Transcript 2-point thresholds

Challenges
lack of invariance
visual
perception
auditory
perception
speech
perception
tactile
perception
no distinct segments
illusions
lightness
contrast
figure-ground problem
pitchsensory
depends on
interactions
loudness
overlapping events
burstare
depends
on
cues
contextfollowing
vowel
dependent
coarticulation
?
?
“bag”
1
Speech is Special because it is linguistic;
this requires an emphasis on the sound source.
Source is central to touch for different reasons
•No problem of getting the object up close
 touch is a so-called “near sense”
(implications for segmentation problem?)
•Qualities of object are qualities of perception
 implicit assumption of direct meaning
Taxonomy of object qualities tied to skin receptors:
•firmness  degree of skin compression
•shape  sequence of skin compressions
2
Speech is Special because it is linguistic;
this requires an emphasis on the sound source.
Source is central to touch for different reasons
•No problem of getting the object up close
 touch is a so-called “near sense”
(implications for segmentation problem?)
•Qualities of object are qualities of perception
 implicit assumption of direct meaning
Taxonomy of object qualities tied to skin receptors:
•firmness  degree of skin compression
•shape  sequence of skin compressions
•smoothness  frequency of skin compressions
•material  thermal conduction efficiencies
Fun fact: People can detect a bump only 1 micrometer high at 75% accuracy!
3
What do the psychophysicists measure?
Poke skin with a Von Frey hair. Do you feel it?
•sensitivity: weakest pressure that can be felt
If the amount of energy is too small, it’s not noticeable: Threshold
A thick hair with a little pressure 
a thin hair with a lot of pressure
 ambiguous input
4
More parallels with vision
Poke skin with 2 hairs. Do you feel 1 or 2?
2-point threshold
•acuity: smallest separation between 2 stimuli that is felt as 2
Can perception be tied to physiology?
1 felt as 1
2 felt as 2
2 felt as 1
receptive field organization
 threshold depends on size of receptive field
5
2-point thresholds
6
4 types of mechanoreceptors
7
• Other types of mechanoreceptors within
muscles, tendons, and joints:
– Kinesthetic receptors: Play an important role in
sense of where limbs are, what kinds of
movements are made
– Muscle spindle: A sensory receptor located in a
muscle that senses its tension
• Receptors in tendons signal tension in muscles
attached to tendons
• Receptors in joints react when joint is bent to an
extreme angle
• Importance of kinesthetic
receptors:
– Strange case of neurological patient
Ian Waterman:
• Cutaneous nerves connecting Waterman’s
kinesthetic mechanoreceptors to brain
destroyed by viral infection
• Lacks kinesthetic senses, dependent on
vision to tell limb positions
http://www.youtube.com/watch?v=FKxyJfE831Q
9
The importance of movement
•A stimulus applied without change eventually “disappears” through adaptation.
•If a stimulus is applied punctately to the hand, object identification is poor
1
2
3
vs.
•If a stimulus is manipulated by the hand, object identification is good
 a difference between passive and active touch.
Challenges notion of temporal integration over images
10
Exploratory procedure: A stereotyped hand movement pattern used
to contact objects in order to perceive their properties; each
exploratory procedure is best for determining one or more object
properties
Example: To determine roughness of an object, use lateral motion
11
Residual activity in the brain makes phantom limb perception possible
•
Phantom limb: Sensation
perceived from a physically
amputated limb of the body.