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the_cross_activation_theory [2010/05/17 15:12]
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the_cross_activation_theory [2010/05/17 15:13] (current)
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 **Evidence from the Phantom Limb** **Evidence from the Phantom Limb**
 Evidence from the phantom limb is proof that brain maps are highly malleable (not fixed at birth). The somatosensory area of the cortex that receives sensory information from the hand is adjacent to the area that receives it from the face. When an arm is amputated, signals from the face activate the original hand area of cortex and higher brain centers interpret this activation as arising from the phantom hand. Evidence from the phantom limb is proof that brain maps are highly malleable (not fixed at birth). The somatosensory area of the cortex that receives sensory information from the hand is adjacent to the area that receives it from the face. When an arm is amputated, signals from the face activate the original hand area of cortex and higher brain centers interpret this activation as arising from the phantom hand.
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 **Evidence from Acquired Cases** **Evidence from Acquired Cases**
 Evidence from patients with [[Definitions|Retinitis Pigmentosa]] provide further proof that brain maps are highly malleable. Some people with this disorder experience tactile sensations as visual phosphenes. Tactile input takes over for the absence of actual visual input and activates visual areas. Evidence from patients with [[Definitions|Retinitis Pigmentosa]] provide further proof that brain maps are highly malleable. Some people with this disorder experience tactile sensations as visual phosphenes. Tactile input takes over for the absence of actual visual input and activates visual areas.
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 How can you explain that Synaesthesia is unidirectional?​ Numbers are seen colored but presenting colors doesn’t evoke letters or numbers. Metaphors follow this same pattern of only following one direction (from auditory to visual modalities). People say “Loud Shirt” but never “Red Sound”. ​ This results from strong anatomical [evolutionary?​] constraints that permit certain types of cross-activation,​ but not others. A speculative response from Ramachandran on this matter: there is “something to do with the manner in which certain sensory dimensions like color are represented in brain maps, as opposed to the way in which numbers are mapped”. When a number evokes a color, there is something in the visual image (the number) that a color can be ascribed to. But what if a color evoked a number? Where would the number be, how big would it be? How can you explain that Synaesthesia is unidirectional?​ Numbers are seen colored but presenting colors doesn’t evoke letters or numbers. Metaphors follow this same pattern of only following one direction (from auditory to visual modalities). People say “Loud Shirt” but never “Red Sound”. ​ This results from strong anatomical [evolutionary?​] constraints that permit certain types of cross-activation,​ but not others. A speculative response from Ramachandran on this matter: there is “something to do with the manner in which certain sensory dimensions like color are represented in brain maps, as opposed to the way in which numbers are mapped”. When a number evokes a color, there is something in the visual image (the number) that a color can be ascribed to. But what if a color evoked a number? Where would the number be, how big would it be?
  
-**Objection from the Disinhibited Feedback Theory** +**Objection from [[The Disinhibited Feedback Theory|The Disinhibited Feedback Theory]]** 
-[[The Disinhibited Feedback Theory|The Disinhibited Feedback Theory]] --information is processed up through several levels of the sensory hierarchy to some multi-modal sensory nexus before being fed back to lower areas (V4). Whereas the cross-activation theory suggests connections are more local- they don’t need to go through all the processing before going to the V4 area again.+ -- In this theory, ​information is processed up through several levels of the sensory hierarchy to some multi-modal sensory nexus before being fed back to lower areas (V4). Whereas the cross-activation theory suggests connections are more local- they don’t need to go through all the processing before going to the V4 area again.
  
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