Tactile Perceptionand

Haptic Interaction

Cecilia R. AragonIEOR 170

UC Berkeley

Spring 2006

Spring 2006 IEOR 170 2

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

[Green]

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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

[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

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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

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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 the

barrier, 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]