Tactile Perception and Haptic Interaction

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Tactile PerceptionandHaptic Interaction

• Cecilia R. Aragon
• IEOR 170
• UC Berkeley
• Spring 2006

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Acknowledgments

• Andrew Green, www.uwm.edu/ag/teach_pdf/
  lecturenotes/perception/12Touch.ppt
• Dean Chang, Immersion Corp., www.immersion.com
• Stephen Wall, http//www.dcs.gla.ac.uk/pdg/teachi
  ng/demms4/notes/Haptics.pdf

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The Sense of Touch

• Everyday Tasks
• Dialing a phone
• Playing a guitar or piano
• Finding a light switch
• Feeling your pulse
• Touch is complex tying a shoelace
• Only bi-directional communication channel both
  input output

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Why is Touch Important?

• Touch-tone phone
• Rich tactile cues
• Can be done without looking
• Effortless
• PC calculator
• No tactile cues
• Only visual feedback
• Painstaking

Chang
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Tactile Perception

• Provides information about our environment
• e.g. hot, cold, smooth, rough
• Provides feedback
• e.g. when trying to lift an object, press
  buttons, etc.
• Examples
• Difficulties if no feedback?

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The Physiology of Touch
Primary Sensory Cortex
Mechanoreceptors
(peripheral)
(cortical)

• Work together to inform us about pressure,
  texture, stretch, motion, vibration

Chang
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Peripheral Pathways of Touch

• Mechanoreceptors - pressure, texture, vibration
• Proprioceptors - body position
• Two pathways for pain (both of which are
  independent from other tactile or proprioceptive
  pathways)
• one fast pathway for sharp pain,
• one slow pathway for dull pain

Green
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Four Receptor Types

• a) Merkel Disks -- constant sources of
  stimulation over a small area, such as if you
  were carrying a pebble
• b) Meissner Corpuscles -- respond best to active
  touch involved in object exploration
• c) Ruffini Endings -- constant stimulation over a
  larger area - also detects skin stretch
• d) Pacinian Corpuscles -- extremely sensitive
  over a large receptive field -- blow gently on
  the palm of your hand

Green
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Cross Section of the Skin
Green
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Receptive Field

• Mechanoreceptors detect skin deformations
• Tactile acuity is determined by how close the
  mechanoreceptors are to each other and by the
  size of the receptive field

Green
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Receptive Field
Green
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Receptive Field
The two-point threshold for any part of the body
is determined by the size of the receptive fields
and the extent of overlap
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Sensation of Touch (Cortex)

• Adjacent portions of skin surface tend to be
  represented by adjacent portions of cortex
• Cortical magnification for lips, nose and fingers

Green
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Cortical Pathways of Touch
Green
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Cortical Magnification

• The receptive fields and cortical representations
  give more acuity to fingers, mouth, nose and
  tongue

Green
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Cortical Plasticity for Touch
Green
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Proprioception

• All muscles have nerve fibers which detect the
  amount the muscle is stretched
• All joints have fibers which detect the relative
  position of each bone
• Together these allow you to determine the
  position of every part of your body.

Green
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Proprioception Includes The Vestibular
SenseOcular Motor
Green
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Haptics
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What is Haptics?

• adj. Of or relating to the sense of touch
  tactile. Greek haptikos, from haptesthai, to
  grasp, touch.
• Haptics involves both proprioceptive and tactile
  senses, in concert with other senses.
• adj. The science of applying touch (tactile)
  sensation and control to interaction with
  computer applications.

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Haptic Interfaces

• Fully duplex channel. You can both transmit and
  receive information simultaneously.
• Requires very high refresh rates of approx.1000
  Hz for realistic feel.
• Requires very high spatial resolution.
• Touch is a complex modality consisting of several
  distinct sensory channels.

Wall
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Tactile Technologies

• Tactile information is produced by perturbing the
  skin
• Pins or other mechanical vibrating elements -
  either alone or in an array, as in devices for
  Braille display
• typically used for fingertip stimulation
• Air jets blow to produce a disturbance
• Cushions of air can be inflated or deflated to
  vary pressure on skin
• Electrical stimulation - low levels of current
  provide a localized tingling sensation
• Typically used in gloves, or for larger body
  areas

Wall
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Force-Feedback Technologies

• Kinesthetic (relating to the feeling of motion)
  info is produced by exerting mechanical forces
• Technologies are easier to produce than tactile
• High-end devices
• Algorithms for force feedback - the KX model to
  produce barriers
• force exerted K X
• where X is the distance beyond thebarrier, K a
  stiffness constant

Wall
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Interaction of Touch Vision
Green
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The Haptic Technology Spectrum

• Mass/Weight
• Stiffness/Detents
• Viscosity/Damping
• Roughness/Texture
• Pulses
• Waveforms
• Vibrations
• Simultaneous Compound Effects

Chang
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Haptics in Medical Simulation

• Simulators before Haptics
• Fruit
• Animals
• Cadavers
• No Touch
• Trends Towards More Reliance on Touch
• Laparoscopy
• Endoscopy

Chang
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Haptics in Medicine

• Photorealistic Graphics
• Life-like Sounds
• Simulated Touch
• Emotion

Chang
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Haptics in Laparoscopy
Chang
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Haptics in Design Simulation
Chang