human sensing & motor controlcs543/2015w2/classnotes/543... · sense • unique integration...

2015-16 W2 / maclean cpsc 543 / class W10b

1

cs543: physical interface design & evaluation

human sensing & motor control

class w10a

outline for today

types of haptic sensing

taction

kinesthesia & proprioception

sensorimotor control


2

messages

• diversity of function & mechanism in haptic sense

• unique integration with motor channel

•  insights for device design & applications:

evolved functions vs. new roles made possible by advanced interfaces

types of human haptic sensing

cutaneous / tactile / somatic: •  heat, pressure, vibration, slip, pain •  sensation arising from stimulus to the skin

kinesthetic / proprioceptive: •  limb position (proprioception), motion (kinesthesia),

force

•  end organs located in muscles, tendons, and joints

•  stimulated by bodily movements


3

tactile sensory receptors

our skin contains an assortment of receptors which lead to complex sensory signals:

thermoreceptors: change in skin temperature mechanoreceptors: pressure, vibration, slip nocioreceptors: pain

to cover sensations ranging from pin-pricks to broad steady pressure, they vary by

physical mechanism, depth & response speed

the tactile sensing pathway

each receptor has a threshold (which can change).

when stimulus > threshold: generates an electronic "action potential" in afferent (in-going) nerve fiber à up spinal cord à thalamus area of lower brain à cortex where signal is processed.

receptor action potential neuron


4

the skin

•  heaviest organ •  prevents body fluids from escaping •  protects us •  provides tactile information

•  hairy vs. glabrous (hairless) skin •  epidermis & dermis

cross section of glabrous skin

(Goldstein, 1999)


5

distribution of tactile sensors Mapping the Human Somatosensory Cortex (Kandel, Schwartz & Jessell, 2000)

high sensor density correlated to body regions involved in exploration and manipulation

example of functional variation: sensorial adaptation

receptors have different rates of adaptation to stimuli:

Slowly Adapting (SA): respond throughout stimulus e.g. joint angle information from skin stretch

Rapidly Adapting (RA): respond at start/end of stimulus; optimized to “block out” extraneous signals, e.g. wearing gloves


6

types of tactile receptors

Merkel Receptor

Meissner Corpuscle

Ruffini Cylinder

Pacinian Corpuscle

Merkel Receptor

shape: disk

stimulus: pressure

location: near border between epidermis & dermis

type: SA (slow adapting)

sensitive frequencies: 0-10 Hz


7

Meissner Corpuscle

shape: stack of flattened cells, with a nerve fiber winding through

stimulus: taps on skin

location: dermis, just below epidermis

type: RA (rapid adapting)


Ruffini Cylinder shape: many-branched fibers inside a roughly cylindrical capsule

stimulus: stretching of skin or movement of joints

location: dermis

type: SA



8

shape: layered capsule surrounding nerve fiber

stimulus: rapid vibration

location: deep in skin

type: RA

sensitive frequencies: 100 - >500 Hz

Pacinian Corpuscle

thermoreceptors and nocioreceptors cold receptors: •  in epidermis; 1-5 / cm2

heat receptors •  in dermis, 0.4 / cm2

•  much higher density than cold receptors

both: •  receptive field of 1-2 mm •  high overlap à low res for heat receptors despite high

density

nocioceptors: sense pain •  trigger at < -15° C and > 45° C •  faster than normal response (rapid neural transmission)


9

spatiotemporal resolution

what spacing is required for distinct perception?

spatial limen (resolution): depends on size of receptor field; resolution reduced by crosstalk & overlap

successiveness limen: 5 msec to perceive as separate 20 msec to determine order …but much more for cortex to process.

masking: stimuli interfere, either spatially or temporally limits the maximum information transmission rate

more on masking

vision: researchers use stimulus masking to elucidate cognitive mechanisms

haptics: developing comparable techniques do similar phenomena exist? e.g. •  change numbness •  haptic perception without attention

approaches: •  sequential or superposed stimuli on same location •  spatially distributed stimuli of varying intensity


10

outline


taction


sensorimotor control


perception of limb position (proprioception)

perception of limb motion, force (kinesthesia)

some cutaneous information is used, especially in hairy skin

main information from mechanoreceptors in muscles


11

muscle mechanoreceptors

two types:

“force sensors”: Golgi tendon organs •  measure force via localized tension •  located serially between muscles / tendons

“position/motion sensors”: muscle spindles •  located in parallel among muscle fibers •  excited by changes in muscle length

(active & passive stretching)

each plays special role in motor control

Golgi tendon organ

located serially between muscles & tendons;

measure localized tension


12

muscle spindle located in parallel between individual muscle fibers;

excited by active & passive stretching

bias: firing rates change depending on muscle length

gain: sensitive to changes in muscle length

density not necessarily correlated with kinesthetic ability

threshold depends on muscle state (contracted or stretched relative to rest length)

muscle spindle, closeup

afferent from bag: sensitive to velocity of muscle stretch afferent from chain: sensitive to muscle length


13

outline


taction

kinesthesia

sensorimotor control (just a tiny bit) à See Dinesh Pai’s class to learn about this

human motor control in haptic design

tightly integrated with sensory apparatus: •  why it’s called “sensorimotor control”

key parameters of control (differ widely by muscle group): •  force / torque capacity and resolution

exploratory tasks: •  dominated by sensing, with limb under force control

manipulation tasks: •  grasp type is important to account for in design •  motor dominant - use both position & force receptors


14

implications for design: force & torque resolution

sensing & control bandwidth

in following: some numbers. WHY? matters for:

•  understanding type of tasks people can do manually – comfortably, or at all

•  appropriate grasp type for a given task

•  device specification: quality of sensors and actuators, sampling bandwidth and response times

force tracking resolution

humans can track small forces with errors of: •  2-3% in ideal conditions: grip force w/ visual feedback

(Mai et al 1985)

•  ~0.04 N / 15%: pushing against a normal surface w/ vis feedback (Srinivasan & Chen, 1993)

•  worse without visual feedback

•  good texture discrimination even in absence of good finger force control (Lederman et al, 2004)

both tactile & kinesthetic sensing involved


15

torque and compliance resolution

torque: •  discrimination: compared test torque to reference,

with JND=13% •  control: subject tried to maintain constant angular

velocity against constant torque resistance, with measured errors of 10-14%

compliance = displacement / force: JND = 22% sensation probably depends on work performed in depressing the spring,

Work = Force x distance (Wu et al, 1999)

variation in frequency limit = function of receptor type:

•  sensing (kinesthetic): 20-30 Hz

•  sensing (tactile): 10-10,000 Hz

•  human ability to control 5-10 Hz our own movement: (limited by mechanical resonance)

sensing & control bandwidth upper limits

auditory range

~same speed you can move your eyes (visual attention)


16

bandwidth detail (Shimoga, 1992)

exploratory procedures: nature of desired

physical information

guides strategic touching

(“action for

perception”)

(Lederman & Klatzky, 1996)


17

force exertion finger contact forces: depend on maximum vs. sustained exertion gender, age, overall strength

fatigue: compromises ability to control grip force

power grasps: high stability and force (50 N maximum / finger)

precision grasps: less force, higher dexterity

(Napier, 1956)

implications for design: grasp type

form of “handle” invites a particular kind of grasp

how strong / precise would a haptic display inside each of these “interfaces” need to be?


18

summary

•  what types of haptic sensing there are •  remarkable & diverse mechanisms and

resolutions for: •  taction

•  kinesthesia & proprioception

•  sensorimotor control: •  numbers (for specification); •  need to understand how human will ‘approach’ the

interface, to present it properly: What user wants to learn from it, or do with it à design language of EPs, grasp

human sensing & motor controlcs543/2015w2/classnotes/543... · sense • unique integration...

Documents