Tactile Perception and Haptic Interaction
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Tactile Perceptionand
Haptic Interaction
Cecilia R. AragonIEOR 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/teaching/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
MechanoreceptorsPrimary Sensory Cortex
• Work together to inform us about pressure, texture, stretch, motion, vibration
[Chang]
(peripheral) (cortical)
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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
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Four Receptor Typesa) 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
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Cross Section of
the Skin
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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
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Receptive Field
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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
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Cortical Pathways of Touch
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Cortical Magnification
• The receptive fields and cortical representations give more acuity to fingers, mouth, nose and tongue
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Cortical Plasticity for Touch
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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.
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Proprioception Includes The Vestibular SenseOcular Motor
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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.
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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
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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 the
barrier, K a stiffness constant
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Interaction of Touch & Vision
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The Haptic Technology Spectrum
• Mass/Weight• Stiffness/Detents• Viscosity/Damping• Roughness/Texture• Pulses• Waveforms• Vibrations• Simultaneous Compound Effects
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Haptics in Medical Simulation• Simulators before Haptics
– Fruit– Animals– Cadavers– No Touch
• Trends Towards More Reliance on Touch– Laparoscopy– Endoscopy
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Haptics in Medicine
• Photorealistic Graphics• Life-like Sounds• Simulated Touch • & Emotion
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Haptics in Laparoscopy
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Haptics in Design & Simulation
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