Capítulo VI 13 De la ciudad a la región
17. La campaña pedagógica sigue su curso
In section 3.4, I have described conventional approaches to bring versatile tactile feedback to in- teractive surfaces. Most conventional approaches of actuation generate a single haptic modality such as vibration, movement or levels of softness. In order to combine tactile actuators for more diverse or rich feedback, a combination of different actuators would have to be implemented into the touch interface. This results in increased technical complexity, space issues due to the (potentially) large number of actuators and increased price. Consequently, additional actuated tangible devices which have to be moved around on the depicted virtual elements can be utilized. However, this approach results in problems such as occlusion, the loss of direct manipulation
142 6 Inherent Characteristics of Remote Tactile Feedback
Figure 6.25: Overview of the HapticArmrest prototype. The system can be seen as the actuated frame of an interactive surface (from [Richter et al., 2011c]).
and impracticality on vertical surfaces. Therefore, I propose to utilize another inherent charac- teristic of remote tactile feedback: the possibility to combine several cheap and simple actuator technologies for meaningful and rich tactile feedback and reduced complexity at the same time. With theHapticArmrestprototype, I present a first simple remote tactile interface to provide two different touch sensations (see figure 6.25 for an overview): We34 used haptic stimuli and tactile signals to render both object-related and object-independent information. Specifically, individual fingers are moved to indicate the features of virtual edges, individual fingertips are stimulated by vibrations to render the type of a virtual element. Based on these stimuli, participants in an evaluation were able to reliably discriminate visually identical interactive elements. Furthermore, we assessed the hedonic and pragmatic quality of the conveyed tactile stimuli in order to improve future implementations. The work was published in [Richter et al., 2011c].
Prototype
As the nameHapticArmrest implies, the prototype is a wooden object35 designed in the length of an adult’s forearm. The decision to develop this form of interface was influenced by an obser- vation made by Ryall et al. [Ryall et al., 2006]: During long-term interactions with interactive tabletops, people tend to lean on the surface with their non-interacting hand or arm. This can result in accidental inputs and erroneous system behavior. Thus, the prototype can be seen as the actuated frame of an interactive tabletop. For a start, the user of the interface is asked to place the non-interacting hand on the front of the interface. For future implementations, in order to avoid the necessity to place the hand on a predefined area, not only the hand but alternatively also the wrist or forearm could be stimulated. In contrast to wearable actuators, the HapticArmrest
delivers optional additional tactile information which can be cut out easily by lifting the arm off the actuators. This also distinguishes this approach from additional actuated input devices, which are necessary to interact at all.
34This work was part of Sebastian Löhmann’s Project thesis [Löhmann, 2011b]. 35dimensions: 60x14x9.5 cm (LxWxH)
6.3 Increased Versatility of Tactile Stimuli 143
Figure 6.26: Actuators of the HapticArmrest prototype. a: eccentric vibration motors, b: linear solenoids (from [Richter et al., 2011c])
The prototype incorporates two forms of simple actuators which provide different stimuli (see figure 6.26): Altogether, sixvibration motors36have been installed. These motors are positioned under the user’s fingertips37and can be activated separately. Stimulus parameters are position and duration of stimulus, which can be combined into more complex tactons (e.g. stimulating several fingers at once or in moving patterns). In addition, we implemented two linear solenoids38
which can lift two individual wooden pads by 4 mm. This feedback can be considered as being ’haptic’, as the receptors in the finger’s joints are stimulated rather than the skin. Again, the two signal parameters are the position and the duration of a stimulus. In total, we designed 12 distinct feedback patterns for each type of actuation. The actuators are controlled by an Arduino which is in turn connected to a tablet PC39which displays the GUI.
Evaluation
In the evaluation, we wanted to analyze the ability of the users to integrate the versatile remote stimuli as additional source of information when interacting with virtual objects. Additionally, we evaluated the subjective hedonic and emotional quality of the signal, as this aspect plays a major role in the acceptance of this form of feedback [Salminen et al., 2008]. We created a task in which 6 visually identical rectangles were presented on the touchscreen (see figure 6.27). Two of these 6 elements shared a common tactile characteristic which could be experienced by manually exploring the element. Haptic feedback from the solenoids was given when the edge of an element was crossed. On touch of an element’s inner zone, a vibrotactile pattern was given. Either solenoid or vibrotactile feedback were presented. The task was to identify the pair of virtual elements with the common tactile representation. Twelve volunteers (6 female, all right- handed) took part in the evaluation and wore earmuffs to reduce unwanted noise coming from the actuators. After an introduction and training phase, each participant was asked to perform 6
36’10 mm diameter pancake 3 V’ for mobile phones
37We added 2 motors to support left-handed users during whose use the prototype is switched and to allow for stimulation of smaller little fingers.
38Black Knight tubular push solenoid, 24 V 39PaceBlade SlimBook P120
144 6 Inherent Characteristics of Remote Tactile Feedback
Figure 6.27: The usage of the HapticArmrest during the evaluation (videostill) [Löhmann, 2011b].
trials (three solenoid, three vibrotactile). The participants did not experience the same stimulus twice and were free to manually explore the touchscreen. In total, we logged 72 selections of haptically identical pairs.
Remote tactile stimuli and the combination of different tactile modalities is a novel form of feed- back. The users’ subjective connotations form an integral part of a subjective experience. There- fore, this time we wanted to analyze the emotional and hedonic impact of the resulting signals instead of evaluating the effects on the system’s usability (see section 5.2). We conducted an eval- uation based on the AttrakDiff method. The method is used to evaluate the interactive product’s capability to fulfill the user’s needs for ’stimulation’ and ’identification’ [Hassenzahl et al., 2003]. Pairs of opposing adjectives (semantic differentials) are presented to the participant who is then asked to rate the system on a scale from -3 to +3 between these adjectives. Instead of comparing two systems, we evaluated our two signal types.
The resulting rates for the identification of matching pairs depend on the type of tactile feedback:
• Vibrotactile feedback: All pairs of virtual elements with identical vibrotactile feedback could be identified by the participants, resulting in a identification rate of 100%.
• Solenoid feedback: In six out of 36 trials, participants were not able to correctly identify the matching pair of virtual objects. This results in a identification rate of 83.33%.
These results indicate that the unlimited time to explore the virtual elements and the lab situation without external disturbances supported the participants in their task. The high number of design parameters for each tactile modality seems to result in highly discriminable stimuli.
The results of the AttrakDiff questionnaire are shown in figure 6.28. Overall, the ratings for both types of tactile stimulation are very similar (i.e. no mean differences above 1.0) and show a tendency towards adjectives with a positive connotation. Two experiences in the ratings of technical quality form an exception: Both vibrotactile and movement feedback are perceived as rathertechnical and somewhatunpredictable. We assume that the prototypical nature of the system entailing noise, latency or rough design of the encasing resulted in the rather negative ratings of the pragmatic quality. The strongest tendencies were found in the ratings of hedonic quality or quality of stimulation of the feedback: Both signal types were described as being
6.3 Increased Versatility of Tactile Stimuli 145
Description of word-pairs
P rag m atic Q ual ity A ttr active ne ss He do ni c Qua lit y Identity He do ni c Qua lit y S tim ul atio n technical - human complicated - simple impractical - practical cumbersome - straightforward unpredictable - predictable confusing - clearly structured unruly - manageable isolating - connective unprofessional - professional tacky - stylish cheap - premium alienating - integrating separates me from people - connecting unpresentable - presentable conventional - inventive unimaginative - creative cautious - bold conservative - innovative dull - captivating undemanding - challenging ordinary - novel unpleasant - pleasant ugly - attractive disagreeable - likeable rejecting - inviting bad - good repelling - appealing discouraging - motivating -3 -2 -1 0 1 2 3 vibrotactile stimulipressure and movement
Figure 6.28: The results from the AttrakDiff method. Discrete values are connected for comparability (from [Richter et al., 2011c]).
differences show that vibrotactile feedback is perceived as more bold than the stimuli coming from the solenoids. However, the moving platform were described as being morepleasantthan the vibrating motors. This result is consistent with my criticism of vibrotactile feedback. In general, both forms of stimulation are rated positively and are utilized as information source to identify matching pairs of virtual elements.
In addition to this project, we used an adapted version of the AttrakDiff method before to compare two more different forms of stimulation: direct and remote tactile feedback (see section 5.2). Still, also in that setting, no strong differences between both modalities were found. Therefore, the AttrakDiff method as a means to identify disparities between forms of stimulation (rather than systems) should be taken with a pinch of salt. However, we still lack standards to evaluate novel forms of sensory feedback. Additionally, we gained minor findings in theHapticArmrest
project for pragmatic and hedonic qualities of feedback. Therefore, we used an adapted version of this method again for the system presented in section 6.3.2.
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Discussion and Conclusions
In summary, theHapticArmrest is a simple system to explore the use of remote tactile feedback in order to create novel tactile stimuli which complement each other. Participants in our user study were able to utilize the stimuli for the discrimination of virtual objects. This work is a first step towards the creation of more versatile and distinctive tactile signals. Here, we used moving platforms and additional design parameters such as location-encoded rhythmic patterns. However, we did not combine the two types of stimulation to form novel sensations. We refer to this notion asactuator fusion. This principle is feasible when different actuators on different body locations simultaneously provide synchronized feedback for a touch interaction. The mul- tiple resulting stimuli melt together forming potentially rich haptic representations. Again, this approach is unique for the concept of spatially separating touch and resulting feedback.