Haptic Perception and Devices

David Johnson

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.

•

The Sense of Touch• Everyday Tasks

– Dialing a phone

– Playing a guitar or piano

– Finding a light switch

– Using a mouse

• Touch is complex: tying a shoelace

• Only bi-directional communication channel – both input & output

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

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.

• Difficulties if no feedback?

Haptics

Surface of average sized adult human: 1.8 m2

(1000 times that of retina)

Weight: 5 kg

Total number of axons: 1.1*106

Retina: 106 axons,

Cochlea: 6*104 axons

Human skin

Haptics and Vision

Information Temporal

capacity (bits/sec) acuity

Fingertip 102 5 ms

Ear 104 0.01 ms

Eye 106-109 25 ms

Peripheral Pathways of Touch

• Mechanoreceptors - pressure, texture, vibration

• Proprioceptors - body position

• Nocioceptors– Two pathways for pain

• one fast pathway for sharp pain, • one slow pathway for dull pain

• Thermoreceptors

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

Functional characteristics of Skin Mechanoreceptors:Receptive field size (I = small, II = large)

and adaptation rate (FA = fast adapting, SA = slow adapting)

Kandel et. al., 2000

Meissner’s Merkel Pacinian RuffiniCorpuscle Cell Complex Corpuscle Ending

Receptors

Receptive

Field

Intensity and Time Course of Neural Signal (adaptation)

NeuralSpike train

Stimulus

FA I SA I FA II SA II

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

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]

Proprioception Includes The Vestibular SenseOcular Motor

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Haptics

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.– On smooth glass surface, dot of height 1-3 µm and

diameter of 550 µm can be detected by the fingertip (Johansson & LaMotte, 1983)

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

Laterotactile

• Induce sensations of indent from lateral movement of skin

Vibrotactile

Electrotactile

Servomotor mechanical

Tactile Vest

Force-Feedback Technologies

• Kinesthetic (relating to the feeling of motion) info is produced by exerting mechanical forces– Haptic devices movie

MPB Freedom7 and Cubic

CyberForce

[Chang]

6DOF Delta

Magnetic Levitation

• CMU• Very high fidelity• Small workspace• movie

Exoskeleton

• 5DOF

Rutgers Hand Master

• Pneumatic

Foot Haptics (locomotion interface)

Sarcos Biport Iwata’s GaitMaster

Omni-directional treadmill

Foot-based interfaces

Whole-Body Haptics

Sarcos Treadport II

CirculaFloor

• Moving floor tiles• An example of

“encountered haptics”

Discussion

• Mechanical aspects are more daunting than for other VR technologies

• Must handle gross positioning (proprioception) and fine detail (tactile)

• Burgeoning area– 10 years ago, 20 papers a year– Now, 1000’s.