Perception • Sensory Maps (cortical maps) • Plasticity • Phantom limb • Blind & braille
Internal: Somatosensory Cortex External: Skin surface “Whoa! That was a good one! Try it, Hobbs – just poke his brain right where my finger is” Cortical Sensory Maps: A correspondence between an external dimension and an internal representation. - there is a topographic organization - Some skin areas are overrepresented in cortex
2-point discrimination Cortex (internal) Skin (external)
Map in Primary Visual Cortex 1. Central vision (fovea) 2. Parafoveal vision 3. Peripheral vision Visual Field 1 2 3 1 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
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?
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
Day 5: Occipital activation too Cortical Maps: Remapping due to SHORT-TERM sensory deprivation (blindfolded for 5 days) impact on cortical activation (touch finger with a brush) impact on performance (reading Braille) Day 1: Somato-sensory activation 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!
hearing: how high a frequency can you hear? • http://www.world-voices.com/software/nchtone.html