Transcript No Slide Title

Human Factors and
Haptic Interfaces
Lynette Jones,
Department of Mechanical Engineering,
Massachusetts Institute of Technology.
Human skin
Surface of average sized adult
human: 1.8 m2
(1000 times that of retinae)
Density: 1250 kg/m3
Weight: 5 kg
Total number of axons
converging on CNS: 1.1*106
Retina: 106 axons,
Cochlea: 6*104 axons
Haptics and Vision
Information
capacity (bits/sec)
Temporal
acuity
Fingertip
102
5 ms
Ear
104
0.01 ms
Eye
106-109
25 ms
Time delays differ for hand and eye – hand is
quicker than the eye
Information Channels in
Human Hand
SENSORY
7 classes of Mechanoreceptor
(17,000 – glabrous skin)
2 classes of Thermoreceptor
4 classes of Nocioceptors
3 classes of Proprioceptor
(0-300 in different muscles)
Sensory Receptor Properties
and Haptic Display Design
Resolution and sensitivity of the sensors
 Temporal processing characteristics
(adaptation, summation)
 Spatial features of processing
 Delays in processing information (0.4-120
m/s)

Tactile Receptor Types (7)
Cutaneous and subcutaneous
Mechanoreceptors
Fiber
group
Modality
Meissner corpuscle
A,
Stroking, fluttering
Merkel disk receptor
A,
Pressure, texture
Pacinian corpuscle
A,
Vibration
Ruffini ending
A,
Skin stretch
Hair tylotrich, hair-guard
A,
Stroking, fluttering
Hair-down
A
Light stroking
Field
A ,
Skin stretch
Receptors Processing Vibration, Texture
Absolute threshold (mm)
Tactile Tuning Curves
1
Meissner’s corpuscles: 20-50 Hz
0.1
Merkel cell: 5-15 Hz
0.01
0.001
Pacinian corpuscles: 60-400 Hz
0.0001
0.1
10
Frequency (Hz)
1000
Perception of Vibrotactile Stimuli –
Frequency and Intensity Interact
 Perceived
intensity of vibration
varies as a function of frequency as
well as amplitude
 If
the amplitude of vibration is
changed
while
frequency
is
maintained constant, at certain levels
a noticeable change in rate occurs
PSE (db re: standard)
Equal subjective intensity curves
1
0
-1
-2
-3
-4
Standard 25 Hz
-5
20
30
40
50
60
Comparison frequency (Hz)
70
Spatial acuity of the skin
Skin movement: 0.1-0.2 mm
(Gould et al.,
1979)
Spatial frequency of grating: fingertip
can distinguish 40-50 µm in spatial
period of 0.7-1.0 mm (Morley et al., 1983)
On smooth glass surface, dot of
height 1-3 µm and diameter of 550
µm can be detected by the fingertip
(Johansson & LaMotte, 1983)
(Johnson & Phillips, 1981)
Temporal variation often improves
acuity and spatially extensive stimuli
improve performance
Temporal acuity and touch
5 ms
20 ms
Successiveness - 2 stimuli (1
ms duration) must be separated
by 5.5 ms to be perceived as 2
at a single locus
Temporal order – 2 successive
stimuli at separate sites must
be separated by 20 ms in order
to determine which site first
Haptic Displays
Surface texture of object
Contact in the environment
Moving probe across surface - volume
Compliance/stiffness of object
Mass of object
Thermal properties of object
Human Perception and
Haptic Display Design
Scaling (gain) of information between
object and operator
 Bandwidth required to present information
 Mechanical properties of interface
 Magnitude of delays that are tolerable symmetric, modality specific

Force-reflecting Interfaces
Scaling
Ring finger
Women: 10 N
Men: 18 N
(gain) of force between object and operator
Middle finger
Women: 14 N
Men: 26 N
Index finger
Women: 19 N
Men: 35 N
Activation force <1 N
Mean force: 0.8-0.9 N
Peak force: 1.8-3.3 N
GOLGI TENDON ORGAN
Tendon of Achilles
0-20 in mammalian muscles
Activation force: 0.5 – 1.7 mN
Differential threshold (N)
Force Discrimination
10
1
0.1
6%
0.01
0.1
10
Force (N)
1000
Weight Discrimination
Weber fraction
0.16
0.12
0.08
0.04
0
Rapid
motion
Active
lifting
Reflex
lifting
Static
position
Hand
passive
Perceived force (%MVC)
Fatigue and Perceived Force
100
80
60
40
20
0
0
50
100
150
Time (s)
200
250
300
Force control - Index finger flexor
Coefficient of variation (%)
15
Haptic
12
9
6
Visual
and haptic
3
0
2
4
Force (N)
6
Viscosity Discrimination
Differential threshold (N.s/m)
1000
100
10
1
1
10
100
Reference Viscosity (N.s/m)
1000
Viscosity Discrimination
Weber fraction (%)
60
40
20
19%
0
1
100
Viscosity (N.s/m)
10000
Discriminability Parameters
Variable
Weber fraction
Amplitude of vibrotactile
stimulation (20-300 Hz)
Frequency of vibrotactile
stimulation (5-200 Hz)
Pressure on skin
Force
25%
0.1m
11%
0.4 Hz
12%
2 gm/mm2
7%
Stiffness/compliance
17%
Viscosity
19%
Temperature (cold)
Resolution
2%
30 mN
0.02oC
Discriminability Parameters
Variable
Weber fraction
Range
Limb position
7%
5-9%
Limb movement
8%
4-19%
Force
7%
5-12%
Stiffness/compliance
17%
7-26%
Viscosity
19%
10-29%
Hand movements and
physical properties
Surface texture
Temperature
Hardness
Size/volume
Weight
Individual Variability
Weber fraction
0.4
0.3
0.2
0.1
0
Subjects
Movement Amplitudes
SD Position (mm)
40
35
30
low
25
20
15
high
10
5
0
1
100
Reference Viscosity (N.s/m)
Movement Velocities
SD Velocity (mm/s)
120
100
low
80
60
high
40
20
0
1
100
Reference Viscosity (N.s/m)
Training for the haptically
inept
Feedback
Optimal
motor strategy
Improve discrimination
but not detection
Interface Mechanical Properties
and Human Operator Performance
Delay (ms)
300
250
200
150
0
500
1000
1500
2000
Interface Stiffness (N/m)
2500
Human Operator
Performance
1
Gain
0.8
0.6
0.4
0.2
0
0
500
1000
1500
2000
Interface stiffness (N/m)
2500
Human Operator
Performance
Time to 0.5 pt on Step
Response Function
750
700
650
600
550
500
450
10
1000
Interface Viscosity (N.s/m)
Human Operator
Performance
1
Gain
0.8
0.6
0.4
0.2
0
10
1000
Interface Viscosity (N.s/m)
Thermal Interfaces and
Perception
Thermoreceptor range: 13-45o C
 Resolution: 0.02-0.05o C (transient)
 Thermal discriminability: 2%
 Neutral thermal sensation: 31-36o C
 Skin temperature correlates well with
perception of cold not warmth
 Thermoreceptors are NOT thermometers

Elevation in skin temperature (deg
C)
Thermal thresholds
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
Area (cm sq)
10
12
14
Thermal Interfaces
Disadvantages
 Slow response
 Poor localization (improves with increases
in temperature – 40° C)
 Prodigious capacity for adaptation and
summation (intensity and areal extent
traded)
But could be analogous to color in visual
displays.
Illusions – can they be
used to trick the haptic
system?
Size-weight illusions – visual and haptic
phenomenon
 Saltation effect
 Use auditory cues to enhance haptic
perception

Size-weight Illusion
Visual
Haptic
Perceived Magnitude
20
3
904 gm
SMALL
15
2.6
2.2
10
LARGE
5
1.8
0
1.4
0
200
400
600
800
350 gm
100
Volume (cc)
Weight (g)
(Masin & Crestoni, 1988)
(Ellis & Lederman, 1993)
Saltation effect
Warning stimulus (P1) 1 s prior
to two taps on skin. Present a
stimulus at one location (P2
red) and a second at another
(P3 blue).
P1/P2 locus
150 ms
110 ms
75 ms
< 25 ms
P3 locus
At short and long time
intervals (20-30 and > 200 ms)
P1 will appear near to or
coincident with P2
As time disparity increases
above 50 ms the first stimulus
travels back to its veridical
locus
Conclusions
• Spatial and temporal processing characteristics
of different modalities (pressure, vibration,
temperature, force) vary, but can be used to
enhance stimulus presentation in a haptic
display
• Cross-modal interactions provide an additional
tool for representing object properties