Vibrotactile stimulation as an instructor for mimicry-based physical exercise

Research Article Vibrotactile Stimulation as an Instructor for Mimicry-Based Physical Exercise Jani Lylykangas,1Jani Heikkinen,2Veikko Surakka,1Roope Raisamo,1 Kalle Myllymaa,1and Arvo Laitinen3 1Tampere Unit for Computer-Human Interaction (TAUCHI), School of Information Sciences, University of Tampere, Kanslerinrinne 1, 33014 Tampere, Finland 2The Unit of Human-Centered Technology (IHTE), Department of Pervasive Computing, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland 3Audio Riders, Ltd., Envallinkuja 4B, 01900 Nurmij¨ arvi, Finland Correspondence should be addressed to Jani Lylykangas; [email protected] Received 18 June 2015; Revised 11 September 2015; Accepted 29 September 2015 Academic Editor: Marco Mamei Copyright © 2015 Jani Lylykangas et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The present aim was to investigate functionality of vibrotactile stimulation in mimicry-based behavioral regulation during physical exercise. Vibrotactile stimuli communicated instructions from an instructor to an exerciser to perform lower extremity movements. A wireless prototype was tested first in controlled laboratory conditions (Study 1) and was followed by a user study (Study 2) that was conducted in a group exercise situation for elderly participants with a new version of the system with improved construction and extended functionality. The results of Study 1 showed that vibrotactile instructions were successful in both supplementing and substituting visual knee lift instructions. Vibrotactile stimuli were accurately recognized, and exercise with the device received affirmative ratings. Interestingly, tactile stimulation appeared to stabilize acceleration magnitude of the knee lifts in comparison to visual instructions. In Study 2 it was found that user experience of the system was mainly positive by both the exercisers and their instructors. For example, exercise with vibrotactile instructions was experienced as more motivating than conventional exercise session. Together the results indicate that tactile instructions could increase possibilities for people having difficulties in following visual and auditory instructions to take part in mimicry-based group training. Both studies also revealed development areas that were primarily related to a slight delay in triggering the vibrotactile stimulation. 1. Introduction Structured physical group exercise is typically based on seeing and listening to instructions of a trainer and then modeling them by trainees who try to do the same movements in synchrony with the trainer. There are many groups, however, likeagedanddisabledpeoplewhocannotbenefitorgetthe full utility from such activities if their sensory or cognitive impairments inhibit them from following visual and auditory instructions. Utilizing the sense of touch as an information channel could partly replace the requirements of the full functionality of visual and auditory perception (see [1] for a review). Following this, touch mediated instructions could increase the achievability of group exercise for special groups and it could actually complement the exercise even in the case of fully functional sensory systems. Motor response to a touch sensation is an innate trait for human beings, and the sense of touch has some advantages over the other senses [2]. For example, reaction times (RTs) to tactile stimuli have been found to be faster than RTs to visual stimuli (e.g., [3]). As compared to auditory RTs, tactile RTs have been found to be less affected by distractions such as a concurrent secondary task (e.g., [4]). This is probably because, in contrast to visual and auditory events, tactile events are in direct physical contact with the organism and thus evoke more readily the interest of an organism [5]. Mechanisms to react to tactile stimulation are among the first ones to develop as evidenced by the palmar grasp reflex Hindawi Publishing Corporation Advances in Human-Computer Interaction Volume 2015, Article ID 953794, 13 pages http://dx.doi.org/10.1155/2015/953794 2Advances in Human-Computer Interaction of fetuses [6]. Furthermore, the importance of the sense of touch has been shown by, for example, remaining of motor responses to tactile stimulation, while the patients are unresponsive to other types of stimulations like visual and auditory stimulations [7]. Relatively recent experimental research has shown that technology-mediated vibrotactile stimulation (i.e., cutaneous stimulation produced by a vibration actuator) can be successfullyusedinassistingphysicalrehabilitationandexerciseby means of sensory substitution and augmentation. Wearable vibrotactilefeedbacksystemshaveproventobeusable,for example, in gait retraining [8], body balance control [9], rowing [10], snowboarding [11], and even swimming [12]. There is also evidence that appropriately designed vibrotactile signals can be intuitively associated with cues suggesting, for example, to accelerate and decelerate the speed of movement [13]. The evidence on intuitive associations between tactile stimulation and human behavior suggests that tactile stimulation might also function as a substitute for another person’s visual demonstration of bodily movements. Lee and his colleagues [14, 15] have empirically tested body balance training with tactile information in the mimicry frame of reference, but otherwise using tactile stimulation in providing interpersonal, mimicry-based behavioral regulation information seems to be still largely unstudied. In a preliminary study by Lee and Sienko [14] the task was to replicate prerecorded trunk tilt movements consisting of a 20∘anterior tilt followed by a 6 s long static hold and a 20∘ posterior trunk tilt back to the upright starting position. The tilt movements were performed at a rate of about 1.12∘/s. The instructions were either visual, tactile, or combined visualtactile cues. Visual instruction was provided with a side-view illustration of a virtual avatar representing the prerecorded example movements of an instructor. Tactile instructions were provided with two separate vibration actuators placed on trunk midline in the navel and back indicating the anterior and posterior tilts, respectively. End of the vibration communicated the attainment of the desired tilt angle. The results showed that the example tilts were mimicked significantly more accurately and faster with combined visual-tactile and tactile instructions as compared to visual instructions. In a follow-up study [15] the speed of the example movement was varied, and this time only tactile instructions were provided. The results showed that slow (approximately 1.12∘/s) example movements were mimicked more accurately as compared to medium (approximately 2.0∘/s) and fast (approximately 4.0∘/s) example movements. Together the results of Lee and colleagues [14, 15] indicate a serious potential of using tactile instructions to mimic physical movement of another person in eyesand hands-free fashion. However, more research is needed to assess the functionality of the concept in other types of mimicry-based physical training. In contrast to earlier work, our aim was to broaden the scope from personal (i.e., one-to-one) balance training towards faster-paced rhythmic knee lift exercise often performed in group training situations. Clearly, the characteristics and requirements of the relatively slow-paced trunk tilt exercise performed in the earlier studies and the rhythmic knee lift exercise (e.g., marching in place) with many participants deviate from each other in many respects. For example, the precise postural mimicry of the angular magnitude of the instructor’s movement considered essential in the earlier trunk tilt studies was not recognized as a central factor in the rhythmic knee lifting task. This is because comfortable lift height range may be widely varied within the exercise group depending on the participants’ physical condition. Accurate temporal mimicry enabling rhythmic synchrony, however, is essential in this type of an exercise in ordertokeepthegroupinthesamephase.So,incontrast to the instructions given in balance training, it is more vital tocommunicatethestarttimeratherthanendpointofthe movement. Another change considered necessary for the current investigation was the replacement of the virtual avatar used in [14] by a human instructor to meet the facilities of a typical group exercise situation. Importantly, we also addressed the exercisers’ subjective experiences on how they considered touch information in the context of physical exercise. We designed a system that measured an instructor’s leg movements and, on the basis of these measurements, tactile stimulations were wirelessly routed to a leg of a participant to instruct the moments to perform leg lifts. Two versions of a wireless and wearable prototype system were designed in an iterative fashion for investigation. In Study 1, the first prototype version was tested in controlled laboratory conditions with individual adults participating in a simulated exercise situation to get basic information on the functionality of the system and to reveal main development areas. In Study 2, thesecondprototypeversionwithmodifiedconstructionand increased functionality needed in actual training situation was tested in realistic conditions with a potential target group consisting of geriatric participants taking part in a structured group exercise. In both studies the participants performed mimicry-based tasks with visual and tactile guidance and then evaluated their experiences of performing the exercise. 2. Study 1: Laboratory Experiment 2.1. Introduction. The aim of the first experiment was to evaluate how a wireless tactile guidance application functions in comparison to conventionally used visual demonstration in a knee lift exercise. Typically in such exercise an instructor shows how and when a knee should be lifted, and the exerciser’s task is to mimic the demonstration movements in the same phase with the instructor. We used prerecorded video instructions in giving the visual guidance stimuli to provide consistent and comparable test conditions. A reflection symmetry motor paradigm by Bavelas et al. [16] was used to instruct the participant to imitate the instructor’s demonstration movements shown in the video so that the participant and the instructor were facing each other and the task was to respond to the instructor’skneeliftasifwatchingone’sownimagereflected by a mirror. Tactile guidance was provided with vibration stimulation on a leg. Tactile stimulus was based on a push metaphor [11, 17]. This means that the task was to withdraw the leg Advances in Human-Computer Interaction 3 away from the stimulus located in the dorsal side of the leg above crook as though the vibration would “push” the limb to an opposite direction. The stimulus-response compatibility between push versus pull stimulation and consecutive body movements has been studied to some extent (e.g., for wrist rotation direction studied in Jansen et al. [17]), but so far established guidelines for optimal stimulus locations, for example, for a knee lift movement, seem to be nonexistent. Location, duration, vibration frequency, and amplitude of the tactile stimulation were chosen based on a pilot test where six participants evaluated vibratory stimulations in different leg locations while performing a knee lift exercise. The overall preference of the two metaphors was almost equally distributed and thus the decision was based on the slightly more affirmative stimulus amplitude ratings given to the push metaphor stimulations. There were three modality conditions to provide knee lift instructions: visual (V), tactile (T), and visual-tactile (VT) guidance. Knowing that a slight delay between the onsets of visual and tactile stimuli will inevitably be present due to an acceleration threshold-based triggering of the tactile stimulus (i.e., the instructor’s leg movement needed to exceed a certain magnitude to set on the tactile stimulus in the exerciser’s leg) as well as operating latency of the vibrotactile actuator, we focusedoncomparingthekneeliftRTbetweenthemodality conditions. RT was considered as an important measure because synchronous-enough timing between the onsets of instructor’s demonstration movement and the tactile guidance stimulus would be a prerequisite for a successful group exercise especially with visually impaired exercisers. We also investigated possible effects of tactile stimulation on the leg’s acceleration magnitude to study the movement dynamics between the different instruction modalities in more detail. In addition to the objective measures of the knee lift RT and acceleration, the participants’ subjective experiences were inquired to assess how they rated the tactile instructions in this type of activity. 2.2. Methods 2.2.1. Participants. Twelve voluntary participants (3 female and 9 male) between the ages of 19 and 48 years (M =26 and SD =9) took part in the study after signing informed consent forms. They were students or staff of the University of Tampere. All reported having normal sense of touch and normal or corrected to normal vision. Eleven of them were rightleggedandonewasleftleggedbytheirownreport.The study was approved by a local research ethics committee. 2.2.2. Stimuli. The knee lift guidance stimuli were presented in three modality conditions. In V modality condition the stimuli were provided with an exercise video (320 × 240 pixel resolution, ∼30 Hz sampling rate) where an instructor facing towards the participant produced the stimuli by demonstrating left knee lift movements (Figure 1). In VT modality condition, a 200 ms long and 285 Hz vibration stimulus in the participant’s right thigh was coupled with each knee lift event presented in the exercise video. Figure 1: A screenshot of the exercise video showing the instructor performing a demonstration movement. The current stimulus duration has been earlier used in wearable vibration systems for body movement instructions by, for example, Sienko et al. [9] and Jansen et al. [17]. The vibration frequency was within the best sensitivity range of Pacinian corpuscle mechanoreceptors around 10–500 Hz [18] and was found to be well perceived in the preexperimental pilot test. The vibration was provided in an early phase of the demonstration knee lift movement as soon as the instructor’s leg acceleration exceeded a triaxial sum vector threshold of 0.75 g calculated as √(𝑔𝑋2)+(𝑔𝑌2)+(𝑔𝑍2)(1) in a baseline-corrected data. The baseline was the mean of the first 200 samples from the beginning of the measurement while the instructor was standing still. The threshold was determined by inspecting accelerations of the demonstration movements shown in the exercise videos. The data showed that the current threshold was required to be exceeded in order to reliably detect the upward phase of each of the demonstration movements. In consequence of the acceleration threshold there was an average of 203 ms (SD = 31ms) delay between the instructor’s initial leg movement and the onset of the tactile stimulus. In T modality condition the vibration stimuli were identical to those in VT, but the visual instructions (i.e., the exercise video) were excluded. In order to reduce the predictability of stimulus onset time, interstimulus interval (ISI) was varied randomly within three durations: 3 (short), 6 (medium), and 9 (long) seconds, approximately. Three separate exercise videos (i.e., one for each modality condition) with differently arranged ISIoccurrencewereusedtoeliminatepossiblelearningeffect regarding the running order of the short, medium, and long ISI trials. 2.2.3. Apparatus. The first prototype device (Figure 2) was built on Arduino Duemilanove prototyping board that was used for processing the data from an accelerometer, controlling a vibration motor and communicating wirelessly with a PC over Bluetooth. The prototyping board, Bluetooth module, and 9 V battery used to power the device were enclosed to a box and placed into a belt bag. Precision Microdrives 4Advances in Human-Computer Interaction (a) (b) Figure 2: (a) Wearable parts of the apparatus including electronics in the enclosure box (middle), accelerometer inside the round housing (right), and vibration motor inside the tube housing (left). Scale is indicated by a coin in diameter of 20 mm. (b) The belt bag containing the enclosure box and the leg band equipped with the accelerometer and vibration motor worn by a participant. vibration motor (model 304-111) encapsulated in a plastic tube was used for stimulating a leg. The typical operating characteristics of the vibration motor included a lag time of 16 ms and a rise time of 28 ms. A 3.3 V output of the Arduino board was used together with a bipolar transistor to drive the vibration motor. The transistor was controlled over the digital output of the prototyping board. Dimension Engineering DEACCM3D triaxial accelerometer sensor encapsulated in a plastic housing measured the acceleration of a participant’s leg movement. The accelerometer featured a ±3gsenserange and 500 Hz bandwidth for 𝑥-axis, 𝑦-axis, and 𝑧-axis. An analog input of the prototyping board was used to read the output of the accelerometer. The vibration motor and the accelerometer were attached to a leg band. The PC and the prototype device communicated with the BlueSMiRF Silver module over serial port. A USB-Bluetooth adapter was used for translating the wireless communication in a sampling rate of 60 Hz. The PC was used for sending the tactile instruction stimulation and presenting the video instructions to the participant and for storing the received acceleration data from the participant’s leg using custom software programmed in Processing.org language. The software was used for receiving acceleration data over the wireless communication from the prototype device and for storing the time stamped data to a file for later analysis. The instructions were based on prerecorded acceleration measurements that were recorded with the device and stored together with the recorded exercise video in synchronization. Visual instructions were presented through a 24󸀠󸀠 Samsung SyncMaster display. 2.2.4. Procedure. After wearing the belt bag including the electronics,thelegbandwasfastenedaroundtheparticipant’s right thigh so that the accelerometer was located in the ventral sideabout10cmabovethekneecapandthevibrationmotor was in the dorsal side of the thigh (Figure 2(b)). Then a hearing protector was put on and two 200 ms long test stimuli were presented to confirm that the participant was able to feelthevibrationandunabletohearthevibrationsound. The participant was guided to about 120 cm distance from the computer display of which center point was 155 cm above the floor. Then the experimenter gave verbal instruction and a visual example of the exercise movement. The task was to lift the right knee until the thigh angle was parallel with the floor, at the maximum, and immediately after that to lay the leg down back in the starting position. The lift was instructed to be done as soon as the visual instruction on the video and/or tactile stimulus was perceived. This instruction was given once before the actual experimental trials. Running order of V, T, and VT conditions and the three exercise videos was fully counterbalanced between the participants. A similar procedure was followed in V, T, and VT conditions apart from the following attributes: (i) In V condition, the video was turned on and the vibration motor off. (ii) In T condition, the video was turned off and the vibration motor on. (iii) In VT condition, both the vibration motor and the video were turned on. After the experimenter had left the room, each condition startedwithaninitiationtrialexcludedfromtheanalysisand was followed by 21 experimental trials consisting of seven short, medium, and long ISI trials. An experimental trial started with a randomly chosen short, medium, or long ISI which was followed by V, T, or VT instruction stimulus depending on the modality condition. The participant’s task wastoimmediatelyrespondtotheinstructionstimulus byakneeliftandthenstarttowaitforanexttrial. One condition took about 2.5 minutes. After completing a condition, the experimenter returned to the testing room and the participant was allowed to have a short break. Then the experimenter announced the instruction modality of the upcoming condition. After performing all the three modality conditions the participant assessed them with rating scales. In accordance with Mehrabian and Russell [19] and Bradley and Lang [20] the scales were bipolar nine-point scales varying from −4to+4.Ratingswereaskedforthepleasantnessof the task (varying from unpleasant to pleasant), easiness of the task (varying from difficult to easy), and interest of the task (varying from boring to interesting). On each scale, 0 represented a neutral experience (e.g., neither unpleasant nor pleasant). Ratings were given using pen and paper. Advances in Human-Computer Interaction 5 Finally, the participant was asked to rate the tactile stimulation regarding its amplitude (too weak, appropriate, or too strong) and duration (too short, appropriate, or too long). In addition, the temporal uniformity of the timing of the tactile stimulations in relation to the visual instructions (too early, appropriate, or too late) presented in the VT condition was askedtovalidatethesubjectiveexperienceofthelagcaused by the technical implementation of the tactile stimulus. 2.2.5. Data Analysis. RTs and peak accelerations of the knee lifts were analyzed with a one-way repeated measures analysis of variance (ANOVA) with modality condition as a withinsubjects factor. If the sphericity assumption of the data was violated, Greenhouse-Geisser corrected degrees of freedom were used to validate 𝐹statistic. Bonferroni corrected pairwise 𝑡-tests were used for post hoc tests. RTs were measured from the moment when the instructor’s demonstration knee lift exceeded the 0.75 g acceleration threshold to the moment when the participant’s knee lift movement reached its peak acceleration. Peak acceleration sum vector was defined as the highest value during an upward phase of the participant’s knee lift event using a similar baseline definition and formula as in determining the threshold for stimulus onset in the exercise video. A total of 33% of the RT and acceleration data (i.e., 4, 5, and 3 participants in V, T, and VT conditions, resp.) was excluded due to technical reasons causing noisy acceleration signal and replaced by a condition specific series means in the analyses. Prior to the imputation, the normality of the obtained RT and peak acceleration data was confirmed using Shapiro-Wilk test of normality. The tests suggested that the assumption of normal distribution was met in the V, T, and VT conditions regarding RT (S-W = 0.95, df = 8, and 𝑝 = 0.67;S-W=0.95,df=7,and𝑝 = 0.76;S-W=0.97,df=9, and 𝑝 = 0.91,resp.)andpeakaccelerationdata(S-W=0.90, df = 8, and 𝑝 = 0.28;S-W=0.95,df=7,and𝑝 = 0.72;S-W= 0.87, df = 9, and 𝑝 = 0.13,resp.). Ratings of pleasantness, easiness, and interest were analyzed with three separate Friedman tests. If the Friedman test showed a significant effect, Wilcoxon Signed-Rank tests were used for pairwise comparisons. 2.3. Results. Means and standard error of the means (SEMs) fortheRTsandpeakaccelerationsofkneeliftsarepresented in Figure 3. Nobody missed any knee lift stimuli in the V, T, and VT conditions. 2.3.1. Reaction Times. A one-way repeated measures analysis of variance (ANOVA) showed a statistically significant effect of modality: 𝐹(1.27,14.00) = 15.66;𝑝 ≤ 0.001.Posthoc pairwise comparisons between the modalities showed that the RTs were significantly faster in V and VT conditions as compared to T condition: MD = 158 ms and 𝑝 < 0.05 and MD = 183ms and 𝑝 < 0.001, respectively. RT difference between V and VT conditions was statistically nonsignificant. 2.3.2. Peak Accelerations. Aone-wayANOVAshoweda statistically significant effect of modality: 𝐹(2,22) = 5.91;𝑝< 0.01. Post hoc pairwise comparisons between the modalities VTVT Instruction modality Reaction time Peak acceleration 0 200 400 600 800 Time (ms) 0 1 2 3 4 Acceleration (g) Figure 3: Mean RTs and mean peak accelerations of knee lifts in visual (V), tactile (T), and visual-tactile (VT) modality conditions. Error bars represent SEMs. Pleasantness Easiness Interest V T VT −4 −3 −2 −1 0 1 2 3 4 Mean rating Figure 4: Mean ratings for pleasantness, easiness, and interest of the knee lift tasks in visual (V), tactile (T), and visual-tactile (VT) modality conditions. Error bars represent SEMs. showed that the peak leg accelerations were significantly greater in VT condition when compared to T condition: MD =0.25gand𝑝 ≤ 0.05. Other pairwise comparisons were statistically nonsignificant. 2.3.3. Subjective Ratings. Means and SEMs of the subjective ratings are shown in Figure 4. Friedman test showed a statistically significant effect for the ratings of interest: 𝜒2= 9.66;𝑝 < 0.01. For the ratings of pleasantness and easiness, the Friedman test revealed no statistically significant effects. Wilcoxon Signed-Rank tests showed that the task was considered in T and VT conditions as significantly more interesting than in V condition: 𝑍 = −2.51and 𝑝 < 0.05and 𝑍 = −2.45 and 𝑝 < 0.05, respectively. Difference between T and VT conditions was not statistically significant. Vibration amplitude was considered as appropriate by each of the twelve participants. No one reported the vibration being too weak or too strong. Vibration duration was assessed as appropriate by eleven participants, while one considered 6Advances in Human-Computer Interaction that the vibration was too long. Nobody considered the vibration too short. In VT condition the vibration timing (i.e., synchrony) with respect to the knee lift shown in the instruction video was agreed as appropriate by five participants and the remainder considered that the vibration cametoolate.Nobodythoughtthatthevibrationwastoo early with respect to the video. 2.4. Discussion. The results of Study 1 showed that tactile instruction channel was functional in a knee lift exercise both alone (i.e., T condition) and when combined with visual instructions (i.e., VT condition). It seems that the parameters (i.e., duration, vibration frequency, amplitude, and location) of the tactile stimulus were applicable because nobody missed any tactile stimuli. In addition, the findings in the subjective ratings and postexperimental interviews showed favorable assessments of tactile instructions. In the interviews stimulus amplitude and duration were considered as appropriate almost unanimously. The temporal synchrony of the visual and tactile instruction in VT condition, however, polarized the opinions, as more than half of the participants thought that the vibration came too late with respect to knee lift shown in the video. The experienced asynchrony was likely due to the relatively robust acceleration threshold causing the 203 ms delay and the 16 ms onset latency of the vibration actuator, which together resulted in a minimum of about 220 ms delay from the instructor’s initial leg movement to the onset of the tactilestimulusintheparticipant’sleg.Inconsequence,the instructor’s leg movement was already visible in the video when the tactile stimulus started. The delay can also explain why the mean RT (i.e., time to reach the peak leg acceleration) in T condition was 158.2 and 182.5 ms slower as compared to V and VT conditions, respectively. If the tactile stimulus onset had been created in exact synchrony with the instructor’s initial leg movement, the RTs in T and VT conditions could, in fact, have been about 40– 60 ms faster than those in V condition. This conclusion is based on subtraction of the lag caused by the technical implementation from the mean RT of T condition and supported by earlier findings showing about 30–40 ms shorter RTs to tactile than visual stimuli (e.g., [3, 5, 21]). Following this, tactile instructions would seem to have the potential to enable even faster knee lift reactions than conventionally used visual instruction provided that the onset of the tactile stimulus couldbereliablysituatedtotheinitialphaseoftheinstructor’s leg movement. However, the aim of the present study was to assess the functionality of tactile instruction system in a realistic exercise situation, where a robust-enough onset method would be required to prevent the instructor from giving false-positive instruction stimuli resulting, for example, from minor or unintentional leg movements between the repetitions. Thus, lowering the acceleration threshold to diminish the onset delay would require further studies to find an acceptable trade-off between the speed and accuracy of providing the tactile instructions. Instructionmodalityalsohadaneffecttotheacceleration magnitude of the leg movements. VT instruction resulted in significantly higher peak acceleration than T instruction. Despite the fact that the mean peak acceleration was the highest in V condition and the lowest in T condition, the difference did not reach statistical significance. As it can be seen in the SEM error bars of Figure 3, this was due to the larger deviation of acceleration magnitude in V condition compared to those found in T and VT conditions. This result may indicate that tactile stimulation stabilized the acceleration of leg movement and enabled more consistent repetitions. Ratings of the pleasantness, easiness, and interest of the exercise task were clearly positive in each modality condition which indicates that tactile instruction channel was well accepted in the current context along with conventionally used visual instructions both unimodally and when combinedwithvisualinstructionmodality.Thiswasdespitethe factthattheparticipantswerefullycapableoffollowingvisual instructions and, therefore, did not necessarily need tactile instructions in this type of activity. Moreover, tactile stimulation provided in T and VT conditions increased significantly the participants’ interest of the task when compared to V condition. This finding suggests that such a device may be of interest to exercisers also in real training situations, which in turn would be important in the light of earlier studies showing that interest towards the training is a central factor in increasing the motivation and exercise adherence (e.g., [22]). 3. Study 2: User Experience and Acceptance of a Vibrotactile Exercise Device among Elderly Participants 3.1. Introduction. In a follow-up user study, the wearable tactile device used in Study 1 was iterated further and redesignedtobeusedinagroupexercisesituationwith elderly participants. This approach was chosen based on a recent trend that has been shifting increasingly from oneto-one personal training to group exercise and training programs [23]. Supervised group exercise is often favored in public and institutional healthcare, because it is clearly more time-effective and cost-effective in comparison to personal training and it has been found to be beneficial in promoting not only physical fitness [24] but also social and mental wellbeing and overall quality of life [25]. Anewversionofthedeviceallowedaninstructorto activate an exerciser’s legs with tactile stimulation automatically and in real time (i.e., in conjunction with the instructor’s demonstration movements) via a wireless link. The main goal of this user study was to evaluate acceptance and user experience (UX) of the tactile exercise device in a context of recreational group exercise among a potential targetpopulation.Theapproachhadthreemainresearch questions: (1) How do elderly participants experience the use of a tactiledeviceinagroupexercisecontext? (2) How does it differ from conventional session without tactile instructions? Advances in Human-Computer Interaction 7 (a) (b) Figure 5: (a) Wearable parts of the exercise device and (b) their attachment locations. (3) Do the elderly participants accept the use of tactile stimulation in a group exercise context? The user study consisted of exercise sessions both with and without the device, UX questionnaires, and interviews inquiring the exercisers’ as well as the instructors’ impressions, experience, and acceptance of using the device. 3.2. Methods 3.2.1. Participants. Participants and premises for the study were provided by a service center for elderly people. The targeted user group consisted of relatively healthy elderly volunteers without any major cognitive disabilities to ensure that they were fully able to answer questionnaires and take part in an interview. They were also required to be able to take part in the physical exercise tasks, including knee lifting used in Study 1. Two male and six female exercisers and two female instructors took part in the study after signing informed consent forms. The exercisers were between the ages of 73 and 92 years (M =83and SD =7). The instructors were 27 and 39 years old. One of the instructors had a formal education in physical therapy. The study consisted of two within-subjects exercise groups, each with one instructor and four exercisers. The study was approved by the local research ethics committee. 3.2.2. Apparatus. The tactile device consisted of two elastic leg bands and a belt bag (Figure 5). Both the leg bands included a tactile actuator and accelerometer, while the belt bag contained an Arduino board and a 9 V battery. The components in the leg bands were connected to the board via flat cables. The study was done with two identical devices. Onedevicewornbyaninstructorfunctionedina“master” mode and the other worn by an exerciser was set in a “slave” mode. The devices communicated via Bluetooth with a PC acting as host and routing the communication between the devices. A more detailed description of the system’s operation principle is given in [26]. The major change from the users’ view point was the fact that, contrary to the device used in Study 1, leg bands were attached to both limbs. In addition, the vibration actuator type was replaced with Solarbotics VPM2 Vibrating Disk Motor due to its closed structure. There was a mechanical delay of 60 ms, on average, measured fromtheonsetoftheappliedvoltage(3V)tothebeginning of the actuation from the motor using a GW Instek GDS2104A oscilloscope. The accelerometers were relocated above the actuators in the dorsal side of the legs. Together these revisions enabled a more compact design of the leg bands. 3.2.3. User Experience Questionnaire. The UX questionnaire was used for studying the research questions 1 and 2. The questionnaire had two variants: one for evaluating the exercise experience while wearing the device and another without it. They had nearly identical scales and distinctive instructions on what to evaluate. The questionnaires were based on UX model by Hassenzahl [27]. The semantic differentials were selected from two different questionnaires: AttrakDiff 2 [28] and Attrak-Work [29]. AttrakDiff 2 questionnaire consists of seven-point semantic differential scales, which are divided into pragmatic qualities (PQ), hedonic qualities of stimulation (HQS) and identification (HQI), and attractiveness (ATT). The Attrak-Work adds a task and goal achievement (TGW) quality, which is essential in work-related contexts. The pragmatic scales are close to the traditional definition of usability (usefulness, utility, and usability). If a product is stimulating, it provides possibilities to gain new knowledge and self-development, while identification can be explained as social self-expression through physical objects and possessions. Three device-centric scales were omitted from the questionnaire without the device: impractical, practical; makes exercise harder, makes exercise easier; and slows down the exercise, speeds up the exercise. A few scales were selected for each of the five themes to keep the questionnaire length on one page. Moreover, some scales hadtobeleftoutastheywerepresumedtobeinapplicable to this study due to the context and nature of the device. The selected scales for each quality are presented in Table 1. 3.2.4. Interview. The group interviews concentrated on qualitative information on the participants’ general impressions of tactile instructions and the device. The interviews were semistructured and started with free-form description of the participants’ impressions of the user experience. This was followed by a discussion about the exercise with and without 8Advances in Human-Computer Interaction Table 1: Qualities and scales used in the UX questionnaires. Quality Scale ID Pragmatic Complex, simple PQ 2 Impractical, practical PQ 3 Challenging, effortless PQ 4 Confusing, clear PQ 6 Hedonic: stimulation Conventional, original HQS 1 Unimaginative, creative HQS 2 Dull, absorbing HQS 5 Hedonic: identification Unprofessional, professional HQI 2 Poor quality, high quality HQI 4 Noninclusive-Inclusive HQI 5 Separates me from people, brings me closer to people HQI 6 Attractiveness Unpleasant, pleasant ATT 1 Unattractive, attractive ATT 3 Bad, good ATT 5 Discouraging, motivating ATT 7 Task and goal achievement Makes exercise harder, makes exercise easier TGW 1 Slows down the exercise, speeds up the exercise TGW 4 Difficulttocontrol,easytocontrol TGW 7 the device, acceptance, and other ideas for the device and applications both the exercisers and instructors might have. 3.2.5. Procedure. The exercisers’ task was to follow and repeat theexerciseguidedbytheinstructor.Theexerciseconsisted of moving legs in seated and standing positions, including various leg lifting tasks, stationary marching, and dancing. The whole exercise was done with background music. The sessions were designed and carried out by the instructors as normally as possible but with emphasizing on legs and lower part of the body. The exercise sessions began with an introductiontothepurposeoftheuserstudyandabrief explanation of the device. The exercisers were told that the instructor’s device sent tactile instructions to the exerciser’s device as an additional signal to start performing the exercise movements. Tactile stimuli were produced concurrently in both the instructor’s device and the exerciser’s device, thus enabling the instructor to confirm a successful sending of a tactile instruction. Due to the limited amount of devices, the exerciser’s device was rotated between the four exercisers in the group. Every 15 minutes the exercise was paused to switch the device to a next exerciser. As a result, each exerciser got to wear and exercise with the device for about 15 minutes duringthe1-hoursession.Theinstructorworetheother device for the whole exercise session. Halfway through the session, the exercisers filled the UX questionnaires evaluating the subjective experience of exercising in the group. The first two exercisers to try the tactile device filled the questionnaire “exercise with the device,” and the other two filled the questionnaire “exercise without the device.” This was repeated at theendofthesessionbutthistimeviceversa.Attheend, each exerciser in the group evaluated the exercise with and without wearing the device. The instructors in both groups evaluated the user experience of exercising with the device after the session. Following the session, the group (including the instructor) took part in 30-minute-long interview. 3.3. Results 3.3.1. User Experience Questionnaire. The exercisers’ ratings given to the UX questionnaire (Figure 6(a)) showed that the exercise both without and with the device was experienced mainly in a positive way. They evaluated the exercise with the device to be more motivating than that without the device (ATT 7), but otherwise the SEM ranges of the ratings were overlapping between the two exercise situations indicating potentially nonsignificant differences. Ratings of the three items reflecting the device use situation only were also positive; the exercisers considered that the device was more practical than impractical (PQ 3), made the exercise somewhat easier (TGW 1), and speeded up the exercise (TGW 4). Interestingly, the instructors’ ratings of the device in Figure 6(b) were mainly outside the SEM range of those given by the exercisers shown in Figure 6(a). One or both of the instructors rated the device more positively than the exercisers regarding 8 items (i.e., PQ 2, PQ 6, HQS 1, HQS 2, HQI 2, HQI 5, HQI 6, and ATT 7) and more negatively regarding 10 items (i.e., PQ 3, PQ 4, HQI 4, ATT 1, ATT 3, ATT 5, ATT 7, TGW 1, TGW 4, and TGW 7). Consensus was found only for item HQS 5; the exercise with the device was found equally absorbing by the exercisers and the two instructors. However, no statistical analysis was performed for the questionnaire data due to low number of the participants. 3.3.2. Interview: Exercise Experience with and without the Device. Exercisers’ expectations of the exercise with the device were summarized into three groups: (1) no expectations, (2) slightly nervous or afraid, and (3) interested. Majority of the exercisers were slightly nervous or afraid of trying a device they did not have any experience with. However, after the exercisers tried the device, many of the expectations were changed in a positive way as exemplified by following quotations: “I was nervous about this thing we were supposed to wear. Then I saw how simple it was and the fear vanished,” an exerciser said. “At first I was nervous and surprised. I didn’t expect it to be this easy,” an exerciser said. On the other hand, one exerciser commented that his/her expectations did not change, and another one had expected much stronger stimulation. First impressions of exercise with the tactile device, for both the exercisers and instructors, were positive and even surprising. These consisted of positive and neutral descriptions, such as nice, pleasant, easy, fun, ordinary, different (i.e., Advances in Human-Computer Interaction 9 Simple Practical Effortless Clear Original Creative Absorbing Professional High quality Inclusive Brings me closer to people Pleasant Attractive Good Motivating Makes exercise easier Speeds up exercise Easy to control [PQ_2] Complex [PQ_4] Challenging [PQ_6] Confusing [HQS_1] Conventional [HQS_2] Unimaginative [HQS_5] Dull [HQI_2] Unprofessional [HQI_4] Poor quality [HQI_5] Noninclusive [HQI_6] Separates me from people [ATT_1] Unpleasant [ATT_3] Unattractive [ATT_5] Bad [ATT_7] Discouraging [TGW_7] Difficult to control ∗)[PQ_3] Impractical ∗)[TGW_1] Makes exercise harder ∗)[TGW_4] Slows down exercise Exercisers without device Exercisers with device −2 −1 0123 −3 Mean rating (a) Simple Practical Effortless Clear Original Creative Absorbing Professional High quality Inclusive Brings me closer to people Pleasant Attractive Good Motivating Makes exercise easier Speeds up exercise Easy to control Complex Impractical Challenging Confusing Conventional Dull Unimaginative Unprofessional Poor quality Noninclusive Separates me from people Unpleasant Unattractive Bad Discouraging Makes exercise harder Slows down exercise Difficult to control Instructor 1 with device Instructor 2 with device 1023 −2 −1−3 Mean rating (b) Figure 6: Mean ratings for the UX questionnaires on 7-point semantic differential scale given by (a) the exercisers and (b) the instructors. Items labeled with ∗)in (a) were excluded from the “exercise without the device” questionnaire. Error bars in (a) represent SEMs. something new), and effortless. The emphasis on the easiness was frequent in the comments. Once the device was put on, the exercisers did not need to concentrate on operating the device. The majority of the exercisers also quickly understood the purpose of the device with a very short introduction. Two of the exercisers needed further instructions. One exerciser had major difficulties in recognizing the tactile stimulation and another was so concentrating on following the tactile instructions that she forgot to pay attention to the actual exercise. The tactile stimuli and the form-factor of the wearable device were comfortable and pleasant according to the exercisers. However, one of the instructors said that wearing the device for an hour became uncomfortable because of the frequent tactile stimulation.