Blakemore and Cooper

• Background: Visual cortex - previous research

  Hubel and Wiesel:

  • Stimulated individual neurons in the visual cortex and found there are columns of cells that respond to 1 particular orientation of a line
  • If an eye sees a line slanted at 45 degrees, only 1 column responds to the electrical signal

  Other research:

  • Animals are born with orientation columns but if they aren’t used they disappear
• Background: Hirsch and Spinelli

  • Raised cats so only one eye was exposed to horizontal lines and the other eye was only exposed to vertical lines
  • Cells that usually responded to vertical lines only responded to input from one eye
  • Therefore vision is monocularly driven instead of binocularly driven
• What were the aims?

  • Look at the physiological and behavioural effects of restricted early visual experience on the development of cells of visual cortex
  • Consider whether brain development / plasticity occurs because of nurture compared to nature
• What was the method?

  • Lab experiment
  • Independent measures
  • Longitudinal

  IV - Raised in horizontal environment or a vertical environment

  DV - Behavioural orientations - 5 months old

  Physiological orientations - 7 and a half months old
• Procedure: Where were the kittens kept?

  • Kitten in completely dark room from birth and allowed binocular vision
  • 1st 2 weeks kitten in dark room permanently
  • Kitten placed in cylinder with black and white vertical or horizontal stripes of different widths, on clear glass floor and wearing black collar to prevent seeing own body
  • 3 weeks - 3 months old for 5 hours everyday, in dark room for rest of day
• Procedure: What was the neurophysiological assessment?

  • At 7.5 months, each kitten anaesthetised and temporarily paralysed to check neurophysiology 
  • Tested using an electrode inserted into each unit, measuring electrical finding of each individual neuron 
  • The cats eyes were shown lines of all possible orientations to test what neurophysiological responses there were
• Procedure: What was the behavioural assesment?

  • Cats initial responses to visual world were observed 
  • Further observations were made over weeks as they learned the new environment 
• What was the sample?

  • 2 cats
  • One raised in vertical and one raised in horizontal
  • New born kittens at the beginning so their visual cortex was only affected by nature

  Behavioural testing - 5 months old

  Neurological testing - 7.5 months old
• Procedure: Exposure to normal environment

  • Took to small well-lit room, with tables & chairs for several hours a week
  • Kittens past critical period at 5 months and visual system fully developed
  • Given artificial lenses ensuring visual struggles not due to astigmatism  
• Results: Behavioural assessment

  • Some reflexes were normal

  Temporary deficit - visual placing reflex not shown immediately (reaching out legs to nearby surface)

  • After 10 hours of visual experience, this reflex has recovered

  Permanent deficit - cats often reached out to touch something that was actually far away

  Difference between horizontal and vertical cats:

  • Rod shaken where kittens chase rod

  Shake rod horizontally - only horizontal kitten responded

  Shake rod vertically - only vertical kitten responded
• Results: Neurophysiological assessment

  • In both cats 75% of cells in visual cortex were binocular and responded in almost every way as a normal animal
  • In horizontal cats the cells in the visual cortex did not respond to lines within 20 degrees of the vertical orientation and only 12 / 52 neurons responded within 45 degrees of the vertical orientation so vertical lines not seen
  • Similar in vertical cats but to horizontal or near horizontal lines

  
• What were the conclusions?

  • Nature (the brain) is modified by nurture so the biological system fits the demand of the environment
  • The unused parts of the innate nervous system don't degenerate and adapt to match the actual visual experience
  • Both conclusions demonstrate brain plasticity