The observations and analysis above capture patterns of interaction that emerge among teachers, students and the TTPs. It is through these interactive patterns that the biofeedback is made meaningful, useful and actionable for movement teaching and learning.
In this section, we articulate intercorporeal biofeedback by presenting four interactive qualities that characterize it as a strong concept: shared frame of reference; fluid meaning allocation, guided attention and action, and interwoven interactional resource. Along with the discussions in prior work on strong concepts [
52], we ground these characteristics
vertically through connecting empirical results to the theoretical underpinnings that help articulate why and how the strong concept works. We also ground each characteristic
horizontally by revisiting similar designs (already presented in Section
3.2.1) showing how they exhibit similar features. Finally, we briefly include examples of our own work with other TTPs in Super Trouper [
77,
124] to show additional applicability of the concept. The horizontal grounding illustrates how the strong concept manifests in different technological instantiations, movement practices and movement learning domains.
6.1 Shared Frame of Reference
The first characteristic of the strong concept concerns the capacity of intercorporeal biofeedback to create a shared frame of reference among teachers and students. This frame of reference is made possible through the biofeedback being perceptually accessible for both parties. Intercorporeal biofeedback augments otherwise elusive aspects of the body [
61], making them accessible and public. As our empirics show, the TTPs’ representations were publicly available to anyone close enough to perceive them.
Mostly, we have used visual or audial cues to this purpose, as they offer modalities that different people can access simultaneously and through the same sense (vision or hearing). For example, BodyLights employed visual augmentations to the environment; the Blower TTP included synchronized sets of LED lights—one facing the wearer and one outwards —as well as sonification that both can hear. As seen in the empirics, this shared actuation allowed teachers and students to orient simultaneously to the feedback. For example, in Super Trouper in Figure
7, the circus instructor and the children trying to balance on the rolla-bolla both look at the Blower TTP's visual feedback and attend to its sonification. In BL Strength, the PT and the student both look at BodyLight's projection while the student is performing the mountain climbers (Figure
6).
The shared frame of reference gives people an additional perspective on their own movement. It complements their felt first-person experience [
105] with third-person augmentation that shows the impact of their movement as it unfolds in space and time [
105]. Through the technological augmentation, people can appreciate aspects of their own body and performance through a new, different sensory modality, which can in turn lead to a new understanding of such aspects. In our empirics, BL Strength students said that BodyLights gave them a new perspective: “
usually you don't see yourself from above, so you can't really realize fully your movement […] with the projection you have a good understanding on how your body moves” (P7). The shared frame of reference thus can provide people with an observational, third-person perspective on their own performance, complementing their felt sensations [
34,
116].
Through the shared frame of reference, people's perception of themselves and the others is enhanced. This reciprocal perceptibility is crucial in constituting and sustaining intercorporeal engagements [
85]. Teachers in both practices and students in BL Strength reflected that the TTPs enhanced their mutual understanding. The technology spotlighted selected movement qualities in a perceptually shared way that gave teachers and students a shared medium upon which they could base their communication and interaction. People could attune and appreciate both their own and the others’ movements, showing how the shared frame also supports second-person perspectives [
34,
86]. For example, students in BL Strength reflected that the TTPs clarified the teachers’ explanations, as captured by P4: “
we [PT and I] were using the light as the language tool to understand what I should be doing” (P4).
By enhancing people's perceptibility of themselves and the others, the shared frame of reference partially bridges the fact that teachers and students are not equally capable of perceiving and understanding movement qualities [
64,
120]. For example, the Mountain Climber example from BL Strength (Figures
3 and
6) illustrates how through BodyLights the PT could articulate very nuanced body positioning issues to a student whose movement literacy was not fully developed. The PT could draw attention to many desired and undesired positionings (Figure
3) and help the student realize his performance errors through referring to the BodyLights’ feedback (Figure
6).
Further, teachers in both practices and students in BL Strength mentioned that the shared reference frame enabled what we can call a
lingering perceptual imprint from the instructions. For example, as P2 performed Mountain Climbers (Figure
3), the projection gave him constant feedback on his posture, which also acted as a benchmark. Interactional biofeedback needs to offer feedback that is synchronized with the movement, so that the frame of reference dynamically evolves in space and time, as with other biofeedback technologies [
115]. This ensures immediacy and synchronization [
51] between what is being represented and the actuation, at the same time as feedback being available all throughout the experience, dynamically reflecting changes in performance. Participants in the empirics reflected on this quality of the shared frame of reference. As one student put it: “
when you receive an instruction and you don't have the light, it's difficult to keep the instruction present […] the light keeps it present all the time, like a constant reminder [on the correct performance], the light is all the time reminding you” (P15). This points to the shared frame of reference bridging the experience of the self to that of others [
74], as it not only fosters empathic observation (ibid.), but enables people to bridge the perceptual imprint of the teacher when demonstrating to their own when performing.
6.1.1 Shared Frame of Reference in Related Work.
Other works also make use of a shared frame of reference. For example, the actuated environment in ExoPranayama leveraged shared visual feedback; the wearable in Go-with-the-Flow leveraged sound; and the rest of the examples (our other TTPs, Enlightened Yoga and Motion Echo Snowboard) leveraged both.
In these works, teachers and students could refer to the shared frame of reference during instruction, performance, assessment, and feedback. For Motion Echo, however, this was only partially true. Since visualizations were placed on the feet, teachers and students could only orient to them during static moments. When participants were descending a slope, the feedback drew people's vision to their feet and away from the environment, which was detrimental to posture and could pose safety issues. This case highlights the need to design shared frames of reference so that they do not disrupt habitual movements and body orientations of the movement practice.
In all of these works, students also reported that the shared actuation form gave them an increased understanding of their own movement and a different perspective of their body. In Go-with-the-Flow, patients with chronic pain became more aware of their real movement capabilities, which led to more self-exploration and ultimately physical activity at home. In Enlightened Yoga, ExoPranayama, and Motion Echo, the biofeedback substantially improved the students’ awareness on movement trajectory and posture, breathing cadence and weight distribution respectively.
The biofeedback in those works also enhanced people's appreciation of other people's movements. It gave teachers a nuanced understanding of elusive aspects of the student's performance, which they used to assess performances and provide further guidance. For instance, the teacher in Enlightened Yoga could sometimes identify errors in hip and back alignment solely by looking at the students’ Laser TTP projection. The snowboarding teachers in Motion Echo used the biofeedback to provide tailored feedback on how they distributed their weight on the board.
Some of these works were less successful in supporting teaching and learning. In particular, ExoPranayama's shared frame of reference proved less useful to address individual performances, as the aggregated breathing data made it difficult to discern and address individual performances. This points to the importance of designing intercorporeal biofeedback in ways that help with identification. However, the teacher in ExoPranayama was seen to be able to employ the actuated environment to instruct and provide collective feedback to the class.
Teachers and students in these projects oriented and referred to this shared frame of reference to build meaning and action. Teachers could instruct movement, demonstrating what to do with the technology so the students imitated.
Some of these works also created a lingering perceptual imprint that worked as a benchmark. For example, in Motion Echo, teachers first demonstrated the effects of the body-weight shift on the augmented snowboard. When students attempted to perform it, they could compare their own weight representations to that of the teachers. In Go-with-the-Flow, the lingering effect extended to distributed settings, and students training individually in their home were able to act on instructions and goals that they had jointly explored with the physiotherapist in the collocated session.
6.2 Fluid Meaning Allocation
The second characteristic of the strong concept concerns fluid meaning allocation, by which we mean the way teachers and students make the shared frame of reference meaningful and actionable in context through ascribing meaning to particular courses of action, and adapting these meanings as needed.
In this process, the role of the teacher is central. Teachers endow the shared frame of reference with contextual meaning, helping students making sense of it in a way that aligns with both the desired performance and students’ individual capabilities. Teachers also make the shared frame of reference actionable for students. This meaning-allocation process has been observed in previous work on movement teaching and learning [
7,
21].
The empirical examples in this paper show how teachers allocated meaning and courses of action to the TTPs’ feedback, through demonstrating and explaining the connection between the performance and the biofeedback actuation. For example, the PT in BL Strength demonstrating the Mountain Climbers in Figure
3(d), saying
remember to not curve or stretch the back while demonstrating an incorrect positioning of the back and the BodyLights’ projection. We also sometimes saw teachers do this without referring to the body movement, instead providing cues on what to do with the technology directly. Examples include the instructor in Super Trouper explaining how to do crunches (Figure
5) by saying
blow, or the instructor for Mountain Climbers in BL Strength (Figure
3(d)) saying
keep the light as stable as you can.
Through such explanations and demonstrations, teachers associate the shared frame of reference with a range of desirable and undesirable movements. These meanings are often prescriptive, related to the movement norms of a practice [
22]. Interview data revealed that teachers from both practices perceived that using TTPs economized instruction, since establishing the relationship between a correct performance and TTP feedback made their instructions linger during the student's performance. BL Strength's PT captured this quality well: “
[with BodyLights] I can see that students acquire [aspects of] the basic technique fast […]. I don't need to repeat the information, like the movement trajectory or posture, every time for each repetition, set, or even session […] I just [trust] the light to take care of it. I give students [more nuanced cues], but I don't repeat the basics”.Fluid meaning allocation also concerns how the allocated meanings are adapted to best suit particular contexts. This is crucial as movement learning goals and needs change depending on particular practice's goals and values [
5,
99,
102]. For example, in Super Trouper's rolla-bolla example (Figure
7), the instruction to blow did not really specify a particular pace or length of exhalation, as the main aim was to make the child to engage the core muscles and, through that, manage balancing. In comparison, BodyLights's Mountain Climbers projection (Figure
3) was linked to both posture and stability, revealing concrete correct and incorrect postures with great precision. Performance correctness was more important in BL Strength.
The meanings ascribed to the biofeedback were also adapted to the individual students and their bodies and capabilities, allowing instruction to address individual needs and goals [
14,
21]. Teachers would concretize or change the meanings and actions they ascribed to the technology, by e.g., emphasizing previously instructed cues, as in the Super Trouper example with the rolla-bolla (Figure
7) when the instructor repeats the instruction
blow. Teachers also linked the biofeedback's actuation to more specific aspects of the performance, as in the Mountain Climber example of BL Strength (Figure
8) where the PT brought attention to pace. Finally, teachers were able to adapt the initially allocated meanings: in the same Mountain Climber example (Figure
8(c)), the PT used a physical prop, a sticky note, to give P2 an even more actionable cue to improve his posture and stability.
Teachers can do these fluid meaning allocations due to their expertise in assessing the students’ needs in real time [
21], and their perpetual reflection in and on action [
39,
103]. Teachers and students negotiate meanings and courses of action to the shared frame of reference, and reach a mutual understanding of the self, the other, and the practice's norms—which is what intercorporeal engagements aim at doing [
40,
85,
86] in movement teaching and learning.
6.2.1 Fluid Meaning Allocation in Related Work.
Fluid meaning allocation is also present in other work. For example, in Motion Echo, teachers used verbal cues, demonstrations, and gestures to map specific actions or movement qualities to specific biofeedback's representations, showing students how braking added weight added on the back of the foot and triggered LED lights, or that a subtle weight shift in the front of the foot increased the red hues in that area.
In most of these works, feedback was used to establish performative norms, by associating it to a range of desirable and undesirable performances. An exception is Go-with-the-Flow, where the wearable was used to explore movement capabilities without normative judgements. In this work, the physiotherapists were particularly careful when telling chronic pain patients if their performance was incorrect, as such information could trigger anxiety about pain for the target group of [
109]. Comparing Enlightened Yoga, Super Trouper, and BL Strength further emphasizes this point. All three projects used similar technologies (Laser TTP, BodyLights) but deployed them differently depending on the context. In Enlightened Yoga, teachers emphasized the pleasure of moving gracefully. In BodyLights, teachers gave the technology more prescriptive meaning, foregrounding movement accuracy and norms. By contrast, in Super Trouper, instructors used the Laser TTP to foster movement exploration and playfulness.
Finally, in all these works teachers adapted the meaning and courses of action they ascribed to the feedback. This was often negotiated and updated in practice to address individual differences, capabilities and needs. For example, in Go-with-the-Flow, physiotherapists commented that the technology enabled setting contextual goals to individual patients. The instructors in ExoPranayama adapted instructions and feedback on the spot, often based on the information they obtained from biofeedback. With the Movement TTP in Super Trouper, teachers cued slowing down to focus the children's movement and balance, challenging them to try to keep the TTP green as much as possible. Teachers adapted this requirement to the individual child. For those with better motor control, teachers often reminded them to keep the TTP green whenever it turned red. With motor-challenged children, teachers instead merely cheered them on whenever they managed to keep it green even briefly.
6.3 Guided Attention and Action
The third characteristic of intercorporeal biofeedback concerns the multiple and changing perceptual relations [
94] between people and technology, and how these were used by teachers to guide students’ attention and action. As with other biofeedback technologies, the attention of a person interacting with biofeedback dynamically fluctuates [
93,
94]. A quote from one BL Strength student captures this quality: “
[my attention to BodyLights’ projection] is like appearing and disappearing, it goes [in] and out” (P15).
Through being fluent and immediate, intercorporeal biofeedback has the capacity to be incorporated into the bodily experience [
48], becoming an extension through which people perceive and act. Our empirical studies illustrate how both teachers and students went about their tasks (e.g., instructing, performing, assessing) while using the TTPs (Figures
3 to
8). Some participants were not only seen to be able to act and perceive through the TTPs, but they consciously experienced such incorporation. This is best captured by a BL Strength participant's quote of training with BodyLights:
“I felt I used [the projection] but I was not only focusing on it […], at the same time I was focusing more on my body” (P14).
The shared frame of reference can be geared towards guiding people's attention, and/or to their inner, felt sensations, helping them hone a first-person perspective of their body movement. Intercorporeal biofeedback can be experienced, to some extent, as in an intimate correspondence [
51] with the person whose movement qualities are being augmented, being merged into their perceptual-bodily selves [
55,
94,
132]. BL Strength participants experienced this correspondence particularly often, as one reflected: “
it's like a mirror […] it's a way in which I can see my body: it's reflecting my movements, how tired I am, how straight I am, how fast I move.” We see this as an important quality, in that it can allow people to act with technology without negatively altering their movements or practice.
Yet, intercorporeal biofeedback can also disrupt our felt sensations through acts of defamiliarization [
48]. Through decoupling acts of first- and third-person perspectives on the body [
49], a person checks what they sense proprioceptively against what the augmentations reveal of their performance. In our empirics, participants’ felt experience and the information the TTPs provided did not always align. A participant in BL Strength reflected:
“without [BodyLights], I thought I had a good alignment in my arms and back, but with it, I saw a small twist, and [realized] I was putting too much effort on one arm in comparison to the other” (P12). The capability of creating defamiliarization is also an important quality, as this can bring attention to performance aspects and errors that are otherwise elusive.
Intercorporeal biofeedback can be also experienced as a quasi-other [
132], as an external object in the world [
116] that draws our explicit attention to it and makes it the focal object of awareness and action [
55,
132]. In the empirics, an explicit attentional focus on the shared frame of reference was sometimes desired and fostered. The teachers replaced verbal cues with actionable cues that brought the attention and action solely to the TTPs, as in the Super Trouper examples with the Blower TTP (Figures
4 and
7) and the verbal cue to
blow; or in BL Strength's Mountain Climber example (Figure
6) and the PT's instruction to
control. An explicit focus on technology feedback was particularly useful for students who found it more difficult to act upon bodily cues, as with the children in the Super Trouper project. It was also more commonly used with beginner and intermediate students in BL Strength.
Explicit focus can also be used for distraction. While distraction risks disconnecting us from our body and our world [
55,
132], it is sometimes sought in movement learning, for example, to distract people from pain or extend performance time. In our empirics, distraction helped children in Super Trouper to concentrate on the task at hand and control their movement and ease unpleasant sensations, and made children engage with the exercise longer (e.g., crunches with Blower TTP Figure
6, where having to blow was made a goal in itself).
Intercorporeal biofeedback can also be used by teachers to guide the students’ attention to specific body areas or movement qualities. In BL Strength, when instructing Mountain Climbers (Figure
3), the PT used verbal cues, gestures, demonstrations, and the biofeedback's behavior to bring to the foci of attention particular postural aspects (e.g., arched or curved back) and movement qualities (e.g., stability), and exemplifying desired and undesired postures. This aligns with the notion of change from motion training [
49], of subdividing bodily experiences into specific areas as a way to deepen people's appreciations of their sensorimotor processes and of the practice's norms.
The use of intercorporeal biofeedback to provide very actionable instructions, as in the rolla-bolla example, helps to address challenges in articulating instructions that stem from asymmetries in movement literacy and perceptual capabilities [
58,
101]. In our empirics, teachers from both practices perceived that demonstrating exercises and particular movements with the TTPs allowed them to simplify and clarify their communication. They mentioned that their explanations of the relation between a desired/undesired performance and its impact on the shared frame of reference was able to cover what otherwise would have needed several verbal cues. As the strength training PT reflected: “
I connect the projection to what is a correct technique for each student, and explain it to them, and [without BodyLights] I would need to give more cues, like “try to adjust your pelvis”.Hence, it can be argued that intercorporeal biofeedback helps to create and sustain co-operative forms of intercorporeality, namely the turn-taking processes through which teachers and students build relevant and situated meanings and action [
40]. Yet, it is important to notice that, as with any technology, intercorporeal biofeedback artefacts are not neutral [
132]. That is, biofeedback will encourage certain sensorimotor appreciations and responses, but might risk obfuscating others [
48]. In our empirics, the teachers were key to addressing performance aspects that were not captured by the biofeedback. For example, in Super Trouper, the instructor explained how to perform a crunch with the Blower TTP (Figure
4), which included raising their heads. This was not something that the Blower TTP could augment, so the instructor brought it to their attention by using other interactional resources: he bodily demonstrated it, touched his own head with his hand, and said that we first raise the head. The fluid meaning allocation that characterizes intercorporeal biofeedback allows teachers and students to decide and negotiate in practice when to attune to and act with the biofeedback. Yet, it also allows them to decide when its use should recede to the background [
77].
6.3.1 Guided Attention and Action in Related Work.
The use of biofeedback to guide attention and action is also present in the other works. In all of them, the biofeedback brought people's attention to the movement quality being augmented. For instance, in Go-with-the-Flow, physiotherapists used the sonification to help patients raise awareness and reflect on their bending capabilities. This approach sometimes disrupted the felt sensations through acts of defamiliarization: moving with the wearable sonification often challenged the patients’ own perception of their capabilities, as they became aware that they could bend their back more than they expected.
In all the works, the technology exhibited intimate correspondence: it formed an extension of the participants’ bodies, impacting their perceptions, movements, and capabilities as they engaged in their practice. However, in some examples, teachers also made technology an explicit focus of attention. For instance, the Movement TTP in Super Trouper helped children attend to their movement pace in balancing exercises, such as walking on a tightwire. This also helped them slow down, which resulted in a better balance.
Explicit interaction can create problems. In Motion Echo, the cues referring to the biofeedback resulted in students looking down towards their feet, which in turn limited the student's abilities to focus on other instructions and feedback. This further points to the importance of designing biofeedback augmentations with care for the practice's movements and body orientations, as discussed in previous work on the TTPs [
77,
104,
121,
124,
127].
In all these works, teachers used the biofeedback to hone, direct, and focus the students’ attention and action. Their instructions often fluctuated between drawing the students’ attention to the body and to the biofeedback. For instance, in Enlightened Yoga, the teacher interlaced cues about the body (e.g.,
“lift your hips…”) with explanations about the subsequent biofeedback response (
“…and the light is going to go all the way up the ceiling”) [
121]. In Motion Echo, teachers explained how adding weight on the ball of the foot to control the board's direction would result in turning the LED lights red around that body area.
Finally, these works also used biofeedback to sustain the students’ attention to particular movement qualities. For instance, the teachers in ExoPranayama drew students’ attention to the different changes in the technology's shape while breathing, so as to keep the students’ attention on different breathing qualities such as pace, rhythm and synchronicity.
6.4 Interwoven Interactional Resource
Finally, intercorporeal biofeedback is an interwoven interactional resource. It is integrated with the pool of other interactional resources that teachers and students already use, and through which intercorporeality is constituted [
86]. These include verbal explanations and commands, body demonstrations, gestures, mobilizations, other material elements, and so forth [
58,
86].
This quality is illustrated in all the examples of our empirics (Figures
3 to
7): teachers and students use verbal cues, act with the technology, and point to it. They build meaning and action by the juxtaposition and simultaneous use of all these multimodal resources. For example, in the Mountain Climber example from BL Strength (Figure
3), the PT instructs the exercise by employing bodily demonstrations, gestures, and verbal explanations, all while using BodyLights. Hence, intercorporeal biofeedback extends the ecology of interactional resources already present in the practice with a distinct material contribution: a perceptually shared augmentation of relevant movement qualities that people render meaningful and that help guide their attention and movement.
As our examples also show, in the context of an unfolding movement learning experience, the technology can be used, ignored when not relevant [
40], and then used again. For example, the instructor in Super Trouper explaining how to perform a crunch with the Blower TTP (Figure
4) first cued to raise the head by providing only bodily and verbal cues; and later cued core engagement by using the TTP.
Like other multimodal resources, intercorporeal biofeedback supports intercorporeal engagements between teachers and students. Yet, as with other resources, it alone does not sustain intercorporeality: it requires other resources to be meaningful and actionable. In our empirics, successful integration of technology with other multimodal resources required iterative exploration during their design process [
77,
124,
127]. This exploration impacted not just the design of the TTPs as such but would for example serve to identify best body locations and uses of the TTPs for particular exercises, just as to identify (and in some cases modification) the exercises that benefitted most from the introduction of technology. In addition, technology needed tweaking when in use. This included hardware adjustments to mitigate bodily differences (e.g., the BL Strength PT in Figure
7, mechanically positioning P2’s BodyLights); and in the case of some of the circus TTPs, through software adjustments such as changes in sensing sensitivity [
77].
6.4.1 Interwoven Interactional Resource in Related Work.
The related works also use technology as an interactional resource for teachers and students to jointly build meaning and action. Participants in ExoPranayama, Enlightened Yoga, Motion Echo and Go-with-the-Flow also used technology in different processes (e.g., instruction, correction, performance) alongside other existing interactional resources, such as verbal instructions, gestures, mobilizations, and so forth.
Some works engaged in embodied design sessions to explore what aspects of the exercises the technology could help articulate and communicate. For instance, in ExoPranayama and Enlightened Yoga, designers and teachers designed a whole class with the biofeedback technology prior to the training with real participants. The exercises featuring in each class were selected, among others, for how well they capitalized on the biofeedback. In ExoPranayama, breathing yoga exercises were favored and the class design adapted the physical layout of the class (how instructors and practitioners positioned themselves) to accommodate the technology. Such adjustments point to the importance of exploring how intercorporeal biofeedback might best support particular contexts during the design process.