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Localization of Head-Mounted Vibrotactile Transducers

These head-mounted transducers are used to aid soldiers in orientation, navigation, and communication.

T he human sensory systems most frequently used in military displays (vision and audition) are sometimes overloaded. When soldiers rely on visual or auditory displays, their situation awareness can be degraded due to the need to attend to the display. A proposed alternative sensory channel for soldier displays is the tactile channel. In military applications, VT displays are primarily being used to aid in orientation, navigation, and communication. Tactile displays can also be used to impart more abstract information such as in command-and-control applications.

Figure 1. A side view of the Tactor Locations. The study’s right and left side sites are in green and the midline sites are in yellow (shown in both drawings).
By presenting information to more than one sensory channel, performance can be improved over using any single channel in isolation. Tactors can be mounted on the head with a dedicated harness or it might be feasible (if acceptable to the appropriate system proponent) to integrate them into headgear already worn, such as helmets or caps.

Prior work investigated and obtained perception thresholds for tactors mounted at seven sites on the head. The sites used were from the set used for electroencephalogram (EEG) recordings. The selected sites were F3, Cz, Pz, O2, T3, T4, and F8 (see Figure 1). Even-numbered sites are right-hemisphere sites, and odd-numbered sites are left-hemisphere sites. Sites with a “z” are midline sites. In Figure 1, the study’s right and left side sites are in green and the midline sites are in yellow (shown in both drawings). The sites were chosen so that all major non-facial skull bone regions (frontal, parietal, occipital, and temporal bones) were represented.

A pilot study determined that at frequencies above 64 Hz, a bone-conducted auditory signal was present in addition to the desired tactile signal. In order to isolate the tactile effects, thresholds were obtained for 32, 45, and 63 Hz, where these auditory signals were absent.

Results of the threshold measurements were that locations Pz, O2, and T3 had significantly lower thresholds than Cz, F3, and F8 (T4 was not significantly different than either group). Also, thresholds at 45 and 63 Hz were significantly higher than 32 Hz. To build on this earlier study’s results, the same seven tactor locations and three frequencies (with substitution of 63.5 Hz for 63 Hz for instrumentation reasons) were used in this localization study.

Seven C-2 tactors were used to generate the VT stimuli. With C-2 tactors, both vibration amplitude and frequency can be controlled. The C-2 tactor is 1.2" in diameter, 0.31" thick, and weighs 17 grams. A piston of 0.3" in the center of the tactor housing moves perpendicularly to the plane of the tactor housing to create the VT signal.

Figure 2. The “Halo” Experimental Fixture used an Advanced Combat Helmet shell as a base.
The tactors were mounted in an experimental “halo” fixture (see Figure 2). The halo was created using a size large Advanced Combat Helmet shell as a base. The entire halo assembly was counterweighted via a weight suspended with a cord through an overhead pulley so that less than 1 oz of weight was applied to the head. This was done so that the weight of the helmet did not cause greater contact pressure for the top tactors.

The response methodology entailed the subject touching a mannequin head at the analogous location they perceived the origin of the tactile signal on their head. The mannequin was marked with duct tape at the seven tactor locations and positioned in front of the participant. Manual data collection was used to record the location indicated by the subject. The tactor stimulation was designed to present a rapid “tap-tap-tap” sensation to the subject; the “taps” were presented at one of the experimental frequencies (32, 45, and 63.5 Hz). Tactor activation was controlled by computer.

Based on the results of this study, and the prior threshold results, the circumferential sites of O2, T3, and T4 have promise for a head-mounted tactile display. The use of 32 Hz as a tactor excitation frequency would be preferred based on its lower detection threshold. A display employing circumferential tactors would allow for information flow such as cueing the location of snipers or providing navigational instructions. The ability to determine active tactor location could also be used to impart abstract information by, for example, activating tactors in certain patterns or combinations.

This work was done by Mary S. Binseel and Joel T. Kalb of the ARL’s Human Research and Engineering Directorate. ARL-0154

Topics:
Anatomy Body regions Displays Head Helmets Human machine interface (HMI) Medical, health and wellness Medical, health, and wellness Physical Sciences Protective equipment Protective systems Test facilities
This Brief includes a Technical Support Package (TSP).
Document cover
Localization of Head-Mounted Vibrotactile Transducers

(reference ARL-0154) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the October, 2013 issue of Defense Tech Briefs Magazine (Vol. 7 No. 5).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Localization of Head-Mounted Vibrotactile Transducers" is a final report authored by Mary S. Binseel and Joel T. Kalb, published in February 2013 by the U.S. Army Research Laboratory. The report details research conducted from January to September 2009, focusing on the development and evaluation of head-mounted vibrotactile transducers, which are devices designed to provide tactile feedback to users.

    The primary objective of the research was to investigate how these transducers can be effectively localized on the head to enhance user experience and interaction. Vibrotactile feedback is increasingly recognized for its potential applications in various fields, including virtual reality, training simulations, and assistive technologies. By providing users with tactile sensations, these devices can improve situational awareness and communication in environments where visual or auditory cues may be limited.

    The report outlines the methodology used in the study, including the design of the transducers, the experimental setup, and the evaluation criteria for assessing their performance. The authors conducted a series of experiments to determine the effectiveness of different configurations and placements of the transducers on the head. The findings indicate that specific placements can significantly influence the perception of tactile stimuli, which is crucial for applications requiring precise feedback.

    Additionally, the report discusses the implications of the research findings for future developments in vibrotactile technology. It emphasizes the importance of understanding human perception and the factors that affect the localization of tactile sensations. The authors suggest that further research is needed to refine the technology and explore its applications in real-world scenarios.

    The document is approved for public release, ensuring that the findings can be disseminated widely for the benefit of researchers, developers, and practitioners in related fields. It serves as a valuable resource for those interested in the intersection of technology and human-computer interaction, particularly in the context of enhancing user experience through tactile feedback.

    In summary, this report contributes to the growing body of knowledge on vibrotactile transducers, highlighting their potential to improve user interaction in various applications while providing insights into the factors that influence tactile perception.

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