1. Perception Sensory Maps (cortical maps) Vision Visual Attention Other sensory systems –Hearing (Audition) –Touch (Somatosensory) –Taste & Smell

2. Cortical Sensory Maps: A correspondence between an external dimension and an internal representation. Internal: Somatosensory Cortex External: Skin surface - 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”

3. Cortex (internal) Skin (external) 2-point discrimination

4. Representation In cortex 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 Congress USA Skin surface

5. Map in Primary Visual Cortex 1 2 3 Visual Field 1. Central vision (fovea) 3. Peripheral vision 2. Parafoveal vision Based on visual field, - fovea is overrepresented in visual cortex - peripheral vision (in blue) is underrepresented The fovea has larger visual acuity: It is easier to discriminate two nearby point in the fovea than in the periphery 1 2 3

6. Cortical Maps : Remapping due to lesion (Phantom limbs)

7. Braille reading activates ‘visual’ areas in blind subjects Cortical Maps : Remapping due to long-term sensory deprivation (blindness) But is this activation causally effective, or epiphenomenal?

8. 2. ‘Lesioning’ occipital cortex with TMS disrupts tactile discrimination, but only in the blind 1. A congenitally blind woman suffered a bilateral occipital strokes & became alexic (couldn’t read Braille anymore) Visual cortex is necessary for Braille reading in the blind

9. Cortical Maps : Remapping due to SHORT-TERM sensory deprivation (blindfolded for 5 days) Scientific American Frontiers: Changing Your Mind, 2000 Alvaro Pascual-Leone impact on performance (reading Braille) impact on cortical activation (touch finger with a brush) Day 1: Somato-sensory activation Day 5: Occipital activation too

10. 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! Is occipital activation necessary for performance?

11. Cortical Maps Learning Violin players (pantev)

12. Commonalities among Perceptual Systems Sensory receptors do transduction –(ex: mechanical --> electrical) Sensory receptors elicit graded potentials – response amplitude is equivalent to stimulus intensity

13. Link to other lectures http://www.pc.rhul.ac.uk/courses/Lectures/PS1061/L6/PS1061_6.htm Dissection of eye http://www.geocities.com/centennial3d/she ep_eye.htmlhttp://www.geocities.com/centennial3d/she ep_eye.html