1. 1 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”

2. 2 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

3. 3 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!

4. 4 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

5. 5 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 22 felt as 1

6. 6 2-point thresholds

7. 7 4 types of mechanoreceptors

8. 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

9. 9 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

10. 10 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

11. 11 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

12. Phantom limb: Sensation perceived from a physically amputated limb of the body. Residual activity in the brain makes phantom limb perception possible