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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.