6.2 Proactive, Reactive and Detached Tactile Feedback
6.2.3 Interactive Watzmann : Tactile Exploration in 3D
The projectInteractive Watzmannis an experimental setup to explore and demonstrate the pos- sibility to provide remote tactile feedback for an interaction above an interactive surface. The wrist-worn vibrotactile actuator matrix provides remote haptic stimuli to a user exploring the space above a surface. Thus, the interaction and the feedback are both spatially detached from the surface. The surface is not interactive per se, but does provide a reference frame for gestu- ral interactions above it. We26 used theInteractive Watzmann to haptically render direction and height of thermal winds over a paper maché model of the Watzmann, a mountain in the Bavarian
25These challenges are currently addressed in another master’s thesis [Polleti, 2012]. However, its results are not available at this point.
138 6 Inherent Characteristics of Remote Tactile Feedback
Figure 6.24: The Interactive Watzmann prototype. a: The user of the system manually explores the space above a paper maché model of the Watzmann. A wrist worn matrix of vibrotactile actuators communicates strength and direction of virtual thermal winds. b: Technical setup of the system.
Alps south of the village of Berchtesgaden (see figure 6.24). The system was deployed in an office of the German Alpine Club27 for three days in order to collect user opinions and observe the use of this experimental prototype in the field.
The human wrist has been analyzed and used as a position for the application of tactile stim- uli before. This location is socially acceptable and we are used to discretely wear small elec- tronic devices there (e.g. wrist watches). This makes it an appropriate location for wear- able tactile actuators to support the interaction with mobile or gestural interfaces. Wear- able vibrotactile actuators have been used to provide navigation information for pedestrians [Bosman et al., 2003], collision feedback for virtual reality scenarios [Schätzle et al., 2011] or non-visual alerts [Lee and Starner, 2010]. Furthermore, matrices of vibrotactile actuators have been used to analyze the tactile sensitivity and the ability of stimulus localization. The fore- arm and wrist has been shown to be not suitable for stimuli which have to be localized ex- actly [Cholewiak and Collins, 2003]. This holds true for both the dorsal and palmar wrist side [Chen et al., 2008]. However, the wrist is a suitable location for directional tactile patterns [Piateski and Jones, 2005]. Additionally, these patterns are more easily identified when they move sideways (i.e. around the wrist rather than between elbow and wrist) [Chen et al., 2008]. These findings and the two-point threshold of up to 40 mm on the forearm (see 3.6) have been taken into account for the design of theInteractive Watzmann’s actuator system and tactile stim- uli.
6.2 Proactive, Reactive and Detached Tactile Feedback 139
The model of the Watzmann was designed in a scale of 1:10000 and build on the basis of maps and contour curves. A satellite image of the region is projected28onto the model. Manual interactions in the space above the model are detected using a Microsoft Kinect29, the GUI is written in C++ and uses the OpenNI30 framework for tracking and OpenCV31 to process images. A mobile aluminum rack holds both projector and Kinect. Finally, a wristband (width: 8 cm) with 18 vibration motors (Lilypad’s vibe boards) serves as remote tactile actuator. The tactile signals describe position and strength for virtual thermal winds on the interacting user’s fingertip32. The upward wind was depicted by activating the columns of vibration motors for 200 ms sequentially from the lowest to the uppermost, with the vibration running around the wrist. We implemented two levels of intensity by doubling the amplitude and halving the inter-stimulus interval.
We deployed the prototype in an office of the German Alpine Club for three days, altogether 35 people interacted with the prototype. Twenty-five persons were willing to take part in the guided interview and to answer questions on the interaction, the relocation of stimuli and their ideas on future uses of the concept33. As a training, the participants were made familiar with the interaction and the resulting feedback. The results are summarized in the following:
Positive adjectives were used to describe the experience of theinteraction, such as ’exciting’, ’mystical’ or ’surprising’. Seven of the 25 participants said the interaction was ’unusual’. Two participants stated that the interaction in mid-air was ’more hygienic’ than touch. Two partic- ipants stated that the interaction ’could be tiring after a while’. Eleven of the 25 people had difficulties to distinguish the different tactile stimulior to recognize the direction of the tactile stimuli. Three people clearly preferred the stimuli on the wrist, six people would have liked to perceive it at the fingertip. Others wished for additional visual feedback. Eleven people used adjectives such as ’good’, ’non-problematic’ or ’OK’ to describe thesensory relocation. Inter- estingly, two participants were reminded of a sleeve for the measurement of blood pressure by the actuator system. In summary, a majority of 21 participants described the novelinteractive systemwith positive adjectives such as ’simple’, ’intuitive’, ’cool’, ’coherent’, ’exciting’ or ’use- ful’. The observedhand postures of the users were very diverse. However, most of the people used slow exploratory movements to detect active areas. Very few users touched the model. With the system, we tested a novel form of interface and a novel form of sensory feedback. The ratings are very basic and describe the users’ experience of 10 minute use. Still, we identified three main findings:
• The relocation of tactile stimuli was understandable and did not pose a problem to the majority of users.
28projector ASK M3
29http://www.microsoft.com/en-us/kinectforwindows/[cited 2013/02/09] 30http://www.openni.org/[cited 2013/02/09]
31http://opencv.willowgarage.com/wiki/[cited 2013/02/09]
32The actual wind data was taken fromhttp://www.xcskies.com/maps[cited 2013/02/09]
140 6 Inherent Characteristics of Remote Tactile Feedback
• Thescenariowas understood and accepted by the participants. We assume that the users had no expectations in the device and no comparable system was known to them. There- fore, we received positive responses.
• The poorly designedtactile stimuliwere criticized the most. We chose structured vibrotac- tile feedback to communicate the (non-visual) information. We assume that the vibrations caused a masking effect for the surrounding area on the wrist, which made it harder to distinguish the moving tactile patterns.
In summary, I consider theInteractive Watzmann a basic platform to collect first user responses to relocated tactile feedback which is detached from a touch surface. The findings from our deployment are moderate, but back the results from previous evaluations: First, the concept of remote tactile feedback is accepted, as long as the interaction loop is tightly closed. Second, the tactile stimuli themselves have to be designed carefully to communicate intended information. Vibrations are very popular in tactile research, due to their simplicity and strength of stimulation (see section 3.1.2). However, we found that vibrotactile actuation can lead to masking effects and can result in indistinct tactile patterns for moving stimuli or different levels of stimulation. In the next chapter, I address the potential of remote tactile feedback to provide more versatile tactile feedback by combining different types of actuators on the body or by using novel tactile media.