Keywords

1 Introduction

The elderly is one of user groups that attract keen attention of product designers. When designing operation interfaces of a product, designers should take into account its intuitive use in addition to its aesthetics (Cheng et al. 2016). Modern products come with more and more functions, but the older people have difficulties in operating these products because they are physically and psychologically restricted due to physical degradation (Hawthorn 2000). Affordance proposed by Gibson (1979) has become a well-known design concept, which emphasizes that creatures perceive external forms and structures of environmental objects through visual perception, acquire characteristics of things, and learn how to interact with them. Norman (1990), a famous psychologist, believes that the perception of affordance of a product is related to past experience and knowledge. A well-designed product allows a user to easily understand how to operate it even at the first use. McGrenere and Ho (2000) proposes that viewers will interpret the perceived messages in the environment based on past experience and respond accordingly to interact with them. Blackler and Hurtienne (2007) points out that the users’ familiarity with technologies depends on how often they use certain products and what functions they use. If the designers have known the intuitive use of the product by users in the first place, they could have designed an operation interface in an intuitive way.

Watching TV is an important form of entertainment for the older people, and they often use a remote control for TVs (Angeletou et al. 2009). As the older people have degraded muscles, low sensitivity of fingers and reduced cognitive ability, they are unable to operate these products smoothly by pressing small buttons. As for the size of buttons, Chen et al. (2013) proposed in related researches on the use of interfaces by the elderly that the size of buttons is related to users’ posture. If the button size is smaller than 20 mm, it takes longer to complete the task when the user is standing up than that when the user is seated; if the button is larger, there is little different in operation time whether the user is standing up or is seated. Xiong et al. (2014) proposed that with the same size of buttons, the older people take about twice as long as young people to complete a task. As the size of buttons decreases, the operation time and the error rate of the elderly increase. As for the arrangement of product interfaces, Chen (2007) pointed out that the elderly are affected by the form of interface display. If the interface display can be adapted to the functions and needs of the product, it will make operation easier for the elderly. Freeman and Lessiter (2007) found in their study of TV remote controls that ordinary people can intuitively ignore buttons that are not needed, while the elderly can hardly do that. Proper arrangement of functional buttons allows operators to press the required buttons more directly and ignore buttons that are not needed. As for the shape of buttons, Breinholt and Krueger (1997) pointed out that the shapes of interface buttons have little impact on the operation speed. This is similar to the viewpoint of Chen et al. (2018), that is, the button shape has little impact on the first tap time and the completion time for the intuitive operation of the elderly. However, Tao et al. (2018) had a different viewpoint, who believes that the contact area of the finger during operation varies with the button shape; when the button is small, a square-shaped button will be easier to press than buttons of other shapes.

This study aims to explore the intuitive use of different forms of operation interfaces by the elderly with regard to the first tap on a button, and to propose a product interface design form suitable for the elderly. Focusing on TV remote controls, the study explores the effect of three design elements, that is, arrangement of button blocks, size of buttons and shape of buttons, on the operation of the elderly, and the research findings provide a reference for designers of operation interfaces of products for the older people. A Subsection Sample

2 Experimental Details

2.1 Participants and Test Interface

A total of 31 participants with a mean age of 69.22 (SD: 2.67) took part in the experiment. Participants had no speech impediment or visual impairment, and all had experience in using remote controls of TVs or other products. The test environment was a quiet classroom in a university. A total of 14 common types of user interfaces were collected for testing operations on common TV remote controls. To prevent the interference of factors such as color and material, the test interface was drawn using drawing software. The operation interfaces under test are represented by black wire frames on a white background (see Fig. 1).

Fig. 1.
figure 1

Test operation interface

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With the MIL-HDBK759 button size as a reference, the diameter of the button with the minimum fingertip area is 10/13 mm, the diameter of the button with the maximum fingertip area is 19 mm, and the interval between single-finger continuous operations is 6 mm. Interfaces A1–A5 are TV remote control interface block arrangement models, B1–B5 are number button size models, and C1–C4 are number button shape models. Operation time of participants is calculated in seconds, and data is quoted up to the second digit after the decimal point. The interface display device used in the experiment is a 10-inch iPad touch screen, and its layout is presented as a 1:1 simulated TV remote control interface. The first tap time of each participant is recorded.

A1 to A5 are the five most common block arrangements based on the collected samples. B1 to B5 depict round number buttons of common TV remote controls, with the maximum button diameter of about 13 mm and the minimum button diameter of about 7 mm. The dimensions of the test interfaces from B1 to B5 are 7 mm, 9 mm, 11 mm, 13 mm, and 15 mm respectively. Due to the size limitation of remote controls, button spacing is not considered here. The four types of number button are respectively of rectangle (C1), circle (C2), capsule (C3), and oval (C4) in shape. Because the button shapes are different, the horizontal spacing of the number buttons is not considered. The vertical spacing is 6 mm. The buttons of C1, C3, and C4 are equal in length and height.

2.2 Operation

Operation tasks are set based on different interfaces. For interfaces A1–A5, there are three types of operation tasks: (1) Change channel with number buttons; (2) change channel with channel tuning buttons; and (3) adjust volume with volume buttons. For interfaces B1–B5 and C1–C4, the operation task is to change channel with the number buttons. There is no time limit on the experiment. During the operation, the task interface appeared randomly. The program automatically recorded the first tap time of each participant (the time between tapping the Power button and then tapping any button on the interface). The operation process is as follows: Tap the red Power button to turn on the TV, use the number buttons to change the channel to 28 (two-digit operation task appears randomly on the screen), and tap the OK button to confirm.

3 Research Results

According to the results of the variation number, from the perspective of the block arrangement, the positions of number buttons in the five interfaces had no significant impact on the first tap time of participants (Table 1). The positions of channel tuning buttons on the five interfaces had significant impact on the results of the first tap time (P = 0.018 < 0.05); in this operation task, the average response time of all 31 participants was the shortest when they performed the operation on interface A5, and was relevantly long when they performed the operation on interface A1 (Table 2). The positions of the volume buttons on the five interfaces showed no significant impact on the intuitive use of participants (Table 3).

Table 1. Tasks of arranging number buttons in blocks
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Table 2. Tasks of arranging channel tuning buttons in blocks
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Table 3. Tasks of arranging volume buttons in blocks
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According to Table 4, the average first tap time of the participants on interface B5 is the shortest, and in comparison, the average response time for interface B2 is longer. Interfaces B2 and B5 (P = 0.024 < 0.05) are significantly different from each other. The other interface variations show no significant difference.

Table 4. Size of number buttons
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According to Table 5, interfaces C1 and C3 (P = 0.014 < 0.05) are significantly different, interfaces C2 and C3 (P = 0.03 < 0.05) are also significantly different, but interface C4 has no significant difference with the other three interfaces. The average first tap time of the participants on interface C3 is longer than that on the other three interfaces. Interfaces C1 and C2 show higher availability than other interfaces in this operation, and the average first tap time on these two interfaces is basically the same.

Table 5. Shape of number buttons
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4 Discussion

The research results show that:

The difference in the arrangement of functional blocks on the interface results in some differences in the intuitive use of the elderly users. This conclusion coincides with the findings of Chen and Liu (2017) and Chen et al. (2018). When changing channel with channel tuning buttons, there is a significant difference between interface A1 and interface A5. The difference may be mainly caused by the fact that the “▵▿, ok, ◃▹” buttons in the digital TV block above the channel tuning buttons of interface A1 are similar to the channel tuning buttons, which caused interference to most participants (tapping the wrong button, or pausing to think about whether the buttons might serve the same purpose). The arrangement of the volume buttons has no interference on the participants when they use the buttons adjust volume; this is because there is a clear distinction between the volume button symbols “+” and “−” and the “◃” and “▹” buttons in the navigation area. The number buttons on interface A1 are separated from the channel tuning and volume buttons. In general, the intuitive use of this interface is low for the participants. At present, the most frequently used buttons on a TV remote control by the elderly are number buttons and channel tuning & volume buttons. When these two blocks are arranged side by side, the elderly may ignore other less used button blocks. In all these operation tasks, interface A5 shows the optimal intuitive use for the elderly due to two possible reasons: First, these elderly people used to grasp the lower part of a TV remote control, so this is a focal area of eyesight (this assumption needs to be further verified). Second, these 31 participants have similar life experience; some remote controls for digital TVs currently available in Taiwan are similar to this interface, and the elderly have certain use experience of this interface.

The size of number buttons has no impact on the intuitive use of the elderly. There is a significant difference between interfaces B2 and B5. However, it should be noted that, according to the average first tap time, neither interface B2 with the smallest number button size nor interface B4 with larger buttons helped the intuitive use of the participants. Related studies before mostly focus on the completion time of operation tasks. The first tap time in this experiment does not suffice to prove the impact of the button size on the operation performance. In subsequent researches, the experiment will be improved and the completion time of operation tasks will be recorded for further discussion.

In tasks related to the shape of number buttons, interface C1 (with rectangular buttons) and interface C2 (with round buttons) show better usability. The difference between the average times of the first tap of the two interfaces is very small. Jung and Im (2015) proposed that the touchable areas and areas touched by fingertips are related to the matching degree between them. The participants perceive the difference in shapes through vision and interact with buttons based on past experience. Number buttons of TV remote controls on the market are mostly of rectangular or round shape, and the participants are familiar with the two interfaces. The result confirms the theory of Blackler and Hurtienne (2007) in the aforementioned literature.

5 Conclusion

This study found that the intuitive use of the elderly mainly depends on their use experience. The arrangement of button blocks on the interface is related to the functions of the products used by the elderly. A reasonable arrangement of function button blocks can lead to better intuitive use experience for the elderly. The size of number buttons has little impact on the intuition of the elderly in terms of the first tap time. The impact of the shape of buttons on the use of interfaces by the elderly mainly depends on the users’ experience.