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Lecture 6

PSC 131 Lecture 6: Blindness and Recovery

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PSC 131
Geng Joy

I. Lecture 6 – V1 and Blindness (April 24, 2017) A. Class Summary 1. What happens to visual cortex when vision is absent? a. Hypothesis 1: Cross-Modal Plasticity i. The brain reorganizes to use visual areas to process other sensory modalities (e.g. touch) ii. Ex: Auditory cortex talking to visual cortex b. Hypothesis 2: Unmasking of existing connections i. Occipital lobe is not just visual, but under typical development, the visual modality dominates ii. Connections already existed, when vision is taken away, we can perceive them (unmasked) c. Hypothesis 3: Visual cortex is completely dormant d. Hypothesis 4: something else takes over, like language processing? i. Plasticity or unmasking can make a different reaction 2. 3 examples from the reading of evidence that visual cortex is used for processing Braille/tactile information in congenitally blind (born blind) a. fMRI visual activation in visual cortex to Braille b. Stroke (take out one part of brain, but can leave other areas untouched) c. TMS (magnetic pulses are put on head and disrupt neuron activity) 3. Unmasking Hypothesis: Teaching braille to blindfolded subjects a. People are blindfolded for a few weeks and learn tactile discrimination b. Experiments to see that other nonvisual properties appear if you’re blindfolded 4. Figure 1 from Amendi et al. (2005). Current Directions in Psychological Science a. Illustrates results from all three studies B. fMRI (Evidence Occipital Cortex is Important for Braille Reading) 1. Braille reading requires fine spatial acuity (from touch) a. Dependent on the ability to discriminate the little dots Different ways to slice a brain b. Analogous to visual cortex in terms of acuity and discrimination 2. What experiment to run if you wanted to know what brain activation in response to Braille reading? a. Control for: i. Touch of bumps (tactile discrimination) ii. Finger motion (other variables) 3. Experiment: a. Stimulus: b. Experienced under 2 condition: i. Braille reading (with purpose of reading) ii. Passive sweep c. What is the visual equivalent? i. Looking at words vs looking at a string of letters ii. Tracking eyes across a text vs just looking across a page 4. Activation associated with Braille reading in blind individuals compared to passive sweep a. (Trials of braille reading) – (Trial of passive sweep) = specific reading part of braille, but not detection of motion/touching b. Lots of occipital activation; more on the left than the right c. Surprising because you’d expect lots of language areas would pop up, but instead you see visual cortex 5. But this is different than it would be in individuals with typical vision? But they can’t read Braille, so how would you test this? a. Maybe, visual neurons have small receptor fields (high acuity vision); when you’re reading braille, you need high acuity processing (that is located in visual cortex, V1) 6. Tactile Discrimination: Braille Character Discrimination a. Ask whether individuals who are normally sighted if they have better or poorer tactile discrimination compared to congenitally blind individuals b. Are blind people better at this discrimination task compared to sighted individuals? 7. Areas with greater activation in blind than sighted tactile discrimination tasks C. *Stroke Case Study: (Evidence Occipital Cortex is Important for Braille Reading) 1. She started to learn to read Braille at age 6, and became a proficient reader. a. She used Braille extensively in college, graduated with a Bachelor's degree, and had been working for the National Radio Station for the Blind in Spain since age 22. b. At work, she would use Braille to communicate with colleagues, take notes, and write her reports and memos, which amounted to 4±6 h of Braille use each day. c. Her reading speed was remarkable, with a rate of 120±150 symbols/min. d. She used both hands and several fingers in each hand for character recognition. 2. She had a stroke – occipital lobe was affected by the stroke 3. Her MRI failed to document any lesions of the sensory motor cortices… did not reveal damage to language centers… no discernible difficulty in performing nonspatial tactile perception tasks... impairment of tactile information processing was apparently limited to her Braille reading skill. 4. On the second day, when she tried to read a Braille card sent to her, she was unable to do so. a. She st
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