JOURNAL OF OBJECT TECHNOLOGY
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`Online at http://www.jot.fm. Published by ETH Zurich, Chair of Software Engineering ©JOT, 2007
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`Vol. 6, No. 3, March – April 2007
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`Minimalist and Intuitive User Interface
`Design Guidelines for Consumer
`Electronics Devices
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`Seonghoon Kang and Won Kim, Samsung Electronics and
`SungKyunKwan University, Suwon, S. Korea
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`Abstract
`People today come in contact with many consumer electronics (CE) devices in their
`daily lives. CE devices have become increasingly complex with added functionality;
`devices from different vendors provide different user interfaces for the same
`functionality; similar devices from the same vendor provide different user interfaces
`for common functionality. As a result, usability of CE devices has become a serious
`challenge for most users. In this paper, we put forth design guidelines for making
`user interfaces for CE devices easy to understand for most everyday users. To do
`this, we first present a taxonomy of user interface dimensions for CE devices. We
`then present our design guidelines against core elements of the taxonomy, and
`apply them against various popular CE devices. The designing guidelines, when
`applied consistently and diligently, can help bring some order to the current state of
`user interfaces for CE devices. The results of this paper should be applicable to a
`good extent to general digital systems
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`Keywords: User Interface, UI, Human Computer Interface, HCI, Usability, CE
`devices,
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`1
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`INTRODUCTION
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`People today use many types of consumer electronics (CE) products, including
`cellular phones, music players, DMB (digital multimedia broadcast) players, personal
`digital assistants, digital
`televisions, video recorders, digital cameras, smart
`refrigerators, video security systems, automobile navigators, digital clocks,
`calculators, etc., besides personal computers, laptops, and computer-based systems
`and equipment at home and work. All the functions these devices (and systems)
`provide, all the information they contain, and all the responses they make to user
`commands are exposed through the user interface (UI). Ideally, the UI should be
`designed so that most everyday users can, without having to consult the user manual,
`easily figure out how to use all of the primary functions of the devices and systems,
`easily comprehend all of the basic information they contain, and easily comprehend
`
`Cite this column as follows: Seonghoon Kang and Won Kim: “Minimalist and Intuitive User Interface
`Design Guidelines for Consumer Electronics Devices”, in Journal of Object Technology, vol. 6, no. 3,
`March – April 2007, pp. 39 - 52 http://www.jot.fm/issues/issue_2007_03/column5
`
`
`Roku EX1034
`U.S. Patent No. 10,334,311
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`MINIMALIST AND INTUITIVE USER INTERFACE DESIGN GUIDELINES FOR CONSUMER
`ELECTRONICS DEVICES
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`most of the responses from them. Sadly, however, the state of UI for CE devices, and
`many of the general digital systems, today is well short of the ideal.
`Many of the CE devices have become rather complex, as vendors have added
`new features and functions in order to differentiate from competitors and also to
`justify raising the price. CE devices of different types have some frequently used
`common functions, such as power on/off, channel up/down, date/time setting, etc;
`however, different vendors offer very different UIs for these functions. Even worse,
`vendors of the same family of CE devices offer different UIs for the devices. Further,
`the UIs are often inconsistent, and difficult or impossible to follow without consulting
`user manuals. For those features that are not often used, each time they are used, the
`manuals need to be consulted.
`The UI may not be the most important factor that determines the commercial
`success of CE devices. For example, the commercial success of digital televisions is
`determined by the picture quality, price, design, functionality, and the brand name.
`However, once parity is established on these factors, UI becomes a key differentiator
`among competing products. Today, due to competitive pressures in the market, parity
`has been established on most of the important factors, and UI remains a factor that can
`help vendors differentiate from others.
`As CE devices are used by everyday users, not just engineers or artists, their UIs
`must be designed for ease use and comprehension by everyday users. Various
`researchers have suggested guidelines for designing a UI. Shneiderman and Plaisant
`suggested “8 golden rules” [1]: A good UI should have consistency, provide universal
`usability, provide meaningful feedback, include an exit interface, prevent errors, make
`rollback easy, be always controllable, and reduce data which should be memorized to
`operate the device. Ferré et al. suggested 5 characteristics of determining usability [2]:
`learnability, efficiency, repeatability, error rate, and satisfaction. Norman suggested
`that basic principles of a good design for human are providing good a conceptual
`model and being visible [3]. Smith and Mosier offer guidelines for designing the UI
`for software in six functional areas: data entry, data display, sequence control, user
`guidance, data transmission, and data protection [4].
`These are all valid guidelines. However, in our view, they have not been well-
`heeded by UI designers of CE devices on the market today, as evidenced by the sad
`state of the UI. As a result, we have decided to see if we can help to bring some order
`into the UI of CE devices by proposing a minimum set of very practical design
`guidelines. To do it, we first developed a taxonomy of user interface dimensions in
`CE devices. The taxonomy provides a framework for understanding more precisely
`how we apply our design guidelines.
`For our research, we analyzed MP3 music players, digital TVs, DVD recorders,
`digital still cameras, DMB players, PMPs (Personal/Portable Multimedia Players),
`and cellular phones. The vendors included Samsung Electronics, LG Electronics,
`TiVO, and Apple Computers. By analyzing the UI of these devices, we arrived at a
`minimum set of design guidelines. (* Although we are not at liberty to divulge our
`findings with respect to Samsung Electronics products, suffice it to say here that we
`have reported our findings and recommendations to the top management for action,
`and the top management has accepted most of our recommendations. *)
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`The contribution of our research is the minimum practical set of guidelines for
`designing the UI of CE devices to substantially help everyday users to comprehend
`the functionality and information contents of the devices. We believe the set of
`guidelines can apply to a large extent to general digital systems, and should also be
`useful to technical users.
`The remainder of this paper is organized as follows. In Section 2, we present a
`taxonomy of user interface dimensions for CE devices. In Section 3, we discuss a
`minimum practical set of design guidelines for CE devices. In Section 4, we make the
`design guidelines concrete, and illustrate the effectiveness of our guidelines by
`identifying how each of them is violated in CE devices. Section 5 concludes the
`paper.
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`2 A TAXONOMY OF USER INTERFACE DIMENSIONS
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`Before proceeding, let us see the reasons for the current sad state of the UI for CE
`devices.
`1. There are many types, and many models for each type, of CE devices
`2. Increasingly many functions are crammed into many of the devices.
`3. The increasing number of functions leads to many types of information to
`store and display.
`4. There are many methods to represent the information
`5. There are many modes of interaction with the users
`6. There are many ways to appeal to the user’s sense of aesthetics and emotions.
`Beyond these, the UI has not been a high-priority item for the vendors, as they have
`chosen to focus on the other, more pressing, items to survive in the market, such as
`cost reduction, pricing, distribution, marketing, design, hardware quality, features, and
`name branding. Further, as we will see shortly, the UI have several dimensions, in our
`view, user interface designers have devoted time on those dimensions that appeal to
`the emotions of the users, and devoted much less energy and thought on those
`dimensions that deal with how everyday users can comprehend the functions and
`information contents of the devices.
`Some researchers proposed taxonomies of the UI and human-computer
`interaction systems. Chignell made an early attempt at a taxonomy of human-
`computer interaction and standardizing terminology [5]. Coomas and Timmermans
`proposed a taxonomy of physical media, representational modalities, and human-
`computer dialogue semantics [6]. Barr et al. considered a principled understanding of
`user-interface metaphors, and provided a taxonomy for discussing and analyzing them
`[7].
`We developed our own taxonomy1 as a framework for understanding all
`dimensions of the UI, and identifying more precisely where we should apply our
`design guidelines. The taxonomy, shown in Figure 1, consists of five parts,
`corresponding to five dimensions of the UI for CE devices; namely, physical vs. non-
`
`1 We note that an earlier version of this taxonomy was the subject of a very short paper by us in Korean
`that we presented in a domestic Korean conference [8]. We include an upgraded version here to
`provide a basis for presenting our design guidelines.
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`MINIMALIST AND INTUITIVE USER INTERFACE DESIGN GUIDELINES FOR CONSUMER
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`physical, aesthetics and emotion, convenience, operation mechanisms, information
`and information architecture. When designing a user interface, every dimension has to
`be accounted for.
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`2.1 Physical vs. Non-Physical
`The first dimension is whether the user interface is physical or non-physical.
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`PUI (Physical User Interface)
`• Physical user interface refers to the physical user interface elements on the CE
`device with which the users interact. This includes physical buttons, switches,
`wheels, knobs, stylus, touch screen, keypad, microphone, monitor, speaker, digital
`camera, video recorder, etc. on CE devices, including remote controls.
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`NPUI (Non-Physical User Interface)
`• Non-physical user interface refers to logical user interface elements, such as
`alphanumeric information or images or video displayed on the monitor, voice or
`sound heard via the speaker, etc. Such information is the result of a command the
`user issues, an action (e.g., turning the power on/off) the user takes, or the
`occurrence of an abnormal condition. Often there are many categories of such
`information, and many of the categories may logically best be decomposed into
`sub-categories. As such, the information has to be organized in a hierarchical
`structure, known as information architecture. Information architecture refers to the
`organization of such information.
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`2.2 Aesthetics and Emotions
`The next dimension in user interface refers to user interface elements that appeal to
`the aesthetics and emotions of the users. This dimension applies to both the physical
`and non-physical aspects of the user interface. This has five aspects, corresponding to
`the five sensory functions of the human. In practice, though, only three aspects are
`relevant.
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`Visual aspect
`• color, brightness, contrast, etc.
`• shape, size, arrangement of the PUI and NPUI user interface elements
`• graphics, images, animation, video, symbols, etc.
`• design and appearance of a device
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`PhysicalPhysical
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`Aesthetics and EmotionsAesthetics and Emotions
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`ConvenienceConvenience
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`Operating mechanismsOperating mechanisms
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`PUIPUI
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`NPUINPUI
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`Visual aspectVisual aspect
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`Auditory aspectAuditory aspect
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`Tactile aspectTactile aspect
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`Ease of operationEase of operation
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`Ease of Element IdentificationEase of Element Identification
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`Common operating mechanismsCommon operating mechanisms
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`Device-specific operating mechanismsDevice-specific operating mechanisms
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`Information and Information ArchitectureInformation and Information Architecture
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`Device-facing informationDevice-facing information
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`Figure 1. Taxonomy of CE User Interfaces
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`User-facing informationUser-facing information
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`Auditory aspect
`•
`tone, loudness of sound, intonation, accent, etc.
`• sound effects (bell sound, animal sound, etc.)
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`Tactile aspect
`texture, weight, elasticity of a device, etc.
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`•
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`2.3 Convenience
`The next dimension of the UI is convenience to the users. This refers to ease of use,
`and is certainly an important determinant of the usability of a device. In particular,
`there are two types of convenience. One is ease of operating a device, and applies to
`the physical aspect of the user interface. Another is ease of identifying user interface
`elements, and applies to both the physical and non-physical aspects of the user
`interface.
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`Ease of Operation
`• shape, size, and layout of PUI elements,
`• sound, flashing or blinking light,
`• other characteristics of a device
`that make it easier to see, understand, press, grasp, touch and feel a device, etc.
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`Ease of Identification
`• shape, size, and color of PUI elements,
`• font size, font style, font color, and background color of text, etc.,
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`• shape, size, color, and layout of NPUI elements, etc.,
`• sound, flashing or blinking light, etc.
`• other characteristics of PUI and NPUI elements
`that make it easier to identify a user interface element.
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`2.4 Operating Mechanisms
`The next dimension in user interface is the operating mechanisms for the devices.
`Broadly, this may be classified into those that are common to many types of devices,
`and those that are specific to a given type of device. The operating mechanisms apply
`to both the physical and non-physical aspects of the user interface. There are many
`mechanisms for operating devices physically, such as, moving a cursor, pressing a
`button, throwing a switch, touching a touch screen, typing on a keypad, gesture,
`motion, etc.
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`Common operating mechanisms
`• power on/off
`• menu operations: open/close, 4 way navigation, select/release, exit/back
`• alphanumeric data input and manipulation of displayed alphanumeric data
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`Device-specific operating mechanisms
`• TV: channel up/down, display modes, picture in picture mode, etc.
`• digital still cameras: zoom in/out, shot mode, flash mode, etc.
`• MP3 music players: media play control (play/pause, fast forward, etc.)
`• other devices: tilting, shaking, touching,……
`Both types of mechanisms have a very important common sub-mechanism, namely,
`error-handling mechanisms. Error-handling mechanisms typically use visual or audio
`information. Sometimes, however, they involve a device lockout. There are two ways
`to handle error.
`• Error prevention: ignoring input, requiring confirmation, circulative menu
`navigation, etc.
`• Error warning: issuing of a warning message (and/or sound, blinking light, etc.)
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`2.5 Information and Information Architecture
`The information and information architecture dimension refers to the information
`content and the organization of the information. In our taxonomy, this refers only to
`the non-physical aspect of the user interface, and does not include the aesthetics and
`emotions dimension. There are two types of information in terms of whether it is to be
`input by the user or to be viewed and manipulated by the user. The use of information
`may be for the installation and operation of a device, or for viewing by the user, as
`shown below.
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`Device-facing information
`installation: initial setting values, etc.
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`•
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`• operation: input for menu navigation, control and data input, input for error
`handling, etc.
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`•
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`User-facing information
`installation: cable connection, help information for initial setting (including on-line
`manual), etc.
`• operation: operating mechanisms for the menus, buttons, switches, etc.
`• representation: labels, icons, symbols, buttons, etc., feedback on user input, device
`status information, error feedback, etc.
`The information may also be classified in terms of the types of data to be input or
`output, as follows.
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`Device-facing information
`• visual information
`-
`image: finger print, pupil, picture, etc.
`-
`text: title, name, description, etc.
`- numeric: channel, setting values, etc.
`- date and time: system time, reservation time
`-
`scalar: volume, play position, etc.
`• audio information: voice, sound, etc.
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`User-facing information
`• visual information
`-
`image: icon, image, graphic, animation, video, etc.
`-
`text: menu label, description, message, etc.
`- numeric: channel, setting values, etc.
`- date and
`time: system
`time,
`reservation
`information, etc.
`-
`scalar: volume, play position, etc.
`- attributes: color, font size, font style, blinking, etc.
`• audio information: voice, melody, sound effect, etc.
`• other modalities: vibration (haptic information)
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`information, program
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`3 DESIGN GUIDELINES
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`We now present our minimal set of guidelines for designing the user interface of CE
`devices with the view to making it as easy as possible for everyday users to
`comprehend all primary functions and primary information contents of CE devices.
`The guidelines apply to all five dimensions in our taxonomy.
`We start with a very simple premise, that is, the UI must be simple. To be simple,
`the types and number of UI elements must be minimal; all UI elements and their
`combinations must be intuitively comprehensible to everyday users with minimal
`exposure to some CE devices; and there must be consistency among all UI elements
`and their combinations. Further, the minimum and intuitiveness guidelines must be
`applied consistently throughout the UI design. Below we examine each of these three
`guidelines for making the UI simple.
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`3.1. Minimum
`As the number and types of features keep increasing, it is easy for UI designers to
`increase the number and types of UI elements. The number and types of UI elements
`must be kept to a minimum. Specifically, the number of symbols, icons, labels, font
`styles, font sizes, text colors, background colors, modalities, the number of items and
`depth of the menu hierarchy, etc. should be kept to the minimum. If some redundancy
`is to be built in, it must be done in very careful consideration of the business
`requirements. The following explains what it means to minimize various UI elements.
`• The number of physical UI elements, such as input buttons on a device, should be
`minimized to correspond to the most frequently used functions. Less frequently
`used functions should be manifested as non-physical UI elements, that is, as items
`on a menu. For example, there should not be buttons on a television remote control
`for functions such as “memorize or erase a channel”; the users should be directed
`to the menu to find items corresponding to such functions. In this way, UI
`designers should prevent the remote control from being crowded with buttons and
`labels for non-frequently used functions.
`• When it is necessary to overlay several functions on one button, the number of
`overlaid functions should be limited to 2. The general public has been accustomed
`to toggle switches, and, for example, it is reasonable to overlay the “on” and “off”
`functions on the “power” button. However, it causes confusion if 3 or more
`functions are overlaid on a button, for example, the “open/close/back” functions
`on a single menu button.
`• The use of icons, symbols, and labels for both physical and non-physical UI
`elements should be minimized. In other words, no icons, symbols, and labels
`should be used unless they are necessary. Icons, symbols, and labels that make no
`sense to the users or are difficult or impossible for them to easily comprehend and
`remember are regarded as “unnecessary,” and should be eliminated or modified.
`• The number of font sizes, font styles, and colors used should be minimized.
`Mixing more than a few font sizes, font styles, and colors in general distracts the
`users.
`• Labels, phrases and sentences on both the physical and non-physical UI elements
`should be brief (and clear).
`• The number of items on a menu screen should be kept to fewer than 7 or 8 to avoid
`cluttering the screen.
`• The depth of a menu hierarchy should be limited to 3 or fewer. It is difficult to
`trace the menu structure and be aware of the nodes and paths followed, if the depth
`is more than 3.
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`3.2. Intuitiveness
`The labels, symbols, icons, words, phrases and sentences on many CE devices and on
`the menu are often difficult to comprehend intuitively. Sometimes, words, phrases,
`and sentences that only engineers can understand appear on the menu or even the
`devices. Further, icons are often not symbolic of the corresponding functions, and
`only their designers can appreciate their meanings. The users need to consult the user
`manuals to be able to operate the devices or navigate the menu. However, to
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`compound the matter, the manuals too are often difficult to understand or may have
`long been misplaced.
`People in reasonably industrialized parts of the world today are exposed to
`everyday UI elements in their daily lives. These include a variety of doors (home,
`office, hotel, automobile,…), combination locks, public transportation systems,
`automobile dashboards, automobile and airplane seatbelts, road signs, traffic signals,
`signs in public places, elevators, toasters, washing machines, hair dryers, treadmills,
`etc. Beyond these, many use some of the many CE devices, personal computers, and
`the World Wide Web. Further, many are exposed to UI elements in performing their
`jobs, such as machine tools, heavy industrial and farming equipment, weapons,
`airplanes, trains, ships, etc. As such, everyday users may reasonably be expected to
`possess some common knowledge and experience-based intuition about the meanings
`and basic ways to operate various UI elements. This includes, for example, the fact
`that the red color or flashing light implies a warning; the power button on a CE device
`is an on/off toggle switch, the lines on a road sign near an exit ramp on the highway
`correspond to streets or other highways, etc.
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`Figure 2. Intuitive Symbols
`The meaning of each physical and non-physical UI element on a CE device must be
`intuitively clear to everyday users. Figure 2 shows some UI symbols whose meanings
`should be intuitively clear to everyday users. The sequence and combination of UI
`elements, too, must be intuitively clear. To design the UI for CE devices to be
`intuitively clear to everyday users, the designers must exploit the common knowledge
`and acquired intuition of the users, and must be very careful not to venture outside of
`the scope of such knowledge and intuition. The ultimate goal of the UI for CE devices
`should be to make it possible for most everyday users to be able to use the CE devices
`without having to consult the user manuals. The following further explains what it
`means for the UI to be intuitive.
`• When it is necessary to overlay several functions on one button, there should be
`relationships among the functions that are intuitively clear. For example, the left
`and right navigation functions are overlaid on the message box button on some
`cellular phones, and the flash mode button on some digital still cameras. This is
`not intuitive, since there is no obvious relationship between the navigation
`function and the messaging function on cellular phones, or between the navigation
`function and the flashing function on digital still cameras. Even if the user is able
`to operate this function by first reading the manual, the user is likely to have to
`consult the manual again after not using the functions for a while.
`• The icons and symbols must be symbolic of the functions they represent. For
`example, on a 4-way navigation button, there should be up/down/left/right
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`symbols; and on a volume up/down button, there should be corresponding
`symbols, such as +/-.
`• The symbols, labels, icons, words, phrases, etc. should be easily comprehensible to
`everyday users. In other words, such technical phrases as “700 Mbytes of storage
`remaining” on a music player should be eliminated. Appropriate color should be
`used for warnings and emphasis.
`
`3.3. Consistency
`Consistency cuts across all aspects of every UI element in every CE device. Once a
`particular symbol is chosen for a particular function, it should be applied consistently
`throughout the UI. This should certainly be done within a particular device, and
`preferably also across devices of different types that happen to share the same
`function. We define inter-device consistency to be consistency between different
`types or models of CE devices, either from the same vendor or different vendors; for
`example, digital televisions and digital still cameras. We define intra-device
`consistency to be consistency among UI elements on one particular type and model of
`device.
`In general, there should be inter-device and intra-device UI consistency. Today,
`as we will illustrate in the next section, both inter-consistency and intra-consistency
`are inadequate. As a result, everyday users have to learn to operate each device,
`separately, because each device has a different menu structure, different icons and
`symbols for the same or similar functions, different words and symbols even on the
`same device, etc. As CE devices of the same type, and even of different types, share
`common functions, the ultimate goal of consistency should be unification (i.e.,
`standardization) of the UI elements for these common functions. The following
`explains further what it means for the UI elements to be consistent.
`• The menu layout, and the navigation and selection of menu items should be
`consistent.
`• The selection of the font style, font size, colors, etc. should be consistent.
`• The selection of icons, symbols, and labels should be consistent for the same or
`similar functions. For example, if a left arrow is used for left navigation on the
`menu of a digital television, it should be used not only on all left navigations on
`the menu, but also on the remote control, and even on the music players from the
`same vendor.
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`4 APPLYING THE DESIGN GUIDELINES TO CE DEVICES
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`In this section, we apply the three design guidelines to the non-physical aspect of the
`UI of several representative CE products from leading vendors. The discussions serve
`two purposes: one is to illustrate each of the design guidelines in concrete contexts,
`and another is to demonstrate the merit of applying the design guidelines in
`identifying the problems and fundamental reasons for the problems with the UI in
`today’s CE devices. To protect the commercial interests of the vendors, we shall not
`name them.
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`Nested menu structure (violation of minimum)
`It has long been established that the depth of a menu hierarchy should be limited to 3
`or under. We have found, for example, that the external connection setting function on
`some digital TV menus is 4-level deep, as shown in Figure 3. Either the top or the
`second level of the menu hierarchy may be eliminated to fix this problem.
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`ChannelChannel
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`External connectionExternal connection
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`External Input 1External Input 1
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`External Input 2External Input 2
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`Component Input 1Component Input 1
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`……
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`VCR/ DVD/ STB/ …VCR/ DVD/ STB/ …
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`VCR/ DVD/ STB/ …VCR/ DVD/ STB/ …
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`VCR/ DVD/ STB/ …VCR/ DVD/ STB/ …
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`
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`Level 1Level 1
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`Level 2Level 2
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`Level 3Level 3
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`Figure 3. The menu structure for the external input connection setting function on a DTV
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`Level 4Level 4
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`Overlaying of functions (violation of minimum and intuitiveness)
`The “menu” button on some digital TV remote controls has three functions overlaid
`on it: open, close, and back. Only the open and close functions should be overlaid to
`make the button a toggle button that the ordinary users would expect. Either the back
`function should be removed from the remote control, or should be placed on the
`menu, or perhaps even overlaid with some other function on another button on the
`remote control.
`
`Hidden functions (violation of intuitiveness)
`The “program reservation” function on some digital TV does not exist on the remote
`control, and it is an item on the “Program Guide” menu screen. This presumes that the
`users will browse through the programs and, upon finding a desired program, will
`reserve a desired program. However, the label “Program Guide” would convey to
`ordinary users the notion that the menu screen would only provide program
`information, and does not convey the notion that the act of reserving programs would
`be a part of it. To fix this problem, either the label “Program Guide” should be
`changed to “Program Guide and Reservation,” or a separate menu screen should be
`created for “Program Reservation” at the same level as “Program Guide”
`
`Use of difficult or non-helpful words or phrases (violation of intuitiveness)
`Some digital TVs and DVD recorders are found to use technical terms or words and
`phrases whose meanings are not clear on the menu screens and help screens. These
`include such words and phrases as “display mode, “audio mode”, “SRS”, “internal
`amplifier”, “v-mode”, “equalizer”, “free space remaining: 70Mbyets”, etc. These
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`would not mean much to a large segment of everyday users. Such technical term as
`“70Mbytes” should be translated to a term that would be both relevant and easily
`comprehensible to the ordinary users, such as “x number of additional songs may be
`recorded”, “x minutes of additional video may be recorded,” etc.
`
`Mismatch of the PUI and NPUI elements (violation of consistency and
`minimum)
`Figure 4 shows volume control interfaces of an MP3 music player. The “up and
`down” movement of the touch pad on the player (PUI) and the circular GUI feedback
`display (NPUI) do not match. The inconsistency between the two UI elements
`burdens the users with one extra UI element and paradigm to deal with.
`
`Figure 4. Inconsistent volume control interfaces (PUI and NPUI)
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`
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`Use of different words, symbols and labels for the same functions within the
`same devices or across different devices (violation of consistency)
`The selection button is labeled variously as “select,” “confirm,” or “OK” on different
`devices Similarly, the “power on/off” button comes with different symbols on
`different devices, as shown in Figure 5.
`
`
`DTV HDDR Cell. Phone
`Figure 5. Examples of the use of different symbols for the same function
`
`Inconsistent operating mechanisms within a menu (violation of consistency)
`The “back” button on digital TVs or DVD recorders is used either to exit the current
`menu or to return to the upper-level menu screen. However, in some devices it is used
`to exit all active menus.
`
`Inconsistent operating mechanisms between similar devices (violation of
`consistency)
`The “menu” button on digital TVs is used for the “menu open” and “menu back”
`functions, while the “menu” button on some of the DVD recorders is used for the
`“menu open” and “menu close” functions.
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`5 CONCLUSION
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`As the number of types and models, and the features and capabilities of consumer
`electronics (CE) devices have increased during the past decade, usability of the
`devices has become a major challenge to everyday users. Unfortunately, the vendors
`have not satisf