tactile perception
TRANSCRIPT
Tactile perception
Mariacarla MemeoRobotics, Brain and Cognitive Science(RBCS)
Multisensory mapping groupIstituto Italiano di Tecnologia (IIT), Italy
● Perceptual process● Human sense of touch
1. Somatosensory system
2. Mechanoreceptors
3. Tactile acuity
4. Receptive field
● Electric metaphor of mechanoreceptors
Outline
Perceptual process
Skin
Skin - heaviest organ in the body
Functions:
Provides tactile information.
Warns us of damaging stimuli.
Contains body fluids and organs.
Protects against bacteria.
Regulates body temperature.
Why touch is important?
Haptic senses—or “touch”—is the most basic of senses; we learn this before vision and smell.
Everyday Tasks:
● Grasping objects;
● Dialing a phone;
● Playing a guitar or piano;
● Finding a light switch;
● Feeling your pulse.
Touch is complex (e.g. tying a shoelace): bi-directional communication channel – both input & output
Human sense of Touch
Touch helps us identify objects and provides unique information (e.g., texture, friction)
Skin structure and mechanoreceptorsu
Somatosensory system
Human Sense of Touch
Somatosensory system
The 'somatosensory system' is a sensory that detects experiences labelled as touch or pressure, temperature(warm or cold), pain(including itch and tickle) and those that belong to proprioception(muscle movement and joint position).
Somatosensory Cortex
Damage to somatosensory cortex destroys ability to recognize objects by touch.
The body is mapped topographically onto somatosensory cortex, but body parts are not represented equally.
Somatosensory Cortex
ANTEROLATERAL SYSTEM
This system is involved in the perception of touch, temperature, and sharp pain. Next instead is selectively involved in the perception of deep, chronic pain.
Somatosensory Pathway
Mechanoreceptors
These are thetissue “filter”between stimulusand nerve ending .
Each type encodesa different aspectof deformation.
(Stimulus)Mechanical
filter
Transducer(mechanical energy →bioelectric signals)
Encoder
Ruffini cylinder
Pacini corpuscole
Meissner corpuscole
Merkel receptors
Two types located close to surface of the skin
Merkel receptor fires continuously while stimulus
is present.
Responsible for sensing fine details
Meissner corpuscle fires only when a stimulus is
first applied and when it is removed.
Responsible for controlling hand-grip
Mechanoreceptors
Mechanoreceptors
Two types located deeper in the skin
Ruffini cylinder fires continuously to stimulation
Associated with perceiving stretching of the skin
Pacinian corpuscle fires only when a stimulus is first applied and when it is removed.
Associated with sensing rapid vibrations and fine texture
Mechanoreceptors
Mechanoreceptors
Mechanoreceptors – temporal features
Mechanoreceptors – spatial features
Tactile acuity thresholds are determined by Merkel receptors (SA1).
● Measuring tactile acuity
● Two-point threshold - minimum separation needed between two points to perceive them as two units
Tactile acuity
● Measuring tactile acuity
● Grating acuity - placing a grooved stimulus on the skin and asking the participant to indicate the orientation of the grating
Tactile acuity
Tactile acuity
Merkel receptors are densely packed on the fingertips - similar to cones in the fovea.
Both two-point thresholds and grating acuity studies show these results
The receptive field of an individual sensory neuron is the particular part of the body surface in which a stimulus will trigger the firing of that neuron.
The two-point threshold for any part of the body is determined by the size of the receptive fields and the extent of overlap.
Receptive Field
Tactile acuity is determined by how close the mechanoreceptors are to each other and by the size of the receptive field
Receptive Field
Inhibitory region
Excitatory
region
Receptive FieldMechanoreceptors found in areas of the body with less tactile acuity tend to have larger receptive fields.
Electrical metaphor
Ruffini cylinder
Pacini corpuscole
Meissner corpuscole
Merkel receptors
● Perceptual process (continue)● Meaning
1. Psychophysics
2. Absolute threshold
3. Differential threshold (Just Noticeable Difference)
● Tactile feedback
● Tactile technologies
● Simulate tactile perception (our robot)
Outline
Perceptual process
Science that focuses on how the physical environment is integrated into our personal, subjective world.
● Ernst Weber & Gustav Fechner -- psychophysicists
Psychophysics
● Weber published “De tactu” describing the minimum amount of tactile stimulation needed to experience a sensation of touch – the absolute threshold.● Using weights he found that holding versus lifting them gave different results
(due to muscles involved).
● He used a tactile compass to study how two-point discrimination varied across the body.● On the fingertip .22 cm, on the lips .30 cm,
on the back 4.06 cm.
Absolute threshold
Aesthesiometric compass
● Weber studied how much a stimulus must change in order for a person to sense the change.● How much heavier must a weight be in order for a person to notice that it is
heavier?
● This amount is called the just noticeable difference JND
Just Noticeable Difference (JND)
1)A stimulus is presented at astarting quantity Q.
1)Once the subject is adapted tothis stimulus, the attribute isincreased …
…each time the subject is asked…
yes or no
if there is a difference in thestimulus.
Just Noticeable Difference (JND)
After repeated trials theincrement T that produces a
perceptible difference
is identified:
75% of right difference inthreshold identified.
Just Noticeable Difference (JND)
After repeated trials theincrement T that produces a
perceptible difference
is identified.
It is calculated when the
75% of right difference inthreshold identified.
Just Noticeable Difference (JND)
When the starting quantity is thestimulus zero value (completeabsence of the stimulus), thenthe first jnd value T is called
… absolute threshold Q0…
This is the minimum stimulusquantity necessary to produceany sensation.
Just Noticeable Difference (JND)
● JND can be expressed as a ratio:
where (Q + Q0) is stimulus magnitude and k is a constant and DQ means the change in R (D usually means change).
or
● Weber's law asserts that the ratio k is constant across a wide range of stimulus quantities, although the value of k is different for different sensory domains or types of stimulus.
kQQ
T
)( 0
Just Noticeable Difference (JND)
kQQ
Q
D
)( 0
● Fechner related the physical and psychological worlds using mathematics.
● Fechner (1860) said:“Psychophysics, already related to physics by name must on one hand be based on psychology, and [on] the other hand promises to give psychology a mathematical foundation.” (pp. 9-10)
● Fechner called Weber’s finding about the JND “Weber’s Law.”
Fechner Contribution
● Fechner's Law allows the estimation of the sensory intensity (S) from the stimulus quantity:
where S is sensation, k is Weber’s constant and R is the magnitude of a stimulus
● The larger the stimulus magnitude, the greater the amount of difference needed to produce a JND.
)log( 0QQkS
Fechner Contribution
Relationship of JND with Stimulus
)log( 0QQkS
● His methods are still used in psychophysics.
● Ideas from signal detection theory have been applied to a wide variety of other topics.● Threshold for criminal behavior, scenic beauty.
● Scaling techniques, including rating scales, were placed on a sound scientific basis, especially by S.S. Stevens modified Fechner’s Log
Law to a Power Function in the early 1950’s.
Fechner Contribution
Goal is to stimulate the skin in a programmable manner to create a desired set of sensations.
Tactile feedback is generated by a tactile device, sometimes called a tactile displays or tactile interfaces.
Tactile feedback aims to create a metaphor to communicate specific information.
Tactile Feedback
Pins or other mechanical vibrating elements, such as servo motors - either alone or in an array, as in devices for Braille display
● typically used for fingertip stimulation
Tactile Technologies
Wagner & Howe 2002
Kyung et al. 2006
Brayda et al. 2010
Cannella 2009
Tactile device, able to deliver simple tactile maps of virtual objects by means of heights information.
TActile MOuse (TAMO)
Cushions of air can be inflated or deflated to vary pressure on skin
Tactile Technologies
Okamura et al. 2014Chih-Hung King 2008
Siarhei Vishniakou et al. 2013
● Skin stretch to simulate moving stimuli.
● Electro-tactile devices.
Hayward et al. 2003-7Provancher et al. 2013
Kajimoto laboratory 2014
Tactile Technologies