Tactile Displays Presented By Mary Wesler Rakesh Dave.

Tactile DisplaysTactile 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.

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

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.

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

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!!!!)

Chapter Part I

Applications– Sensory substitution visual/auditory– Remote tactile sensing or feedback

Technology for production– Static– Vibratory– Electro Tactile

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

Uses Of Tactile Substitution

Audio to Tactile Converters Virtual Reality Telerobotic Manipulators Prosthetic Limbs

(Courtesy Unitech Research)

Low Tech

Braille Sign Language Tadoma

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

Tactile Auditory Feedback

Tacticon and AudioTact– Adjusting the perceived intensity of electrodes

based on different intensities of sound (Vocoder principle)

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)

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

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

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.

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.

Current Technology

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

(Courtesy C M Research Group)

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

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!!!!!!!!!!!!)

Limitations

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

Salient features may be blurred by meaningless details

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

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.

Static Display

Braille

Sign Language

Tadoma

Vibrotactile Display

Electrotactile DisplayTypes Chapter 9, Fig. 9-9 Surface Subdermal Percutaneous WireAdvantages to Subdermal and Wire Low JND high consistency mechanical stability no mountingSensations - tingle, itch, vibration,

buzz, touch, pressure, pinch, and sharp or burning pain

Dynamic Range

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

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.

Tactile Display PrinciplesStatic Vibrotactile Electrotactile

Principles: Displaydeforms theskin exactly asthe sesor arrayis deformed bythe object

External stimulation of mostcutameous afferent nerve fibergives rise to tactile sensation

Deliver controlled information bymeans of electrical stimulation ofsmall distinct patches of skin withsurface and electrodes

Perception: Normal Touch Dependant on:Skin location – fingertips aremost sensative.Tactor sizeGap between tactorsAmplitude and frequency

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

Adaptation: Rapid 7-25 min conditioningvibrotactile stimulus results infull adaptation.Full recovery in 2 min.

Varies with frequency: little at 10 Hzwithin seconds at 1000 HzBursts of stimulation reduceadaptation

Safety: Heat burnsShockSkin Irritation

Heat burnsShockStingingSkin Irritation

Comfort: Comfortable with amplitudes0.5-1 mm diameter stimulator.

Varies - stimulus adjustment andquick off ideal. Best if electrode iswet.

PowerConsumption:

Staticmechanical:1W per pixel

Varies: 250 Hz, 12.6 mm2 = 0.4mW to 138 mW sine waves atthreshold

Average 1WSubdermal 10-22W

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

Key Terms balanced-biphasic coaxial distal attribution efference copy electrotactile functionally

monophasic haptic display haptic perception just-noticeable

difference kinesthetic

perception masking

percutaneouselectrodes

sensory substitution spatial integration static tactile subdermal

electrodes tactile perception telepresence temporal integration texture vibrotactile virtual environment

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