. WIREs Cogn Sci 2013, 4:357-374. DOI: 10.1002/wcs.1238 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Feeling through Tactile Displays: A Study on the Effect of the Array Density and Size on the Discrimination of Tactile Patterns

Tactile arrays are devices that can provide spatially distributed cutaneous signals delivering crucial information during virtual haptic exploration or remote manipulation procedures. Two of the key specifications of a tactile array are the tactor spacing and array size that are believed to directly affect the device performance. In most of the systems developed so far, these two parameters have been chosen by trial and error or by trying to match the tactor density to the spatial resolution in the human fingertip. The objective of this work is to study the effect of tactor spacing and array size on the tactile arrays performance by measuring human tactile discrimination ability. Psychophysical experiments were performed to obtain the differential threshold for discrimination of a ridge angle and the shape recognition performance while exploring edge-based patterns. The patterns were explored through different passive (nonactuated) tactile arrays of vertically moving pins and also directly with the finger. Results indicate that a tactile array of 1.8 mm tactor spacing and 1 cm(2) array size transmits the pattern information with a good level of accuracy. This work shows that tactile devices with low complexity (small number of tactors) are still effective in conveying tactile cues. Moreover, this work provides performance measures that determinate the capabilities of tactile pin arrays to convey accurately tactile information.

Raised-angle discrimination under passive finger movement

The characteristics of raised-line drawing discrimination can be defined as the sum of the discriminability of the length, curvature, and angles of the edges. The size of the angle between two edges constitutes an important feature of these tactile stimuli. In the first experiment, five standard angles (30 degrees, 60 degrees, 90 degrees, 120 degrees, and 150 degrees) and twenty comparison angles for each standard angle were used to investigate the human capacity for tactile discrimination of raised angles by passive finger movement. The subjects in this study were asked to identify the larger angle of each pair by passive finger movement. We found that the threshold doubled when the standard angle was increased from 30 degrees to 90 degrees; however, the threshold remained unchanged when the standard angle was greater than 90 degrees. In the second experiment, to investigate the influence of the endpoints on angle discriminability, we used one standard angle (60 degrees) and seven comparison angles that changed in four bisector orientations. The results indicate that cutaneous feedback from the local apex and endpoints of the angle contributed to the discrimination of acute angles. Taken together, these results suggest that, when an acute angle is presented, both local apex and endpoint informations are used, while cutaneous mechanoreceptors rely more on apex information to discriminate the angle size when an obtuse angle is presented.

[Visual cuing effect for haptic angle judgment]

We investigated whether visual cues are useful for judging haptic angles. Participants explored three-dimensional angles with a virtual haptic feedback device. For visual cues, we use a location cue, which synchronizes haptic exploration, and a space cue, which specifies the haptic space. In Experiment 1, angles were judged more correctly with both cues, but were overestimated with a location cue only. In Experiment 2, the visual cues emphasized depth, and overestimation with location cues occurred, but space cues had no influence. The results showed that (a) when both cues are presented, haptic angles are judged more correctly. (b) Location cues facilitate only motion information, and not depth information. (c) Haptic angles are apt to be overestimated when there is both haptic and visual information.