BikeFlow: Environmental Augmentation through the Projection of Optical Flow

Juan Pablo Gomez Arrunategui Department of Mechanical Engineering

University of British Columbia Vancouver, BC, Canada, V6T 1Z4 j.gomezarrunategui@alumni.ubc.ca

Abstract—This project studies the effect of optic flow on the cycling activity. The enhanced illusion of optical flow was generated by a laser system that projected intermittent lines on either side of the front wheel. The frequency of the laser rotation was varied to obtain differences in the optic flow pattern and measure its effect on pacing, heart rate and real perceived exertion (RPE). The emotional experience generated by the system was also assessed. The results showed no significant differences in pacing, heart rate or RPE in any of the trials.

Categories and Subject Descriptors Interactive Device – Pacing, RPE, Heart Rate General Terms Design, Cycling Keywords Bicycle, environmental augmentation, optical flow

I. INTRODUCTION The human body has the ability to utilize external and internal cues to generate an awareness of its surroundings. External cues are picked up by the sensory system, predominantly in the form of visual, auditory or tactile feedback. Internal cues refer to changes in the physiological system, such as the cardiovascular system and muscle activation patterns that provide the brain with information on the body’s response to the environment. Study of physiological response to physical activity represents a way of analyzing the predominant factors in the regulation of the human body. Recent studies have shown that the body can accurately analyze and extrapolate the information received by

the peripheral nervous system (external cues) and central nervous system (internal cues) to regulate its activity level over long periods of time. For instance, self-regulation allows for appropriate control of fuel reserves and exertion levels during intense activity in what has commonly been called “teleoanticipation”. Teleoanticipation dictates the pacing strategies of athletes based on information on distance, time and environmental conditions. Studies by Albertus et al. have supported the idea of teleoanticipation by demonstrating that inaccurate distance cues have no effect on a runners pacing strategy, which is set beforehand. Likewise, studies by Ainsley et al (2004) corroborated this finding by evaluating performance during short-lived peak exertion trials. The results showed that individuals maintained constant performance for trials in which the duration was known, but saw a decrease in performance for trials in which the duration was unexpectedly extended, even if the two trials lasted the same amount of time. Therefore, participants correctly regulated performance based on prior knowledge of duration (they paced themselves) but failed to maintain it upon distortions in the duration of the activity. Moreover, while pacing is predetermined by the expected intensity in physical activity, rated perceived exertion (RPE) has been shown to vary more wildly depending on environmental cues. Baden et al. (2005) showed that RPE is not perfectly correlated to the level of physical exertion. Baden’s study asked individuals to run on a treadmill for three different time periods: 10 minutes, 20 minutes and an undisclosed amount of time (also 20 minutes). Upon completion of the 10-minute trial, participants were asked to continue for 10 more minutes. Subjects in the 10-minute trial saw a sudden increase in RPE between the 10-11-minute mark as a result of the increased duration of the trial but showed no changes in pacing strategy or heart rate. This highlights that RPE is dependent on both cognitive and affective physiological factors. The aforementioned studies triggered changes in performance, pacing and RPE by giving participants inaccurate information about the expected duration of activity. However, it should also be possible to trick the regulatory centers of the body in their estimation of pace, performance and RPE by distorting the

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perception of external cues. Creating optic flow is one such way to achieve this goal. Optic flow refers to the apparent motion of an individual with respect to the objects around them. It has a strong influence on the idea of self-motion, orientation and visuospatial cognition []. As such, optic flow plays a major role in the perception of the outside world. Optic flow can be generated by creating patterns in the visual field that convey motion. For instance, Ferrari et al. generated optic flow in Parkinson’s patients by placing LED lights on glasses and activating them at distinct time intervals to generate a waveform pattern on the user’s peripheral field of view. The purpose of this study is to evaluate the effect of optic flow augmentation in a cyclist’s ability to control pace and rate of perceived exertion. In order to achieve this, the FlowBike was fitted with a laser projection system capable of changing the speed of rotating light patterns during cycling. Participants were asked to perform a series of self paced cycling trials with variation in the flow patterns. Heart rate, pace and RPE were measured at the end of the trials and a questionnaire evaluated the qualitative effects of the system on the cycling activity. Some elements of this study, such as the idea that optic flow can generate changes in pace and RPE during cycling have already been studied in laboratory settings [13]. However, optic flow augmentation has never been studied in activities with high intensity levels and in completely unconstrained settings. This represents the major contribution of the present study.

II. BACKGROUND RESEARCH

A. Optic Flow as a way to increase cadence The effect of optical flow on motor activity has been

extensively studied over the past decade in an effort to improve mobility of Parkinson’s patients [4,9,10,19]. Parkinson’s disease is a neurodegenerative disorder that affects the patient’s ability to walk, leading to reduced cadence, shorter steps and episodes of “freezing”; where the patient is unable to start a motor action [15]. These symptoms are due to reduced sensorimotor integration and difficulty in switching between sensory modalities [5]. However, it has been previously reported that gait difficulties can be partially corrected by providing visual cues that facilitate the placement of each step. These cues can be given in the form of floor markings, colored tiles [4,14] or projection systems with lasers indicating the desired step location [13]. The use of external cues has been theorized to overcome the motor deficit by activating a more conscious brain response to the act of walking, therefore changing the automatic neural response of the basal ganglia for alternate neural pathways [12]. More recently, researchers have also investigated the effect of optical flow on locomotion of Parkinson’s patients [4,9,10,19]. Studies have theorized that optical flow activates visuo-motor pathways that bypass the functions of the basal ganglia, allowing Parkinson’s patients to improve gait [11,22].

The ability of optical flow to supersede the functions of the basal ganglia in semi-automatic activities (such as biking) is of particular importance to this study. According to Prokop et al. [18], optic flow is helpful in integrating visual and leg proprioceptive information and is therefore important in modulating walking velocity in healthy subjects. Indeed, studies by Ferrari et al. [9] demonstrate that optic flow sequences in healthy subjects results in a minor increase in gait velocities due to increases in gait cadence and stride length. Ferrari’s study sequentially activates LED lights placed in glasses to generate wave patterns that give an augmented optic flow illusion.

B. Image Projection in Cycling The field of image projection has been previously applied

to increase the safety of cyclers. Two separate studies have projected laser images to alert car drivers of the presence of bikers [7,8] In the first case, the projection consisted of a bicycle incased in a triangle and simply warned other transit users of the biker’s presence [7]. In the second case, red lasers were projected on the side of the cyclist to create “biking lanes” that gave car drivers information on the required separation between the vehicle and the bicycle [8]. A third research team projected a square grid in front of the biker to alert of any possible irregularities in the terrain. Potholes and topographical accidents would distort the grid, alerting the biker of their existence [18].

III. RELATED WORK There have been a number of studies on the effect of optical flow in physical activity. Parry et al. investigated the effect of optical flow on the distance perception, pacing and the rated perceived exertion (RPE) of both cyclists and runners [13,14]. Their experiments were performed in a laboratory setting, where participants were first asked to perform a self-paced trial to obtain a baseline measurement. In further trials, participants were shown video footage of a track at 3 different speeds. The first video was sped up by 15%, the second video was representative of their actual speed, and the third video was 15% slower. The results show that optical flow distorts the perceived distance and the RPE but has no effect on the pacing strategy. While relevant, the studies by Parry et al. are performed in a very constrained setting. The present study differentiates itself by generating an optical flow pattern in an unconstrained environment. Participants experience an augmented reality, rather than an immersion in a completely virtual system. This differentiation is valuable, because it positions the participants of this study in a more realistic setting.

IV. PROTOTYPE DESIGN The design of the system allowed for easy mounting on any bicycle, facilitating tests and user interaction. The final prototype is illustrated in Figure 1.

Figure 1 - Bicycle with System The optical flow is generated by projecting “moving lines” on either side of a bicycle. The lines are generated by rotating lasers, which provide a homogenous beam of light that can be focused over large distances in most lighting conditions. The lasers are placed on the handles of the bike and are rotated simultaneously by an axle connected to a motor gearbox. The lasers are housed in a casing with slits on the lower half (facing the ground) and rotated at different speeds, depending on the testing conditions. The only sensor in the bicycle is composed of a reed switch located on the front wheel. The reed switch is implemented as a tachometer, which measures the duration of a complete rotation of the wheel. This measurement is converted into speed and relayed to the microcontroller. The microcontroller (Arduino UNO) then varies the speed of the motor through pulse width modulation (PWM). Finally, the information on the bike trials is recorded with a smartphone app known as Strava. The app records the time of the trial, the distance and elevation change. With this data it is possible to obtain the speed during every segment of the trial, the variability in speed and the average pace of the user. The heart rate of the user is measured with a Myo band placed on the wrist of the user. A flow diagram of the system is presented below:

Figure 2 - Control System The sensor and actuator implementation is as follows:

• A reed switch is mounted on the front wheel bicycle fork. A magnet is mounted on the spokes of the front wheel, so that is passes next to the reed switch every time the well turns. The magnet has an associated magnetic field that closes the circuit in the reed switch after each turn, allowing for calculations of speed and distance during the ride.

• The Arduino is used as the microcontroller. It measures the speed of the bike and controls the servo motors accordingly.

• The microcontroller, and batteries are placed in a bag near the handles of the bicycle.

• The lasers are mounted on a gearbox and are controlled by a servo motor connected to the handlebar. The lasers rotate simultaneously and project a laser light in the lower plane of their rotation. In this manner, the lasers do not present a hazard to individuals in the surroundings.

• The smartphone is mounted in the middle of the bicycle handles. It is used to measure, record and track the user’s progress. It measures the speed of the bicycle, distance travelled, and acceleration when the bicycle is in motion.

• The Myo band measures the heart rate during the trials Figure 3 the location of the different components of the bike.

Figure 3 - Location of bicycle components

V. EXPERIMENTAL DESIGN A. Introduction The study tested two hypotheses:

• H1: By rotating lasers in the BikeFlow at a predetermined speed, we are capable of generating the perception of travelling at faster speeds (create the perception of optical flow). This augmented perception of optical flow will generate changes in the pacing strategy and RPE of the user

o H1 with laser rotation at 2rev/second o H1 with laser rotation at 2.5rev/second

• H2: By adjusting the speed of rotation of the lasers to

respond users own speed, we are capable of creating a feedback loop, that distorts the effect of optic flow on pacing, heart rate and RPE.

In this test the lasers create an optical flow opposing the speed of the user. As such, if the user speeds up, the rotating system will slow down, trying to reduce the pace of the user. Conversely if the user slows down, the rotating system will speed up to increase the speed of the user. We hypothesize that this feedback loop will to reduce the variability in the velocity observed throughout the trial.

B. Participants Six people (N=6) participated in the study. There were 4 males and 2 females with a mean age of 23 (range 21 to 25 years old). Of the four participants, one declared to ride bicycles often (once a week), two declared to ride bicycles sporadically (once a month), and three declared to rarely ride bicycles (once a year), All participants signed a consent form at the start of the study. The objectives of the study were not disclosed until the end.

C. Design Tests were performed at night time (after 8pm) to make the lasers more visible and enhance the optical flow generated by the rotating lights. Mt. Pleasant Park served as the location for all of the tests. The park has a well-maintained asphalt track and has little elevation changes. Furthermore, the track has a length of approximately 800m, which represented an ideal length for the tests. Upon arrival, participants were introduced to the FlowBike. The laser-projection system was activated to allow the users to familiarize themselves with the bike. Once they felt comfortable, participants were given a tour of Mt. Pleasant Park. The tour was designed to give participants an idea of the conditions of the track and the distance that needed to be completed. Participants were then given a Myo band to monitor their heart rate. A smartphone was also connected to the handle bars to measure distance, time and speed during the experiment.

The experimental procedure required the participants to complete four trials, wherein a trial corresponded to one lap around Mt. Pleasant Park. The four different trials were as follows:

1. No visual feedback (lasers off) 2. Continuous visual feedback stage 1: Lasers rotated at

2 rev/sec. 3. Continuous visual feedback stage 2: Lasers rotated at

2.5rev/sec. 4. Varying visual feedback (laser rotation dependent on

the speed of the user). The four different trials were necessary to properly quantify the effect of augmented optical stimuli on cyclists. The first trial asked the participants to establish a self-determined paced that they would follow thereafter for all the other trials. This trial lacked visual feedback and established a baseline behavior for each of the participants. As such, it acted as a control test against which the other two tests could be compared. The second test evaluated the effect (if any) of the laser system on the pacing, heart rate and RPE of the user. The third test also evaluated the effect of a higher rotating speed (higher optical flow) system on the pacing, heart rate and RPE of the user (if any). The fourth test varied the speed of the laser system to oppose the user’s speed. This test offered the possibility of evaluating whether sudden variations in the optical flow stimuli affected the immediate behavior of the user and maintained a more constant pace throughout the trial. All participants were tracked during their cycling runs with the Strava app. Their cycling data was logged and recorded for each of the trials. Their cycling runs were analyzed to measure the change in heart rate over time. RPE and the overall qualitative impression the system had on the participants were evaluated at the end of the trials with a questionnaire.

D. Experimental Outcome Primary Outcome: To test the user’s quantitative reaction to the projection of an optical illusion while biking. This will be measured by comparing the following parameters among the different trials:

• The bikers pace (measured as speed) • The bikers heart rate

To understand the user’s perceived exertion reaction to the projection of the optical illusion while cycling. This will be measured by assessing the RPE score at the end of each trial. Secondary Outcome: To understand the credibility of the optical illusion on the biker and assess the emotional response of the participant to the BikeFlow system. This will be tested with the following interview questions:

a. Did you observe the laser projections during cycling? b. Did you feel that you rode faster in any of the trials?

If so, which one?

c. Did the you notice any difference in the behavior of the lights between the different trials?

d. Overall, how would you rate your experience with the laser projection system?

VI. EVALUATION OF THE SPEED OF OPTICAL FLOW ON CYCLISTS

A. Hypothesis (H1) The rotating lasers are hypothesized to convey an illusion of optical flow. The faster the rotation of the lasers, the faster the optical flow. Faster optical flows will increase the RPE of the user.

B. Evaluation Measures The effect of optical flow on the cycling activity will be analyzed through changes in the:

• Average cycling speed • Average change in heart rate (at end of trial – at start

of trial) • Average RPE scores

C. Results

Figure 4 - Average Speed (km/hr)

Figure 5 - Average Change in Heart Rate

Figure 6 - Average RPE Scores

D. Discussion A single variance ANOVA was run for of the three measured variables (speed, heart rate and RPE) with a significance level of p<0.05. The ANOVA test for the the average speed showed that there were no statistically significant differences between the three trials. In fact, the p-value was of merely 0.85. Similar results were found for the average change in heart rate (p=0.83) and for the RPE score (p=0.37). Therefore, all of the studied variables failed to provide statistically significant differences in participant behavior as a function of optical flow. Upon further examination of the results, it is possible to conclude that the power of the experiment was very low for a statistically significant finding to occur. The RPE values, for instance show a trend of increasing RPE values with increasing optical flow. However, the differences are sufficiently small and the number of participants so limited, that they do not have any statistical significance.

VII. EVALUATION OF THE VARIABLE OPTICAL FLOW ON CYCLISTS

A. Hypothesis (H2) The speed of rotation of the lasers will oppose changes in the velocity of the user, reducing the variability in speed during the trial.

B. Evaluation Measures The effect of changing the speed of rotation of the lasers will be evaluated by comparing variation in speeds in the fourth trials (variable laser speed) to the previous 3 trials. This will be done with a Brown-Forsythe test.

C. Results

F P-value F crit

0.05 0.82 4.00 Table 1 - Brown Forsythe Test Results

15.57 15.04 14.96

10

12

14

16

18

No Lasers Lasers at 2rev/sec

Lasers at 2.5rev/sec

Ave

rgae

Spe

ed (k

m/h

our)

Type of Trial

Average Speed (km/hour)

60.3365.83 64.50

40455055606570

No Lasers Lasers at 2rev/sec

Lasers at 2.5rev/sec

Cha

nge

in H

eart

Rat

e(bp

m)

Type of Trial

Average Change in Heart Rate

3.50 3.83 4.00

1

2

3

4

5

No Lasers Lasers at 2rev/sec Lasers at 2.5rev/sec

RPE

Sco

re

Type of Trial

Average RPE Scores

D. Discussion The Brown Forsythe test is utilized to test whether there is any statistically significant variability in the pace among the different trials. The fourth trial hypothesized that the generation of negative feedback would reduce the variability in the speed with respect to the other trials. However, the table shows that the variability among all of the tests is similar, as evidenced by the high P-value =0.82. A cruder measure of variability could be the maximum speed reached in the trials. However, this measure would also fail, given that the differences in maximum speed among the trials where also insignificant.

VIII. DISCUSSION OF INTERVIEW QUESTIONS

Four of the participants (n=4) mentioned that they frequently observed the lasers during riding. Instead, the other two participants (n=2) mentioned that they observed the lasers sporadically and preferred to concentrate on the surroundings instead. Both of these participants mentioned that they did not feel entirely comfortable looking at the lasers for extended periods of time as they felt it would distract them and cause a potential collision with a surrounding object. In terms of the effect of riding on the different trials, two of the participants (n=2) mentioned that they felt they rode faster during the laser trails, but were unable to differentiate changes in pace between any of the laser trials. Three of the participants (n= 3) felt there was no change in pace in any of the trials. Finally, one participant (n=1) mentioned that they felt faster during the trial without lasers. The interviews therefore provided little coherence in the perception of pace with the different conditions. None of the participants noticed changes in the laser’s speed among the different trials. This suggests that the changes in rotating speed are not particularly noticeable. The participants expressed surprise when the the trials were further explained as they had not expected the speeds of laser rotation to be different. One participant mentioned that the sound of the gearbox had felt different but that he had not paid too much attention to it. It is important to note that the gearbox produces a loud noise when rotating the lasers. This is an unwanted effect of the design but it was left unchanged because it did not appear to affect the experimental procedure. Finally, the question on the emotional experience with the BikeFlow system presented mixed results. Three of the participants (n=3) had positive comments about the device. One participant in particular mentioned how it made them feel like they had someone accompanying them during the ride. Two of the participants (n=2) had a neutral response to the system. They mentioned how they would not use it again because it had not created any particular. These two participants were among those who felt no differences in pacing among any of the trials. The final participant (n=1) presented largely negative views on the bike. This participant felt that the laser system called too

much attention upon himself, even when the park was largely empty during the trial.

IX. CONCLUSION To conclude, the study was unable to show any statistically significant differences in the pacing, heart rate or RPE of cyclists in any of the trials. The results hint at a possible correlation between higher optical flow and an increase in rated perceived exertion, but the number of participants is too small for this to be significant. Overall, the results are consistent with previous findings in literature. Parry et al, studied optical flow patterns in a laboratory setting and also found no statistically significant correlation between pacing and optical flow. They did find, however that slower optical flow resulted in a decrease of RPE, which appears to agree with our own findings. The interview questions showed that there were mixed reviews on the BikeFlow system. Some participants claimed to have felt an increase in their pacing strategy during the optical flow trials, while others felt the complete opposite. The reception of the device also appeared to cover the entire spectrum, with some participants showing positive reviews and others expressing largely negative sentiments towards the system. In future studies it would be interesting to recruit a larger number of participants. This would allow for a larger database and could provide more conclusive evidence to the effect of optical flow on pacing, heart rate and RPE. It would also be useful to extend the duration of each trial. A single lap (800m) does not provide sufficiently high levels of exertion to reach the upper levels of the RPE test, limiting the findings of the study significantly.

ACKNOWLEDGEMENTS Our thanks to test participants, Professor Sidney Fels and teaching assistant Victor Zappi for making this project possible.

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