HAPTICS Sensing Manipulation - Purdue Universityece511/lectureNotes2006/... · 2007. 11. 24. · HAPTICS. Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005 Haptic Perception &

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Sensing

Tactile Kinesthetic(position / force)

B R A I L L E

Manipulation

HAPTICS

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Haptic Perception &Human Response to VibrationsHaptic Perception &Human Response to Vibrations

Outline:

1. Neural Coding of Touch Primitives

2. Functions of Peripheral Receptors

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

1. Neural Coding of Touch Primitives1. Neural Coding of Touch Primitives

• Touch Receptors– Mechanoreceptors and their Function

– Other skin receptors: thermal, pain

– Kinesthetic receptors

• Pathways from receptors to brain

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Touch ReceptorsTouch Receptors

• Touch sensations are mediated by receptors that respond to pressure, vibration, and heat flow.

• The receptors are found in two regions:

-- Within skin: cutaneous sensing pressure, temperature, pain

-- Beneath skin in muscles, tendons, joints:

kinesthetic sensinglimb position and movement

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Classes of ReceptorsClasses of Receptors

• Receptors that respond to pressure and vibration are called mechanoreceptors

• Mechanoreceptors are found in skin (cutaneous) and muscles, tendons, and joints (kinesthesis)

• The skin also includes other receptors – that signal skin warming and cooling (thermo-receptors)

– that signal pain (nociceptors)

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Skin Mechanoreceptors have specialized endingsSkin Mechanoreceptors have specialized endings

Johannson & Valbo, 1983

Epidermis

Dermis

Subcutis

Meissner

Merkel

Ruffini

Pacinian

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Functional characteristics of Skin Mechanoreceptors:Receptive field size (I = small, II = large)and adaptation rate (FA = fast adapting, SA = slow adapting)

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

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Distribution of Mechanoreceptors on the Palm: Receptors with small receptive fields are densely packed on fingertips.

Distribution of Mechanoreceptors on the Palm: Receptors with small receptive fields are densely packed on fingertips.

Result: ~.5 mm 2-point discrimination on fingertip

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Frequency Sensitivity: One-channel-per-mechanoreceptor modelFrequency Sensitivity: One-channel-per-mechanoreceptor model

Amplitude required for threshold response at given frequency(dB relative to 1 μm)

Bolanowski et al., 1988

SA I SA II

FA I

FA II (PC)

Average data

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Thermo-ReceptorsThermo-Receptors

Thermo-receptors lack specialized endings; respond to temperature change.

Two populations of nerve fibers: warm and cold

Kenshalo, 1976

NormalBody temp

Cold fibers

Warmfibers

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

The brain: Primary and Secondary Somatosensory CortexThe brain: Primary and Secondary Somatosensory Cortex

SI includes Brodmann areas:3a: Muscle3b: Skin (SA and FA)1: Skin (FA)2: Pressure, joints

SI projects to SII, 5, 7

SI

SII

Central Sulcus SI Areas 5 & 7

SIILateral Sulcus

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Somatosensory “Homunculus” in SIresults from somatotopic mapping*Somatosensory “Homunculus” in SIresults from somatotopic mapping*

*Adjacent on skin⇒Adjacent in SI

There are severalsuch maps in SI and SII.

Penfield & Rasmussan, 1950

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Somatosensory areas in brain are plastic: Re-assignment of receptive fields after amputation of a digit

Somatosensory areas in brain are plastic: Re-assignment of receptive fields after amputation of a digit

Areas in SI that once responded to 3rd fingertip are now activated by finger 2 and 4, plus base of 3

Merzenich et al., 1984

Amputation point

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Cortical plasticity causes phantom limb painCortical plasticity causes phantom limb pain

ThumbIndex finger5th digit

Stimulating face and arm activates cortical areas previously responsive to fingers, now taken over by face and arm.

face finge

rs

arm

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

2. Functions of peripheral receptors2. Functions of peripheral receptors

• Slowly adapting cutaneous mechanoreceptors provide array (tactile) sensing.

• Fast adapting cutaneous receptors signal pressure changes on the skin.

• Kinesthetic mechanoreceptors provide a sense of limb position.

• Therefore, the mechanoreceptor populations support different human abilities.

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Grasping is supported by FAI mechanoreceptors that detect incipient slipGrasping is supported by FAI mechanoreceptors that detect incipient slip

FAIs fire under near-slipGrasp, lift… Return

Load Force N

Grip Force N

Position mm

Grip: Load ratio

Time

Load Force N

Grip Force N

Position mm

Force Ratio

FA ISA IFA IISA II

Slip threshold

Johansson & Westling, 1984; Westling, 1986

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Tactile Pattern Perception is based on SAI mechanoreceptorsTactile Pattern Perception is based on SAI mechanoreceptors

Input pattern

Response

Phillips, Johansson & Johnson, 1990

Spatial plot of the response of a skin mechanoreceptor to a Braille pattern swept through its receptive field: Each tick mark is a neural impulse given contact from that stimulus location.

PatternpreservationSA I

FA I

SA II

FA II

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Curvature perception also reflects SA I responsesCurvature perception also reflects SA I responses

-4 -2 0 2 4Distance of receptive field from center of indentation (mm)

MeanSA IResponse

Data are shown for 7 curves, ranging from radius zero to radius 1.44 mm

Goodwin et al., 1995

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

PC receptors (FA II) signal causes of deep vibrationsPC receptors (FA II) signal causes of deep vibrations• Transient vibrations from contact•Micron-element textural variations, as in this stimulus

Only Pacinian Corpuscles respond continuously to the textured portion of a half-textured plate with ht. 1 μm

Srinivasan, Whitehouse, & LaMotte, 1990

Stimulus plate Receptor Responses Therefore, PCs underlie roughness percept at micro-scale.

Slide courtesy of Prof. Roberta L. Klatzky, CMU, 2005

Impact on functions of cutaneous receptors when skin is covered with a rigid sheath

Impact on functions of cutaneous receptors when skin is covered with a rigid sheath

Decrements in spatial resolution, differential force sensing, pattern perception --but vibration (sensed by deeper PCs) remains essentially intact

Lederman & Klatzky, 1999

This simulates some force-feedback environments.