Transcript Perception
Perception
• Sensory Maps (cortical maps) • Vision • Visual Attention • Other sensory systems – Hearing (Audition) – Touch (Somatosensory) – Taste & Smell
Cortical Sensory Maps: A correspondence between an
external dimension
and an
internal representation
.
External
: Skin surface
Internal
: Somatosensory Cortex - there is a topographic organization - Some skin areas are overrepresented in cortex “Whoa!
That
was a good one! Try it, Hobbs – just poke his brain right where my finger is”
2-point discrimination Skin (external) Cortex (internal)
USA Skin surface Representation in Congress
Based on sq footage (skin)
, New Jersey is overrepresented Wyoming is underrepresented
Based on # of people (nerve endings, sensory acuity)
no difference bt NJ & WY Representation In cortex
Map in Primary Visual Cortex Visual Field 1 2 3 1. Central vision (fovea) 2. Parafoveal vision 1 3. Peripheral vision 2
Based on visual field
, - fovea is overrepresented in visual cortex - peripheral vision (in blue) is underrepresented 3 The fovea has larger visual acuity: It is easier to discriminate two nearby point in the fovea than in the periphery
Cortical Maps : Remapping due to lesion (Phantom limbs)
Cortical Maps : Remapping due to long-term sensory deprivation (blindness) Braille reading activates ‘visual’ areas in blind subjects But is this activation causally effective, or epiphenomenal?
Visual cortex is necessary for Braille reading in the blind
1. A congenitally blind woman suffered a bilateral occipital strokes & became alexic (couldn’t read Braille anymore) 2. ‘Lesioning’ occipital cortex with TMS disrupts tactile discrimination, but only in the blind
Cortical Maps : Remapping due to SHORT-TERM sensory deprivation (blindfolded for 5 days) impact on performance (reading Braille) impact on cortical activation (touch finger with a brush) Day 1: Somato-sensory activation
Day 5:
Occipital activation too Scientific American Frontiers: Changing Your Mind, 2000
Alvaro Pascual-Leone
Is occipital activation necessary for performance?
• Subject blinfolded for 5 days • Discrimination task: stimulate finger with pairs of Braille letters • TMS in visual cortex for 10 mins: decreases accuracy • Take off blindfold and allow vision • TMS in visual cortex after a few hours of vision: does
not
affect performance!
• Cortical Maps • Learning •Violin players (pantev)
Commonalities among Perceptual Systems
• Sensory receptors do transduction – (ex: mechanical --> electrical) • Sensory receptors elicit graded potentials – response amplitude is equivalent to stimulus intensity
Link to other lectures
• http://www.pc.rhul.ac.uk/courses/Lectures/PS1061/L6/PS1061_6.htm