Texture perception via active touch

Movement Kinematics of the Braille-reading Finger

A new means of measuring the movement properties of the braille-reading finger is described and exemplified in an experiment in which experienced readers of braille encountered sentences comprised of keywords in which word and orthographic frequencies were manipulated. These new data are considered in theoretical and practical terms.

The Design of Tactile Thematic Symbols

The study reported here investigated the design and legibility of tactile thematic maps, focusing on symbolization and the comprehension of spatial patterns on the maps. The results indicate that discriminable and effective tactile thematic maps can be produced using classed data with a microcapsule paper production method. The participants demonstrated that they could describe the spatial data patterns that were displayed.

An empirical approach on the design of tactile maps and diagrams: The cognitive tactualization approach

Tactile maps and diagrams need to be carefully designed in order to be readable by the visually impaired user. In the Tactile Inkjet Mapping Project, we attempt to provide a new orientation for tactile map design through a rigorous programme of experimental research on design issues ( cognitive tactualization approach). In this article we discuss three of our studies. The first study evaluates the use of different background materials for tactile graphics. The second study looks at the minimal perceptible distance between two lines. The third study investigates the optimal elevation (height off the paper) at which graphics are produced. We argue that experimental studies like these represent a necessary basis for the design of tactile maps.

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.

Texture information in tactual space perception

The significance of texture as a source of information in tactual space perception was studied using a linear positioning task. A spatial texture gradient, whose elements changed with position and distance, a homogeneous raised-element pattern and a smooth surface were used. Participants had to reproduce locations and distances on these surfaces under various conditions. In active conditions, participants moved their indexfinger across the surface. In passive conditions, the texture was moved beneath the indexfinger of the participant. In conditions with equal movement speed, movement speeds' of criterion and reproduction phase were matched, in conditions with unequal movement speed, they did not match. The largest errors were obtained for the combined passive movement-unequal movement speed conditions. In these conditions, differences between textures were visible for signed and unsigned errors, indicating that textures may differ in the cutaneous specification of distance and location.

Exploration of surface-textures in congenitally blind infants

The haptic exploratory procedures that eight congenitally blind infants aged 8-24 months used to explore a gradient surface texture were investigated. Exploration of the gradient texture was examined over five sessions with 2 weeks between sessions, followed after 1 week by a sixth session, in which exploration of the gradient texture was compared to exploration of two other textures. Results showed that the infants have a wide range of exploratory strategies available and that the older infants can use these strategies in a specific manner. Results are discussed with reference to current ideas about the exploratory possibilities of congenitally blind infants. Use of texture in the stimulation of exploration of blind infants is discussed.