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.
 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 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
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 Range = Perceived Magnitude at
Maximal Current (IM) without discomfort.
Proposed
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 Principles
Static
Perception:
Display
deforms the
skin exactly as
the sesor array
is deformed by
the object
Normal Touch
Adaptation:
Rapid
Principles:
Safety:
Vibrotactile
Electrotactile
External stimulation of most
cutameous afferent nerve fiber
gives rise to tactile sensation
Deliver controlled information by
means of electrical stimulation of
small distinct patches of skin with
surface and electrodes
Dependant on:
Skin location – fingertips are
most sensative.
Tactor size
Gap between tactors
Amplitude and frequency
7-25 min conditioning
vibrotactile stimulus results in
full adaptation.
Full recovery in 2 min.
Heat burns
Shock
Skin Irritation
Sensations - tingle, itch, vibration,
buzz, touch, pressure, pinch, and
sharp or burning pain
Comfort:
Comfortable with amplitudes
0.5-1 mm diameter stimulator.
Static
Power
Consumption: mechanical:
1W per pixel
Varies: 250 Hz, 12.6 mm2 = 0.4
mW to 138 mW sine waves at
threshold
Varies with frequency: little at 10 Hz
within seconds at 1000 Hz
Bursts of stimulation reduce
adaptation
Heat burns
Shock
Stinging
Skin Irritation
Varies - stimulus adjustment and
quick off ideal. Best if electrode is
wet.
Average 1W
Subdermal 10-22W
Display Performance Criteria
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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
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balanced-biphasic
coaxial
distal attribution
efference copy
electrotactile
functionally
monophasic
haptic display
haptic perception
just-noticeable
difference
kinesthetic
perception
masking
 percutaneous
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electrodes
sensory substitution
spatial integration
static tactile
subdermal
electrodes
tactile perception
telepresence
temporal integration
texture
vibrotactile
virtual environment
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