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
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)
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
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
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
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