4.4.5 The Main Lesson from Low-tech Aids

146 4 Haptics as a Substitute for Vision

used). The guide dog is useful for many aspects of mobility, but it cannot be made responsible for orientation in the larger environment. These constraints have motivated many efforts to construct devices that compensate for the constraints, called ETAs (Electronic Travel Aids). The compensating senses may be hearing or haptics, sometimes in combination. Options based on haptic information will be discussed here; also options based on hearing are discussed by Farmer and Smith (1997) and Jansson (2000b).

An early device intended for the guidance of locomotion was the Electrophthalm (Starkiewicz and Kuliszewski 1963) which reproduced visual information obtained from a camera onto a matrix of pins fastened on the forehead; a later version with a larger matrix (Palacz and Kurcz 1978) is shown in Figure 4.1.

A related device is the Tactile Vision Substitution System (TVSS) with some stationary versions presenting information via vibrating pins to, for instance, the back or, concerning mobile versions, via electrodes to the chest (Bach-y-Rita 1972); a version of the latter kind is also shown in Figure 4.1.

In these devices the camera on the head picks up environmental visual information that is transformed to a tactile matrix attached to the forehead, the chest or the back. The pattern changes according to motions in the environment and the movements of the pedestrian, as picked up by the video camera. One task is to localise and identify objects at a distance in three-dimensional space, another to guide the user to reach goal objects and to avoid obstacles during walking. These are tasks other than those usually performed by touch, that is, to inform about objects and events in contact with the skin. The skin can be seen to work in a way analogous to the retina of the eye (Bach-y-Rita 1972, p 30). However, for the tactile displays there are apparent limitations in spatial resolution that reduce the possibilities of object identification, as well as collecting distance information. In spite of this it has been reported that users can perceive objects external to the body as localized in the space in front of them (White et al. 1970). The reports are anecdotal, however, and there are also conflicting reports of not attaining external localization in spite of long training (Guarniero 1974, 1977).

On the other hand, it has been shown that tactile information provided by the Electrophthalm can guide walking (Jansson 1983). In an experiment the walking person had to make a slalom walk around two poles and towards a goal pole guided only by tactile information from a 12×18 matrix of vibrators on the forehead. The

Figure 4.1. Two devices with a matrix of point stimuli fed from a camera, the Electrophthalm (left) and a version of the Tactile Visual Substitution System (right). (Based on photographs taken by the author)

matrix information is depicted in Figure 4.2 and the resulting movement path is shown in Figure 4.3 together with a visually guided path. Even if the tactually guided walk is not as smooth as the one that is visually guided, it is not too bad.

A related experiment was made with a stationary 20×20 tactile display on the back of the user (Jansson and Brabyn 1981) where the task was to bat a ball running in front of the seated player (Figure 4.4); the tactile information is shown in Figure 4.5. The total time of a game was about 3.5 s, during which time the player had to pick up the tactile information, organize the response and perform appropriate movements. Trained players could perform this task quite well.

Both these experiments demonstrate that tactile information can guide movements in tasks of this kind. However, the visual information transformed to tactual information in these cases is very restricted compared with the information in real

Figure 4.2. Example of a momentary tactile stimulation. From the “slalom walking” study, three vertical bars of different widths depicting the slalom poles at different distances and the arrows the directions of their motions (Reprinted from Int. J. Neuroscience, 1983, Vol 19, pp. 37–46, Jansson G., Tactile Guidance of Movement, © Gordon and Breach (now part of Taylor and Francis Group) http://www.informaworld.com. Used with permission.)

Figure 4.3. Slalom walking movement paths of visual and tactile guidance, respectively (Reprinted from Int. J. Neuroscience, 1983, Vol 19, pp. 37–46, Jansson G., Tactile Guidance of Movement, © Gordon and Breach (now part of Taylor and Francis Group) http://www.informaworld.com. Used with permission.)