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Haptics Technologies:Bringing Touch to Multimedia

C3: Human Haptic Perception

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Introduction Understanding of the Human perception process To design and develop of haptic devices

Psychophysics What are the smallest stimulus intensities that the

human skin can sense for various stimulus conditions? What is the response to stimulus magnitude increment?

Neurophysiology: cognitive science What organs are involved in tactile stimuli? What is the path for the sensed information transmitted

to the brain What parts of the brain processes the information

Pathway of Tactile Perception

Skin Spine Brain

Receptors Spinal Cord

Thalamus

Cortex

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Touch and Cognition Touch is different from other senses(smell,

hearing, visual) Touch is bidirectional(sensing and acting)

Touch can be either Passive & Active Passive tactile is limited to the zone of contact with objects Kinesthetic perceptions are integrated by cutaneous perceptions

and voluntary movement to compensate exploration

Touch provides information about spatial and physical properties of the environment : Texture, mass, direction, shape, size, etc. Touch is perceived through haptic receptors

Touch and Cognition Haptic perceptors(3) (1) Thermo receptors

Temperature signals such as heat or cold

(2) Nociceptors Perception of pain

(3) Mechanoreceptors Mechanical actions: Force,vibration and pressure

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Human Haptic System Four Components:

Mechanical, sensory, motor and cognitive.

Mechanical Arm, Forearm and the Hand The Hand possess more than 21 degrees of freedom

for dexterous exploration and manipulation Sensory(Somesthetic) Various classes of receptors and nerve endings in the

skin, joints, tendons and muscles:

Human Haptic System

Motor & Cognitive Physical stimulus activates

receptors and causes them to convey sensory information via afferent neurons to central nervous system.

Then, the brain analyses and “perceives” this information and release appropriate motor commands to activate the muscles and initiate hand or arm movements

Brain

Muscles

Hand

Skin Sensors

Motor

CommandsMotion

Contact

Forces

Tactile/Kinesthetic

Information

Arm-Hand Haptic System Human Hand Anatomy

Opposite to the wrist and at the outer edge of the palm, are five digits: the thumb, index, middle, ring and little.

Mechanical Replication Allows fine and gross motor actions The metacarpals articulate with the carpal

bones, which, in turn, articulate with the ulna and radius bones of the forearm to form the wrist joint

Different electromechanical and kinematic models of the hand's finger tendons and their relations to the finger joints have been proposed

Arm-Hand Haptic System Mechanical Replication

Different electromechanical and kinematic models of the hand have been proposed

Aspects of static and kinetic friction are major challenges in the control of a mechanical hand model.

linearity relationships between tendon displacement and joint angles play an important role in deriving accurate, dynamic models.

Currently, no electro-mechanical tactile display can present multiple cutaneous sensations at once

Arm-Hand Haptic System Forearm

The structure on the upper limb that is sandwiched between the elbow and the wrist

The elbow behaves like a hinge joint between the humerus and ulna; the movement is along one direction and is comparable to a mechanism by which a door or a lid opens and closes.

In robotics, when a robot arm grasps an object, the interaction involves the real world.

The capability of grasping for a robot involves many considerations to cover even basic human activities

Human Sensory System

Characteristics of somesthetic system Human body, including skin senses, proprioception and feeling

in the internal organs. The system is non-homogenous(widely disperse and diverse)

Components of Somesthetic system (1) Touch receptors.

The “input devices” of the human body

(2) Connections to the brain The “wiring” between the brain and the receptors

(3) The touch mapped in the brain Where the information is processed

[Greek sma, body; see soma + Greek aisthtikos, of sense perception; see aesthetic.]

Touch Receptors

Characteristics of sensory receptor Transform a physical stimulus into a signal readable by the

nervous system.

Transformation steps (1) First step: to cause a change in the electrical conductance

Changing the conductance of the membrane channel of the receptor.

(2) To create an impulsive discharge The action of a nerve cell generating an impulse

The change in the conductance of the membrane channel increase its potential resulting on a propagation signal.

Mechanical deformation of the skin is processed by cutaneous mechanoreceptors

Cutaneous Mechanoreceptors Four: Meissner’s

corpuscles, Pacinian corpuscles, Merkel disks and Rufffini endings

The mechanoreceptors differ in their frequency range, responding stimulus quality, receptive field size and adaptation

Mechanoreceptors FeaturesMeissner's Corpuscle Merkel Disk Ruffini’s Ending Pacinian 

Corpuscle

Position Below the epidermis Between Epidermis and dermis Dermis Dermis(Deep)

Frequency Range 10‐60 Hz 0.4‐100 Hz 0.4‐100 Hz. 70‐1000 Hz

Perceiving    Property Flutter Pressure

Stretching Vibration

Receptive FieldSmall small

Large Large

Receptive Area13 mm2 11mm2

59mm2 101mm2

Touch System in the Brain

Homunculus : outer layer of the brain(Primary somatosensory cortex (SI))

Lips & Fingers have high acuity of perception and comprise large areas

of the homunculus

From the somatosensory cortex, messages about sensory input are sent to other areas of the brain, like motor areas for generating actions.

somatosensory system - the faculty of bodily perception; sensory systems associated with the body; includes skin senses and proprioception and the internal organs

The Motor System

The motor subsystem comprises contractile organs (such as muscles) by which movements of the various organs and body

parts are affected.

The median and ulnar nerves are the major nerves of the hand.

The movements of the human hand are accomplished by two sets of muscles and tendons: the flexors, for bending the fingers and

thumb, and the extensors, for straightening out the digits

Haptic Cognition

“Haptic cognition includes the processes of assigning meaning to sensed patterns and of executing intentional acts”.[Reiner 2004]

Haptic Cognition involves tactile and kinesthetic perception

Active exploration a cyclic process Assigning meaning to sensory patterns Not all of the sensory information is needed

Haptic Exploration

Haptic perceptual exploration allows to recognize objects and their spatial features

Active and Passive tactile Recognition Exploratory Procedures[Lederman and Kaltzky] Typical movements patterns employed to

perceive a certain tactile attribute

Exploration of Perceptual Metrics

Sensing bandwidth is the Maximum frequency at which a touch stimulus

can be sensed Sensing Bandwidth is asymmetric: humans can sense haptic stimuli much faster that they

can respond Well-established metrics of roughness, hardness,

and stickiness characterize the state of haptic perception.

Exploration of Perceptual Metrics The bandwidth with which a human can react to

unexpected force/position signals is 1-2 Hz. The ability of hands and fingers to exert force is about 5-

10 Hz. The human fingers and hand require the force input

signal to be present at about 30Hz (from 20-50Hz) in order to perceive meaningful information.

the bandwidth beyond which the human hand and fingers can discriminate two consecutive force input signals to be at about 320 Hz, after which they are just sensed as vibrations.

The bandwidth of tactile sensing varies from 5 Hz up to 10 KHz.

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Concept of Illusion

Visual illusion creates an ambiguous situation and confuses the brain: Example: when sitting on a train and looking out the

window at a neighboring train, if the other train starts moving, there is an ambiguous situation: which train is actually moving?

For centuries, perceptual illusions were thought to concern only the visual system due to some specific properties such as color, and temporal and spatial sensitivity.

Concept of Illusion Three important geometric

illusions are well discussed in the literature: the Muller- Lyer illusion, the vertical-horizontal illusion, and the Delboeuf illusion.

Research evidence shows that illusions also occur when stimuli are presented tactually and are pretty similar to vision

Muller-Lyer illusion

Delboeuf Illusion

Perceptual Parameters for Design & Development of Haptic Devices Haptic devices try to recreate the stimulus that a

real environment might exert on our skin and muscles.

Due to the fact that the haptic system is bidirectional design deals with different limitations: Force & Torque simulations

Two functions: measuring the position and contact forces of the user's hand and/or other parts of the body, and displaying contact forces and positions and/or their spatial and temporal distributions to the user.

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Human Factors for Design & Development of Haptic Devices

Influenced by the fundamentals of biomechanical, sensorimotor, and cognitive abilities of the human haptic system.

The human factors that influence the quantitative performance of force-reflecting haptic interfaces have been studied by many researchers:

The following perceptual elements are considered: (1) force sensing, (2) pressure sensing (3) position sensing

resolution, (4) stiffness, (5) human force control, (6) temperature perception, and (7) friction perception.

Kinesthetic Perception

Quantitative measures for the design specifications of force-feedback haptic interfaces

Perception presentation Force sensing

range between 2.5 to 410 Newtons

Position sensing resolution. as the smallest change on the end effector of a haptic device

that can be detected in dpi or in millimeters (Single point of interaction

Kinaesthetic Perception Stiffness requires a minimum

threshold to emulate a rigid object in a virtual environment(VE)

Experimental Study: Minimal stiffness for a rigid

object perception is 242 N/cm.

Range varies with from 153 to 415 N/cm according with standard deviation of l

Tactile & Kinaesthetcic Perception Pressure is a tactile sensation and proprioceptive

or kinesthetic perception Refers to the awareness of one's body state when

perceiving a continuous physical force exerted on or against it

The perceptual thresholds for touch depend on location, stimulus type, and timing states. For example, in order to apply two separate stimuli to

the index finger, the tactile actuators should be at least 2.5 mm apart.

Tactile & Kinaesthetcic Perception Pressure findings present different levels of

sensitivity dependent on body loci and gender, hence the JND values vary from 5 milligrams (mg) on a woman's face to 355 mg on a man's big toe.

kinesthetic devices: For example, pressure decreased at a ratio of 1:4

(from15.6% to 3.7%) when the contact area increased by a factor of 16 (from 1.3 to 40.4cm2) humans are less sensitive to pressure changes when the

contact area of the forearm is reduced

Perception of Temperature

Temperature is sensed by thermo-receptors that responds to specific temperatures and to changes in temperature

Two types: Warm fiber : Increases its response rate as the

temperature is increased and continues to fire as long as the high temperature continues

Cold fiber : Increases its response rate as the temperature is decreased and continues to fire at low temperatures.

Perception of Temperature Cold receptors are more numerous than warm

receptors by a ratio of up to 30:1 when the skin temperature is maintained at 30-

36◦C, no thermal sensation is noted The properties of the human thermal system:

Friction Perception

Resistance to motion in haptic interfaces has also been considered in the design and development of such devices

Quantifying perceptual thresholds of friction: the resistance defined under Coulomb friction; viscous

and inertial forces; and mechanical imperfections. observers perceived small differences around 0.2

microns at high frequencies.

Outline

Introduction Touch and Cognition Human Haptic System Concept of Illusion Human Perceptual Parameters Remarks

Closing remarks

Haptic perception is typically characterized as the process of recognizing objects through touch

The flow of sensory information through biological elements such as sensory receptors and sensory afferent neurons.

The study of haptic perception has encouraged the new research domain of haptic technology.

Future research into the sense of touch must recognize the complexity of reproducing this type of interaction.

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