This paper describes our study about how to make use of a tactile belt with 8 vibrators to present rich spatial information for blind and visually impaired people while exploring indoor environments. In order to conduct a Wizard-of-Oz evaluation with 12 sighted subjects, a tablet based application has been developed for setting indoor scenarios and exploration interaction. Two sets of tactile patterns for presentation of distance, direction and type of objects, have been evaluated based on one single actuator and multiple actuators, respectively. The results indicated that the subjects can acquire the rich object information through both of the two sets, and they were more sensitive on the vibration position than the vibration intensity.
The tactile pin-matrix displays offer novel experiences for blind
and visually impaired people to explore maps [
Copyright is held by the owner/author(s). 2.
There have been many navigation aids with tactile feedback. In
recent years, various approaches have been implemented and
discussed. For example, a number of previous systems make use
of a smartphone to offer tactile feedback, like PocketNavigator [
In order to provide richer tactile information, some systems
employed multiple vibrators, such as a tactile vest and a tactile
belt. The researchers in [
To display complex information by vibrators, the concept of Tactons has been introduced by Brewster et al.:
“Tactons are structured, abstract messages that can be used to
communicate complex concepts to users non-visually.” [
Several design principles were presented in their work,
especially the concept of "Transformational Tactons" which inspired
this work. There, each property is assigned to its own parameter.
As an example of this design principle, a 3-parameter has been
used to notice users about upcoming appointment information
[
The presentation of highly complex properties is a challenge in
the design of Tactons. There must be found a parameter with
many distinguishable levels. Not every parameter is suitable for
this. The researchers in [
In this work, a tactile waist belt from the company Elitac is used (see Figure 1). The detailed technical specifications can be found on their website1. The belt can be controlled by a host device (e.g. a smartphone or a tablet) via Bluetooth. The movements of the vibrators are transmitted by the corresponding haptic patterns that are previously defined in a XML-based file, and are saved on the host device. This format of haptic patterns allows to configure start time, intensity, duration and location of a vibration. For example, Figure 2 illustrates how to make one vibrator vibrated two times at 0 millisecond and 500 millisecond respectively.
The tactile waist belt is equipped with eight actuators, and
each covers a range of 45° of the body of the user (see Figure 1).
This configuration already has been used successfully in several
prototypes and is valid for managing navigation [
The tactile belt offers the developers various parameters. With their help information can be transmit to the wearer of the belt. The following parameters are available:
Position The 8 actuators are attached around the body of the
subject in a horizontal plane. Each actuator occupies a fixed
posi<ArrayOfAction>
<Action> <!-- first vibration -->
<Time>0</Time> <!-- starting time -->
<Address>1</Address> <!-- actuator number -->
<!-- vibration intensity (0-15) -->
<Intensity>11</Intensity>
<!-- vibration duration in ms -->
<Duration>250</Duration>
</Action>
<Action> <!-- second vibration -->
<Time>500</Time>
<Address>1</Address>
<Intensity>11</Intensity>
<Duration>250</Duration>
</Action>
</ArrayOfAction>
tion, which can be linked to specific information. From the
perspective of tactile perception 36 actuators on the belt are possible,
corresponding to a resolution of 10 ° in the horizontal plane [
Rhythm Rhythms are generated by grouping vibrations with
different durations and different intervals [
Intensity By changing the amplitude of the sine wave
different vibration levels can be generated. In [
An indoor assisted system with a room exploration functionality should allow visually impaired users to acquire rich spatial information of surrounded environments. In this study, three attributes of surrounded objects are presented:
Direction: In which direction the object is?
Distance: How far away the object is located?
To convey such complex spatial information through haptic
feedback, the design principles of the "Transformational Tactons"
[
The Tacton parameter for coding the direction is not difficult. The
tactile belt is equipped with eight evenly distributed actuators,
which are quite intuitively associated with a direction for users.
This method was tested successfully by several researches. Thus,
the 8 vibrator position can simply indicate 8 different directions.
It’s true that the parameter level of direction could theoretically be
increased to 36 levels [
In previous studies, the frequency and the intensity were used for presenting distance information. At present, our belt does not provide the ability to change the frequency of a single vibration. Therefore we made use of the intensity to encode distance information. Theoretically, for a common vibrator 15 different intensities can be presented. But the preliminary tests and research work have shown that differences in intensity can be very poorly perceived. Therefore in our study the distance is encoded only with two levels: “near” (all objects with a distance less than two meters) and “far” (all objects with a distance more or equal than two meters).
In general there are various objects in rooms and buildings, but the focus of this work was on the four important ones for visually impaired people: walls, stairs, doors and obstacles. Thus, the parameter should cover at least four distinguishable stages for the 4 target types. In order to convey information about object types for users, two different haptic feedback based methods have been employed: a single actuator method and multiple actuator method.
In the single-actuator method the tactile patterns are encoded via different rhythms on a single actuator. Four distinguishable rhythms were selected for this work, as shown in Figure 3. The grey areas represent vibration pulses, and the white fields show the vibration breaks. A rhythm takes a second and for a better recognition it is always played twice. As a basic metric, the 1/16 pulse is the shortest one and has a length of 62.5ms, and each pulse should be followed by a pause of at least 125ms, except the 1/16 pulse, where it is followed by a pause of at least 62,5ms. It is also possible to add additional object types in the future.
With the single-actuator method the characterizing rhythm is
played on the pioneering actuator with the corresponding
intensity. Therefore, in contrast to [
For a belt with eight actuators there are 12 pairs with a
recognition rate of at least 80% [
To support a Wizard conveniently and precisely to simulate subjects’ movements (i.e., position and heading direction), we developed a special touch interaction method, see Figure 6. In the App, it was easy to configure the test room with different types of objects, and the position and the heading direction of the subject was represented by a red point and a black line, respectively. When touching on the red point, an outer orientation ring is rendered. The Wizard can change the orientation by moving his finger around the user circle, but within the orientation ring. The Wizard also can simulate subjects’ walking paths by moving the finger easily, like in the Walking Mode. With a double-tap on any object, the App sends the corresponding tactile patterns to the tactile belt, by calculating the direction and the distance of this object to users automatically.
Two rooms were simulated and each one had 12 or 13 objects from the four types (see Figure 7). The position and orientation of the subjects was the same and was fixed in each test. Additionally, the order of displaying the objects was fixed. Thus, all subjects had the same conditions.
The test was performed with six male and six female individuals. Two subjects were 58 years old, the others were around 23 to 30 years old. Every subject tested the two sets of Tactons. The two rooms were tested in the same order for all subjects, but the order of the two sets of Tactons were different. Regarding to the test order, six subjects tested the single-actuator-method firstly, and the other six ones tested the multi-actuator-method firstly.
Each subject at first received a brief introduction to their tasks and the Tactons. Subsequently, a training phase was followed to learn the Tactons in a training setting. The real test didn’t start until the subjects claimed they had learnt all. In real tests all objects were displayed one by one, triggered in the WizzApp by a Wizard. Note that, the subjects did not allow to watch the screen at any time during the test. The subjects were asked to loudly speak out the object type, the direction (i.e., eight cardinal directions) and the distance immediately once they recognized. The accuracy of these statements and the recognition time were noted. The subjects had to evaluate the two methods in the two test rooms accordingly, and the test arrangement was counterbalanced. In the end, the subjects had to fill in a questionnaire:
The comparison of the results between the single-actuator-method and the multi-actuator-method is shown in Table 1. The two methods have achieved similar results for encoding the direction and the distance. The object type was detected better with the multi-actuator-method, as well as a better recognition performance of the whole Tacton2. For the two methods the direction and the object type have a very high recognition accuracy (more than 94%), while the recognition accuracy of the distance was less than identifying the object type. However, the overall recognition accuracy of the Tactons dropped to 78% for the single-actuatormethod and 81% for the multi-actuator-method, responsively. Besides, the subjects spent 437ms and 634ms averagely to recognize one Tacton, accordingly.
The two-way MANOVA (at the 95% confidence level) revealed only the two methods had significant multivariate main effect for the recognition accuracy of object type, direction, distance, the whole Tacton and spending time, Wilks’ λ = 0.369, F(5, 16) = 5.47, p = 0.04. Furthermore, the univariate ANOVA tests (at the 95% confidence level) only found the two methods had main 2 When all of the 3 attributes (i.e., type, direction, and distance) of one object were identified correctly, we countered the Tacton was recognized successfully. effect for the spending time (F(1, 20) = 24.804, p < 0.001, and the interaction between the two methods and the test rooms had main effect for the recognition accuracy of a whole Tacton ( F(1, 20) = 4.634, p = 0.044. The paired T-test (at the 95% confidence level) found the mean accuracy of distance recognition had significant differences to the mean accuracy of direction recognition (t = 4.252, p < 0.001) and the mean accuracy of type recognition (t = 4.684, p < 0.001) both.
The analysis of the questionnaires showed that, on one hand the multi-actuator-method was easier to learn for 7 of 12 subjects, because they felt “less complex”, “easier perceptive”, “shorter learning time”, or “good spatial imagination”; on the other hand, there were still 7 subjects who chose for the single-actuatormethod, because they thought the Tacton were “shorter”, “more intuitive”, “more memorable” and “more practicable”.
From the evaluation, it found the subjects were more sensitive to the position of vibrations (e.g. for presentation of direction and object type), than the intensity feature (e.g. for presentation of distance). It seems to be hard to distinguish the intensity of vibration because of users’ clothes with different texture or fixing the belt with different strength. In order to inform users the distance information, a set of extra vibrators can be placed vertically on other body part, like on the arm, and the closer vibration means closer objects. Additionally, it might be also possible to change the vibration frequency for indicating the distance information.
In this study, due to only 4 different object types involved, the subjects spent more or less equal time to learn the tactile patterns. When more object types are involved, we expect users have to spend more time for learning the single-actuator method than the multi-actuator method, and we need to further tests to confirm that.
Due to lack of tactile feedback, blind and visually impaired people is hard to access spatial information (e.g., maps, layout of the surroundings) through common touchscreen devices. On one hand, many new displays, like the pin-matrix display and the under-developing BlindPad3 system, have been used to improve the accessibility of spatial information. On the other hand, we think the vibrotactile feedback might be a low-cost solution to reach the goal by combining touchscreen displays. Specifically, the vibrotactile feedback also can be used while walking. Although in this evaluation we let a Wizard touch the display to trigger and simulate an exploration task of indoor objects, we think it is possible to allow blind and visually impaired people to explore by themselves after a few improvement of the WizzApp, like importing semantic sounds. Moreover, there should be no a large delay of vibrations when exploring on the touchscreen displays, otherwise, users might make mistakes to understand the position and direction information of objects. 6
For blind and visually impaired people, it is challenging to acquire spatial information of surrounding environments, like how many objects in front of them, as well as their properties. In this paper we presented how to make use of a tactile belt with 8 vibrators to convey spatial information of indoor objects (i.e., walls, stairs, doors and general obstacles) by pre-designed tactile patterns. In addition to rendering distance and direction information, we studied two different methods to inform users about object type information via a single actuator and multiple actuators, respectably.
Through a pilot WoZ evaluation with 12 sighted people, we found the subjects were able to acquire the spatial information of surrounding objects by both of the two methods. The subjects had more sensitive on the vibration position than the vibration intensity. Additionally, a tablet based application has been implemented to support the evaluation, for setting the room layout and exploring objects one by one.
In the future, in addition to evaluating the tactile patterns with blind and visually impaired individuals, it’s important to evaluate the exploration task by blind and visually impaired people directly, rather than simulating the exploration behaviours by a sighted Wizard. 7
The authors were grateful to all of the subjects who took part in the evaluation. This study was supported by the Range-IT4 project within the framework of EU FP7 SME Program (Grant no. 605998).