An Investigation into the Design of
Structured Vibrotactile Messages for Non Visual Information Display
Vibrotactile displays are becoming increasingly common in everyday devices,
with mobile phones, pagers and games controllers all featuring vibration
feedback. However, the vibrations used in such devices are usually basic
and do not fully exploit the potential of vibration as a means of communication.
In order to create more effective messages, it is necessary to systematically
investigate how best to use vibration in computer interfaces. Therefore
this research brings together an understanding of cutaneous perception
and interaction design and investigates how to construct effective vibrotactile
messages. This document presents the background to this work, the results
so far, and discusses plans for future work.
Tactons  are structured vibrotactile messages which can be used to
communicate information non-visually. They are the tactile equivalent
of audio Earcons  and visual icons, and could be used for communication
in situations where vision is overloaded, restricted, or unavailable,
such as navigation systems for blind people, or in mobile/wearable computers.
This research aims to show that multidimensional information can be encoded
in Tactons using parameters of vibration such as waveform, rhythm and
spatial location, and that users can learn mappings between Tactons and
their meanings, and retrieve information or alerts from Tactons when used
in mobile or desktop computer interfaces.
Tactons can be displayed using small vibrating transducers. Figure 1 shows
the transducer used in this research: the Engineering Acoustics C2 Tactor
Figure 1: Engineering Acoustics C2 Tactor (www.eaiinfo.com).
Main Contributions of this Research
While tactile messages (both vibrotactile and electrotactile) have been
proposed and used by a number of researchers [3, 4] there have been no
formal studies of how best to design such messages. The novel contribution
of this research is a formal evaluation of Tactons, and of the individual
parameters used to construct them, in order that a set of guidelines for
designing effective Tactons can be produced. In addition, the use of Tactons
in mobile and desktop applications will be evaluated so that their effectiveness
in real world applications can be assessed.
Work carried out so far
Identifying Parameters for Tactons
Before Tactons can be created, appropriate vibrotactile parameters in
which information can be encoded must be identified. So far, two parameters,
namely waveform and rhythm, have been tested and identified as successful
parameters for Tactons . Other parameters such as spatial location
are currently being investigated. The waveforms used in this research
are amplitude-modulated sinusoids and are categorised in terms of how
"rough" they feel. Three values of roughness which can be distinguished
from one another were identified through a forced choice experiment in
which participants were presented with pairs of vibrations and asked "which
feels rougher?". The second parameter which has been investigated
is rhythm. Three distinguishable rhythms were created based on Brewster's
guidelines for Earcon design  which state that a different number of
notes should be used in each rhythm so that they are as different as possible.
Figure 2: A 250Hz sinusoid modulated by a 30Hz sinusoid.
Figure 3: Rhythms used to represent calls/messages
First Evaluation of Tactons
In order to create effective Tactons it is necessary that users are able
to learn the mapping between Tactons and the data encoded in them. An
experiment was therefore carried out to determine whether people could
learn and identify Tactons which used roughness and rhythm as parameters.
Tactons were created to represent alerts which might occur when a call
or a message arrived on a mobile phone. Two pieces of information were
encoded into each Tacton: the type of call/message (voice call/text message/multimedia
message) was encoded in the rhythm, while the priority of the call/message
(low/medium/high) was encoded in the roughness (smooth/rough/very rough).
After being trained to understand the mapping between Tactons and the
data encoded in them, participants were presented with Tactons and asked
to identify the type and priority of the call/message. The results showed
71% average overall identification of the Tactons, with 93% average identification
of type/rhythm and 80% identification of priority/roughness .
Conclusions and Future Work
Overall the results so far results indicate that Tactons can be an effective
means of communicating information non-visually. The results compare favourably
to those for their audio counterpart, Earcons, where overall recognition
is also around 70% . Research has shown that Earcons are able to encode
information in three parameters , therefore future work will investigate
the effect of adding a third parameter (namely spatial location) to Tactons.
Tactile perception may be affected by being engaged in another activity,
such as walking. Since one potential use of Tactons is in mobile and wearable
computing interfaces, future work will investigate identification of Tactons
when used in a mobile application. This will significantly further understanding
of Tacton perception and allow more effective vibrotactile interfaces
to be created.
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Non-Speech Audio into Human-Computer Interfaces", PhD Thesis, University
of York, UK, 1994
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