Comparing Vibrotactile Feedback for Navigation on a Head Mounted Device vs an Abdomen Mounted DeviceApurva Gupta

Georgia Institute of Technologyapurva.gupta@gatech.edu

Shashank JagirdarGeorgia Institute of Technologyshashank.jagirdar@gatech.edu

Manasvi LalwaniGeorgia Institute of Technology

manasvi.lalwani@gatech.edu

ABSTRACT

There are instances when the astronauts have to navigate extra-terrestrial surface towards the base station or to explore the surroundings. This puts a very heavy demand on their visual system to gauge the surroundings. What happens when the visibility is compromised due to sandstorms or any other such calamity? This project tries to explore the tactile display for such situations to help astronauts in directing and navigation. We are trying to find the feasibility of a specific instance on such displays i.e head mounted tactile display and comparing it with a torso belt tactile display for comfort, response time, task completion time and hausdorff distance.

Author KeywordsWearable; Haptics; NASA, Haptics; Directing.

INTRODUCTION[1] found out that at same frequency the sensitivity of head was better than abdomen and forearms and equivalent to the fingertips. Additionally they found that the parietal region is most suited for vibrotactile display followed by specific point in temporal and occipital regions. In [2] the authors defined the guidelines for the head tactile display.

Based on the available threshold data and the guideline in [1, 2] we designed the head tactile display and compared it with a torso belt which had given good results when tested on soldiers [4].All the studies done so far have been to design tactile displays for head and testing their efficiency. We try to compare and contrast it with an already tested tactile display for the abdomen. The study would also generate useful insights on whether head display is a better option against a waist belt and if it is better, more efficient and comfortable than the waist belt. Van Erp et. Al [3] demonstrated an effect called ‘tap-on-the-shoulder’ which leads to an immediate percept of external direction. This is akin to someone tapping

Van Erp [3] showed that a vibro-tactile stimulus on the torso immediately leads to a percept of external direction, an effect which we call the "tap on the shoulder" principle.

The aim of this study was to compare and contrast head mounted tactile display with a more established abdomen-mounted tactile display. The objective was to evaluate each tactile display for error rate, completion times, accuracy and comfort level of the users in response to the tactile stimulus while performing a simulated navigation task.

We hypothesized that since head is more sensitive to vibration stimulation than the abdomen at the comfortable frequency range, there would be less error rates and more accuracy in the condition of head mounted tactile display. We also hypothesized that since in general people are more attuned to wear accessories on waist and not on head, abdomen mounted tactile display would fare better in the comfort rating.

METHOD

9 Participants (6 men, 3 women, mean age = ~23) for the study were recruited from the Georgia Institute of Technology community. The study was a within-subject design, so each participant was subjected to both the conditions (head-band and waist belt). The order of the conditions was randomized to overcome the order bias and learning effect. EquipmentWe designed two tactile displays one each for head and abdomen using the form factor of head band and waist belt respectively. We used a circular array of 4 vibration motors as tactors aligned with the direction of front, left, right and back. This arrangement was chosen since in [..], authors propose the circular array as a guideline for designing HMTD.To keep the study consistent, similar arrangement was used in the waist-belt. While (Glang et al.) mentions in [5] that active tactors for vibrotactile feedback should be at least 3 cm apart on the abdomen, we did not find any work that measures a similar distance

between tactors for vibrotactile feedback on the head. If we do use the same distance of 3 cm between motors on the head, we would be able to use a maximum of 6 tactors to get the maximum localization per Cholewiak et al. (2004) in [6]. Using 6 tactors on the head to map them to the four cardinal directions used in navigation would make it unnecessary complexity in our tasks. So, to keep it simple, we decided to use 4 tactors on both the head and abdomen.Stimulus is given as continuous pulses as proposed in [...] for better delivery of information.

ProtocolWe set out to conduct two experiments to try and prove or disprove our hypothesis. The next two subsections describe the two experiments in detail. For both the experiments, the stimulus was mapped as:

● Front tactor buzz - UP arrow● Left tactor buzz - LEFT arrow● Right tactor buzz - RIGHT arrow● Back tactor buzz - BACK arrow

Experiment 19 participants (6 men, 3 women, mean age =~23) were recruited for a within subject design study where they were subjected to two conditions of head-band and waist belt respectively. For each condition, participants were asked to complete a simple simulation game of moving an object along a fixed path from a start point to an end point along a fixed path as seen in the snapshot in figure 4. The participants were not allowed to look at the game display and were allowed to move the object by pressing only the direction keys on a keyboard. Based on the tactile stimulus received from the band/belt, participants had to press the corresponding key on the keyboard. Figure 2 shows a sketch of the design for this experiment. The start and the end of simulation was marked by short buzz from all tactors. To give a clearer picture of how the simulation game worked, in Figure 4, the red line indicates the current orientation of the object (or an astronaut, indicated by the blue circle). The green line indicates the direction in which the object should be facing. Users were randomly assigned to either navigate through Waypoint 1 or Waypoint 2 to reach the END point. To make the object turn in that direction, the right tactor would buzz telling the user to press the right key. When the red line overlaps the green line, the back tactor would buzz to tell the user to stop pressing the right key. Then, the front tactor would buzz to tell the user to press the UP direction / arrow key to move the object in that direction. Due to the inherent delay in interpreting a change in tactor buzz location, the user almost always overshoots the expected orientation and moves in a direction slightly different than the expected direction. The game keeps correcting the user every time they move in the wrong direction by buzzing the correct set of tactors.

Experiment 2

RESULTS:

At the end of every task in both the experiments, participants were asked to fill a short questionnaire asking their comfort rating for the task. They were also asked to rate the device which they preferred after they were subjected to both the conditions.

For each condition we measured the following dependent variables:1. Accuracy: Accuracy was measured by calculating the hausdorff distance for each condition2. Completion time: This was recorded as the time difference between the start and the end of the simulation3. Comfort level: This was a subjective measure based on 5-scale likert response of the participants4. Average Response Time: The time taken by a user to respond to a change in stimuli

Experiment 1 Results:1. Accuracy:

The average accuracy, measured as the Hausdorff Distance, for this experiment across the entire set of users was found to be 36.63 when the Head Band was used and 45.99 when the Abdomen Band was used

2. Completion Time:Users took an average of 8.5 minutes to complete the task while using the Head Band with a standard deviation of 1.12 minutes and took an average of 7 minutes to complete the task while using the Abdomen Band with a standard deviation of 3.56 minutes. It is important to note here that the variance is considerably higher for the Abdomen band. Our reasoning is that the form factor of the waist can vary considerably from person to person and hence affecting their ability to interpret the vibrations. The form factor for the head is much more consistent from person to person and this is why the variance is considerably low.

3. Comfort Level:70% of our users who participated in this experiment said that the Abdomen Band was more comfortable than the head band. Of the 30% that preferred the Head Band, almost everyone indicated that they deemed performance was more important than comfort and also that the stomach area is private for such interactions

4. Average Response Time:The average response time across all participants as recorded by us was found to be ~140ms for the Head Band and ~154ms for the Abdomen Band.

5. The participants also mentioned that it was just as easy to interpret vibrations on both the bands.

Experiment 2 Results:1. Accuracy:

Figure 1

Figure 2 Figure 3

Figure 4

CONCLUSIONgjgjg

ACKNOWLEDGMENTSWe would like to acknowledge the invaluable insight and advice provided by Dr. Thad Starner (Professor in the College of Computing at Georgia Tech) and Clint Zeagler, (Dr. Starner’s PhD student). We would also like to thank NASA for giving us an opportunity to present our work at the 5th Wearable Tech Symposium held at the Johnson Space Center.

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ABERDEEN PROVING GROUND MD HUMAN RESEARCH AND ENGINEERING DIRECTORATE, 2009.2. Myles, Kimberly, and Joel T. Kalb. Guidelines for head tactile communication. No. ARL-TR-5116. ARMY

RESEARCH LAB ABERDEEN PROVING GROUND MD HUMAN RESEARCH AND ENGINEERING DIRECTORATE, 2010.

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4. Elliot, Linda R., et al. Tactile guidance for land navigation. No. ARL-TR-3814. ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD HUMAN RESEARCH AND ENGINEERING DIRECTORATE, 2006.

5. Glang, Wayne et al. Multimodal Interface. 1st ed. Toronto: Defence R&D Canada, 2015. Web. 30 Apr. 2015.6. Cholewiak, R.W.; Brill, J.C.;Schwab, A. Vibrotactile localization on the abdomen: Effects of place and space. Perception

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