4.3 The Capacity of Bare Fingers in Real Environments

The space covered by the two senses is also a very important difference. Vision allows the sensing of information kilometres away, while haptics is mainly restricted to the space within arm’s reach. There are possibilities of extending the haptically reachable space with tools, for instance, the long cane for the visually impaired and, to some extent, via information projected onto the skin. Both of these mechanisms are discussed in the sequel. Thus, haptics can provide spatial information, but it has a more limited capacity for overview and 3D space covered than vision.

In spite of these differences it is sometimes possible to use direct translation from visual forms to tactile forms when presenting forms tactually, namely when the figures are not too complicated. However, the more complicated the figure is, the less suitable it may be (Lederman and Campbell 1982).

A very important aspect of choosing tactile symbols is that they should be chosen on the basis of their discriminability tactually. Symbols that are easy to discriminate visually may be quite hard to discriminate when presented for tactual reading (Jansson 1972; Lederman and Kinch 1979).

One possibility to improve the functioning of tactile graphics is to provide redundant information, for instance by making symbols differ in both size and form (Schiff and Isikow 1966).

4.3 The Capacity of Bare Fingers in Real Environments

When investigating the usefulness of technical devices utilizing haptics it is instructive to understand the natural functioning of haptics. It is very often used both for guiding actions and for picking up information, also for sighted people. An everyday example is when you are searching for an object in your pocket or bag without the help of vision. With haptics you can identify the object wanted, grasp it with suitable force and take it out for the use you want. The potential to identify common objects by haptics is quite high, close to perfect within a few seconds (Klatzky et al. 1985).

Katz (1989) gave many examples of the capacity of haptics. For instance, it is remarkable that haptics can demonstrate transparency capabilities, as when physicians by palpation of the surface of a body can obtain information about the conditions of an organ under the skin and fat layers. A related property of haptics is remote touching, that is, the experience of a distant object via some medium. Physicians can perceive properties of the inner parts of the body also via instruments. Visually impaired persons with a long cane can perceive the properties of the ground at the end of the tip of the cane when touching it with the cane. A car driver can feel the goodness of the road via the tyres. In the latter example, the observer does not only receive information via the hands, but also via other parts of the body. Very sensitive parts of the body tactually are the lips and the mouth, which is important for the perception of food. The capacity of the tongue has more recently been used in the context of sensory substitution; see the work due to Bach-y-Rita et al. (1998, 2003) and Bach-y-Rita and Kercel (2003). Katz also reported on experiments with arm amputees, asking them to explore

140 4 Haptics as a Substitute for Vision

surfaces with information from the stump only. Even if the performance was not as good as with the hand, it was remarkably good, which makes understandable that amputees sometimes complain about perception being impoverished with an artificial limb attached.

4.3.1 Visually Impaired People’s Use of Haptics Without any Technical Aid

People with severe loss of vision have to rely on other senses, mainly haptics and hearing, in many everyday tasks, for instance, find the exact location of a chair to sit on, pick up an object lost on the floor, get the tooth-brush in the bathroom, experience the presence of other persons in the room, and so on. Learning to exploit these alternative possibilities is a lifelong process. Blind people with additional handicaps concerning the other senses have, of course, a much harder time.

Several aspects of visually impaired people’s use of haptics are covered in multiauthored books edited by Schiff and Foulke (1982), Heller and Schiff (1991), Heller (2000) and Ballesteros Jim´enez and Heller (2004).

In addition to other uses already mentioned here, social touching, that is handshaking, encouraging pats on the back, hugging, and other more or less intimate contacts between people, may be mentioned. Social touching plays a great role emotionally for most people, handicapped or not, but especially for visually impaired people who are deprived of visual emotional contacts (Thayer 1982). In the case of vulnerable visually impaired and blind people, it is absolutely essential that the person be told who is making the social contact before any physical contact proceeds. This gives the vulnerable person time to decide whether they will accept the social physical contact and in what form they will accept it.

4.3.2 Speech Perceived by Hard-of-hearing People Using Bare Hands

Many people with hearing problems use, especially in communication with other hard-of-hearing people, sign language, that is, they use more or less standardized gestures as a replacement for talking and listening. When communicating with a speaking person they often use visual information from the lip movements of the speaker for understanding (lip reading). One of the problems with lip reading is that it provides ambiguous information about some speech sounds, especially between voiced and voiceless sounds with the same lip movements (b/p, d/t and g/k). A method for a sighted deaf person to enhance the information from visual lip reading is to get tactile information about the vibrations in the vocal tract by holding a hand on the speaker’s neck. An elaboration of this method was developed by Ohngren¨ (1992) in cooperation with a totally deaf man. The background of this method was that this man as a boy found out by himself that he could understand speech better if he held a hand on some outer parts of the speaker’s vocal tract. As an adult he refined this method further. He even learned to understand a foreign language without ever having heard it spoken.

Lip reading cannot be used by deaf blind people. A remarkable capacity of haptics is revealed by deaf blind people’s ability to recognize speech only via haptics. Some