Advanced
Effect of Tactile Feedback for Button GUI on Mobile Touch Devices
Effect of Tactile Feedback for Button GUI on Mobile Touch Devices
ETRI Journal. 2014. Oct, 36(6): 979-987
Copyright © 2014, Electronics and Telecommunications Research Institute(ETRI)
  • Received : January 28, 2014
  • Accepted : November 06, 2014
  • Published : October 01, 2014
Download
PDF
e-PUB
PubReader
PPT
Export by style
Share
Article
Author
Metrics
Cited by
TagCloud
About the Authors
Heesook Shin
Jeong-Mook Lim
Jong-Uk Lee
Geehyuk Lee
Ki-Uk Kyung

Abstract
This paper describes new tactile feedback patterns and the effect of their input performance for a button GUI activated by a tap gesture on mobile touch devices. Based on an analysis of touch interaction and informal user tests, several tactile feedback patterns were designed. Using these patterns, three user experiments were performed to investigate appropriate tactile feedback patterns and their input performance during interaction with a touch button. The results showed that a tactile pattern responding to each touch and release gesture with a rapid response time and short falling time provides the feeling of physically clicking a button. The suggested tactile feedback pattern has a significantly positive effect on the number of typing errors and typing task completion time compared to the performance when no feedback is provided.
Keywords
I. Introduction
As a touch interface is becoming more popular in various devices such as mobile phones, tablet PCs, and media players, there is a rising interest in the area of high-quality tactile feedback responding to users’ touch gestures for enhancing the value of touch interaction.
Following this trend, various haptic application program interfaces (APIs) have appeared and are supporting developers based on the linear motor mainly working with mobile devices [1] . In contrast, some researchers have attempted to develop new tactile actuators to enlarge the scope of tactile expression [2] [3] . In addition, new study findings were recently reported on the effect of tactile feedback on large interactive surfaces, as large interactive touch surfaces have begun to be used in various environments [4] .
Particularly in the field of mobile devices, as the demand for high-quality tactile feedback is growing more rapidly compared with other touch devices, many related studies are being carried out, and new products with advanced technology are being launched.
Although there have been various works supporting high-quality tactile feedback, currently used tactile expressions are insufficient to simulate the feeling of physically clicking a button and improve the input performance of button GUI manipulation.
This study was therefore conducted to identify appropriate tactile feedback patterns of clicking gestures on a button GUI and to investigate their effect on typing performance based on interaction in hand-held mobile devices such as smartphones.
The remainder of this paper is organized as follows. In Section II, other works related to this topic are described. Next, the implementation of a hardware and software platform is introduced in Section III. The design of tactile feedback patterns, user experiments, and experimental results are then presented in Section IV. Finally, some concluding remarks, as well as our important findings and contributions, are provided in Section V.
II. Related Works
In an early related work on tactile touch feedback for a button GUI, the use of Active Click [5] was reported with brief evaluation results using voice coils. This study showed that tactile feedback is effective in improving the input speed of a number of entry tasks, especially under noisy conditions, as compared to without tactile or audio feedback. However, this study showed limited tactile feelings and patterns owing to the actuator characteristics.
Other studies regarding tactile interfaces coupled with GUI elements were introduced by Poupyrev and others [6] [7] . User studies [6] have also demonstrated the effectiveness of tactile feedback in terms of task completion time for tilting interfaces with a list GUI element. They also reported that tactile feedback is most effective when the GUI elements need to be touched or dragged across the screen, such as a button or scroll bar [7] .
In [8] , Hoggan and others described that the addition of tactile feedback to a touch screen improves finger-based text entry. The authors tested this in both static and mobile environments using a physical keyboard, a standard touchscreen, and a touchscreen with tactile feedback added. Their study showed the clear effect of tactile feedback for mobile devices; however, there was limited tactile expression owing to the commercial actuator characteristics and the use of only one tactile pattern for a button-clicking event. The authors also mentioned that higher-specification tactile actuators can improve performance even further.
Lee and others [9] discussed virtual button performance; the impact of audio and vibrato-tactile feedback; the impact of different types of touch sensors on use, behavior, and performance; and a quantitative comparison of finger and stylus operation. They demonstrated that tactile or audio feedback improved the speed of finger-operated virtual buttons more so than without feedback. Because they were not concerned about tactile feedback patterns, they used only one vibrato-tactile pattern generated through the built-in actuator (force activated resistive sensor) for a button-clicking event.
SemFeel [10] introduced an advanced tactile expression to inform the user about the presence of an object and additional semantic information about that object using multiple vibration motors. In addition, haptic numbers [11] provide a tactile way to inform a user of the numbers on a mobile touch screen device instead of a visual or auditory representation. They defined three different tactile patterns for the numbers and compared the effect of the representation models in terms of user performance and satisfaction. That study, in common with Tacton [12] [13] , is a research branch of non-visual information presentation especially using tactile stimuli.
There was also a study on identifying the most pleasant tactile feedback for a mobile touch screen button [14] . As satisfaction is an important element in human–computer interaction usability, the authors evaluated the pleasantness of various kinds of tactile stimuli and their effect on typing performance.
As previously mentioned, earlier studies have demonstrated the various aspects of the benefits of tactile feedback, such as an enhancement of usability, task performance, and user preference. Furthermore, some researches are concerned about methods of information representation using tactile stimuli.
With reference to the aforementioned studies, this research aims at finding tactile patterns simulating the feeling of physically clicking a button, as well as evaluating the performance of these feedback patterns in interaction with a button GUI on mobile touch devices. To generate various tactile feedback patterns, a new mobile device bumper case through a built-in film-type vibration actuator was designed and implemented. Based on mobile devices covered with this type of bumper case, several tactile feedback patterns were designed, and three user experiments were conducted. The findings of these user studies have contributed to an investigation into important elements used in designing tactile patterns for simulating the sensation of touching a physical button when interacting with mobile touch devices and the effect of using the suggested feedback pattern on the typing performance.
III. Implementation
- 1. Tactile Bumper Case
To enlarge the scope of tactile feedback expression, a new type of actuator and hardware platform was implemented [15] [16] .
The actuator uses an electro-active polymer (EAP) exhibiting a high deformation rate, low driving voltage, low weight, and thin thickness. Mechanical movement can be made using other characteristics of changing size or shape when an electric field is simulated. A new tactile bumper case built into an EAP film was implemented, and various types of tactile feedback were generated through the case covering mobile touch devices in response to the user’s touch.
In this study, an EAP film measuring 34 mm × 38 mm × 0.5 mm was used, and its response time was within 5 ms. The response time was measured from the occurrence time of a touch event to the generation time of tactile stimulation. Figure 1 illustrates the frequency response characteristics of the tactile actuator used in this study.
Elongation is proportional to the input voltage. The tactile actuator has a wide operating frequency range and resonant frequency of around 90 Hz. Here, a zero level indicates a zero input voltage, and a 255 level means a 3.3 voltage, as shown in Fig. 1 .
PPT Slide
Lager Image
Frequency response characteristics of EAP film–type actuator.
The bumper case contains an EAP film actuator, a micro-controller unit, a communication (Bluetooth) module, an amplifier, and a battery. All electronic and mechanical parts are installed under a protective cover plate. Figure 2 shows the appearance of the case. Reference [15] describes in detail how this actuator can be used with a mobile touch device.
PPT Slide
Lager Image
Bumper case.
- 2. Control Flow
To design and evaluate various tactile patterns, we defined and implemented a tactile SDK in a haptic library module. This provides the overall APIs for controlling the bumper case; for example, the play, stop, resume, pause, add, and delete functions of the tactile patterns in pattern storage with several options, such as the repetition time, interval time, duration, and play type.
The pattern storage maintains predefined patterns pre-designed by users or application providers. Some APIs support the creation and playing of new patterns defined by parameter values of frequency, amplitude, and duration.
From a user touch action or an application command, a control message of a specific tactile pattern is sent to the bumper case, the actuator in the case is moved according to the control message, and tactile feedback is generated to the user.
Figure 3 shows the working structure of the new hardware and software platform. Owing to the fast response time (less than 5 ms) of the actuator, tactile feedback can be generated with little time delay in the visual and auditory display from the perspective of human perception [17] . In our experimental studies, we used only basic visual and controlled tactile feedback.
PPT Slide
Lager Image
Working structure of new hardware and software platform.
Tactile pattern editors were also implemented for the easy design and evaluation of various patterns, as shown in Fig. 4 . These editors support the editing of tactile patterns that have several parameters, such as frequency, amplitude, duration, and interval, allowing a modification of the predefined tactile patterns. Arbitrary tactile patterns can be easily generated, tested, and modified using such editors on mobile touch devices.
PPT Slide
Lager Image
Tactile pattern editors: (a) drawing a new pattern and (b) modifying a predefined pattern.
- 3. Touch Gesture
As indicated in Table 1 , four popular touch gestures were selected, and the combinations of their unit actions analyzed [18] .
Analysis of touch gestures.
Touch gesture Combination of unit action Usage case (representative GUI)
Tap Touch + release Button
Drag Touch + move + release SeekBar
Flick Touch + quickly move + release List
Press Touch + hold + release Text
Among the four touch gestures, the tactile stimulation of the bumper case was applied to button GUI manipulation feedback with a tapping gesture, which is the most frequently used touch gesture and usage case for a mobile touch device.
Tactile patterns can be designed and applied to the unit actions of each touch gesture with consideration of usage and meaning. A tapping gesture consists of touch and release unit actions and is mainly used for manipulation of the button GUI element.
Many different feedback patterns for a button GUI can be designed by mapping different patterns to the each touch and release unit action. Through a pilot test, we selected six such patterns, as shown in Fig. 5 , according to the feeling of realistic button clicking and the suitability of button touch feedback. Each of the six selected patterns was made based on a simple impact or a combination of simple and vibration impacts. A simple impact has a 100 Hz square wave, whereas a vibration impact has a 200 Hz square wave with a 40 ms duration and can be sequentially displayed only before or after a simple impact. All patterns were simulated using 3.3 V (255 level) input voltages.
PPT Slide
Lager Image
Design of tactile patterns for simulating the sensation of physical button tapping.
IV. User Experiments
- 1. Tactile Pattern User Test I
Six patterns for button touch feedback were designed, as shown in the previous section. To investigate the important elements of tactile patterns for simulating the sensation of touching a physical button in interaction with mobile touch devices, a user experiment was first conducted [19] .
Four females and four males in their 20s and 30s (average age of 30.4) participated in this first evaluation. After a free button tapping trial and a comparison of the six different tactile feedback patterns, the participants were then requested to rank the feedback patterns based on their resemblance to the feedback felt from touching a physical button (see Fig. 6 ).
PPT Slide
Lager Image
User experiment application and environment: (a) application for measuring the reality aspect of tactile feedback patterns and (b) participant with noise cancellation headset.
Ten trials were performed for each task, and a total of 120 trials were carried out. The experimental results are shown in Fig. 7 . The rank scores of the six patterns differed significantly (based on a Kruskal–Wallis test, p = 0.007). Pattern 3 received the highest rank at a score of around 1.5, and patterns 2, 4, and 5 ranked much lower than pattern 3 (based on a Tukey HSD post-hoc test).
From user interviews and surveys, seven of eight participant users answered that short and clear patterns, such as a simple pulse with impact, are suitable for a button GUI simulation because they felt that the impact was similar to the sensations felt while typing on a physical keyboard. Moreover, they reported that a vibration feeling, such as a buzzing, is uncomfortable for a button click feedback because it seems like an alert or warning. The experimental results also showed that tactile patterns responding to each touch and release gesture provide the feeling of physically clicking a button, as shown in the experimental results of Fig. 7 .
PPT Slide
Lager Image
Average rank of tactile patterns with a realistic description of physical button clicking by an EAP film–type actuator.
- 2. Tactile Pattern User Test II
From the previous user experiment, three patterns (patterns 1, 3, and 6) according to their ranking were selected and compared on two different HW platforms. The first was a bumper case using an EAP film–type actuator, and the second was a commonly used touch device using a linear resonant actuator (LRA). On commercial devices, a sharp single click (click effect, narrow pulse, and 100% power) pattern [1] was used against a simple impact pattern, and a 40 ms vibration pattern [1] was used against a vibration impact pattern. The resonant frequency of the LRA was around 200 Hz, and the rising and falling times were 50 ms and 80 ms, respectively.
The second user experiment was carried out under the same conditions and for the same task as the first user experiment with two different types of actuators.
The tasks were performed by twelve participants (eight females and four males, with an average age of 26.7 years), the results of which are shown in Fig. 8 . All six patterns showed meaningful differences (Kruskal-Wallis, p = 0.003), and the T + R (EAP) pattern ranked highest (Tukey HSD post-hoc test).
PPT Slide
Lager Image
Average rank of tactile patterns with a realistic description of physical button clicking by LRA and EAP film–type actuators.
The T + R pattern of the EAP-film type and LRA actuators ranked highest in both groups, although only the rank of the T + R pattern of the EAP type was statistically meaningful. Most participants determined the ranking of the tactile patterns according to the value of the rapid response time, the short and clear pulse pattern, and the activated pattern on both touch and release gestures, similar to the previous experiment.
Some reasons for these experimental results may be inferred from the actuator’s characteristics. The EAP-type actuator has both a rapid response time and a short falling time; thus, it can generate a shorter tactile simulation more quickly than the LRA.
In addition, it was found that the tactile stimulation at the time of the touch and release gestures can produce a sensation similar to that of clicking a real physical button. Users seem to experience the feeling of pushing a physical button when the first tactile feedback, such as a simple impulse is generated for a touch gesture, and the feeling of a physical button rising when the second feedback is generated for the release gesture.
As in the preceding user interviews, most participants answered that a vibration feeling seems like an alert or a warning rather than a click. Because the feeling of depth and an after-image of the vibration feedback disturbed the feeling of short and sharp falling tactile patterns, the vibration pattern was found to be unsuitable for the tactile feedback of clicking a button GUI on a mobile touch device.
- 3. Text Input Performance User Test
In this user test, the effect of selected feedback patterns on typing performance was evaluated in comparison with a case without feedback. From the previous experiment, two patterns (patterns 1 and 3) were selected according to the rank of physical button resemblance and user surveys.
The T + R pattern ranked highest, and all users selected it as an appropriate tactile pattern for touch feedback for typing tasks on mobile touch devices. The Touch pattern and T + Vib + R pattern showed a similar rank as in previous tests, but the Touch pattern was preferred to the tactile feedback in the user surveys because users favored simpler tactile feedback for fast and accurate typing during interaction with button touches. This may be because they have experience using the Touch pattern provided by many commercial mobile touch devices.
These two feedback patterns generated by the EAP-type actuator and the case without feedback were compared in this user experiment. For this evaluation, virtual keypads with assigned digits and characters were implemented for a mobile touch device. Four different types of keypads were designed with different levels of layout complexity and different button sizes to measure the effect of feedback patterns on the typing performance according to the level of keypad layout difficulty.
Figure 9 shows the controlled experimental environment with twelve task conditions. Six females and eight males in their 20s and 30s (average age of 26.4) participated in this evaluation. They were required to enter a given expression comprising two four-digit numbers and one character as quickly and correctly as possible under the conditions of various keypad layouts and various types of tactile feedback. An example expression is “1234 + 5678.” All of the fifteen trials were conducted under each of the twelve task conditions, and a minimum 10 trials of free typing was allowed for each keypad layout, allowing the participants to become familiar with each one.
PPT Slide
Lager Image
Applications for text input performance test: (a) 3 × 3 button layout (16 mm × 16 mm button size), (b) 4 × 4 button layout (12 mm × 12 mm button size), (c) 5 × 5 button layout (9 mm × 9 mm button size), and (d) 6 × 6 button layout (7 mm × 7 mm button size).
A total of over 2,520 trials were carried out because the input time was measured and counted as a valid trial for a trial without typing errors. The test application recorded the input time and error count of each typing trial. This experimental design selected a Latin-square order and balance between subjects.
The experimental results for input speed without error are shown in Fig. 10 . Pattern 0 indicates no tactile feedback, and patterns 1 and 2 are a Touch pattern and T + R pattern, respectively. As the level of button layout complexity increased, the mean input time increased with significant differences (repeated measure ANOVA, p = 0.000, α = 0.05). In addition, the input speed was fastest with a 3 × 3 keypad layout. The input speed with a 4 × 4 layout was faster than with a 5 × 5 or 6 × 6 keypad layout (Scheffe’s post-hoc test, p = 0.000).
PPT Slide
Lager Image
Average input times for four types of keypad layouts and three types of tactile feedback patterns.
In relation to the type of tactile feedback pattern, the mean input time showed some differences. The T + R tactile pattern led to a rapid input time compared to without a feedback pattern, especially in a complex layout such as a 5 × 5 or 6 × 6 keypad layout, but the increase was not statistically significant. There was no two-way interaction between the feedback pattern type and keypad layout type ( p = 0.951). From the above result, we found that tactile feedback patterns do not have a positive effect on typing speed, assuming that the input tasks are conducted with no typing errors.
The effect on the error count was also evaluated during the typing tasks. The error count, which included any type of error that occurred, was measured during all fifteen trials. As the complexity of the keypad layout continued to increase, the mean error count increased with a significant difference (repeated measure ANOVA, p = 0.026, α = 0.05). The different tactile feedback patterns also showed different error counts with statistical meaning (repeated measure ANOVA, p = 0.010, α = 0.05), as indicated in Fig. 11 .
PPT Slide
Lager Image
Error counts for four types of keypad layouts and three types of tactile feedback patterns.
The lowest error count was found when pattern 2 (T + R) was used. Moreover, the tactile feedback showed fewer errors than the case without tactile feedback (based on a Turkey HSD test and Scheffe’s post-hoc test, p < 0.038). There was no two-way interaction between the feedback pattern type and keypad layout type ( p = 0.757). These results showed that tactile feedback patterns had a significant positive effect on the number of typing errors compared to the number of errors when no feedback was provided. In addition, the T + R pattern led to the lowest error count among the three patterns. Therefore, if the input time is measured to include the error correction time, then tactile feedback pattern 2 can be expected to stand out with regard to both the input speed and error count.
Figure 12 shows the average typing task completion times, which includes the error correction time. As the experimental results show, the different tactile feedback patterns have different typing completion times with statistical significance (repeated measure ANOVA, p = 0.013, α = 0.05). In addition, tactile feedback pattern 2 showed a faster time than the case without tactile feedback (based on a Turkey HSD test and Scheffe’s post-hoc test, p < 0.021). This means that tactile feedback pattern 2 is more effective in terms of input speed for general typing tasks including the error correcting time compared to the input speed performance without tactile feedback. This input task performance of the tactile pattern shows the remarkable effectiveness of a complex keypad layout such as the 5 × 5 and 6 × 6 button layouts. It should also be noted that the T + R tactile pattern was ranked highest, and in previous tests, all users selected it as an appropriate tactile pattern with touch feedback for typing tasks on mobile touch devices. The results from user interviews and surveys are summarized in Fig. 13 .
PPT Slide
Lager Image
Average typing task completion time for four keypad layouts and three tactile feedback patterns.
PPT Slide
Lager Image
Average rank of suitability pattern, preference pattern, and predicted input performance depending on the tactile feedback pattern.
The rank scores regarding the suitability of the tactile feedback patterns differed significantly (Friedman test, p = 0.000). Most users answered that it was comfortable to be provided tactile feedback on a mobile touch device, and the two proposed patterns were more acceptable than the currently used tactile feedback for commercial devices. The rankings of preference of the tactile feedback patterns were also significantly different (Friedman test, p = 0.002).
Moreover, the rank of the predicted input performance resulted in significant differences depending on the tactile feedback patterns (Friedman test, p = 0.003). The participants stated that they felt they could enter the given expressions more quickly and accurately when tactile feedback patterns were generated during the typing task. From the aspect of suitability, preference, and predicted input performance, patterns 1 and 2 generally show similar rankings. Although pattern 2 has slightly outstanding features of suitability and predicted input performance, users preferred pattern 1 as tactile feedback in mobile touch devices. This result may indicate that users are more familiar with a tactile feedback pattern similar to pattern 1 (Touch pattern), which is used mainly in commercial mobile touch devices, and they do not want to be bothered with excessive feedback when they concentrate on typing.
V. Conclusion
This study showed an investigation of tactile feedback patterns for a button GUI on mobile touch devices. A new bumper case was implemented using an EAP film–type actuator providing a wide range of tactile feedback expressions. In addition, a software architecture was introduced that included a haptic library operating on a mobile touch platform.
Several tactile feedback patterns were designed for a tapping gesture to manipulate a button GUI. In addition, the designed tactile patterns were evaluated through three user experiments. The first set of experimental results showed that tactile patterns responding to the touch and release gestures with a rapid response time and short falling time, respectively, provide the feeling of physically clicking a button. The T + R pattern was ranked as the best tactile pattern for simulating physical button-clicking feedback. In the second experiment, this pattern also ranked as the most suitable touch feedback for typing tasks on both an EAP film–type actuator and a linear resonant actuator. Most users stated that short and clear patterns, such as a simple pulse with impact, are suitable for a button GUI because they felt the impact was similar to the sensations felt while typing on a keyboard. Moreover, they reported that a vibration sensation, such as a buzzing, is uncomfortable for button-click feedback because it feels like an alert or warning.
This study also showed how these various patterns affect the input performance of button GUI manipulation. A comparison of the two designed tactile feedback patterns (T + R and Touch patterns) and no feedback suggest that tactile patterns have a significant positive effect on the number of typing errors. In addition, T + R tactile feedback patterns, including the error correction time, have a significant positive effect on the input speed for the typing tasks performed in this study. The participants stated that the typing tasks were conducted more quickly and correctly when the proposed tactile feedback patterns were provided, which was confirmed by the actual results. User interviews and questionnaires showed that most users want to be provided tactile feedback in interactions with mobile touch devices, and suggested that patterns are more acceptable than the tactile feedback currently used on commercial devices.
This study evaluated different tactile feedback patterns used during interaction with a button GUI to find the most appropriate, as well as assessing their effect on typing performance. We hope that these research results will be applied to various mobile touch devices, such as smartphones and tablet PCs. Further research efforts are required to expand to other kinds of touch gestures and GUIs, such as a dragging gesture on a scroll bar and the flicking gesture on a list GUI.
This work was supported by the S/W Computing R&D Program of MKE/KEIT, Rep. of Korea (10044308, Development of Surface UX Technologies based on Multimodal Display for Interactive Services and 10035360, TAXEL: Visio-haptic Display and Rendering Engine).
BIO
Corresponding Author  hsshin8@etri.re.kr
Heesook Shin received her MS degree in computer science and engineering from Pohang University of Science and Technology, Pohang, Rep. of Korea, in 2000. Since 2001, she has been with the Software Content Research Laboratory Department, Electronics and Telecommunications Research Institute, Daejeon, Rep. of Korea, where she is now a senior researcher of the engineering staff. Her research interests include human–computer interaction, usability, human factors, and accessibility.
jmlim21@etri.re.kr
Jeong-Mook Lim received his BS and MS degrees in computer science from Chungnam National University, Daejeon, Rep. of Korea, in 1998 and 2000, respectively. From 2000 to 2001, he worked on the Intelligent Transportation System Team for LG Information and Communications, Seoul, Rep. of Korea, as a researcher. Since 2001, he has been working at the Electronics and Telecommunications Research Institute, Daejeon, Rep. of Korea, where he has developed an operation and management system for access networks. He is currently interested in designing an unconventional HCI for mobile devices.
scinfuture@etri.re.kr
Jong-Uk Lee received his BS and MS degrees in computer science engineering and information and communications engineering from the Korea Advanced Institute of Science and Technology, Daejeon, Rep. of Korea, in 2007 and 2009, respectively. Since 2009, he has been a research engineer at the Electronics and Telecommunications Research Institute, Daejeon, Rep. of Korea. His research interests include real-time and embedded systems and human and computer interaction.
geehyuk@gmail.com
Geehyuk Lee received his BS and MS degrees in physics from the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Rep. of Korea, in 1990 and 1992, respectively and his PhD in electrical engineering from the University of Pennsylvania, Philadelphia, USA, in 2000. He is currently an associate professor at the Department of Computer Science, KAIST, Daejeon, Rep. of Korea. His primary research interests are interaction devices and techniques for smart information appliances; wearable computers; and smart environments.
kyungku@etri.re.kr
Ki-Uk Kyung is a managing director of the Transparent Transducer & UX Creative Research Center at the Electronics and Telecommunications Research Institute, Daejeon, Rep. of Korea. He is also directing the Pioneer Research Center for Reconfigurable Center. He received his PhD in mechanical engineering from the Korea Advanced Institute of Science and Technology, Daejeon, Rep. of Korea, in 2006. His research interests are flexible sensors/actuators and their applications to human–computer/robot interaction systems.
References
Immersion Corporation 2012 Haptic Develop. Platform for Android, Developer Guide, Effects Available in the UHL Immersion http://www2.immersion.com/developers/
Bau O. “TeslaTouch: Electrovibration for Touch Surfaces,” Proc. ACM Symp. User Interface Softw. Technol. New York, NY, USA Oct. 3–6, 2010 283 - 292    DOI : 10.1145/1866029.1866074
Poupyrev I. , Rekimoto J. , Maruyama S. “TouchEngine: A Tactile Display for Handheld Devices,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Minneapolis, MN, USA Apr. 20–25, 2002 644 - 645    DOI : 10.1145/506443.506525
Seifert J. , Packeiser M. , Rukzio E. “Adding Vibrotactile Feedback to Large Interactive Surfaces,” Proc. IFIP TC 13 Conf. Human-Comput. Interaction Cape Town, South Africa Sept. 2-6, 2013 507 - 514    DOI : 10.1007/978-3-642-40498-6_39
Fukumoto M. , Sugimura T. “Active Click: Tactile Feedback for Touch Panels,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Seattle, WA, USA Mar. 31–Apr. 5, 2001 121 - 122    DOI : 10.1145/634067.634141
Poupyrev I. , Maruyama S. , Rekimoto J. “Ambient Touch: Designing Tactile Interfaces for Handheld Devices,” Proc. ACM Symp. User Interface Softw. Technol. Paris, France Oct. 27–30, 2002 51 - 60    DOI : 10.1145/571985.571993
Poupyrev I. , Maruyama S. “Tactile Interfaces for Small Touch Screens,” Proc. ACM Symp. User Interface Softw. Technol. Vancouver, Canada Nov. 2–5, 2003 217 - 220    DOI : 10.1145/964696.964721
Hoggan E. , Brewster S. , Johnston J. “Investigating the Effectiveness of Tactile Feedback for Mobile Touchscreens,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Florence, Italy Apr. 5–10, 2008 1573 - 1582    DOI : 10.1145/1357054.1357300
Lee S. , Zhai S. “The Performance of Touch Screen Soft Buttons,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Boston, MA, USA Apr. 4–9, 2009 309 - 318    DOI : 10.1145/1518701.1518750
Yatani K. , Truong K.N. “SemFeel: A User Interface with Semantic Tactile Feedback for Mobile Touch-Screen Devices,” Proc. ACM Symp. User Interface Softw. Technol. Victoria, Canada Oct. 4–7, 2009 111 - 120    DOI : 10.1145/1622176.1622198
Pakkanen T. “Haptic Numbers: Three Haptic Representation Models for Numbers on a Touch Screen Phone,” Proc. ACM Int. Conf. Multimodal Interfaces Workshop Mach. Learn. Multimodal Interaction Beijing, China Nov. 8–12, 2010    DOI : 10.1145/1891903.1891949
Hoggan E. , Brewster S. “New Parameters for Tacton Design,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Florence, Italy Apr. 5–10, 2007 2417 - 2422    DOI : 10.1145/1240866.1241017
Brewster S. , Brown L. “Tactons: Structured Tactile Messages for Non-visual Information Display,” Proc. Conf. Australasian User Interface Dunedin, New Zealand Jan. 18–22, 2004 28 15 - 23
Koskinen E. , Kaaresoja T. , Laitinen P. “Feel-Good Touch: Finding the Most Pleasant Tactile Feedback for a Mobile Touch Screen Button,” Proc. ACM Int. Conf. Multimodal Interaction Crete, Greece Oct. 20–22, 2008 297 - 304    DOI : 10.1145/1452392.1452453
Lee J. “SHIFT: Interactive Smartphone Bumper Case,” Proc. EuroHaptics Tampere, Finland June 13–15, 2012 91 - 96    DOI : 10.1007/978-3-642-31404-9_16
Lee J. “Haptic Interaction with User Manipulation for Smartphone,” IEEE Int. Conf. Consum. Electron Las Vegas, NV, USA Jan. 11–14, 2013 47 - 48    DOI : 10.1109/ICCE.2013.6486789
Cholewiak R. , Collins A. 1991 The Psychology of Touch Lawrence Erlbaum Associates Inc. Hillsdale, NJ, USA “Sensory and Physiological Bases of Touch,” 23 - 60
Saffer D. 2008 “Designing Gestural Interfaces: Touchscreens and Interactive Devices,” O’Reilly Media Inc. Press Sebastopol, Canada
Shin H. “Tactile Feedback for Button GUI on Touch Devices,” Proc. ACM SIGCHI Conf. Human Factors Comput. Syst. Austin, TX, USA May 5–10, 2012 2633 - 2636    DOI : 10.1145/2212776.2223848