Arne Harder & Jochen Schneider

Usability of the Acoustic Positioning Device

Abstract and Index

Abstract. The study tested the usability of the Acoustic Positioning Device (APD), a tactile map construction-aid prototype designed for the blind by Jochen Schneider (2000). 16 blindfolded sighted subjects reconstructed routes using either the APD or verbal instructions. They reconstructed the routes faster with the APD, but tended to get a better route understanding with verbal instructions.

Keywords. Acoustic Positioning Device, blind persons, mobility, orientation, tactile maps, usability.

  1. Goal
  2. Method
  3. Results
  4. Discussion
  5. References
  6. Acknowledgements and Author Communication

I Goal

With tactile maps blind persons are able to travel through unfamiliar routes within unknown environments (Brambring & Weber, 1981; Espinosa et al., 1998). However, many blind persons do not have experience with tactile maps, particularly because of the high costs associated with map production.

To change this situation, Jochen Schneider (2000, 2001) designed the Acoustic Positioning Device (APD; see Figure 1). With this tool, blind persons should be able to reconstruct tactile maps of pre-defined routes while they are monitored and advised by a computer. The reported study tested the usability of the APD for the first time.

APD-users will reconstruct a pre-defined route with special bricks by positioning one brick after the other on a working array (see figure 2 for the bricks). A computer with the stored route layout will monitor the working array with a connected video camera.

For the brick to be positioned, the APD will emit an acoustic and a verbal signal. The former represents the difference between the actual and the correct position of the brick within the route. The latter represents the direction for correction.

The acoustic signal used for experimental purposes is a MIDI marimba chord sound that can be repeated within a range of 0.5-30 times per second. A high repetition rate codes a low distance between the brick and its correct position within the route and vice versa. The direction for correction is indicated verbally. Thus, an APD-user who hears the sound vibrating 25 times per second followed by the word "left" will have to move the brick slightly to the left for placing it correctly within the route.

Figure 1. Demonstration of the Acoustic Positioning Device (APD). The participant turns the brick in order to place it correctly within the route with his/her hand according to the acoustic and the verbal signal emitted from the APD (see text above).

Figure 2 Demonstration of an experimental brick. The bricks can be put together so that they form a "brick-chain" that marks the spatial layout of a pre-defined route.

II Method

Design, Conditions, and Tasks

16 sighted blindfolded persons (age-range 16-30 years, m =25, s =6) served as experimental subjects. Two experimental routes and two experimental conditions were used. The experimental route A was shorter than route B. The experimental conditions were named as follows:

Each subject underwent both experimental conditions and routes. For each subject the first experimental condition and the route for that condition were randomly selected.

For the VBC-condition, each subject received an A3-sheet of swell-paper. It tactually presented a coordinate system with one square-centemetre coordinates. The tactile lines were 1.5 mm high and 1.0 mm thick. All subjects reported that they tactually distinguished the lines and coordinates easily. For the beginning of the particular route, the coordinates for the first experimental brick were verbally indicated. As every brick had the same size, for each successive brick only one additional coordinate determined its spatial position. All necessary coordinates were verbally indicated to the subject, and he or she had to immediately position the particular brick according to the indicated coordinates. The APD-condition has been described within the last passage of the Goal-paragraph.

While a subject underwent an experimental condition, he or she had to solve the following tasks successively:

  1. Reconstruction of the particular experimental route. To accomplish that task, either verbal information (VBC-condition) or a combination of sound and verbal feedback (APD-condition) was presented for each brick route.
  2. Memorizing the experimental route layout by actively touching the priviously reconstructed brick layout of the particular experimental route.
  3. Exploration of the tactile map (see figure 3) presenting:
    1. both experimental routes,
    2. additional route information for the experimental routes (bus stop and traffic-light symbols),
    3. distraction information (additional routes).
  4. Determination of the spatial position for each additional information item on the brick route for each experimental route.

Procedure and Statistical Analysis

Each subject reconstructed both experimental routes with the special bricks. To reconstruct route A, he or she had to use eight bricks, for reconstructing route B, ten bricks had to be used. When the subject had correctly reconstructed his or her first experimental route, he or she tactually explored its brick layout to memorize its spatial layout. After that, he or she reconstructed the second experimental route with the bricks.

Both experimental routes had to be reconstructed under a different experimental condition (VBC or APD). As soon as both experimental routes had been reconstructed, the subject actively touched and memorized the tactile map (see figure 3). He or she was asked to memorize the spatial position of each additional information item within the corresponding experimental route.

After the tactile map had been explored, the subject was exposed to his or her first experimental brick layout. He or she then tried to point out the spatial position of each additional information item experienced in the map. The same sequence of tasks was repeated for the subject's second experimental route. No time limits were given for any experimental task.

The following two dependent variables were registered per subject for each experimental condition:

For the data of each dependent variable an ANOVA was calculated. The significance level was set to 0.05 for each ANOVA. Both ANOVAS had the following three independentt variables:

  1. Sequence (first or second tryal),
  2. Route (A or B), and
  3. Reconstruction Method (VBC or APD).

Figure 3 Demonstration of the experimental tactile map. The tactile map represents the experimental routes and some distraction routes. Only the experimental routes contain additional information symbols.

III Results

Verbal Description

Under the VBC condition the everage route was reconstructed in approximately thirteen minutes (m =12.72; sd =8.08), but under the APD condition less than three minutes were needed to accomplish that task (m =2.84; sd =0.68). Under the VBC condition the everage value of Recall Quality was 51% (m =50,89; sd =20.23), under the APD condition it was 35% (m =34.82; sd =31.91).

The reconstruction times for the APD condition were significantly shorter than for the VBC condition (F1,15 =21.41; p <0.001). The subjects tended to show higher reconstruction qualities with the VBC than with the APD condition (F1,15 =2.20; p <0.12). No other main or interaction effect was statistically significant or showed a remarkable tendency.

Table of Main Results

  m (sd) m (sd) p <
Reconstruction Time 12.72 (8.08) 2.84 (0.68 0.001 sig.
Recall Quality 50.89 (20.23) 34.82 (31.91) 0.120 n.s.
Comment. Abbreviations. APD: Acoustic Positioning Device. n.s.: not statistically significant. m: mean value. (sd): standard deviation. sig.: statistically significant (p <0.05 for each dependent variable). VBC: Verbal Brick Coordinates.
Dependent Variables. Reconstruction Time: minutes for route reconstruction with the bricks. Recall Quality: percentage of correctly recalled items of the tactile map.

IV Discussion

The APD proved to be a more appropriate device for pure route reconstruction than the VBC. One may expect this effect to be stronger with blind and mobile persons, as they daily make use of sounds when they solve spatial navigation tasks.

While using the VBC and actively touching the tactile coordinate system, the subjects who were unfamiliar with tactile maps may have learned some appropriate strategies for map reading. This effect might not occur with blind persons who are used to read tactile maps.

The results of this study show that the APD principally is a usable tool. Further studies with blind participants will have to demonstrate its real value as an orientation aid for the blind.

V References

  1. Brambring, M. & Weber, C. (1981). Taktile, verbale und motorische Informationen zur geographischen Orientierung Blinder (tactile, verbal and geographic informations for a geographic orientation of the blind). Zeitschrift für experimentelle und angewandte Psychologie, 28, pp. 23-37.
  2. Espinosa, M. A., Ungar, S., Ochaita, E., Blades, M. & Spencer, C. (1998). Comparing methods for introducing blind and visually impaired people to unfamiliar environments. Environmental Psychology, 18, pp. 277-287.
  3. Schneider, J. (2000). Constructing the yellow brick road: Route bricks on virtual tactile maps. In: R. Wagner & R. Vollmar (eds.). Proc. International Conference on Computers Helping People with Special needs; University of Karlsruhe, July 17-21 2000 (pp. 641-648). Wien: Österreichische Computer Gesellschaft.
  4. Schneider, J. (2001). Konstruktive Exploration räumlicher Daten (constructive exploration of spatial data). Unpublished dissertation, Faculty for Computer Science, University of Magdeburg, Germany.

VI Acknowledgements and Author Communigation

We thank Dr. Heiner Rinderman at the University of Magdeburg for his methodological considerations. We furthermore thank Marilia Russo for editing the manuscript. Finally we thank the German Society of Research (Deutsche Forschungsgemeinschaft) for the award that enabled Dr. Harder to introduce the Acoustic Positioning Device at the Eleventh International Mobility Conference at Stellenbosch, South Africa in April 2003.

Dr. Arne Harder c/o Julia e.V.
Hohenstaufenring 8
D-50674 Köln,
Dr. Jochen Schneider
D-39016Magdeburg Germany

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