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10.1080/08874417.2018.1425644 To link to this article: https://doi.org/10.1080/08874417.2018.1425644 Published online: 01 Mar 2018.Submit your article to this journal Article views: 464View related articles View Crossmark dataCiting articles: 2 View citing articles Usability evaluation of menu interfaces for smartwatches Kyeongjin Park, Meuel Jeong, and Kyungdoh Kim Department of Industrial Engineering, Hongik University, Seoul, Korea ABSTRACTCurrently, there are various smartwatch products on the market, and the number of users is expected to continue to increase. The functions of smartwatches have also been diversified, and the amount of information displayed on their screens is also increasing. However, as there are many restrictions on the rather small screen size, it is difficult to apply the methods used to provide information on the existing smart devices. Therefore, this study investigated how menu should be provided on the touch screen of smartwatches and derived a more effective menu structure. For our purposes, we conducted twoexperiments. In the first experiment, we provided 40 items in grid view and list view layout styles and tried to search for a given item by scrolling or paging. Efficiency was higher for the list view layout, in which many items were displayed on the screen and task completion time was shortened. However, the overall satisfaction was higher for the grid view layout, in which fewer items were displayed on the screen. In the second experiment, we derived an efficient menu structure when displaying hierarchicalitems that could be grouped into upper and lower categories. Likewise, many items on a single screen were excellent in terms of task completion time and efficiency. Providing depth of menu by categoriza- tion showed satisfactory results in task completion time, efficiency, and overall satisfaction. KEYWORDSSmartwatch; small screen; usability; menu structure Introduction In the 1960s, the concept of wearable computers began to emerge. At first, only simple functions such as calculations were incorporated; however, this functionality has been evol- ving constantly. The number of products has also been increasing every year. The McKinsey Global Institute 1esti- mates that wearable computers can generate more than $4 trillion in value when interoperating between IoT applica- tions. Typical wearable devices are smartwatches, which have various advantages owing to their portability and posi- tive market prospects. A variety of products are currently available, and the number of smartwatch users is expected to grow continuously. 2 Smartwatches are wearable smart phones in the form of wrist watches having small monitors, which can perform a variety of functions, including connecting to the Internet. 3 Similar to wrist watches, these provide user friendliness. 4 Smartwatches are often connected to peripherals to enable active interaction with devices. 5They also provide informa- tion in the background and can provide additional informa- tion because they have sensors attached. 4,6It is possible to continuously integrate computer processing through smart- watches and process the desired information without restric- tion of place and time. 7Smartwatches also have the advantage of freeing users ’hands. 8These features make smartwatches suitable as wearable computing devices. 9A study by the Consumer Electronics Association also found that wrists are the most suitable body parts to wear wearable devices. 10 However, smartwatches have a limited interface size compared to other smart devices, such as smart phones.

Small displays introduce many limitations when using smartwatches. As functions on mobile devices have become more diverse, user interfaces (UI) provided in mobile environments have been actively studied, because smaller screens are not suitable for incorporating the UI format of desktop machines. 11 It is not practical to simply apply the interface used on the existing desktop machines to devices with smaller screens without considering the display differences. 12 There is a limit to applying the existing interface to the screen of a smartwatch, which is relatively smallerthanthatofasmartphone.Therefore,smartwatch manufacturers should design the interface by taking into consideration factors such as the icons and layout suitable for the small screen. 13 Currently, various functions have been introduced in smartwatch es, but the information that can be displayed on the screen is limited. 14 Despite this situation, there is a dearth of research on the menu inter- face of smartwatches. This study attempts to derive a method to provide a menu that enables efficient information search on the lim- ited size of the touch screen of smartwatches. Through a comparative study of list view and grid view layout styles, the number of items displayed on a single screen, and the number of items provided in one row, we desire to find a waytoprovideaneffectivemenuonthesmalltouchscreen of smart watches. CONTACT Kyungdoh Kim [email protected] Hongik University, 94 Wausan-ro, Mapo-gu, Seoul 121-791, Korea. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ucis . JOURNAL OF COMPUTER INFORMATION SYSTEMS2020, VOL. 60, NO. 2, 156 –165 https://doi.org/10.1080/08874417.2018.1425644 © 2018 International Association for Computer Information Systems Related works With the proliferation of smart phones and the development of wireless Internet, people started to use various functions such as games, online shopping, etc. on their mobile phones. 15 Chae and Kim 16 derived three characteristics of mobile Internet through comparison with the Internet, and one of them was a small screen. Due to the small screen size, there is a limit to the information provided on the Internet. Smartwatches are smart devices with a very small screen that can be worn on the wrist and have screen constraints to provide various functions. 14 In particular, it is an obscure interface for finger manipulation because of the smaller screen size than traditional smart phones. 17 Therefore, it is essential to study how to provide menus on a small screen such as smartwatches. The effect of smartwatches ’display format and character arrangement for readability and preference was studied. 18 Although the outline form of the display did not affect read- ability, text aligned with straight lines and curves was more readable than text with diagonal lines. Additionally, the combi- nation of individual sentences was more readable than when sentences were presented as paragraphs, but the reading time was slow. Text readability by display ratio and font size was studied. 19 As a result, they showed that the readability is best with aspect ratio of 16:9 and 9 pt. in circle shaped smartwatches.

Smartwatches ’virtual keyboard layout that allows efficient text entry in situations where there is an increasing need for manip- ulation on smartwatches was presented. 20In the situation where all the contents of the keyboard cannot be contained, the com- bination of the alphabet provided with the group and various control keys suggest a virtual keyboard suitable for smart- watches. The performance and satisfaction of task performance of elderly users according to the number of icons and the spacing of the arrangements were studied. 21 As a result, fewer icons were better, and four icon menus were most suitable on a single screen. The icon menu for single line grid view, two-line grid view, space rotation type, and honeycomb shapes was compared. 13 The task completion time of the menu structure provided in two lines was the fastest. It was found that the speed and readability of the user are influenced by the arrangement of the icons and the spacing between the icons. Plaumann, Müller, and Rukzio 22 presented an item on list view interface in the clock screen and experimented on how to locate it. On a small screen such as a clock, many items resulted in a higher percen- tage of participants failing the task. However, the study was conducted only on the list view interface, and other factors that make up the interface were insignificant. As a result of the literature survey, smartwatches showed a very different result of satisfaction and task completion according to minute changes to font size, the way of providing information, and the aspect ratio due to the small screen. These suggest that the type of information, layout, and interaction means provided by the existing smart devices should be changed to fit small screen characteristics.

Menu type There are two types (list and grid view) of interface representa- tion. The list view is a simple representation of information in one dimension, and the grid view is a representation of infor- mation horizontally and vertically in a two-dimensional layout representation. 23 The list view is a series of items arranged in one direction, and the user searches the items to be searched one-dimensionally. The list view menu improves search effi- ciency because there is little variance in the line of sight move- ment during navigation. By contrast, the grid view menu is provided as a two-dimensional array of width and height. The user can quickly access a lot of items and can easily view the entire screen of the provided menu. 24 Depending on the menu type (list view or grid view), the user is affected in various ways.

First, in the web environment, when the same amount of information is provided as a grid view, the user has a good evaluation of the reliability of the received information com- pared to when it is provided as a list view. 25 In the study by Salomon, 26conducted in the mobile environments, users could feel less cognitive load when presented with information as a list view and icon. List view and grid view menus on mobile screens provided during a simulation were also compared. 27The parti- cipants in the experiment shortened the task completion time in list view menus rather than grid view menus. It showed higher satisfaction and faster task completion time when providing grid view menu that shows all information at once than list view menu of text type on iPhone. 28Thus, it can be seen that the provided menu type affects the user ’staskcompletiontimeand subjective evaluation, and the result depends on the usage environment (see Table 1 ). Paging, depth, and scroll The smaller screen has a limitation in displaying the informa- tion to be provided on a single screen. Therefore, information is provided by scrolling or paging method in which the screen is divided into appropriate pages. Scrolling provides informa- tion that goes beyond the size of the screen, one row at a time, allowing the user to navigate continuously and incrementally.

When much information is provided, paging and scrolling are useful. 11 If the user cannot find the desired menu or informa- tion on the provided screen, the user can navigate through the page conversion. 29 When information was provided on a small screen, it was more of a screen transition than on a large screen. 30 Four types of navigation techniques including scrolling and paging were surveyed. 30 As a result, the time tends to be longer when it is provided via scrolling. Menus Table 1. Menu type studies. Literature Year Findings Devices 27 2009 The participants shortened the task completion time in list view menus rather than grid view menus in driving simulation. Mobile phone 25 2010 When the same amount of information is provided as a grid view, the user had a good evaluation of the reliability of the received information compared to when it is provided as a list view. PC 28 2013 Higher satisfaction and faster task completion time when providing grid view menu than listview menu were shown. Mobilephone 26 2014 Users could feel less cognitive load when presented with information as a list view andicon. Mobile phone JOURNAL OF COMPUTER INFORMATION SYSTEMS 157 using scrolling generated more visual fatigue than menus using paging. 31 In previous studies, user performance and subjective measurement were highly evaluated when pre- sented as paging rather than by scrolling. However, there were some conflicting conclusions. For example, it showed that menus using paging were less popular than menu using scrolling. 29 In the past, scrolling was a factor that hindered usability. However, nowadays, as users have more experience using the internet, they have become accustomed to the scrol- ling method and are being used variously. 32This means that it is necessary to derive a suitable method for the user of very small screen devices where the use of paging and scrolling is inevitable. When items are bundled in the same category, there is a method for structuring menus by defining information as a superordinate concept and a subordinate concept. There is a method for presenting a menu indicating the category of infor- mation and presenting it through several steps. This step is called depth when you are going through several steps. When the information is composed on a screen using a wide range, its size is called “breadth, ”and many studies on proper breadth and depth have been conducted to efficiently provide the given information. Users prefer menus with wider breadth to menus with more depth. 33,34 Jacko and Salvendy 35 also argued that structures with much depth are complicated and inconvenient to users. At this time, if all contents cannot be provided on a single screen due to the limitation of the screen, information is provided by using the scroll. 30 However, a lot scrolling is perceived to the user as a “deeper ”depth. 36 Dawkins 37 argues that scrolling should be avoided as much as possible. Thus, more depth is preferred over wide breadth when a lot of cursor movement is required. 38 This is in contrast to previous studies that favor wide breadth over depth. Table 2 shows a summary of paging, depth, and scroll studies.

Touch screen Smartwatches are provided as a touch screen, and the menu should be designed considering the size limitation of these screens. The touch interface is very intuitive because it allows the devices to be operated without a separate controller or input device, and the input and output occur at the same time. 39 Additionally, unlike a display that simply presents information, the size of the item to be touched, the item spacing, and the like must be considered in the design of a touch interface. 40 The optimal size of the touch key is 9.2 mm to 9.6 mm 41; however, they experimented on a large screen and their conclusion is difficult to apply to smartwatches which have relatively smaller screens than smart phones. Schedlbauer 42 suggested that the spacing of touch keys does not affect usability, but Kim, Kim, Lim, and Jung 43 recommended maintaining a gap of at least 1 mm. In addition, Parhi, Karlson, and Benderson 41 suggested that the minimum touch key size perceived by a user is 2 mm to 3mm. Table 3 summarizes previous touch screen studies. Therefore, this study investigates the effect of a menu struc- ture used to provide information to users of smartwatches derives an efficient menu structure. This study is conducted through two experiments. In experiment 1, when items of the same type are given, we try to find out which menu structure is good on the small screen of smartwatches. That is, we provide a total of 40 items as grid view and list view menu types, and search for a given item using scrolling or paging. In experiment 2, we want to derive an efficient menu structure when hierarch- ical items are grouped into upper and lower categories. A total of 4,096 items is divided into upper and lower categories and provided step by step. To search an item, a top-down menu structure is formed in which an upper item category is first selected. Experiments to compare the menu type and the depth of the information structure provided differently. As a result, the two experiments show how to provide an efficient menu in smartwatches.

Experiment 1 Experiment 1 evaluates the effect of the menu type (the list view, the grid view), navigation method (Paging, Scrolling) and the number of items displayed on a single screen (4, 9) on task completion time and subjective measurement in smartwatches.

Experiment 1 provides 40 fruit items, and the participants per- form a task to search, on a given menu, for a specific fruit.

Methods Experiment environment Experiments were conducted on a 1.6 × 1.6 inch screen (screen size of about 40 mm × 40 mm). This is the size of Samsung ’s Galaxy Gear, Gear 2 and Gear 2 Neo, smartwatches from Sony, Apple watch, and many other smartwatch pro- ducts. In this experiment, we made our application using Table 2. Paging, depth, and scroll studies. Literature Year Findings Devices 33 1981 Users prefer menus with wider breadth to menus with more depth. Mini PC 34 1986 Users prefer menus with wider breadth to menus with more depth. PC 31 1988 Menus using scrolling generated more visual fatigue than menus using paging. PC 30 1990 When information was provided on a small screen, it was more of a screen transition than on a large screen. Micro-computer 35 1995 Much depth is complicated and inconvenient to users. PC 32 1997 As Internet usage increases, users become accustomed to scrolling. PC 11 1999 When much information is provided, paging and scrolling are useful. PC 38 2004 More depth is preferred over wide breadth when a lot of cursor movement is required. Handhelddevice 37 2007 Scrolling should be avoided as much as possible. Mobile phone 29 2009 On online survey, time tends to be longer when it is provided via scrolling. PC Table 3. Touch screen studies. Literature Year Findings Devices 41 2006 The optimal size of the touch key is 9.2 mm to 9.6 mm. PocketPC 42 2007 The spacing of touch keys does not affect usability. PC 43 2012 The gap of touch key space maintaining at least 1 mm was recommended. Mobile phone 158 K. PARK ET AL. Android studio. We built a smartwatch screen on Samsung Galaxy Note 5 and set it to be disabled except for limited screens. Considering the use of smartwatches, the experiment was conducted by fixing the screen to the wrist position through the manufactured band.

Subjects This experiment was conducted for students at Hongik University. A total of 40 students were recruited through online and offline recruiting. All participants had no visual problems and had experience using touch screens. In parti- cular, two of them had experience using smartwatches. The participants were composed of 29 males and 11 females. The mean age was 24.3 years, and the standard deviation was 1.88.

The experiments were carried out in an independent space, and one person at a time. The experiment time took no longer than 30 minutes, and a compensation of 5,000 won was given.

Independent variables The menu type indicates the form of the menu to be pre- sented. In this experiment, two menu types are provided: list view and grid view. The corresponding items in the list view and grid view types are provided in the form of text (Figure 1 ). Because the user can influence the cognitive level of the corresponding item to navigate the menu, the items provided for the exact comparison of the two menu types are limited to text. The number of paging refers to the number of screens divided by 40 items. Thus, Paging 1 provides all items in one breadth. A total of four levels (one to four) is provided per paging. For example, Paging 3 means that 40 items are divided into three screens. To move between screens, a “Next ” and “Back ”touch screen buttons are shown at the bottom of the screen. For many items per breadth, one must scroll through the items that are not shown on a single screen. On the contrary, if there are few items per breadth, the items are divided into several pages, so that one has to move the screen with the Next button. The number of items means the number of items shown on a single screen ( Figure 1 ). In the case of smartwatches, it is necessary to consider both characteristics of small screen size and touch screen image. Therefore, the number of items that can be provided on a single screen is limited. In this study, we set the number of items displayed on a single screen at two levels: four and nine. The grid view is provided in 2 × 2 and 3 × 3 arrays, and the items are all of the same size and at the same level. The list view is provided with the same height length of menus, and in the case of level nine, the height is very small, i.e., 3.3 mm. If it exceeds level nine, it becomes smaller than the minimum perceptible size of 3 mm. 41 Dependent variables As an objective measure, we used task completion time to find agiven item. Task completion time means the time it takes to find an item from the start of the search on the presented screen to the touch of the target item. The unit of measure is second. In addition to the scroll operation and button click for searching, we measured the frequency of errors, which means unnecessary touch or wrong touch frequency. As a subjective measure, Nielsen and Landauer 44 used the efficiency and overall satisfaction as a usability evaluation measure of UI (User Interface) design. Efficiency is a question of whether it was easy to navigate to the desired item. The overall satisfaction is a question of whether the method pro- viding the menu is satisfactory. All of the measurements were collected with a 7-point Likert scale.

Experiment design and experiment procedure This experiment provides the same level of information (40 items) in different menu types. 40 items were found in Plaumann et al. 22 participants experienced only one form of grid view or list view presented, and for the remaining inde- pendent variables, the nested factorial design was given as the within subject factor. This experiment experiences menu type, the number of items and four types of paging displayed on a single screen. A total of eight environments (1 × 2 × 4) were tested. Eight experiments were given randomly. We measured the time to search for three items in each of the eight envir- onments, measured the time to search for three items in different positions, and used the average value for analysis.

The search order of items at three different locations was provided randomly. After three times of measurement in one situation, subjective evaluation of the method providing the menu was conducted through a questionnaire. To mea- sure the number of error touches, all experimental conditions were recorded. Participants were given plenty of practice opportunities to become familiar with menu navigation and manipulation. The items to be searched were placed on the notebook screen in front of the experiment, and the time is measured when the start of the search is announced. When the participant touched the target item, the measurement is completed once. Figure 2 shows a participant experimenting using the smartwatches menu. (a) The list view (b) The grid view Figure 1. Menu type and the number of items in a screen. JOURNAL OF COMPUTER INFORMATION SYSTEMS 159 Results The collected data were from 40 people, and they were used for analysis without any missing values. A three-way ANOVA test was conducted.

Objective measures The difference in task completion time by the menu type am ong the main factors was not statistically significant (F1;282ðÞ ¼ :36;p¼ :549). If the amount of information dis- played on the small screen of smartwatches is at the same level, the menu type does not affect the task completion time of the user. However, there was a difference due to the number of items displayed on the screen ( F3;282ðÞ ¼ 33:60;p< :001). The participants in the experiment executed the task quicker when relatively many items ( M = 9.2, SD = 3.16) were shown on a single screen rather than relatively few items ( M = 11.4, SD = 3.99). There was also a difference in task completion time due to the number of paging to switch ( F3;282ðÞ ¼ 8:84;p< :001). Tukey ’s HSD test showed the slowest completion time in Paging 3 ( Figure 3 ). Paging 3 occurs when scroll occurs at a certain point and movement between screens occurs twice at most. There was no interaction between the number of paging and the number of items displayed on a single screen (F3;282ðÞ ¼ :86;p¼ :449). But, there was an interaction between the menu type and the number of items displayed on a single screen ( F3;282ðÞ ¼ 4:83;p¼ :029 ;Figure 4-A ). On the one hand, the grid view type ( M = 10.9, SD = 3.94) tends to be faster than the list view type ( M = 11.9, SD = 4.78) when the number of items shown on a single screen is four ðF1;158ðÞ ¼ 2:88;p¼ :092). On the other hand, there was no difference between list view type ( M = 8.9, SD = 3.29) and grid view type ( M = 9.5, SD = 2.45) when the number of items shown was nine ( F1;158ðÞ ¼ 1:48;p¼ :225). Also, there was an interaction effect between menu type and number of paging (F3;282ðÞ ¼ 2:71;p¼ :045 ;Figure 4-B ). The grid view type (M = 11.0, SD = 3.34) showed a tendency to be faster than the list view type ( M = 12.9, SD = 5.75) in the case of Paging 3ðF1;78ðÞ ¼ 3:51;p¼ :065). Finally, there was a three-way interaction effect between menu type, number of paging, and number of items shown on a single screen for task completion time (F2;282ðÞ ¼ 3:09;p¼ :027). The difference in task completion times between the grid view ( M = 11.2, SD = 3.24) and the list view ( M = 15.9, SD = 6.25) was noticeable in the Paging 3 environment where four items were displayed on a single screen ( F1;36ðÞ ¼ 8:29;p¼ :006). Additionally, the number of errors was measured. The total number of errors measured was 110, and most of them were Figure 2. Snap shot of the experiment. Figure 3. Results for the Tukey HSD test between paging numbers on comple- tion time. Figure 4. Interaction effect plot of task completion time (seconds) as a function of(a) the number of items and menu type and (b) the number of paging andmenu type in Experiment 1. 160 K. PARK ET AL. observed in list view type (89 times) in which many items were displayed on a single screen.

Subjective ratings Only the number of items displayed on a single screen among the main factors affected the efficiency (F3;282ðÞ ¼ :35;p¼ :793). The experiments showed a high efficiency in a situation where relatively many items were displayed on a single screen ( M = 4.9, SD = 1.58) than the situation where relatively few items were displayed on a single screen ( M = 4.3, SD = 1.57). However, there was no difference in efficiency by menu type ( F1;282ðÞ ¼ :56;p¼ :454), and the number of paging ( F3;282ðÞ ¼ :35;p¼ :793). There was an interaction in the efficiency between menu type and the number of items shown on a single screen (F1;282ðÞ ¼ 6:80;p¼ :010 ; Figure 5 ). When nine items were displayed on a single screen, the efficiency of the list view type was higher than that of the grid view type, and the statistically significant difference is shown in Figure 5 (F1;158ðÞ ¼ 5:7;p¼ :018). However, there was no statistically significant difference in efficiency for grid view and list view type when four items were shown on a single screen ( F1;158ðÞ ¼ :1:71;p¼ :193). There was no interaction effect between menu type and the number of paging ( F1;282ðÞ ¼ :38;p¼ :766). In addition, there was no interaction effect between the number of paging and the number of items displayed on a single screen ( F1;282ðÞ ¼ :06;p¼ :981). In efficiency, the three-way interaction effect on menu type, the number of paging, and the number of items dis- played on a single screen was statistically significant (F3;282ðÞ ¼ 2:93;p¼ :034 Þ. When relatively few items were shown, the efficiency of Paging 3 was the most negative in the list view type ( M = 3.6, SD = 2.46), with a large difference from the grid view type ( M = 4.7, SD = 2.77) (F1;38ðÞ ¼ 4:22;p¼ :046). On the contrary, when relatively many items are displayed on a single screen, efficiency eva- luation of Paging 3 was significantly lower in the list view (M = 5.4, SD = 1.39), with a large difference from the grid view type ( M = 4.2, SD = 1.81) ( F1;38ðÞ ¼ 5:98;p¼ :019). The difference in the number of items displayed on a single screen among the main factors that affect the overall satisfac- tion was statistically significant ( F1;282ðÞ ¼ 8:52;p¼ :005). High overall satisfaction was obtained when relatively few items ( M = 4.5, SD = 1.70) were shown on a single screen rather than many items ( M = 3.9, SD = 1.69) on a single screen. On the other hand, there was no difference in the overall satisfaction with the menu type (F1;282ðÞ ¼ 1:33;p¼ :249) and the number of paging times ( F1;282ðÞ ¼ 1:36;p¼ :255) There was an interaction in the overall satisfaction between menu type and the number of items shown on a single screen (F1;282ðÞ ¼ 23:88;p<:001 ;Figure 6 ). When relatively few items are shown on a single screen, the overall satisfaction of the grid view was higher than list view (F1;158ðÞ ¼ 6:80;p¼ :010). When relatively many items are displayed on a single screen, the overall satisfaction of the list view was measured higher than that of the grid view (F1;158ðÞ ¼ 19:30;p<:001). However, there was no interaction between the menu type and number of paging (F1;282ðÞ ¼ :56;p¼ :641), and no interaction between the number of paging and the number of items displayed on a single screen ( F1;282ðÞ ¼ :30;p¼ :824). In addition, there was no 3-way interaction effect between three independent vari- ables on the overall satisfaction ( F1;282ðÞ ¼ 1:8;p¼ :913). Summary and discussion In the environment where relatively many items are displayed on a single screen, fast task completion times and high effi- ciency were observed. In this case, the list view type is better, whereas in the environment where few items are displayed, the grid view type gives better results. In the study by Shneiderman and Plaisnat, 24 the list view menu ensured that the user ’s gaze moved sequentially in the vertical direc- tion and the search proceeded, so that the user ’s attention was not dispersed and the search was easy. However, the grid view menu had a two-dimensional form, which allowed the user to easily see the entire object, requir- ing less motion and allowing for a quick selection. In Kammerer and Peter, 23eye tracking analysis shows that in the list view environment, the user moves the gaze in a linear way, moving from top to bottom, while in the grid view environment it is not linear and the movement of the eye follows in units of a row-column. Therefore, when many Figure 5. Interaction effect plot of efficiency (points) as a function of the number of items and menu type in Experiment 1. Figure 6. Interaction effect plot of Satisfaction (points) as a function of the number of items and menu type in Experiment 1. JOURNAL OF COMPUTER INFORMATION SYSTEMS 161 items are displayed on the small screen of smartwatches, it is considered that the performance is low in grid view type because it is highly dispersed in the vertical and horizontal directions and confusing to the users. However, when fewer items are displayed on a single screen, the movement of the gaze is relatively small, and it is considered that the grid view type is then appropriate for the task by grasping the whole object at a glance. This showed a faster task completion time and high efficiency. In this experiment, when three-page movements were required, and relatively few items were shown, efficiency was lower and the task completion time was slower in a list view environment. According to Norman ’sstudy, 29 this is because paging has a merit that makes it easy to grasp the overall image of a menu belonging to the next screen with one key operation. However, the newly changing screen can confuse users and reduce the sense of context. Additionally, a moderate level of the scroll has the advantage that a con- tinuous sense of navigation is maintained, though many levels of the scroll can disrupt location sense and cause confusion. If relatively few items are displayed on a single screen, the scrolling time is f aster than when many items are displayed because the time to search for items on a single screen is relatively faster. Esp ecially, in list view environ- ment, since the scroll direction and the line of sight coincide with each other, the user has a faster task completion time and generates a fast scroll. This fast scroll may cause missing items. Missing items will result in repeated searches that take a long time to complete the task. In addition to these cases, when the number of paging is increased, the menu structure becomes more congested, in which case the task completion takes a long time. In other words, in the list view environ- ment in which fewer items are displayed, if scrolling and paging are mixed, and the structure of a complicated menu is presented, this resulted in shorter task completion times and lowest efficiency. The frequency of errors was mostly observed in a situation where nine items on a single screen were provided as a list view type. According to a survey by Dandekar, Raju, and Srinivasan, 45 the average fingertip size of users is 8 –10 mm. It is claimed that at least 8 mm × 8 mm touch key size would be satisfactory. However, if nine items on a screen are pro- vided as list view type, the length is only 3.33 mm, much smaller than 8 mm. As a result, it seems that the frequency of errors is measured by clicking the items in the vicinity during the operation process. The overall satisfaction was high when the number of items displayed on a single screen was fewer. It is considered that the overall satisfaction is higher when the item menu size is relatively large due to the small screen of smartwatches.

Experiment 2 Experiment 2 derived an efficient menu form on a small screen when the menu items provided could be categorized into upper categories and lower categories. Therefore, it was designed to find a specific public institution in a specific country and city, and a total of 64 public institution classes, eight cities, and eight countries were used. Methods Experiment environment and subjects Experiment 2 was conducted in the environment similar to Experiment 1. A total of 11 female and 25 male students attending Hongik University were recruited ( M = 24.1, SD = 1.81) for Experiment 2. All of the participants, including two with experience using smartwatches, had experience using smart devices with touch screens. The experiment was conducted in an independent space, and the experiment time did not exceed 30 minutes. The 5,000 won was given for participation.

Variables The menu type and the number of the items displayed on a single screen are used as independent variables, and the level of each factor is the same as in experiment 1. Additionally, two levels of depth, representing a hierarchical menu, were selected as independent variables. We set the depth level to take into account the task situation of this experiment. Depth 2 has a 64 × 64 structure, and Depth 3 has a depth of 8 × 8 × 64. The dependent variable used the same task completion time, frequency of errors, efficiency, and overall satisfaction as in experiment 1.

Experiment design and experiment procedure In Experiment 2, only one form of grid view or list view was experienced, and for the remaining independent variable level, it was designed as a nested factorial design, which served as the within subject factor. The participants experimented with four (1 × 2 × 2) menu conditions. The participants performed tasks to find items at three different positions in each menu environment. Items at three different location levels were randomly provided. In this experiment, the average time is used to measure the time to search for three items in different positions. The task is given as follows: “You have to find a High court in Galindo in Peru. ”The experiment sequence of all four environments was provided randomly, and when the time measurement of the three items in one situation was com- pleted, a subjective evaluation was conducted through the questionnaire. We also collected the frequency of errors.

Results The collected data, from 36 people, were used for analysis without any missing values. A three-way between-subject ANOVA test was conducted.

Objective measures Task completion time showed statistical difference in the number of items shown on a single screen ( F1;268ðÞ ¼ 17:72;p<:001) and depth ( F1;268ðÞ ¼ 17:72;p<:001). When the number of items displayed on a single screen were many ( M =19.8, SD = 6.67), measurement of task completion time was faster than when the number of items displayed on a single screen were few ( M = 24.1, SD = 6.62). Also, when the menu was categorized, measurement of task completion time was faster in Depth 3 ( M = 19.4, SD = 5.87), and provided a deeper structure 162 K. PARK ET AL. than Depth 2 ( M = 22.1, SD = 7.02). On the other hand, there was no difference in task completion time by menu type ( F1;268ðÞ ¼ 2:46;p¼ :119). There was an interaction between menu type and depth for task completion time ( Figure 7 ). There was no difference in the list view and the grid view type when depth was provided in three steps. However, when depth was provided in two steps, the task performed faster in the list view, compared to the grid view, and the difference was statistically significant.

Also, the frequency of errors was measured. The frequency of errors was measured 96 times throughout the experiment.

Within these, 86 times were observed in the list view type, where relatively many items were displayed on a single screen.

Subjective ratings In the case of efficiency, the difference due to depth was significant (F1;268ðÞ ¼ 8:21;p¼ :005). Efficiency was evalu- ated by providing three levels of depth ( M = 4.6, SD = 2.03) rather than providing two levels of depth ( M = 3.6, SD = 1.81). On the other hand, the difference between menu type ( F1;268ðÞ ¼ 1:09;¼ :299) and the number of items displayed on a single screen ( F1;268ðÞ ¼ 3:33;p¼ :070) was not statistically significant. However, when relatively many items were displayed ( M = 4.4, SD = 1.96), efficiency was higher than when relatively few items were provided on a single screen ( M = 3.8, SD = 1.95). There was no interaction between independent variables on efficiency ( F1;268ðÞ ¼ :00;p¼ 1:000, F1;268ðÞ ¼ 37;p¼ :544 ;F1;268ðÞ ¼ 1:09;p¼ :299). There was also no three-way interaction effect between the three independent variables on efficiency ( F1;268ðÞ ¼ :483 ;p¼ :488 Þ. Among the main factors that affect the overall satisfaction, the difference due to the depth was significant (F1;268ðÞ ¼ 10:81;p<:001). Participants of the experiment were satisfied with the menu structure provided by dividing the depth level into three levels ( M = 4.6, SD = 1.90), com- pared to the menu structure provided by the two levels of depth ( M = 3.5, SD = 1.96). On the other hand, the difference in the number of items displayed on a single screen (F1;268ðÞ ¼ 1:97;p¼ :168) and the menu type (F1;268ðÞ ¼ :00;p¼ 1:000) was not statistically significant. Likewise, there was no interaction effect between all independent variables on the overall satisfaction (F1;268ðÞ ¼ 3:30;p¼ :071 ;F1;268ðÞ ¼ :91;p¼ :34, F1;268ðÞ ¼ :91;p¼ :343). There was also no 3-way interac- tion effect between the three independent variables on satis- faction ( F1;268ðÞ ¼ :27;p¼ :604). Summary and discussion The difference between task completion time by the depth and the number of items displayed on the screen was statis- tically significant. It was faster to measure the task completion time in a menu structure of 8 × 8 × 64, compared to a structure of 64 × 64. This is considered to be due to an increase in scrolling when 64 items on a small screen are provided to one breadth. This is consistent with previous studies. 36,38 Although the sizes of the screens on which the experiment was conducted were different, the user had a faster searching speed in a divided depth than a wide breadth requiring many scrolls. Also, relatively many items, even on small screens, contributed to the speed of task completion time. In the menu structure of depth 2, the list view type was performed faster than the grid view type. It is considered that the scroll direction coincides with the search. Again, most of the touch errors were measured on the list view of level 9 on a single screen. This is due to the size of the touch environment for relatively smaller item. There was a statistically significant difference in the effi- ciency and overall satisfaction due to depth level. In menu structure of depth 3, participants showed high efficiency and overall satisfaction. It is considered that the situation of pro- viding the step by step structure, without additional scrolling, increases the efficiency and overall satisfaction of the partici- pant. In a small screen environment, it can be concluded that when considering the menu structure, depth constituting the menu structure in stages is more suitable than scroll.

General discussion The result of Experiment 1 shows relatively more items on the screen, shortened task completion time and increased per- ceived efficiency. On the other hand, when relatively few items were displayed on a single screen, satisfaction was high. The fewer the items displayed on a screen, the larger the size of the item. It is believed that the overall satisfaction is increased when the item size is relatively large due to the small screen of smartwatches. On the navigation side of the menu, the task completion time was shortest in Paging 3, where scrolling and paging were mixed. Experimental results in the case of providing items at the same level did not show the results of task completion time, efficiency, and overall satisfaction. For task completion time and subjective efficiency in the process of searching, it is desirable to design many items to be displayed on a single screen. In parti- cular, when relatively many items were displayed on a single screen, the list view type menu had higher efficiency and overall satisfaction than the grid view type. On the other hand, when relatively few items were displayed on a single screen, the overall Figure 7. Interaction effect plot of completion time (seconds) as a function of depth and menu type in Experiment 2. JOURNAL OF COMPUTER INFORMATION SYSTEMS 163 satisfaction was high. In this case, the grid view menu had higher overall satisfaction than the list view menu. In Paging 3, which is a complex mixture of scrolling and paging, the list view menu with few items on a single screen showed slow task completion time and negative efficiency.

This is because the confusion caused by the many levels of the scroll and the complex paging method is likely to have reduced the user ’s sense of context. In the search experiment of the menu, which can be categorized by the concept of upper and lower level, when relatively many items are displayed on a single screen, task completion time is shortened, and efficiency is high. Also, the categorized menu structure shortened task completion time and showed good evaluation in efficiency and overall satisfac- tion. This is consistent with the results of research conducted on a larger screen than smartwatches. 36,38 Based on the results of this study, we propose an efficient menu method as follows: Providing the same level of items on a small screen, 1. In terms of task completion time and efficiency, it should be designed to show many items on a single screen.

1–1. In particular, the list view type seems to be appro- priate in order to improve efficiency.

2. From the viewpoint of satisfaction, it should be designed to show few items on a single screen.

2–1. In this case, it is judged that the grid view type is appropriate.

3. Do not mix scrolling and paging methods.

Providing items that can be categorized into top and bot- tom concepts, (1) In terms of task completion time and efficiency, it should be designed to show many items on a single screen. (2) Categorize to provide depth of menu.

In both cases, when many items are displayed on a single screen, task completion time and efficiency are good. On the other hand, in terms of the overall satisfaction, it is good that few items are displayed on a single screen. Taking these results into consideration, makers of smartwatches will have to make decisions about the menu interface of smartwatches.Thesalesvolumeofsmartwatchesisonthe rise, and the market is expected to remain buoyant. Various functions are applied to smartwatches, but it is restricted to the small screen. There are limitations in applying the guidelines applicable to a larger screen to smartwatches of a smaller screen. This study experimented with an efficient menu for providing methods on a small screen. Based on the results, it was possible to derive an efficient way of providing menus in two universal situations in which menus are provided (the same level of menus, and the menu structure that can be categorized into higher-level concepts). This study has several limitations. Experiments were con- ducted in smart phones environment assuming a universal smartwatches screen size. We also experimented with the assumption of square smartwatches enclosure. At present, there are also circle-shaped smartwatches (for example, Samsung Gear S3), and it seems necessary to study possible differences resulting from the outer shape. In addition, smart- watches often operate on the move. This experiment was conducted assuming a static situation in an independent experimental space. Studies that consider movement are also likely to be needed in the future.

Funding This research was partially supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Grant No. 2015R1C1A1A01053529).

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