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User Interfaces for Digital Television:a Navigator Case Study

Leena EronenHelsinki University of TechnologyP.O.Box 9700, FI-02015 HUTFinlandTel. +358-9-451 5130leronen @tcm.hut . fi

Pet r i Vuor imaaHelsinki University of TechnologyP.O.Box 9700, FI-02015 HUTFinlandTel. +358-9-451 4794Petri .V uorim aa @ hut. fi

A B S T R A C TDigital televis ion user interfaces are composed of text, graphicsand video. Usability issues that arise include informationvisualization, searching and navigation. This paper introduces twouser interface prototypes for digita l television. Both prototypeswere tested with real users and the test results are discussed.KeywordsDigital televis ion, usability, user interfaces, prototypes,navigation.1 I N T R O D U C T I O NDigital television is a promise of better video and audio, hundredsof channels, WWW browsing, email, games and other interactiveservices. The challenge of digital television is to introduce, adaptand implement the new technology for the mass TV market whereboth content and technology must gai n consumer acceptance.Set-top box is an important part of the new technology. It givessoftware developers a means to develop enterta ining andcompelling applications for the digital television environment.Navigator is the main user interface of the digital television.Navigator is the 'system software' in set-top boxes that givesaccess to Electronic program guides (EPG), text TV pages andChannel information. It is also used to tune the TV channels,configure the set-top box and launch applications like WWWbrowser and email client.The idea of a 'system software' resembles the personal computer.However, there are three main areas where the digital television isdifferent from the personal computer. These are the displaytechnology, the input device and the information content. Indigital television, the TV screen is designed for displaying movingimages to be looked at from a distance. Unlike the personalcomputer, the TV screen is not good at displaying detailedimages. The remote control is an interaction device that can not beused to point at an arbitrary object on the TV screen. The cursorPermiss ion to make digi tal or hand oopie of al l or part of thiswork for personal or c lassroom use is granted without fee provi-ded that copies are not m ade or dis t r ibuted for prof i t or commer-cial advantage, and that copies bear this notice and the full cita-t ion on the f irst page. To copy otherwise, to republish, to post onservers or to redistribute to l ists, requires prior specif ic permis-s ion and/or a fee.AVI 2000, Palermo, Italy. 2000 ACM 1-58113-252-2/00/0005.. 5.00

has to be positioned to the right place with the arrow keys on thremote control. The information content of the digital televisioand its applications has a lot of audio and video material.1.1 Aim of the StudyIn this study, we wanted to design and implement new useinterfaces for the digital television. We also wanted to know whafeatures contribute to usability in digital television environmen(cf. Section 2.). While implementing the new user interfaces, wtook advantage of the pragmatic and action oriented approach ousabil ity engineer ing [1]. Two Navigator prototypes werimplemented and they are presented in Section 3. The Navigatoprototypes were tested in user tests and the results are found iSection 4. The area of research included:* Information searching in EPGs* Navigation in digital television environ mentConclusio n and discussion are fou nd in Section 5. Somimportant areas of digital television research are not inc luded ithis study. For example, research on the interactive applicationtaking advantage of the return path o r information searching ilarge video-on-demand services are not included.2 USABILITY OF DIGITAL TELEVISIONUsers of the digital television have both entertainment aninformation search oriented tasks. Usability research of the digitatelevision is needed for many reasons: User's needs vary from passive content viewing forelaxation to more specific informat ion searching. The user shoulbe able to switch back and forth between channel surfing, text TVpages, EPG information and Navigator views. The user should bable to launch applications like banking, WWW browser anemail. The digital television should support both individual usand working in groups as TV watching often takes place in family. An average user is not interested in interaction wittechnology. He is interested in watching TV: What's o n tonighat 21.30 ? The user interface should be simple and intuitive, athe main use of the digital television will be for entertainment. Users are a heterogeneous user group. It is estimated thaabout 15 % of the European population has a disability, includindifficulties due to old age. Within three decades, about a third othe population will be over 60 years. The digital television shoulsupport users with varying physical and cognitive skills anabilities.

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I ;he digi tal televis ion should maintain the famil iar l iving room TVexper ience. A s imple access to informat ion services should beprovided: TV programming informat ion, spor ts s tat is t ics ,adver t is ing, product offer ings and var ious other services . Al linformat ion searching should be easy and natural .2 1 Navigation and Scrolling in digitalTelevisionNavigat ion and scrol l ing in digi tal televis ion is di f ferent f rom thepersonal computers and the t radi t ional GUIs . As s tated in Sect ion1, the display technology, the input device and the informat ioncontent are dif ferent f rom the personal computer . Navigat ion andscrol l ing takes place in the channel surf ing, wi thin the interact iveappl icat ions and the switch f rom one appl icat ion into another . Atpresent , navigat ion and scrol l ing is based on the remote control .There are three types of remote control bu t tons in use: a r row keys (Up/Down/Lef t /Right ) and ok key color keys (Red/Green/Yel low/Blue) digits (0-9)The cur sor movem ent wi th ar row keys complet ed with the okkey is the most intui t ive type of navigat ion, as the movement ofthe cursor can be seen ins tant ly on the TV screen. At the moment ,approximate ly 77% of TV viewer s hold the r emote cont ro l i n onehand and press the but tons with a thumb [2] . According to thiss tudy, the most important act ivi ty is to surf the channels . ChannelUp/Down but tons ar e used in approximate ly 52% of the r emotecontrol but ton presses . Volume +/- and digi ts (0-9) are used inapprox imately 19% and 17% o f the remote control but ton pressesrespect ively [3] . The data indicates that the remote control for thedigi tal televis ion should support the ' thumb navigat ion' .As the TV screen is not good at displaying detai led images , theamoun t of informat ion in s ight must be decreased. This is incontras t to personal computers where large informat ion s t ructures

and mult iple select ions can be visual ized at the same t ime. I t i stherefore concluded that navigat ion is par t of the funct ional i ty andcontent . Navigat ion can not be des igned independent ly f rom thetwo. When ei ther funct ional i ty or content of the user interfacechanges , the navigat ion must be redesigned as wel l .3 PROTOTYPES AND TEST MET HODSTwo Navigator proto types were implemented for the purposes ofthe s tudy. Prototype A and Prototype B were implemented in athree-member t eam which inc luded a usabi l i t y engineer , agraphica l des igner and a mul t imedia programmer . Th e proto typeswere tes ted with real users . The es t imated workload for prototypeimplementat ions and the user tes ts was 12 man months . Theimplementa t ions were done wi th the a id of a mul t imediaauthor ing program Macromedia Di r ec tor t ha t was run onWindows 95/98/NT computer . The output was shown on a TVscreen wi th the a id of SC AR T con nector t o a graphics card . Theproto types inc luded an 8-day t e l evi s ion programming informat iondatabase of 12 TV channels and 12 l ive TV show s which weres imulated with the aid of shor t videocl ips . The prototypes wereaccessed with a remote control . The infrared s ignals were sent toan infrared s ignal receive r and fur ther t rans lated for Macrom ediaDirector .3.1 PrototypesAs discussed in Sect ion 1, the Navigator is the main user interfaceof the digi tal televis ion. The N avigato r is of ten confused withEPG. The Navigator provides informat ion about t he cur r ent andnext avai lable TV shows ( i .e. , Channel informat ion) , whereasEPG has informat ion for s evera l days ahead. The TVprogramming informat ion is taken f rom the DVB (Digit a l VideoBroadcast ing) Serv ice Informat ion (SI) data f ields [4]. A subset ofTV channel broadcast and the SI data const i tute a mult iplex(MUX) . In our approach, EPG i s i nc luded in the Navigator as oneof the appl icat ions .

i......................Channel 4Heart Beat. Based on theautobiographyof artist andwriter Carolyn Casstdy, histow-budget gem of a moviestars Sissy Spacek as Carolynand Nick Nolle as her hush..

( ok ) - r emind , video.

17:00 v Live rpo ol v Manchester U..18:30 r Well Woman18:55 The Wings Of The Dove19:30 Cricket: CGU National Le..20:10 v Tiny Time: Da ppledown E.21:00 Grotbags21:4 5 Jake s Progress

(22:00 Heart Beat 122:30 v Secrets Of World War U23:10 r Collectors' Corner

(a) (b)

Figure 1. Prototype A: (a) Main menu. (b) Quick guide.

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(a) (b)Fig ure 2 . Proto type B: ( a) Main menu. (b) Program guide .

The main des ign idea in Prototype A was s implici ty. There was anassumption that the user wants to complete one task at a t ime andthe number of s e l ec t ions on the TV screen should be kept t o aminimum. In Proto type A, t he t e l evi s ion programminginformat ion is avai lable in three appl icat ions: Channels , Quickguide and TV program types . These ar e acces sed f rom the Mainmenu (cf . Fig. 1. (a)) . The Main menu is act ivated with the

Navig but ton on the r emote cont ro l. The appl i ca t ions ar ese l ec t ed and ac t iva t ed wi th the ar row keys and the ok key on theremote cont ro l . The Quick guide g ives informat ion aboutindividual programs (cf . Fig. 1. (b)) . When the user moves thefocus on the l is t on the r ight hand s ide, the program informat ion isupdated on the lef t . The l is t i s scrol lable. The three but tons

Back , Dow n and Up are ac t iva ted wi th the color keys onthe r emote . A l ive TV show can be s een on the upper l e f t comer .The m ain des ign idea in Proto type B was ef f i c i ency. There was anassumption that the user wants to s tay in one appf icat ion whilebrows ing the t e l evi s ion programming information . In Proto type B,this informat ion is avai lable in one appl icat ion, the Programguide. I t i s accessed f rom the Main menu (cf . Fig. 2. (a)) . Thesel ec t ions Thi s channel and Al l channel s both open up a v i ewinto the Program guide (cf . Fig. 2. (b)) . The Program guide givesinformat ion about i ndiv idual programs . When the user changes aChannel or a Type value f rom the four color keys on the r emote ,the program informat ion is updated on the l is t . The l is t i ss crol lable . The Date value i s changed wi th Lef t and Rightar row keys on the r emote . U nl ike Proto type A , t here i s no l i ve TVshow in Proto type B.Our a im was to t es t which of t he two user i n t er f ace approaches ,Proto type A or Proto type B, i s more appl i cable indig i t a lt e l evi s ion envi ronment . I n both proto types, a l l TV p rogramminginformat ion is shown in l is ts . As s tated in Sect ion 2, the TVscreen i s not good a t d i sp l aying deta i l ed images . Therefore wedecided not t o use the popular ' g r id ' l ayout common in exi s t ingEPGs and pas t research done in the area [5] . In our opinion, a l is ttakes less space on the TV screen than a gr id. Also, i t i s fas ter andeasier to read than a gr id.

3 2 User TestsThe user tes t setup included a TV set , a remote control , a PC, aninf r ar ed s ignal r eceiver , a v ideo camera and a microphone. TheTV set was p l aced on a t able and the PC was h idden f rom theview. As the tes t users were deal ing with a remote control and aTV set , they fel t they were tes t ing digi tal televis ion appl icat ionsrather than a PC. Th e num ber of user tes ts was kept smal l (s ix) asi t i s known that a smal l number o f t est s can ca t ch the major i ty ofuser interface problems. According to a s tudy [6] , s ix tes ts show90 percen t of the usabi l i ty bugs in an average user interface.Our t es t user s were under 25 year s o ld : two women, t hr ee menand two chi ldren (which made the t es t t ogether ) . None of t heusers had taken technology related courses in univers i t ies or hadany other t raining in the f ield. A think-aloud evaluat ion protocolwas used to provide ins ight into the user ' s intent ions . Videorecordings and notes were made dur ing each t es t . Every user wasgiven four shor t tasks to be completed with both protoV.pes . Thetasks r epresented user s ' i nformat ion n eeds f rom everyday l i fe :1 . W h a t ' s o n i n W S O Y c h a n n e l a t t h e m o m e n t ?2 . W h a t ' s o n i n C i t y T V c h a n n e l t o m o r r o w a t 2 1 . 1 5 ?3. In y our opin ion , what i s the mos t in te re s t ing spor t s programt h e d a y a f t e r t o m o r r o w ?4. You wan t to s e e a mov ie . Mov ie c a l l e d Chain Re ac t i on s tar t so n M o v i e c h a n n e l t o m o r r o w a t 0 0 . 0 0. A t a l m o s t t h e s a m e ti m e,a t 2 3 . 2 0, s t a r t s a m o v i e c a l l e d W e e k l y W e s t e r n o n T V 2c h a n n e l. P l e a s e t a k e a l o o k a t t h e p r o g r a m i n f o r m a t i o n o f b o t hmov ie s . In y our opin ion , whic h o f the mov ie s i s more in le re s t ing ?W h y ?Hal f of t he users s t ar t ed wi th Proto type A and the o ther ha l f wi ththe Proto type B. Shor t ques t ions were made dur ing each t es t :

' P le a se e x p l a i n h o w y o u g o t t o t h i s p a g e , P l e a s e ex p l a i n w h a ty o u s ee a t t h e m o m e n t a n d P l e a s e e x p l a i n h o w t h e s y s t e mw o r k s a s a w h o l e . As the t asks were complet ed , user preferencesand dev elopme nt i deas were col l ec t ed in a br i ef d i s cus s ion .

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4 R E S U L T SThe general result from user test ing the Navigator prototypes was

tha t the use rs were no t so in te res ted in f ind ing some spec i f icinforma tion on the TV screen. Instead, they would have l iked tobrowse through the al ternatives. The users also wanted to see ageneral picture of the available TV shows. The users l ikedscroll ing in program lis t ings except when the l is t was very long.All users read the texts on the TV screen carefully. Some userspreferred Prototype A over Prototype B as i t included the l ive TVshow. Accord ing to use rs, 'You don ' t want to lose wha t you werewatch ing a t ' . The p resence o f the l ive TV show was one o f thereasons for some users to say that 'Prototype A was more l ike TVand Prototype B was more l ike PC' . In Prototype A, the Quickguide was users ' favouri te applicat ion as i t was very simple touse. According to users , 'This is where you see what 's on inwhich channe l . You can change a channe l ' . In genera l, use rs d idnot l ike to switch the navigation from arrow keys to color keysand back. They examined the arrow keys before considering thecolor keys. In users ' opinion, the four color keys were inconne ction with the user interface colors. This w as no t t rue, but i tmade u sers hesi tant to try the color keys.Neither of the prototypes was faster to use than the other . Usersspent 22 minutes on the average on the tasks with both prototypesA and B. I t is anticipated that there is two things that can be doneto make the prototypes faster to use: for Prototype A, the numberof applicat ions available in the Main me nu must be decreased. Fo rPro totype B , the am ount o f in format ion in s igh t in Program gu idemust be decreased. Also, the change of Date and Channel valuesshould be easier as i t was very diff icult for many users to changethese values.I t was not possible to conclude which of the two prototypes wasmore eff icient to use or had a better usabil i ty. I t was suppo sed thatPrototype A w il l be fast and ea sy to use. This turned out to betrue. In Prototype A, the television programming information wasavailable in three applicat ions: Channels , Quick guide, and TVprogram types. The amount of applicat ions was not a problem forthe users as the simple Main menu helped them to found theinformation they were looking for . I t was also suppo sed thatPrototype B wil l be eff icient to use but hard to learn. This alsoturned out to be true, as the Program guide was diff icult to usewhen the use r wanted to change the Date and Channe l va lues .Therefore i t is conc luded that both approaches had their s trengths,and they were equ ally fast to use. I t must be stated thoug h that theusers were delighted in the presence of the l ive TV show and thesimple applicat ion designs in Prototype A.5 C O N C L U S I O NIn th is s tudy , we wanted to des ign and implement new userinterfaces for the digi tal television. Two Navigator prototypeswere designed and implemented. The prototypes were tested withreal users and the test results were discussed. Th e area o f researchwas restr icted to inform ation searching in EPGs an d naviga tion indigital television environment. In user interfaces, navigation isconsidered a part of the function ali ty and content , and i t can notbe des igned ind ependen t ly f rom the two .

5 1 D i s c u s s i o nResul ts o f th i s s tudy a re used in the des ign and implem enta t ion o ffuture Navigator prototypes. An interest ing topic for futureresearch i s the use r ' s nav iga t ion be tween mul t ip le app l ica t ions .What fea tu res con t r ibu te to usab i l i ty when the amount o fapplicat ions grows? In a way, this resembles the WWWenvi ronm ent where every WW W s i te can be cons idered a separa teapplicat ion. The huge amount of s i tes (applicat ions) makes i tdiff icult for the user to recall the mult iple s i tes . According to astudy [7] , users do not form mental models of the si tes they havevisi ted. With out a mental model , the user is forced to navigate inthe moment , based on the in format ion in s igh t a t a g ivenmoment. The user t r ies to el iminate the l inks that seem obviouslywrong and pick the o nes that are lef t .Based on this data, i t is assumed that TV viewers wil l ut i l ise the

e l imina te and p ick nav iga t ion s tyle fo r te lev i s ion env i ronmentas the number of applicat ions grows. If this is the case, the usersshould not be forced to form mental models of the applicat ionsthey use. Instead, every digital television applicat ion shouldsuppor t use r ' s nav iga t ion in the moment . The use r in te rfaceshould give eno ugh hints for the user and an ins tant feedback.A C K N O W L E D G M E N T SThe authors would l ike to express their appreciat ion for M.Sc.s tuden ts Juha Vie r inen and W esa Aapro , o f H e ls ink i Univers i ty o fTechnology for their efforts in creat ing the two prototypes. Theauthors would also l ike to thank their other colleagues from theFuture TV pro jec t fo r va luab le comments on p ro to type des ignsand the test users for part icipating in the user tests .R E F E R E N C E S[1] Nielsen, J . , Usabil i ty Engineering . AP Professional , Boston,

MA, 1994.[2] Logan R. J . , Augalt is S., and Ren k T., Design of s implif ied

television remote controls: a case for behavioral andemot iona l usab i li ty . P roceed ings o f the Hum an Fac tors andErgon omics Society 38th Annua l Meeting, Oct 24-28 1994.

[3] Logan R. J . , Augait is S., Miller R. H., and Wehm eyer K.,Living room culture - an anthropological s tudy of televisionusage behav iors . P roceed ings o f the Human Fac tors andErgonomics Society, Oct 9-13 1995.

[4] ETSI TR 101 200, Digital Video Broadc ast ing (DVB) - Aguideline for the use of the DVB specif icat ions ands tandards. European Te lecommu nica t ion S tandard iza t ionInstitute (ETSI), 1997.h t tp : / /www.ebu .ch /dvb /dvb_ar t i cles /dvb_cook .h tm

[5] Coope r R.L.W., Jourdan P., Ferrier C., and Tazine N.-E.,User interface for mult ichan nel television. IEE ConferencePublic at ion No. 413, Sep 14-18 1995.

[6 ] Landauer T . K . , The Trouble Wi th Compute rs : Usefu lness ,Usabil i ty, and Productivi ty, chapter 13. MassachussettsInst i tute of Technology, second print ing, 1995.

[7] Spool J. M., Scanlon T., Schroede r W., Snyder C., andDeAngelo T . , Web S i te Usab i l i ty : A Des igner ' s Guide ,chapters 1-3. User Interface Engineering, Massachussetts ,1997.

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