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Challenges

visual perception

auditory perception

speech perception

lack of invariance no distinct segments

lightness contrast

pitch depends on loudness

burst depends on following vowel

figure-ground problem

overlapping events

coarticulation

tactile perception ? ?

illusions

sensory interactions

cues are context-dependent

“bag”

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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?)

Speech is Special because it is linguistic; this requires an emphasis on the sound

source.

•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

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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?)

Speech is Special because it is linguistic; this requires an emphasis on the sound

source.

•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!

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What do the psychophysicists measure?

A thick hair with a little pressure a thin hair with a lot of pressure

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

ambiguous input

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Poke skin with 2 hairs. Do you feel 1 or 2?

•acuity: smallest separation between 2 stimuli that is felt as 2

2-point threshold

More parallels with vision

receptive field organization

1 felt as 1

Can perception be tied to physiology?

threshold depends on size of receptive field

2 felt as 2 2 felt as 1

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2-point thresholds

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4 types of mechanoreceptors

• 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

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• 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

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•A stimulus applied without change eventually “disappears” through adaptation.•If a stimulus is applied punctately to the hand, object identification is poor

Challenges notion of temporal integration over images

The importance of movement

a difference between passive and active touch.

1 2 3

vs.

•If a stimulus is manipulated by the hand, object identification is good

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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

• Phantom limb: Sensation perceived from a physically amputated limb of the body.

Residual activity in the brain makes phantom limb perception possible