SoundWear: Effect of Non-speech Sound Augmentation on the Outdoor Play Experience of Children

Jiwoo Hong HyeonBeom Yi Jaehoon Pyun Woohun Lee Department of Industrial Design, KAIST, Daejeon, South Korea {jwhong10, hyeonbeom, jhp960918, woohun.lee}@kaist.ac.kr

ABSTRACT This study aims to clarify the effect of non-speech sound augmentation (i.e., everyday and instrumental sounds) on outdoor play for children, where has been lacking in empirical examination. In a within-subject observational study, sixteen children (ages 10–11) were divided into four equally sized groups and equipped with SoundWear, which is a wearable bracelet that allowed them to explore sounds, pick a desired sound, generate the sound with a swinging movement, and transfer the sound between multiple devices. Both the quantitative and qualitative results revealed that augmenting everyday sounds led to distinct play types with differences in physical, social, and imaginative behaviors, whereas instrumental sounds were naturally integrated into traditional games. Thus, sound augmentation with specific digital design features (e.g., transparent technology to provide new perspectives, margin for interpretation, and ownership through a sense of achievement) is significant for shaping distinctions in digitally enhanced play and requires considerable design attention.

Author Keywords Children; outdoor play; open-ended play; sound; wearable; design; interactions; social interaction; physical activities; imagination; playful experiences CCS Concepts • Human-centered computing~Interaction design~Empirical studies in interaction design

INTRODUCTION Open-ended play is a free form of play that is non-narrative and non-competitive, affording self-determination and freedom [15,41]. Interaction in open-ended play is structured by the constraints of technology; however, there is a scope for creation and improvisation, which differs from highly structured games [64,65]. In open-ended play, children are encouraged to allocate different meanings

following their own interpretations and to play spontaneously with or without personalized structures [53].

Previously, a large part of children’s open-ended play used to take place outdoors. In recent years, however, there has been growing concern that children spend most of their playing time watching TV, playing computer games, and using mobile phones (i.e., only indoors) [29,32]. The lack of outdoor play may deprive children of irreplaceable benefits such as physical activity, social skills, and a social life [6,11]. Furthermore, playing outdoors can provide more opportunities to develop and share one’s imagination [3,11]. Researchers have focused on leveraging the opportunities of outdoor play by creating digitally enhanced playthings and environments [13,38,58,60] to support children’s engagement in physical activity [28,59], social collaboration [3–5], and creative rulemaking [21,61]. However, because outdoor play has intrinsic “head-up” play patterns, the integration of technology into outdoor play can compromise its benefits and must be realized wisely [22].

Among the feedback modalities for play and playful interaction, sound can activate physical movement [35], make players aware of and interact with others [56], and facilitate pretense-related thoughts depending on its type [23,52,56]. However, several research gaps exist in the use of sound interaction as a technology to augment children’s outdoor play: (1) it is difficult to design interactive objects that use only sound due to its abstractness and subtleness when conveying information and shaping experiences [56]; (2) various types of sounds (e.g., everyday, instrumental) are fragmented rather than integrated in such designs; and (3) it is not clear how sound augmentation affects children’s outdoor play because of the lack of empirical investigation and evidence [22].

This study focused on sound augmentation as a core digital feature to clarify how the presence and type of sound influence outdoor play. We present a bracelet-type wearable device, called SoundWear, with which children can explore, select, sonify, and transfer sounds for open-ended play outdoors. Experimental results indicate the two major contributions of this study: a design mechanism for considering sound augmentation in children’s outdoor play and empirical verification of whether and how sound augmentation promotes or compromises physical, social, and imaginative aspects of their experience.

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RELATED WORKS

Interactive Playthings for Children's Open-ended Play Recent studies on child-centered human–computer interaction (HCI) have shown increasing interest in the design of digitally augmented artifacts and environments for open-ended play [26]. Artifacts have long been praised for their role in developing creativity in children [45,48,67]; thus, playthings such as toys, props, and everyday items have commonly been augmented as interactive objects [39].

Bekker et al. designed original interactive objects to examine their novel opportunities to stimulate children’s social and physical interactions [4]. Among these objects, LEDtube [5] and ColorFlare [3] are cylinder-shaped objects that respond to player movements (e.g. rolling, shaking) by changing the color of light, and their open-endedness allows children to devise their own challenges and create diverse games. Several studies have created hybrid toys that use digital augmentation to present new perspectives for facilitating the pretend element of open-ended play experience [24,43].

Multiple studies have shown that pervasive technology can be integrated with outdoor play in the form of objects, wearable devices, and interactive playgrounds [13,70]. An interactive pathway was designed where motors placed along the path rotated to stimulate children to run and jump [59]. Through simple and open-ended interactions, children exhibited various play themes and patterns from running to pretending to be a train, and this was not limited to specific games. Morel is a cylindrical plaything for facilitating physical outdoor play by encouraging players to either play known games or create their own [28].

Head-up games (HUG) have emerged as a new approach to augment outdoor games. If pervasive games extend the digital game to the real world [36], HUG pursues an out-of-screen approach where players can play naturally while benefiting from technology [60]. For example, players in Camelot are divided into two teams that need to compete at collecting virtual resources to earn parts of a physical castle; the team that finishes the castle first wins [66]. RaPIDO and Scratch are prototyping platforms that include sensor-based objects and coding software for children to create outdoor games with their own rules [21,61].

Sound Augmentation to Motivate Playful Experiences Sound augmentation has been identified as beneficial for open-ended play. Audio or sound augmentation refers to using auditory feedback to augment the user experience during interactions with intelligent systems [35] and has been widely explored for designing products, interactive art, and displays [50,57].

Sound augmentation can function as a playful motivator that helps children in becoming more engaged [51], learning [46,52], performing physical activities [31,35], and playing social games [9,16,37]. For example, Rydeman et al. devised a wearable that generates sound with movement

for visually impaired children to play social games [37]; they improvised sounds to design their own games.

In open-ended play, the feedback modality has been reported to influence children’s play depending on its characteristics and combinations [25,27]. Several studies have used non-speech sound to augment play. The sound effects from the interactive wearable devices FeetUp [54] and Statue [55] not only support free play with active physical movement but also lead to fantasy play. The Wearable Sound Kit (WSK) is a movement-to-sound interaction accessory that includes both instrumental sounds and everyday sounds to explore how children incorporate sounds into free play in an indoor playground [56]. In other instances, the melody, tone, and pitch of instrumental sounds have been manipulated to follow the placement of table tennis balls on a table [12] or being squeezed by the player [28]. Van Hoeve et al. developed Toinggg, which uses interactive trampolines with different animal sounds, to allow children to play pretense-related games [23]. Though the described design cases fully demonstrate the potential for non-speech sound augmentation as a means to enrich play experience, further research remains on its design, involving various types of sound and interactions, and the consideration of unique play context outdoors.

Comparison between Digital and Non-digital Play Previous studies on HCI investigated the effect of digital technology on children’s behavior and experiences compared to non-digital play in different contexts, such as in smart storytelling [30] or in the usage of tablet apps [20]. The evaluation of interactive objects for open-ended play has focused on exploratory and iterative aspects while observing the overall play behavior and reactions of children; however, comparative studies have been relatively limited.

Hong et al. demonstrated that augmented toys using generic forms of hardware and audiovisual augmentation enables children to form new interpretations of the toys, which results in a larger variety of themes and greater imagination compared to non-digital social pretense play [24]. Huysduynen et al. used donut-shaped interactive objects called MagicBuns and compared the effects of three different combinations of interaction feedback on the play forms and behaviors of both younger and older children groups [27].

For outdoor play, Hitron et al. developed a stick-type object that emits light to verify how the existence of and differences in digital features influence physical activity, social interaction, and rulemaking [22]. Their results indicated that using a throw-sensing event was superior to a shake event, and the score feedback drastically increased competitiveness while the animation feedback improved collaboration. To compare play behaviors, they used a modified Outdoor Play Observational Scheme (OPOS), which is a well-known and valid approach to evaluating outdoor games intended for children [2].

Thus, the literature indicates that sound augmentation can potentially enrich ludic and playful experiences by allowing improvisation [68] and enhancing social awareness because of its ambient and omnidirectional characteristics. Furthermore, designing sound-based wearable devices is an unobtrusive way to augment play that can encourage natural interaction with active physical activity while leaving the hands and eyes free [57,60]. However, few studies have investigated the effects of digital features of playthings on children’s open-ended play, particularly the use of sound augmentation in an outdoor environment.

DESIGN AND IMPLEMENTATION To verify the effects of sound augmentation on outdoor play, we designed an wearable device to enrich the experience in the physical, social, and imaginative aspects.

Design Requirements and Scenario The design of the device was based on these requirements.

• R1: For open-ended play, the design needed to present abstract interaction rules and scenarios without clear goals to support the improvisation to construct games and explore many different ways of play [49,64].

• R2: As in the literature, differences in meaningfulness (i.e., margin for interpretation) between non-speech everyday sounds and instrumental sounds were expected to have different influences on play. We had to consider the difference when composing sounds.

• R3: The design needed to include the creation of as many objects as each child can use with sufficient individual interactions. This can support parallel play and encourages associative and cooperative play [55].

• R4: We also considered the spatial element of the system that can be a place of social activity to afford children to cooperate and develop play socially [12].

• R5: Methods were also needed to support collaborative play through the use of social capabilities to exchange or transfer digital features [3,27,28].

• R6: For outdoor play, the device must be able to interpret interactions with intense and unpredictable movements because unintentional feedback could be frustrating and spoil the social play. Also, the interaction for children should be designed as simple as possible [49]. Therefore, the input method needed to be carefully considered.

• R7: We had to ensure that the research objective of examining the effect of sound augmentation was not obscured by minimizing other feedback modalities.

To meet these requirements, we designed SoundWear, which is a wearable device that can be worn on the wrist and allows each child to play with sounds (R3), and a table with SoundPalette to serve as a hub of digitally augmented play (R4). SoundWear allows intensive use of sound augmentation for play in an open-ended way (R1). The device provides a simple visual feedback to inform the progress, success, and failure of an interaction (R7).

Figure 1 shows the four phases of the user scenario: exploration, selection, sonification, and transmission.

• Exploration: Placing SoundWear on SoundPalette causes the sounds stored in the latter to be generated from the former. Various sounds are listed on SoundPalette, which are designed for children to navigate freely while listening to each sound. Sound is played once each time, and a short white light flickers once during playback.

• Selection: Children can select a sound by holding the push button on top of SoundWear while placing their wrist on SoundPalette. While pressing the push button, the white light gradually fills up. If the sound is successfully picked up, the green light will flash; otherwise, the red light will flash.

• Sonification: SoundWear generates a sound when the arm is intentionally swung (R6). The selected sound is played once per swing. No visual effects are assigned.

• Transmission: A communicative function allows sounds to be transferred between multiple wearable devices (R5). When the fronts of the SoundWear devices are facing each other, the child transferring the sound presses the button, and the white light fills up gradually. If the transmission is successful, the green light flashes; otherwise, the red light flashes.

These phases are required for interaction with SoundWear; but, there was no intention to restrict children’s play.

Implementation Four standalone SoundWear wearable devices were created. Each SoundWear was equipped with an MP3 board, a speaker, an infrared (IR) light-emitting diode (LED), an infrared receiver, an inertial measurement unit (IMU) 9-axis accelerometer, a radiofrequency identification (RFID) reader, stick-type Neopixel LEDs, a push button, and an Arduino Nano microcontroller (Figure 2D). The IMU accelerometer detected whether a child swung their arm. This was processed by the microcontroller, which then

Figure 1. Four phases of the SoundWear user scenario: (A)

exploration, (B) selection, (C) sonification, and (D) transmission.

generated a signal for the speaker to emit sounds stored in a microSD card in the MP3 board. If the value of two acceleration axes in the direction perpendicular to the wrist (x, y) was greater than the value in the direction parallel to the wrist (z) for a certain coefficient value, a swinging movement was judged to have occurred. The IR LED and receiver were positioned to face the corresponding IR LED and receiver of another SoundWear when in contact. To enable sound transmission, the IR LED was coded to send its own sound ID at 0.5-s intervals. When the push button was pressed and the IR receiver received the same sound ID for more than 2 s, the microcontroller changed its ID to the received ID. All codes were programmed with “Arduino (arduino.cc)”.

The circuit board was wrapped with a 3D-printed 65 mm × 40 mm × 36 mm rectangular solid case. The case was fastened to the wrist by an elastic fabric band with a Velcro fastener to fit wrists of various sizes. Only the RFID reader was placed in a separate case below the wrist and wired to the main circuit in the rectangular case, which allowed the RFID tags of SoundPalette placed below to be detected. A rechargeable 350 mAh lithium polymer battery was placed to guarantee a power supply for the circuit board.

SoundPalette comprised 3D-printed units on a white acrylic plate (Figure 2C). Underneath each unit, RFID tags were assigned with different sounds. To ensure that children did not have preconceptions about the interpretation of each

sound, the units were marked by engraved Arabic numbers. SoundPalette was placed on a sufficiently wide bench table that was low enough in height to be accessible to children.

Collecting and Selecting Sound Non-speech sound can be classified as meaningful everyday sounds or abstract instrumental sounds. These are used by two design methods for auditory interfaces [17]: auditory icons [18] use meaningful and recognizable sounds while earcons [8] deliver information by using abstract and musical phrases. Differences in meaningfulness can significantly affect play where children interpret and improvise. Thus, we collected both everyday sounds and instrumental sounds (R2).

FreeSfx (freesfx.co.uk) is an open-source sound effect library that was used to collect everyday sound effects from categories such as animals, household, nature, vehicles, and explosions and instrumental sound effects from various instrument categories. We collected sound effects based on three criteria: (1) the length of time matched the short swinging movement (<3 s); (2) the sound was satisfying rather than annoying; (3) the sound was sufficiently clear to distinguish between everyday and instrumental sounds. In total, 39 everyday sounds and 32 instrumental sounds were collected.

A small workshop with children [14] was conducted to determine the sounds to be assigned to the number of units on SoundPalette, which was limited to not be burdensome to navigate. In addition, we obtained feedback on the usability of SoundWear with regard to the user scenario and detection of swinging movements. The workshop was conducted with three 10-year-old children (two female and one male) who were close friends and recruited via a mailing list from our institution.

The workshop was conducted in a meeting room in a laboratory. Half of the space was emptied to allow the children to experience SoundWear while moving freely, and the other half had a table with laptops for inquiries on sound preferences. Each participant wore a SoundWear prototype (Figure 2A) on the wrist and experienced scenarios involving swinging movements, which lasted approximately 10 min (Figure 3A). The participating

Non-speech sounds

Categories (Number of sounds)

Everyday Animals (3), explosions (2), household (3), nature (1), vehicles (2), weapons (1)

Instrumental Bass (1), bells (1), brass (1), drums/ percussion (2), guitar (1), piano (2), strings (1), synthesizers (3)

Table 1. Non-speech sound effects selected from the workshop and assigned as units of SoundPalette.

Figure 2. Design of the SoundWear system: (A) first

prototype in the workshop, (B) final prototype in the user study, (C) SoundPalette involving units marked 5-8, and

(D) internal structure and components.

Figure 3. Workshop with children: (A) a child participant

experiencing SoundWear and (B) another participant rating sound preferences.

children were allowed to share their experiences, discoveries, and other points with their friends and moderators. Then, the children spent approximately 30 min in front of a laptop to evaluate their preferences for the sound on a program, developed using “Processing (processing.org)” (Figure 3B). In the program, each of the 71 previously collected sounds was presented in sequence with a video showing the recorded swinging of the arm. The children rated their sound preferences on a five-point scale considering how each sound fit the swinging movement and the amount of fun it would be for outdoor play, and the score was logged in a TXT file. Each child had a moderator to help with possible discomfort associated with the laptops and repetitive tasks.

The children clearly showed a preference for certain sounds that they felt fun and pleasing. From the various everyday and instrumental sounds, a total of 12 sounds were selected with scores of four or more on the five-point scale and spanning various sound categories (Table 1). The participants said it was easy to pick up a sound and generate it with the swinging movement, and they expected that any child of their age would learn this scenario quickly. We also determined the optimal coefficient value for detecting the swinging movement based on their movements.

USER STUDY We investigated whether and how the sound augmentation of SoundWear promotes outdoor play benefits in children for several high-level categories: type of play, physical activity, social interaction, and imaginative utterances. To consider the influence of sound interpretation, we prepared two SoundPalettes with different types of sounds and configured three different experimental conditions: no sound (baseline), everyday sounds, and instrumental sounds.

Participants Sixteen children were recruited through the institution’s mailing list and the Open Lab program participants list. Parents were invited by text message or email with an introduction to the Open Lab program including our user study. To be included in the study, children were asked to participate as a group of four children interested in outdoor play and intimate relationships to allow for natural and social play. Our final sample included four groups of 13 boys and 3 girls; there were more boys because they actively expressed their interest in outdoor play. Of the 16 children, five were 10 years old, and the rest were 11 years old. All children were Asian and residing in South Korea, and all had the same cultural background. Because the children were recruited with the Open Lab program as a reward, they had a good understanding of technology and above-average socioeconomic status. We obtained ethical approval from our institution’s institutional review board (IRB) prior to the study as well as verbal and written consent from the parents and children for the audiovisual recording and use of anonymized photographs.

Setup and Procedure The study was conducted in a 30 m × 16 m outdoor space surrounded by trees large enough for children to play around and covered with grass to ensure safety during intense physical play. Cars and pedestrians could travel along the sides of the space, so traffic cones were placed for safety. Both audio and video were recorded. Two camcorders captured the children’s play in the space from different angles. To deal with the difficulty of recording voices away from the camera, all children wore a portable voice recorder modified as a necklace by a strap.

At the start of the study, children were informed of the play space and locations of the camcorders [47]. Then, each child was equipped with a SoundWear (Figure 2B) and necklace-type voice recorder. A moderator introduced SoundWear as “a bracelet that allows you to pick and play your favorite sound” and provided further instructions regarding the scenario phases. After the children expressed that they were accustomed to SoundWear, each group of children was guided to participate under the three different experimental conditions. For the everyday and instrumental sound conditions, each corresponding SoundPalette was placed on the bench table at the center of the space. Because the children commonly played with props, we prepared basic age-appropriate toys for outdoor play: a boomerang, round disc, and soft ball. Children were allowed to play freely without any restrictions on the games or use of props.

Each condition lasted 10–15 min, and the order of conditions was counterbalanced among the four participant groups. After each condition, a short semi-structured interview was conducted based on our high-level categories. The moderator casually asked the children the basis for their answers to determine their intentions, preferences, and thoughts underlying their behavior.

Measures and Analysis The play behaviors were quantified with Boris Observer, which is an event-logging software for coding audio and video files. Four video files for the four groups (eight video files and 16 audio files) were quantified for each participant, which were sampled equally for 10 min from the start of each condition. Participants were coded as P1–P16. Among the high-level categories, the type of play and physical activity were sampled by time, and social interactions and imaginative utterances were sampled by event. The type of play was recorded in terms of what play the children exhibited and how long the play lasted. Physical activity was coded as intense (e.g., running, jumping) or light (e.g., standing still, walking slowly) according to OPOS [2]. Social interactions were rated following Hitron et al.’s scheme [22] and according to the work by Tsiakara and Digelidis [63] and Parten [44] as competitive, collaborative, or general (i.e., noncompetitive and non-collaborative). We recorded the moment when children made imaginative utterances, which were defined

as oral expressions associated with imagining objects or situations that do not exist in reality [7].

Following OPOS, one researcher coded all of the data and another researcher coded 25%. A comparison between the results showed almost perfect agreement in intercoder reliability (Cohen’s kappa = 0.856). The independent variable of sound augmentation was used to evaluate the coded results for the dependent variables of physical activity, social interaction, and imaginative utterances through repeated measures one-way analysis of variance (ANOVA) in SPSS 22.0 (IBM).

The qualitative analysis was coded in ATLAS.ti. A thematic analysis was conducted on integrated video files. We converted chunks of actions or conversations into quotation segments and coded emerging themes from multiple segments. For each participant group, we developed a collaborative affinity diagram that printed quotations according to codes and divided them into high-level categories on a panel. Thus, the results of the quantitative and qualitative analyses could be reported in a complementary manner.

RESULTS

Type of Play Figure 4 shows the types of play and their durations observed during the study. Under the baseline condition with no sound, the children played with the props based on their already-known plays and rules. Several children played on their own by throwing the ball or boomerang (4/16). We observed collaborative play (7/16), where the children socially exchanged props, and competitive tag play (10/16), where children attempted to steal or protect props from others. One group of participants (P1–P4) teamed up and played dodgeball the entire time. Another group (P9–P12) played a game of football and used the gap between trees as a goalpost; they also created a game of throwing the boomerang onto a bamboo pole held by a child (designated as the boomerang-in-pole game), similar to basketball.

When sound augmentation was provided, new play types emerged, while others were previously observed under the baseline condition. Differences in the types and lengths of play were observed between the two sound conditions. One of the most popular types of play with sound augmentation was bodily play with sound using the sonification of the swinging movement, which was observed with both everyday sounds (15/16) and instrumental sounds (11/16). This type of play lasted for a longer duration with everyday sounds than with instrumental sounds.

With sound augmentation, the children exhibited pretense-related roleplay where they discussed, assigned, and played roles. In particular, participants performed roleplay more often with everyday sounds (10/16) than with instrumental sounds (7/16), as well as longer. These results indicate that everyday sounds seemed to evoke pretense and imagination more easily because they gave strong meaning to specific

interpretations. For example, a group of participants (P9–P12) interpreted one of the everyday sounds as a laser gun and roleplayed as shooting, dodging, and dying with invisible laser guns (Figure 5C).

Many groups played a blind tag game using sound. Instead of the traditional blind tag game that the children were used to, the game’s tagger now had to catch other children while

Figure 4. Number of children who participated in

observed play types and mean time duration of each play type under each condition.

Figure 5. Play with SoundWear in the user study.

listening to sounds from SoundWear. This game was observed more often and lasted longer with instrumental sounds (12/16) than with everyday sounds (4/16).

Combination of Sounds with Existing Play or Props The participants used props and rules in new ways when playing with sound augmentation. The children perceived the sounds and combined them with play or props differently depending on the margin for interpretation.

Everyday sounds encouraged imaginative thoughts, so the children combined existing play types with the sounds by imagining associations. The props were used as objects related to the imagination or with imaginary attributes. During their throw and catch play using sound (Figure 5A), P13 called to P14, “Hey! Here is a ball!” and threw the ball as if shooting an energy wave: “Energy wave!” P14 laughed and responded, “It sounds like it is not that strong.”

Instrumental sounds were frequently combined with existing play and games such as dodgeball (8/16), blind tag (12/16), and boomerang-in-pole (4/16) as a new element. The children focused on how the characteristics of the sound modality could be used rather than what the sound meant. For example, in the blind tag game, the sound was used by players to grab the attention of a tagger and run away, rather than imagine an association. As another example, one group (P1–P4) combined sound augmentation with the dodgeball game by creating a rule that required the same team to make the same sound, which did not indicate imagining any association with the sound.

Social Interaction Figure 6 shows the differences in social interaction under the different sound conditions. We found that competitive social interaction (F(2,30) = 0.885, p = 0.423) and general social interaction (F(2,30) = 0.229, p = 0.797) were preserved across the three sound conditions. However, collaborative social interaction was significantly influenced by the sound condition (F(2,30) = 10.022, p = 0). We conducted a post hoc test using a Bonferroni adjusted alpha level of 0.017 (0.05/3) and found that augmentation with everyday sounds decreased collaborative social interaction compared with the baseline (p < 0.017). This reduction with everyday sounds seemed to result from the children mainly exhibiting bodily play using sounds, which commonly accompanied general social interaction rather than collaborative social interaction. Instrumental sounds tended to be used to augment play transparently within the frame of existing play, so it supported social interaction as in the baseline.

Communication Referring to Sounds Using Numbers, Imaginations, and Melodies The children using SoundWear expressed their satisfaction with the sounds and showed general social interaction with others by sharing and recommending sounds. They used the numbers assigned on SoundPalette to communicate (e.g., P5 asked P6, “What did you pick?” and P6 answered, “Six, but I think eleven is also fine.”).

The children also referred to everyday and instrumental sounds differently. They referred and shared everyday sounds by adding interpretations and imagination. For example, when navigating SoundPalette, P12 said to the others, “Oh! This is boom-boom sound... and this sounds like something cracking.” P13 generated a sound while holding a branch and exclaimed, “Look! This is when Voldemort’s horcrux is destroyed. Aaaaaaaah!” In contrast, the children referred to instrumental sounds by using the melodies and displayed general social interaction with each other. For example, P13 suggested, “Hey, this sounds nice. Listen to number three.” Meanwhile, P14 sang the melody while laughing, “It’s like ting-rrr.”

Social Use of Sound for Attention and Awareness Sound augmentation led to competitive and collaborative social interaction by letting the children use sounds to promote attention and awareness during social play. Sound is effective at attracting attention and raising awareness in public, even in outdoor play where children scream and vocalize. The same held true for SoundWear. P9 said, “When we played, the sound played, so [we] could know the sound from far away.”

The children behaved similarly with particular instrumental sounds. They augmented play by using sound to attract social attention in existing plays, such as tag and dodgeball. With regard to blind tag, the traditional version was regarded as requiring more effort by the players trying to attract the attention of the tagger. Sound augmentation was used as a new means to attract attention more effectively by both taggers and players, which enabled social interactions unsupported by the traditional game. P7 explained, “In a blind tag game, players do not make sounds, so playing as a tagger is hard, and we should open our eyes slightly. But with this [SoundWear], we do not have to worry about it.” P6 agreed, “Right, in the original, we had to shout or clap hands.”

Children negotiated and cooperated with each other to build a play script and make rules for the sound augmented play. In their blind tag game, P5 (a player) and P8 (a tagger) conversed: “You are a tagger, right?” “Yes.” “Okay, do not cross over this space with grass. Start with the countdown!” “10...9...8...7...” “Hey! Come here to catch!”

Figure 6. Differences in social interaction under the baseline, everyday sound, and instrumental sound

conditions: competitive (left), collaborative (middle), and general (right).

Because such attention-catching characteristics had a major role, the children used other stimuli along with the sound from SoundWear to attract more attention. They were observed to use props to hit others, make direct physical contact, or verbally call out. Another observed strategy for social play was making no sound. To do so, children did not move at all or moved very carefully and slowly. For example, P6 wanted to cooperate with other children to not be noticed by the tagger while standing still (Figure 5B). P13 said, “I wanted to cheat by turning this off to avoid the tagger.”

Directional sound generation was observed to attract attention more clearly. P13 stood in front of P14 and shook his SoundWear near the other’s ear saying, “Listen to this.” This was one of the ways that the children attempted to resolve difficulties with unclear sound when children used the devices simultaneously.

Collaboration While Sharing Ownership and Identity Participants were observed to display ownership of the sounds that they picked and shared the ownership with other children. This could be a basis for social collaboration in outdoor play. P15 asked, “What’s your sound?” P14 answered, “I am… this sound.” Children expressed ownership when using the sound transfer function as if they were giving and receiving their own items. Interestingly, during tag play, P14 and P16 referred to such a transfer as dealing music (Figure 5D). P14 suggested, “I suggest a deal. I will not catch you, so deal a music with me.” P16 accepted and approached so that their SoundWear devices faced each other and said, “Okay, make a deal.”

Children sometimes attempted to engage the same sound through the sound transfer function or from SoundPalette. P2 suggested, “Let’s do all the same sound, number five.” P3 said, “Unify with the same sound!” This engagement with ownership created the same identity for playing a game. When using the same sound, the children tended to look at the others and mimic or mirror movements. This indicates that sharing the same identity through digital features affects expressive behavior. For example, P13 imitated shooting an energy wave with two hands, “Hey, energy wave!” P16 and P15 then mimicked the action one by one (Figure 5F).

The shared identity from using the same sound was also used to cooperatively form teams and alliances in play. After deciding to play a blind tag game, P7 asked, “But how do we make teams?” P8 answered, “We have to do rock-paper-scissors.” P7 said, “You two are the same sound.” P5 agreed, “Oh, yes, then we two are the same team.” As another example, a group of participants (P1–P4) devised a game called sound dodgeball, where the same team played dodgeball with the same sound. When children were hit by the ball, they switched teams and needed to change to the sound of the opposing team. Several children generated the same sound at the same time to express a united identity, like a sports team screaming a slogan.

In the blind tag game, players used the same sound to confuse a tagger based on the idea that the latter could not distinguish between them if they all sounded the same. P1 offered, “Hey, let’s tease him [a tagger] by doing the same sound... three of us.” Social interaction was observed when children combined different sounds owned by each. P11 said, “If you load, I'll shoot cock-a-doodle-doo.” P10 said, “Load.” Then, P11 threw a ball while playing a sound, “Cock-a-doodle-doo shot!”

Physical Activity The results of the statistical analysis indicated significant differences in intense physical activity (F(2,30) = 10.876, p = 0) and light physical activity (F(2,30) = 8.063, p < 0.05) under the three sound conditions (Figure 7). The post hoc test with the Bonferroni correction showed that the instrumental sound and baseline conditions had greater intense physical activity than the everyday sound condition (p < 0.017). Light physical activity was greater with everyday sounds than under the baseline condition (p < 0.017). The swinging movement supported by SoundWear is a light physical activity and was frequently observed under the everyday sound condition, where bodily play using sound was as a major play type. Under the instrumental sound condition, SoundWear supported intense movements similar to that under the baseline condition by augmenting existing play and games.

From Light Swinging Toward Intense Physical Activity The children explored various postures and showed more complex and intense physical activities than simple swinging movements. While performing various postures, they wondered how positions sounded and how they could be used for play. We observed children swinging or shaking their arms, walking, running, jumping, and rolling. P11 exclaimed to his friends while running, “Hey, run! Running makes the sound keep playing!”

The movements expressed by children differed significantly under each sound condition with different margins for interpretation. The everyday sounds allowed the children to make imitative actions related to their imagination. P6 made claws with her fingers and said, “This sounds like a lion crying! Grr!” Some children creatively used multiple sounds together. P6 picked a sound to represent sucking and combined it with another sound representing ice on

Figure 7. Differences in intense physical activity (left),

light physical activity (middle), and imaginative utterances (right) under the baseline, everyday, and

instrumental sound conditions.

SoundPalette. She put her SoundWear on the ice sound and quickly brought her hand near her mouth to generate the sucking sound to pretend as if she was chewing the ice.

With instrumental sounds, children expressed melodies with their bodily movements. P14 walked by turning his hands in a circle to express a melody with his SoundWear, while P13 laughed at him.

Sense of Achievement Motivating Physical Activity The participants noted a sense of achievement from SoundWear and SoundPalette, which motivated their physical activity. Searching and choosing desired sounds on SoundPalette gave the children a feeling of accomplishment. P5 said, “It was fun... I loved it because I could pick what I want... not just what was provided.” Children emphasized that the sound was made by their own movement with SoundWear. P16 explained, “Usually, there’s nothing I play with sound... Just jumping rope with the music? This was more fun because I played it myself.” The sense of achievement was also expressed when sounds were transferred. P11 successfully transferred P9’s sound to his own device and said, “Oh! It sounds! This is your sound, isn’t it?”

Making sounds with movement rewarded the children’s physical activity with instant sound, which could be a trigger for them to repeatedly attempt intense movements. P7 and P6 noted, “I moved a lot... It sounds like it’s going to be fun if I keep playing.” P6 agreed, “Me too. I did it with excitement.” P14 said, “If I wear this on my legs and neck, I can move more and more.”

Imaginative Utterances The three sound conditions indicated that sound augmentation had a significant influence on imaginative utterances (Figure 7; F(2,30) = 8.873, p < 0.05). Post-hoc analysis with the Bonferroni correction revealed that everyday sounds significantly increased imaginative utterances compared with the baseline (p < 0.017).

Depending on the margin for interpretation of the sounds, the children accepted and imagined them differently in play. Everyday sounds were accepted as meaningful stimuli and reminded the children of a specific object or situation. P14 said, “I came up with some thoughts... it was different [from other times].” One of the sounds sparked P16 to imagine he had a lightsaber: “Lightsaber was my favorite... When I hit a friend with the sound, [I] felt like I hit him with a lightsaber for real.” During bodily play using sounds, the children often made imaginative utterances while sharing their own interpretations associated with everyday sounds. P16 said to P13 and P14, “I feel like something is inside of this [SoundWear].” P14 responded with his own interpretation, “I... It keeps a shooting gun inside.” Some children roleplayed by socially developing imagination and making imitative actions triggered by sound.

On the other hand, the instrumental sounds had no particular meaning, so they were accepted as music, sound

effects, or songs. While exploring SoundPalette, P8 said, “This number six sound like the sound, you know, famous sound in YouTube.” P9 said, “This plays a song.” P12 responded, “Love this! I'll do this do this... I think we can even perform a dance show.” Sometimes, instrumental sounds were associated with something specific, such as animated films related to a sound effect or song. For example, P7 imitated playing a guitar and said to P8 (Figure 5E), “Hey, I like this. Look at me.” P8 answered, “Are you Coco?” P7 agreed, “Yes. This feels like a Coco sound.” (Coco is an animated film where a character plays a guitar.)

DISCUSSION The results of our study showed the impact of two different types of sound augmentation compared to the baseline condition on outdoor play. The results suggest that children’s play type and behavior can be actually influenced by the designer’s decisions on digital features with regard to the interaction style, input method, feedback modality, and open-endedness. Below, we discuss how the interaction with SoundWear contributed to such differences and what design aspects should be considered to promote the benefits of digitally augmented outdoor play for children.

Transparent Technology We found that open-ended sound augmentation led to rich and varied outdoor play while maintaining the framework of existing play and games, rather than turning children to games that previously did not exist. The everyday sounds enhanced the children’s imagination by letting them add attributes to play objects that made sounds when provoked. Meanwhile, the instrumental sounds naturally integrated existing play and technology, and the children used the sound characteristics as a new play element, such as attracting attention or forming a team. Despite being more ambient and indirect than other modalities, sound functions as a transparent technology [69] that is sufficiently stimulating and imaginative simultaneously, and it allows children to modify and develop existing play without being immersed in the technology itself [60]. Also, as a wearable device, SoundWear is not intended to induce new play or behavior but instead augment existing play environments or props by a simple swinging, which led the children to experience sound in a transparent manner. Prior studies indicated that combining sound and a wearable allows for natural interactions with head-up patterns [56,57], and our results supported this in the context of play outdoors.

Thus, the design of toolkits and systems with open-ended mechanism, involving sound modality and gestural interaction in our case, remains a space for children to keep and use their inherent cognitive and behavioral abilities as in traditional non-digital play, instead of requiring to learn new rules and goals within technology, and consequently can afford a transparent way of augmenting play.

Margin for Interpretation and Imagination We found that the meaningfulness (i.e., margin for interpretation) of the feedback modality can affect physical

and social behaviors by shaping how children accept sounds, develop their imagination, and create play. Everyday sounds evoked imagination, which led to play types distinct from the play under the baseline condition. Instrumental sounds were accepted as songs or sound effects and supported the reference and movement central to its melody. Although abstract instrumental sounds may have a further margin for interpretation, the children chose to combine its flexibility with existing games rather than using them for extensive imagination.

Interestingly, the children did not just interpret sounds as we intended. If there was a margin for interpretation, they used their own interpretations. For example, one participant regarded the sound of a bird as an elephant. Some of the unexpected interpretations had a strong dependency on existing mental models from other digital media, animated films or digital games such as Iron Man, Coco, and Harry Potter. By allowing broad interpretations, open-ended interaction can encourage more imaginative thinking than the limited options provided. This in line with other studies noting unexpected improvisation evoked by the digital features of interactive playthings [24,64]. Thus, more design attention on this aspect is needed to understand and cultivate one’s creativity during digitally augmented play.

Sense of Achievement, Ownership, and Identity The children felt fulfilled by the sounds they explored and selected and expressed ownership while using SoundWear. The children experienced a sense of achievement when picking sounds, generating sounds while moving, and transferring sounds. This confirms the previous notion of playful sound augmentation motivating children to actively engage in immersion and exploration [35]. Particularly for social interaction, we saw children using sound augmentation to share sounds that they picked and expressing ownership of the sounds. Children developed identities by using the same or different sounds in social play, such as engaging in the same play with unified sounds or distinguishing teams with different sounds.

Embodiment was revealed to play an important role in the children gaining a sense of achievement and ownership. The children directly related their movements to having control over the interaction and play. They could navigate directly with their own devices and embody the relationship with their own digital stimuli; this provided them with a sense of accomplishment and ownership as insubstantial rewards. This suggests that embodied interaction with digital augmentation can serve as a source of self-efficacy. Previous works afforded self-efficacy from embodied enactment leading to positive action courses in storytelling or learning [1,10,34], and showed that an open artifact can foster a sense of autonomy and pride [33]. Thus, play with embodiment can help facilitate children’s self-efficacy and encourage engagement in playful interactions. This is a novel approach that differs from goal-oriented rewards, such as scoring in pervasive or digital games [22,40].

Besides, the free sound choice on SoundPalette could act as a means to let children more engage in improvising for an open-ended play, and this implies the need to give more chances for children to explore, determine, and design interactions with technology by themselves, as previous studies on prototyping platforms for children’s play [21,61].

Limitations Our study included participants with limited diversity: Asian children with above-average socioeconomic status. Although we did not restrict the participants with regard to sex, most of our final sample was boys. Prior research has shown that play behavior differs with the sex and sociocultural context [42,62]. Thus, further research should focus on diverse backgrounds and gender balance so that the results will represent the general population. In addition, sound stimuli were determined by children’s preferences in a workshop; however, the bias of the researchers were inevitably included by the initial collection from the library. Because the children tended to exhibit unpredictable interpretations, the preferences and selections may vary for a large number of children in the general population.

The play space for our study was not where the children typically played, and the presence of observing moderators may have hindered natural play [19,47]. We tried our best to mitigate this difficulty by giving the children enough time to adjust to the situation and recruiting children who normally play together, but it is possible that the context of the experimental environment produced results different from their usual outdoor play. However, this limitation applies to all conditions, so we thought that the results can still be valued as valid and meaningful.

CONCLUSION This study indicated how non-speech sound augmentation with wearable devices can promote children’s outdoor play in physical, social, and imaginative aspects. With SoundWear, children were allowed to explore multiple sounds on SoundPalette, pick a desired sound, sonify, and transfer the sound. The empirically gathered results of the user study with 16 children indicated that the different types of non-speech sounds affected the play types in different ways. Everyday sounds triggered their imagination and resulted in distinct play behaviors, whereas instrumental sounds were transparently integrated with existing outdoor games. Our results add to the understanding on the design of interactive playthings by identifying how the specific digital features of our system contributed to differences in the children’s outdoor play. We believe that this study can contribute to the discussion on open-ended play with HCI and the use of sound augmentation and wearable accessories to enrich playful experiences.

ACKNOWLEDGEMENTS This work was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea [grant number NRF-2018S1A5A2A01032415]

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