Keywords

1 Introduction

According to United Nations statistics, the number of people aged over 60 in the world was 962 million in 2017, more than twice the number of 382 million the elderly in 1980. It is expected that by 2050, the number of elderly people will double again to reach nearly 2.1 billion [7]. The problems and needs of the elderly who are declining in their physical function are one of the focuses of many studies today. The use of mobile devices by the elderly has gradually spread. Although most users are between the ages of 20 and 50, there is an increasing number among older users who are older than 50 or even 60 [6]. Mobile services can enhance social ability and entertainment of the elderly, thereby promoting their quality of life, and the elderly have the ability to learn about information and communication technology. Because the elder are accustomed to the use of traditional mobile phones, it is an important factor for researchers to consider how the elderly adapt to use smart mobile devices [18].

In terms of using mobile devices, it is more difficult for an elderly to touch a button or to operate complicated gesture with a small interface. On the other hand, due to the decline in visual and auditory acuity, inconvenient mobility, and memory loss in the elderly, it often makes them feel anxious and unacceptable to use mobile devices. Although many studies have been solved these problems, there is still room for improvement [3].

A review of the literature on tactile perception indicates that devices that communicate messages to the body through physical contact or physical touch are called tactile sensor, and tactile perception techniques have been developed by researchers and companies in the past forty years, and also indicated that the tactile perception technology in the future will be the trends [17]. To further understand the problems faced by the elderly in operating mobile devices, the following will review the literature on the tactile degeneration, multi-touch gestures and feedback of the elderly.

1.1 The Impact of Hand Degeneration in the Elderly

Due to the physiological deterioration of the elderly, the sensitivity and stability of their hands are declined, which makes them more difficult to do complicated movements. In terms of using mobile devices, miniaturized design makes it difficult to use and read, and the range of hand wrist activity is reduced, which may cause hand function, muscle and bone damage [4]. In addition, as the age increases, the body muscle fibers gradually decrease and shorten, and it makes the elderly operate mobile devices more difficult. Moreover, slower neural responses may affect the brain’s ability to receive and process information, affecting its coordination and stability [12].

Some studies have conducted experiments on the exertion and coordination of the fingers of the elderly and young people, and measured the ability of the fingers to generate force and moment. The results show that the elderly need higher forces and showed less accurate when performing the tasks. The study inferred that ageing can affect the coordination of fingertips [13]. In the study of finger tactile acuity, it was found that the fingers tactile recognition ability of the older subjects was lower than young subjects [14]. In view of the above, the physiological decline may increase the fatigue and burden of the elderly using the mobile device, and may reduce the willingness of the elderly to operate the mobile device.

1.2 Elderly and Multi-touch Gesture

Touch gesture is a common method of operation on mobile devices. Although elderly people have lower touch accuracy and sensitivity than younger people, touch operation is more efficient than mouse or other assisting devices [8]. For the elderly, direct operation of the mobile device is better than operation through the assisting device, and the gesture operation can promote the interaction of the elderly and effectively reduce the error rate [5].

Nowadays, more and more software and hardware support the operation of multi-touch technology. Some studies have pointed out that the elderly are acceptable for touch gestures and clearly indicate that it is helpful for the initial software or hardware learning [11]. However, for operating mobile devices, the elderly prefer single-touch gestures and they are less willing to perform multi-touch gestures. These results show that multi-touch gestures increase the difficulty and complexity of the elderly to operate the mobile devices [15].

Therefore, the physiological changes increase the limitation of the elderly in operating multi-touch gestures, and it is an important issue to find out how to effectively help the elderly to operate gestures to improve the coordination and stability of the mobile devices.

1.3 Multi-haptic Feedback

Tactile feedback is a physical response when touched the devices. Studied have shown that for visually impaired users, increasing tactile feedback in the graphical user interface can improve operational efficiency [16]. The use of gestures to operate the mobile device with tactile feedback enhances usability and provides a better user experience [10]. In addition, tactile feedback can create richer interactions than visual and auditory feedback [1]. Tactile feedback is used as an aid when using mobile devices, and operations can be performed more accurately [9], and another research suggest that adding visual feedback when operating software can help the elderly understand the operation of multi-touch gestures [11]. In the study of using keyboard input, it is pointed out that adding a keyboard with tactile feedback will allow the user to input more words and fewer errors. On the other hand, in the moving environment, the benefits of tactile feedback are slightly reduced, but it can still effectively reduce errors [2].

According to above literature, the elderly are more difficult to perform multi-touch gestures due to tactile degeneration, so additional tactile feedback may be able to improve operational performance. Therefore, the purpose of this study is to investigate whether tactile vibration feedback can help the use of multi-touch gestures in the elderly, and further compare the task performance of different vibration samples.

2 Method

The purpose of the experiment is to investigate whether haptic feedback can increase the performance of multi-touch gestures in the elderly. There are 29 subjects including 4 males and 25 females who are over 50 years old with experience in using smart phones. The experiment device is Xiaomi - Mi 6, equipped with a linear motor and Android system. And the experiment tasks and the data recording are setting by Unity program. And there are four types of vibration mode for tasks, which are pinch open, pinch close, clockwise rotation and counter-clockwise rotation.

The experiment analyzes the completion time and the idle ratio. The completion time is the time when the subject completes the task and the idle ratio is the ratio of the time when the subject’s finger away from the screen and the total time. If the idle ratio is higher, it means that the subject is less aware of whether he or she has reached the task goal.

2.1 Subjects

According to the literature, humans sense began to degenerate at the age of 50. Therefore, the community recruited a total of 29 elderly (male 4; female 25). And all subjects have the experience of using smart phones.

2.2 Vibration Samples

This experiment sets four tactile vibration samples. Shown as Table 1, non-vibration (general operation), touch vibration (when the user starts zooming), lasted-vibration (keep vibrating during operation) and reminded-vibration (to alert the user when the task is not completed), respectively. In touch vibration is given to subjects vibration feedback as if they touch the screen. The lasted-vibration provides vibration feedback during the whole task, and reminded-vibration is a reminder when the subject finishes the operation without completing the task.

Table 1. Vibration sample
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2.3 Procedure

This experiment uses basic multi-touch gestures (pinch open/close and clockwise/counter-clockwise rotation gestures) with four different vibration modes to allow subjects to perform task. To understand whether the different vibration mode can assist the subjects to complete the task, and compare the task completion time and the idle ratio in different vibration modes.

Task description: (1) enlarge the photo to the specified size; (2) reduce the photo to the specified size; (3) rotate the photo clockwise to the specified size; (4) rotate the photo counterclockwise to the specified size, as shown in Table 2.

Table 2. Experiment task diagram
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3 Result

3.1 Average Completion Time

This study explores performance of the basic multi-touch gestures and four types of vibration mode. The pinch open (PO), pinch close (PC), clockwise rotation (CR) and counter-clockwise rotation (CCR) are respectively compared with average completion time of non-vibration, touch vibration, lasted-vibration and reminded-vibration. If the average completion time of the vibration mode is shorter than non-vibration mode, it means that the vibration mode can improve the performance of the elderly. The results are shown in Table 3.

Table 3. Average completion time between gestures and vibration modes
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The results of comparing average completion time of each vibration mode show that the completion time of lasted-vibration mode is shorter than the non-vibration mode by nearly 1 s, as shown in Table 4.

Table 4. Average completion time in different mode
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In order to investigate whether the various vibration samples are different from the current non-vibration mode, we perform paired sample t-test with non-vibration, touch vibration, lasted vibration and reminded-vibration. The results show that there has significant difference (p-value = 0.011) between non-vibration and lasted-vibration, as shown in Table 5.

Table 5. Completion time verification result
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3.2 Idle Ratio

Comparing the idle ratio of four vibration modes by four multi-touch gestures respectively. The results show that non-vibration mode has the highest idle ratio with pinch open gesture; the touch vibration mode has the lowest idle ratio with clockwise rotation gesture, as shown in Table 6.

Table 6. Idle ratio
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Furthermore, using t-test to analyze four gesture to find out whether there has any different between them. And the results show that in pinch open gesture has a significant different between both non-vibration versus lasted vibration (p-value = 0.04) and non-vibration versus reminded-vibration (p-value = 0.039), as shown in Table 7.

Table 7. Idle ratio verification result
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4 Discussion

The study explores four basic multi-touch gestures including pinch open and close, clockwise and counter-clockwise rotation. According to the experimental results, in terms of the average completion time of different gestures, the average completion time of clockwise rotation gesture in non-vibration mode is the shortest, and the pinch close gesture is the longest, indicating that the elderly are easier to operate the clockwise rotation gesture. The differences could result from the characteristic of rotation gesture. Through observation, subjects were able to use one of their fingers as supporting point to assist performing the task. In terms of average completion time of different vibration modes, the vibration mode with gestures is shorter than the non-vibration mode. If we further analyze each vibration mode with the non-vibration mode, we can find that the lasted-vibration mode is significantly shortened than the non-vibration mode. In addition, in terms of idle ratio, pinch close gesture is the highest, and the touch vibration mode has the lowest idle ratio with the clockwise rotation gesture. Further analysis shows that the idle ratio is significantly reduced when performing the task of pinch open on the photo with vibration mode.

To sum up, the elderly encounter more difficulties in operating pinch gestures than rotation gestures, but with vibration feedback can significantly shorten the completion time of the pinch gestures, and the effect of lasted-vibration mode is most obvious due to the feedback and reminder that provided by haptic feedback. On the other hand, the vibration feedback is less obvious for rotating tasks that are easier to perform. However, as for the average, subjects still have better performance when conduct tasks that combined with haptic feedback. In conclusion, adding haptic feedback is helpful for the elderly to perform multi-touch gestures.

Further research could improve this study in three directions. First, explore more on the feedback mode by considering the subjective feelings of the elderly. Second, explore more on the auxiliary level by examination the vibration duration period and intensity. Last but not least, this study using paired t-test as statistical method to reduce the difference between subjects which inevitably face the effect of repeat tests. Further research could recruit different groups of subjects for each vibration sample to further verification the effect of haptic feedback.