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In the last few years, Touch screen is using in public information system such as ATM machines and information kiosks. Nowadays the technology explosions of touch screen devices are popular and offer easier life for personal consumers such as Apple's iPhone, iPod Touch, iPad, HTC's Hero and Samsung's Galaxy Tab. There are many advantages of using touch screen devices such as control the interface directly, no extra input devices, faster operations and little or no training. Moreover it will reduce some of the human computer interaction (HCI) problems such as compatibility between devices and software functions. However, there are HCI problems of the interface of a touch screen such as usability, size of the finger and feedback. In this paper we will describes the user interaction issues on touch screen interface and end up with discussion of how to prevent this interaction issues.
Keywords: HCI, Touch Screen, User Interaction Issues, User Interface Design
Nowadays touch screens are widely used in applications such as ATMs, information kiosks, ticketing machines and personal usage such as environmental control, game, security and health care. In addition, Huang and Chen (2010) mention that replacing of conventional buttons to touch screen will get benefits of intuitive operations, software flexibility, space, simple and ease operation, fast response and cost savings. Moreover Lee, Poliakoff and Spence (2009) discuss touch screen has one to one relationship with control device and display and also no addition training necessary. Therefore touch screen application become popular in electronic products.
According to the Wikipedia, "A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area". Touch screen technology is potentially substitute mouse and keyboard functions. Many application of touch screen interface are improve human-computer interaction (HCI). According to eHow, there are three different types of touch screen technologies which are resistive, capacitive and surface wave. Each technology has their distinct advantage and disadvantage.
Resistive touch screen technology is widely used in variety of applications and environments. Its offered tremendous resolution and durability. Most of the resistive touch screen using in restaurants, factories and hospitals because its deliver cost effective, affordability, consistent and durable performance. Moreover resistive touch screen is not affect by dust or water.
Figure 1 - Resistive touch screen
The popularity of capacitive touch screen technology is stylus and capacitive panel can touch using finger. (For example apple iPhone) Capacitive touch screen is robust, high performance, good proximity, durable, high sensitive, maintain optical high clarity and also not affect by dust-proof.
Figure 2 - Capacitive touch screen
Surface wave technology is the most advanced of the touch screen types and offering excellent clarity and light transmission. The disadvantage of surface wave touch as is easy to damage the touch screen elements. Surface wave touch screen can use in Healthcare, POS and Hospitality sectors.
Figure 3 - Surface wave touch screen
The remainder of this paper will elaborate the literature reviews of interface issues for touch screen, human computer interaction issues, problem and statement of touch screen and end up with discussion of findings.
Touch Screen Interaction Design Considerations
Accommodation for Human Diversity
As a rapidly improvements of touch screen's functionalities and features, there is the challenge for designers to optimize the usability of the touch screen interface for various users (Matthew, Mark, Tom & Alex, 2009). According to the studied of difficulties of small touch screen for various age group conducted by Lee and Kuo (2007), current digital products are more focus on compactness, portable and easy to carry. On the other hand, the elderly people are facing the problem with small digital gadgets. The paper mentioned that elderly users have more difficult to operate the small touch screen device than younger users. Besides, due to the degeneration of human abilities and memory impairment of elderly users, the paper found out that they are difficult to press the touch screen and operate complex interface using their fingers. Finally the paper concluded that the common difficulties for using of small touch screen interface by various groups are motion, perception and cognition.
In addition, Jin, Plocher and Kiff (2007) mentioned that there is qualitatively different between older adults and younger adults when pointing and moving of the touch screen interface. Moreover touching or pointing the touch screen's small target, the older adult is more corrective movement than the younger adult. Lastly the paper suggested that button size (touch sensitive area) and spacing (between buttons) should consider carefully for the target application users when designer develop the touch screen devices application.
McKnight and Fitton (2010), pointed out the interactions with touch screen devices by children may cause the trouble with surface and gestural computing. In addition, clear instructions are important for children because the child knows only a few vocabulary ranges and should reduce the ability of reading for children in order to reduce the confusion and distress. The studies found out some important issues and suggestions for children when using touch screen interface which is children are struggling using touch screen interface and instructions did not effectively support to the children. To solving this problem, paper suggested that support some animation or mixture of audio and textual instructions is more useful than pure text instructions.
According to Neisser (2009), "Cognition is the act of knowing, and cognitive psychology is the study of all human activities related to knowledge. These activities include attention, creativity, memory, perception, problem solving, thinking, and the use of language". Lee, Poliakoff and Spence (2009) mentioned that various groups of user can benefits the using touch screen interface such as people who are unfamiliar recent technology developments, complex functions and structures, degeneration of aging issues (memory, sensory and visual perception) and other aspects of cognitive processing. In addition, Tsai and Lee (2009) mentioned in their studies; users are characterized their habits and characteristics when the interaction with touch screen interface. This means users need standard procedure of cognitive skills such as attention, interaction, perception, memory and decision making to avoid incorrect manipulation.
Visual & Tactile Perception
According to Wikipedia, "Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye". Ling and Schaik (2002) highlighted in their research paper that several researchers suggested usage of color can improve the empirical focus and faster search times. Besides users can faster search when higher contrasts between text and background color.
Altinsoy and Merchel (2009) mentioned most of the touch screen devices are missing the audio/tactile feedback to complete/confirmation of the successful process. Besides tactile feedback increase the productivity, easy to use as well as user experiences satisfaction. Moreover audio/tactile feedback compliance users to feel and the sound will met the perception when touch for touch screen's visual button. In addition, Lee and Spence (2008) also pointed out many users reported that lack of response after they touch the visual button from touch screen interface.
Huang and Chen (2010) discussed in their paper, depth of the touch screen icons provided better than the flat icons for the tactile feedback. In addition, the novice users were unfamiliar with touch screen interface and more strong tactile feedback. However, experienced users prefer less depth of the icons.
Direct manipulation is better in visual memory for interface design concept because it will reduce the "gulf of evaluation" (user must translate the display) and the "gulf of execution" (user must determine how to operate the system). Users can clearly understand the display (UI) of the system state and easily find out how to process the system (David, James & David, 2001). To maximize the working memory, designers should avoid displaying unnecessarily and redundancy information. (Reeves et al, 2004)
Touch Screen Interaction Issues
The touch screen is more intuitive compare to the conventional input method, such as keyboard and mouse. User can have direct interaction with the information on the screen, which will give user a stronger feeling of control.  Along with the increase in the popularity of the touch screen technology, the user issues introduced by this technology are also surfacing. We are going to analysis these issues in system status feedback; match between system and the real world; and flexibility and efficiency of use these three areas.
System status feedback
With the conventional input tools, such as keyboard and mouse, user will be able to get the feedback from the physical key pressed. As some good examples showed, the tactile feedback will help user improve the pointing interactions.  Although touch screen is more convenient for mobile devices than mechanical keyboard. Lack of tactile feedback is the drawback for this method. According to the touch screen market leader Apple, "although numerous attempts made to introduce an alternative to the standard keyboard, they have failed to replace or duplicate the commercial success of the conventional mechanical keyboard."
This is one of the most discussed and investigated problem that all the touch screen providers trying to resolve, till now there is no conclusive solution. Study shows that the tactile feedback will benefit the touch screen user interaction for both static and dynamic situation. Currently there are a few methods used in the market to overcome this issue, visual feedback, vibrotactile feedback and acoustic feedback. Visual feedback highlights the key that user clicked for a short period of time, this is already like a market practices for all the touch screen input devices. But this requires user to focus on the screen while typing as the display time is short that may sometime be ignored by user. Vibrotactile feedback is one of the major directions that mobile manufacturers are working on. With the technology advance, this feedback method could give user the mechanical keyboard experience. As released by Nokia, the C7 has the Enhanced haptic feature. This feature vibrates every single key when clicked in the touch screen keyboard instead of the entire device vibration while clicking. Acoustic feedback can enhance the user awareness, but the sounds target all the people around user, it could be a bad user experience in social environment. There are researches carrying on by market leaders using varies technologies, like piezoelectric actuation, solenoid, pin matrices, or ciliated surfaces . Although there is no perfect solution yet, researchers already proved in many studies (e.g. , , ) that the tactile feedback can improve performance and decrease error rates.
Match between system and the real world
A user friendly system users the terms that user familiar and make information appear in a natural and logical order. The touch screen allows user to act directly on the information which will give user a better experience of simulating the real world. But as most of the users have experience with conventional input methods, we also need to consider the match between the touch screen system and the conventional system.
With conventional input tools, there is a mouse over function. This function shows user the information or tooltip of the object when user points the mouse over it. The object can be a button or a tab in the application. Without really click on the object, user can have a brief understanding of the object function and user can decide whether want to click on it or make another selection. This will be helpful when user experiencing new applications or new functions. But in touch screen, this effect is not available yet. Once user touches the icon or tab, the function will be activated. The lack of mouse over function could make a lot of web applications less effective or unusable. Without mouse over function, the view URL in the status bar without clicking the URL, or view the dropdown list without clicking on the button, etc., all these features will not be functioning.
Flexibility and efficiency of use
There are a few of issues regarding the flexibility and efficiency of use of the touch screen devices. Most of the touch screen, phones or tablet computers, limited the size to a relatively small scale. When user needs to click some icon or key in some text, the finger will block the view of the user. The screen size is design in certain standard, but the human fingers are varying between people. When user has a bigger finger, it will be very difficult for the user to navigate in touch screen devices. Also the key size in the touch screen is limited due to the screen size limitation. The distance between two keys is relatively small that user may key in the wrong information if not carefully watching the screen.
When gestures get more complex, the number of people that are able to perform these gestures without instructions decreases. According to Saffer , "the complexity of the
gesture should match the complexity of the task at hand". Major challenges have to be faced when trying to defineintuitive, self-revealing gestures for complex tasks that go
beyond zooming, rotating and swiping. Saffer proposes that complex tasks should be realised with simple gestures (e.g. with buttons or menu systems), and additionally provide more sophisticated gestures for expert users.
technological challenges. As an example, a touch target should be greater than 11.5 mm, according to Wang and Ren .
If you are blind you are simply out of luck. p.s., we are all blind at times - such as when lights are out, or our eyes are occupied elsewhere - such as on the road). On their own, soft touch screen interfaces are nearly all "eyes on". You cannot "touch type", so to speak, while your eyes are occupied elsewhere (one exception is so-called "heads-up" touch entry using single stroke gestures such as Graffiti that are location independent). With an all touch-screen interface you generally cannot start, stop, or pause your MP3 player, for example, by reaching into your pocket/purse/briefcase. Likewise, unless you augment the touch screen with speech recognition for all functions, you risk a serious accident trying to operate it while driving. On the other hand, MP3 players and mobile phones mechanical keys can to a certain degree be operated eyes free - the extreme case being some 12-17 year old kids who can text without looking!
· Your finger is not transparent: The smaller the touch screen the more the finger(s) obscure what is being pointed at. Fingers do not shrink in the same way that chips and displays do. That is one reason a stylus is sometimes of value: it is a proxy for the finger that is very skinny, and therefore does not obscure the screen.
· Sunshine: We have all suffered trying to read the colour LCD display on our MP3 player, mobile phone and digital camera when we are outside in the sun. At least with these devices, there are mechanical controls for some functions. For example, even if you can't see what is on the screen, you can still point the camera in the appropriate direction and push the shutter button. With interfaces that rely exclusively on touch screens, this is not the case. Unless the device has an outstanding reflective display, the device risks being unusable in bright sunlight.
Case Study: iPhone's Touch Screen Interface
Not surprisingly, since iPhone launched in year 2007, touch screens have been widely and successfully in used in Smartphone, and we now expect to see touch screen technology to be used in every new Smartphone. There is no denying that the most influential touch screen mobile phone is iPhone, the multimedia-enabled Smartphone designed and marketed by Apple Inc. The invention of iPhone is definitely the revolution of touch screen mobile phone. On January 9th 2001, MOTO Development Group, a product design and development firm, named iPhone as the Smartphone having the best touch screen display. After comparing the touch screen interface of rival's Smartphones such as Android powered Nexus One with iPhone, Chris Verplaetse, the vice president of the Moto Development Group said:
'It's like asking what makes a Mercedes door close like a Mercedes door and a Hyundai door close like one though they use the same steel. There's clearly a difference.'
In this section, we will discuss why iPhone's interface and interaction techniques received extensive media interest and brought iPhone to the front position of the multi-touch Smartphone market.
Match between system and the real world
The interaction concept presented by the iPhone is often considered to add to its intuitive nature. Rather than using computer-based model of scrolling where a scroll bar sits to the right of the screen, iPhone's physical interaction model encourages users to freely browse anywhere on the screen. Dragging and scrolling a page in iPhone is very smooth and very much like interacting with an actual, physical object. In this way, users are able to focus on page content and maximises screen real estate. On the other hand, the virtual keyboard in iPhone is mostly welcomed as it uses QWERTY layout which is the most common modern-day physical keyboard layout.
Recognition rather than recall
As with non-touch screen devices, readily understand any iconography on the phone screen at a glance is essential. The colourful collection of default items and the downloaded applications on iPhone 'Home' screen always receive positive comments, as the icons largely considered as depictive rather than abstract. With the additional descriptive labels underneath the application icons, it provide users a good understanding of the functionality presented.
Visibility of System Status
Touch-response time is imperative one of the important factors that impact the usability of touch-screen interfaces. If the responsiveness of the touch screen is low, user might not know the status well. This delay will confuse user and encouraging repeated selection of targets elements. With its underlying capacitive technology, the iPhone is generally considered more responsive than competitor devices that relied on direct pressure. For iPhone, only lightest touch was required. On the other hand, the "magnification bubble" on the on-screen QWERTY keyboard provides user a good perception and feedback on the status of the text entry.
Consistency and Standard
Consistency is, largely, a key attribute contributing to the usability of the human interaction interface. iPhone is typically being praised for this respect. All applications in iPhone are accessible from home screen and the virtual keyboard can be accessed by tapping in a text entry field across all application. Also, there is a consistent position of the Back buttons.
To support user's navigation, the iPhone interface follows the Apple philosophy of achieving ease of use through simplicity. iPhone has a clear and direct path to the Main Menu or 'Home' area. The Main Menu also creating a shallow menu structure that is practically impossible to get lost. The menu also limits the number of option available to make it as simple as possible. All these interface design will prevent user making error thus minimise potential frustration.
Help users recognize, diagnose, and recover from errors
The single physical 'Home' button provides a constantly visible route to exit from application menue to the phone's default Home screen. If user encounter any problem when navigating in the iPhone, they can easily escape from the dilemma by pressing the 'Home' button any time to go to the Home screen This function enable user to explore the iPhone by scrolling anywhere freely on the screen as they have no worries on making mistakes.
Flexibility and efficiency of use
If users have problems with finding, selecting and using the most basic functionality, then they will feel negative about the product. The iPhone interface follows the Apple philosophy of achieving ease of use through simplicity. On the other hand, iPhone also provides advance function for experienced users, such as double-press the 'Home' to access 'Favourite Contacts'.
Shortcoming of iPhone Interactive Interface
Although we can safely iPhone is the best smartphone on the market from the consumer's perspective. There are still pain points in term of interaction interface that Apple Inc should improve on iPhone. One notable example is, in some setting users need to save their changes explicitly, whereas in other settings alterations are saved automatically. Users are confused by this inconsistency design as they are not sure whether or not a performed action had been accepted or confirmed.
Phone's display recorded much more accurate the inputs, being able to draw straight and smooth lines no matter how fast you move the finger or how much it gets in touch with the screen.
The size and the space between the application icons, as well as the
iPhone won the race because it has a small sensor and a high sampling rate being able to process exactly where the finger is it. On the other hand Droid has a low quality sensor, which cannot determine correctly the input.
wrapping a button-bashing existence for a softer sensing interface we can press, swipe, pinch and zoom, means we can now do a little bit more than simply stare into that pint-sized screen of ours.
Touch screens are attractive because they save space and allow dynamic simulation of electromechanical controls, they provides high level of immediacy in interaction by allowing the user to touch, push, and drag information directly with their fingers.