Tactile Displays

Kaczmarek, K.A. and Bach-Y-Rita, P. (1995), Tactile displays, in Virtual Environments and

Advanced Interface Design, Barfield and Furness, pp. 349-414.

Summarized by Geb Thomas

Your 2m2 of skin

90% hairy, 10% glabrous (hairless) Accessible Richly innervated Precise discrimination Adaptable to spatial and temporal displays

Covered Here

Present and potential applications

Mechanisms of normal touch perception

Technology for producing tactile displays

Practical considerations

Traditional displays for the blind

Braille (6-dot matrix, 2.3mm separation,

125 words*min-1)

Sign language: finger spelling: 6 letters*

sec-1, American Sign Language: 4-5

syllables*sec-1)

Tadoma 3 syllables*sec-1

Tactile Feedback from tactile sensors For people with poor haptic perception in their

hands (Hansen’s disease, suited astronauts) strain guages on a glove to forhead electrodes:

can detect shape and texture! Movable pins, enhanced fingerpads, tactile

pads, glove-hand adhesion, removable glove fingertip

Sample task: no feedback: 92s, force feedback 63s, barehanded: 14s

Tactile auditory substitution

Auditory prosthesis which adjusts the perceived intensity of 16 electrodes, each corresponding to the sound intensity of a given passband in the audio spectrum.

Improve speech clarity for deaf children Improve auditory discrimination and

comprehension in older patients

Tactile vision substitution (TVS)

Television Camera to users skin with a vibrotactile or electrotactile stimulators array.

Stimulation intensity is controlled by grayscale

Distal attribution -- with practice, user perceives the stimulation to be in front of them

Tactile Reading

Optacon 6x24-row vibrating fingerpad 90 words*min-1 exceptional 28 words*min-1

normal Now discontinued Significant underground calling for its

resurgance

Static tactile displays

64-solenoid, four level display presenting graphical information

Another model has one prime mover and many piezoelectric latches

Muscle wire display

Virtual tactile tablet

Fingerpad vibrotactile stimulation array on a mouse

5x20 array of pin vibrotactors mounted directly above t-shaped mouse

Minsky’s sandpaper display

Human Tactile Perception

Six types of cutaneous receptors, four functions– Fast adapting, broad receptive field (FAII) --

high-frequency vibration– Fast adapting, small receptive field (FAI) --

localized movement fine form and texture– Slow adapting, large-field (SAII) -- maybe not

involved in haptics– Slow adapting, small-field (SAI) -- form and

roughness

Measures

Smallest amount of pressure Two-point limen (two point discrimination

threshold TPDT) Affected by location, practice, fatigue,

distraction Modeling attempts include convolving

integral, low-pass filter or Gaussian blur

Design Criteria

Static tactile displays Vibrotactile displays Electrotactile displays

Static

High power consumption Rapid adaptation to static stimuli 12-20mm height to match Optacon

accuracy

Vibrotactile

Threshold: 5 micro-m at 25-650 Hz for small areas (<.05 cm2)

Adaptation to strong stimuli Full recovery requires 2 min. 160 Hz is best 10dB over threshold 1 mm diameter stimulator with .5mm

movement

Electrotactile Displays

Current through skin Current-limited Balanced, biphasic pulses with zero net DC

current Electrodes to produce appropriate ions (gold,

platinum, silver) Electrode size is important Some are implantable

Important Issues

Pain threshold Skin condition Sensory adaptation Subjective magnitude of electrotactile

stimulation