No abstract

In this study, we explore the conditions for accurate localization of vibrotactile stimuli presented to the abdomen. Tactile orientation systems intended to provide mobility information for people who are blind depend on accurate identification of location of stimuli on the skin, as do systems designed to indicate target positions in space or the status of remotely operated devices to pilots or engineers. The spatial acuity of the skin has been examined for simple touch, but not for the types of vibrating signals used in such devices. The ability to localize vibratory stimuli was examined at sites around the abdomen and found to be a function of separation among loci and, most significantly, of place on the trunk. Neither the structures underlying the skin nor the types of tactor tested appeared to affect localization. Evidence was found for anatomically defined anchor points that provide localization referents that enhance performance even with wide target spacing.

Vibrotactile prostheses for deaf or blind persons have been applied to any number of different locations on the body, including the finger, wrist, forearm, abdomen, back, and nape of the neck. The discriminability of patterns presented by such devices can be affected by the acuity of the site of application and the resolution of the display. In addition, the mutual influences among stimuli close together in both space and time can affect percepts within a broad range of parameters. For example, consideration must be given to a variety of tactile illusions often associated with the spatial separations and the range of temporal intervals typically used in cutaneous communication displays. Experiments are reported in which magnitude estimates and cross-modality matches of perceived extent produced by pairs of vibrotactile taps presented to separate loci were obtained on three different body sites. Perceived distance was directly related both to the timing between the taps and to their physical separation. The findings show a consistent relationship to cortical magnification across body sites.

In order to provide information regarding orientation or direction, a convenient code employs vectors (lines) because they have both length and direction. Potential users of such information, encoded tactually, could include persons who are blind, as well as pilots, astronauts, and scuba divers, all of whom need to maintain spatial awareness in their respective unusual environments. In these situations, a tactile display can enhance environmental awareness. In this study, optimal parameters were explored for lines presented dynamically to the skin with vibrotactile arrays on three body sites, with veridical and saltatory presentation modes. Perceived length, straightness, spatial distribution, and smoothness were judged while the durations of the discrete taps making up the "drawn" dotted lines and the times between them were varied. The results indicate that the two modes produce equivalent sensations and that similar sets of timing parameters, within the ranges tested, result in "good" lines at each site.In situations in which vision and/or audition are absent or are available but limited by information overload, an efficient use of the available sensory modalities might be to employ the sense of touch for the accurate perception ofalerts, position, mobility, or navigation (see, e.g., Korteling & van Emmerik, 1998). With such a system, involving spatial orientation and attitude awareness, it might be necessary to present tactile patterns in different orientations, on different body sites, for extended periods oftime, and/or in the presence of distracting noise or competing stimuli from other sensory modalities. Thus, for best use, the tactile patterns employed should produce readily perceived sensations whose meanings are intuitive or at least, as Penders (1953) described, "meaningful within their situation" (p. 15). One such pattern could be a directional line, a vector. The purpose ofthe present experiments was to examine the parameters of linear vibrotactile patterns that would allow them to be readily appreciated. These include exploration of the body sites and presentation conditions for generating "good" vibrotactile lines, for even the simplest oflinear patterns can differ greatly in salience,