156 4 Haptics as a Substitute for Vision

Figure 4.8. Practice results in proportion correct and exploration time (s) for a very successful participant in an experiment with identification of four forms in six different sizes. The practice consisted of three blocks of stimuli during each of three days (Can the Efficiency of a Haptic Display be Increased by Short-time Practice in Exploration?, Jansson G., Iv˚as A., in Haptic Human–Computer Interaction, Brewster S., Murray-Smith R., 2001,

©Springer-Verlag. Used with permission.)

4.7.2.5Co-location of Visual and Haptic Space

In natural environments objects are usually perceived to occupy the same location visually and tactually. In virtual worlds they are often not co-located, that is, the visual presentation is made on a screen and the tactual presentation in another location. This may be a drawback not only for sighted people, but also for visually impaired people with remains of vision. It is reasonable to expect advantages with co-location, as that is the natural condition. Some such effects were shown for a targeting task (Wall et al. 2002) and for perception of form (Jansson and Oström¨ 2004). Under stereo conditions in the latter study there was a significant effect in judging the depth dimension of a distorted object. Informally it was also found that performing tasks such as finding knobs and regaining contact with lost virtual objects were facilitated under co-location conditions.

4.7.3 Haptic Displays as Aids for the Visually Impaired

There are many potential applications of haptic displays, for instance, in medical training and for computer games (for an overview, see Burdea and Coiffet 2003). Here their potentials as aids for the visually impaired will be discussed. Users with severe visual impairment have to work without the extra information obtained from vision, which makes the task more difficult, especially concerning getting an overview and not loosing contact with an object explored, as well as finding interesting parts of the object to touch. In spite of this, haptic displays may be useful for visually impaired people, as it is the only way in some contexts for getting direct information (Brewster and Murray-Smith 2001; Jansson 1999, 2001; Sjöström 2002; Yu et al. 2001).

One context where haptic displays may be useful for visually impaired people is to experience art at museums. It is usually not allowed to touch statues at museums, for instance. The EU project Pure-Form (PFM, undated) aimed to develop