168 Touch
aided performance, but the same grid was confusing when
subjects had to find the coordinates of an intersection. Pat-
terns of scanning also affect the utility of a display (Berlá,
1982).
Basic research on haptic perception indicates that the
iconic value of a symbol may be different in touch than in vi-
sion. For example, the limited spatial resolution of the finger-
tip may make it difficult to determine the direction of a raised
arrow, whereas a pattern that is rough in one direction and
smooth in the other can be read quickly as a directional signal
(Schiff, Kaufer, & Mosak, 1966). Research by Lambert and
Lederman (1989) extended this notion by designing raised
point symbols for designating interior landmarks of build-
ings, in which the three-dimensional structure inherently sug-
gested the intended meaning of the symbol.
Technological advances have permitted increasingly
sophisticated aids for blind persons. Touch tablets are an
electronic means of displaying maps to visually impaired in-
dividuals. The display is divided into a matrix, and when a
cell is touched, a synthesized speech message is invoked.
This is the basis for the NOMAD system (Parkes, 1988).
Another system, MoBIC (The MoBIC Consortium, 1997),
combines a computer-based map, global positioning sensing,
and speech synthesis. It can be used to preview and plan a
journey (virtual travel), or it can be consulted en route by
means of a keypad in order to get information about current
position and a travel plan. The initial system did not include
a tactual map. In an experimental test, however, Bringham-
mar, Jansson, and Douglas (1997) found that after planning
and walking with the system, visually impaired participants
had high ratings for usability and satisfaction, but augment-
ing the system with a tactual map increased satisfaction rat-
ings and measures of route understanding.
The development of aids for the blind will undoubtedly
benefit from a two-pronged approach, in which applied re-
search is coupled with work on the basic capabilities of the
haptic system. Sensory limitations such as spatial thresholds
are important, but so are many higher-level factors. In order
to develop effective displays for people without vision, one
must deal with issues such as what properties of stimuli are
available, how these properties emerge in perceptual process-
ing, how exploration alters what is encoded, and how haptic
information is remembered, particularly in the context of a
real, multimodal environment.
Haptic Augmentation of Speech Perception
Speech perception and production are the focus of the chapter
by Fowler in this volume. The use of haptic stimulation to
augment speech perception is motivated in part by the success
of the Tadoma method for speech communication to deaf and
blind individuals (Reed et al., 1985). In this method, shown in
Figure 6.8, the receiver of communication places his or her
hand on the face and neck of a speaker and monitors the
movements of the speech musculature. In addition to chang-
ing position of the jaw and lips, users have access to changes
in air flow, temperature, and vibration. Experienced users can
achieve high levels of speech understanding based on multi-
ple sources of sensory information.
Efforts to create haptic stimulators to produce similar ef-
fects have varied both with respect to the type of device and
the aspect of the speech signal that they attempt to convey.
The first formant of the speech signal (F0, or fundamental
frequency) has been conveyed by vibration and more re-
cently by vibration-spatial coupling (i.e., both the location
and the frequency of the vibration are manipulated; see
Auer, Bernstein, & Coulter, 1998, for review). An advantage
of conveying F0 is that it is related to several aspects of
speech, including voicing, stress, intonation (question vs.
statement), and syntactic boundaries. Auer et al. found that
when vision was combined with a spatio-temporal display
of F0, intonation identification was augmented relative to vi-
sion alone.Figure 6.8 The Tadoma method for conveying speech
to the blind and deaf.