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Tactile Displays . Presented By Mary Wesler Rakesh Dave. Definitions. Tactile: A sensation perceived by the sense of touch; pressure or traction exerted on the skin is perceived; sensitivity to vibration or movement to stimulation of nerves.

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Tactile displays l.jpg

Tactile Displays

Presented By

Mary Wesler

Rakesh Dave


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Definitions

  • Tactile: A sensation perceived by the sense of touch; pressure or traction exerted on the skin is perceived; sensitivity to vibration or movement to stimulation of nerves.

  • Distal Attribution: Refers to the referencing of our perceptions to an external space beyond the limits of the sensory organs themselves (Loomis, 1992).


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Definitions

  • Kinesthetic information: Describes relative positions and movements of body parts as well as muscular effort when touching and manipulating objects

  • Haptic perception involves both tactile perception through the skin and kinesthetic perception of the position and movement of the joints and muscles. E.g Cube ,through the skin of our fingers and the position of our fingers.


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Advantages

  • Accessible, extensive in area, richly innervated and capable of precise discrimination

  • Does not interfere materially with other functions

  • Number of similarities to retina

  • Spatial+Temporal integration

  • Visual and tactual patterns can be learned and identified interchangeably

  • Mach Band phenomenon demonstrable on skin(Mach's bands, the tendency of the human eye to see bright or dark bands near the boundaries between areas of sharply differing illumination)

  • Functions as exteroceptor


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Necessity

  • Tactile Cues refine and moderate manual activity

  • Necessary for faithful telepresence

  • Environments where visual is less useful

  • Some operations inherently tactile

  • Entertainment value (Free to speculate!!!!)


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Chapter Part I

  • Applications

    • Sensory substitution visual/auditory

    • Remote tactile sensing or feedback

  • Technology for production

    • Static

    • Vibratory

    • Electro Tactile


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Uses Of Tactile Substitution

  • Enhancing accessibility for the blind

    • To enhance access to computer graphical user interfaces

    • To enhance mobility in controlled environments

    • To allow for learning of visual concepts

  • Communication of visual information to the brain in situations where the visual system is already overloaded

    • Race car drivers

    • Airplane pilots

    • Operating rooms


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Uses Of Tactile Substitution

  • Audio to Tactile Converters

  • Virtual Reality

  • Telerobotic Manipulators

  • Prosthetic Limbs

    (Courtesy Unitech Research)


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Low Tech

  • Braille

  • Sign Language

  • Tadoma


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Force Feed Back

  • Spatial information integrated with kinesthetic information received by manually scanning objects and texture information by time dependent frictional vibrations recorded by sensors. Applied to people with Hansen’s Disease and Astronauts in space


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Tactile Auditory Feedback

  • Tacticon and AudioTact

    • Adjusting the perceived intensity of electrodes based on different intensities of sound (Vocoder principle)


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Tactile Visual Feedback

  • VideoTact

    • Uses 768 point array of tactors for Image translation (capable of translating BMP or DIB format bitmaps as well as NTSC or PAL/SECAM video into an electro-tactile equivalent)


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Tactile Vision Substitution

  • Device which converts printed matter to vibrotactile letter outlines on users finger pad. No longer in production due to high cost and low demand


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Interactive Haptic Displays

  • Static Tactile Displays

  • Virtual tactile tablet (finger pad mounted on a mouse)

  • Force Display to feel texture

  • Electropthalm Vibrotactile forehead display + finger display

  • Steerable water jet display


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Current Technology

  • Linear and Planar Graspers at MIT TOUCH Lab

    Description

    . The Linear Grasper is now capable of simulating fundamental mechanical properties of objects such as compliance, viscosity and mass during haptic interactions. Virtual wall and corner software algorithms were developed for the Planar Grasper, in addition to the simulation of two springs within its workspace.


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Current Technology

  • Harvard Robotics Lab

    • Deformable tactile sensors. Using this technology, deformed shape of the sensor on-line is reconstructed This sensor is currently being used in manipulation tasks and in the development of a tool for minimally invasive surgery.


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Current Technology

  • Allows for feeling temperature at the fingertips.Used for telepresence in remote manipulators

    (Courtesy C M Research Group)


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Sensory Physiology

  • Salient Features

    • Skin Anatomy

      • Besides fibers for pain skin has six types of receptors

        Response measures of these determine the amount and type of information that can be presented and classification of these have functional roles


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Sensory Physiology

  • Perception of non vibrating stimuli

    • Static force up to a minimum of 5 dynes applied by a fine wire is detectable by human body.

      ( Particularly notable fact is that threshold for women is less than that for men!!!!!!!!!!!!)


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Limitations

  • As Field of view tactually increases tactile recognition reduces when compared to visual recognition.

  • Salient features may be blurred by meaningless details


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Distal Attribution

  • Telepresence - sense of being present in a remote environment

  • Feedback - sensory information (afference)

    • visual

    • auditory

    • tactile

  • Motor Control over the sensed environment (efference)

  • Perceptual Model

  • Problems

    • time delays

    • low spatial resolution

    • conflicting information


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Tactile Display Design Considerations

  • Must accommodate the unique sensory characteristics of the skin, particularly if cross-modality sensory substitution is attempted.

  • The perceived stimulation magnitude should closely match the same pressure stimulus on the skin.

  • Spatial Resolution - whole frame presentation is prohibitive tracing, slit-scan presentation, edge enhancement, and zoom features are beneficial.

  • Display type should match the information presentation.

  • Humans are resistant to change.


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Static Display

  • Braille

  • Sign Language

  • Tadoma



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Electrotactile Display

Types Chapter 9, Fig. 9-9

  • Surface

  • Subdermal

  • Percutaneous Wire

    Advantages to Subdermal and Wire

  • Low JND

  • high consistency

  • mechanical stability

  • no mounting

    Sensations - tingle, itch, vibration, buzz, touch, pressure, pinch, and sharp or burning pain

    Dynamic Range


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Dynamic Range

Dynamic range = threshold pain (IP)/threshold sensation (IS)

  • Skin - varies from 2-10 or 6-20dB

    • definition of pain

    • training

    • presentation of other stimuli

    • electrode material, size, placement, and stimulation waveform

  • Ear 120dB

  • Eye 70dB


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Authors’ Recommendation

Dynamic RangeProposed = Perceived Magnitude at Maximal Current (IM) without discomfort.

Note: IP = 1.3 IM

Justification: IP/IS is an electrical measure not a perception measure. Maximizing IP/IS does not guarantee a usefully strong or comfortable sensation.

Chapter 9, Fig. 9-15.



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Display Performance Criteria

  • Minimal power consumption

  • Maximal stimulation comfort

  • Minimal post-stimulation skin irritation

  • Minimal sensory adaptation

  • Maximal information transfer measured by:

    • minimal JND of the modulation parameters current, width, frequency, and number of pulses per burst

    • minimal error in identifying the absolute stimulation level of a randomly stimulated electrode

    • minimal error in manually tracking a randomly varying target stimulus

  • Maximal dynamic range:

    • maximal comfortable level/sensory threshold

    • maximal range of perceived intensities

  • Minimal variation of sensory threshold and maximal comfort level with precise electrode location on a given skin region

  • Fastest and most accurate spatial pattern recognition



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REFERENCES

Kaczmarek, K.A. and Bach-Rita, P., (1995). Chapter 9: Tactile Displays. In Barfield and Furness, Eds. Virtual Environments and Advanced Interface Techniques. (pp.349-401).

Goodwin-Johansson, S. Palmer, D. Mancusi, J. Nawankwo, H., Wesler, M.Mc., and Marshak, W.P., (1999). Tactile interface on a mobile computing platform. In Proceedings of the US Army Federated Laboratory Advanced and Interactive Displays Symposium. (pp. 51-55). College Park, MD: Army Research Laboratory.

Gilliland, K. and Schlegel., (1994). Tactile Stimulation of the human head for information display. In Human Factors 36(4) 700-717.

Korteling, J.E. and Van Emmerik, M.L. (1998). Continuous haptic information in target tracking from moving platform. In Human Factors 40(2), 198-208

Sheridan, T.B., Thompson, J.M., Hu, J.J., and Ottensmeyer, M., (1997). Haptics and supervisory control in telesurgery. In Proceedings of the Human Factors and Ergonomics Society 41st Annual Meeting (1134-1137). Santa Monica, CA: Human Factors and Ergonomics Society.

Yeh, M. and Wickens, C.D., (1999). Target cueing in augmented reality: a comparison of head mounted with hand-held displays. In Proceedings of the Human Factors and Ergonomics Society 43rd Annual Meeting, (pp 1228-1232). Santa Monica, CA: Human Factors and Ergonomics Society.

Dow, S. Thomas, G., and Johnson, L., (1999). Signal detection performance with a haptic device. In Proceedings of the Human Factors and Ergonomics Society 43rd Annual Meeting, (pp1233-1237). Santa Monica, CA: Human Factors and Ergonomics Society.

Venkatraman, M. and Drury, C. Cross modal displays for haptic information. In Proceedings of the Human Factors and Ergonomics Society 43rd Annual Meeting, Sata Clara, CA. 1238-1242

Bullinger, H-J., Bauer, W., and Braun, M., (1997). Virtual Environments: Haptic, Kinesthetic, and Other Perceptions. In Gavriel Salvendy, Ed. Handbook of Human Factors and Ergonomics. (pp 1742-1746).

Sanders, M.S., and McCormick, E.J., (1987). Information Input: Tactile Displays. In Human Factors In Engineering Design. McGraw Hill Book Company, NY, (pp 160-167).

Sharedd Virtual Environments: with haptic and visual feedback. www.rcs.ee.washington.edu/BRL/project/shared/

CyberTiuch, www.virtex.com

Bach-y-Rita, P. , Kaczmarek, KA, Tyler, ME., Garcia-Lara, J., DDS Form perception with a 49-point electrotactile stimulus array on the tongue. Center for Neuroscience and the Department of Rehabilitation Medicine, Trace R&D Center, University of Wisconsin, Madison, WI


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