blakemore and cooper

• previous research- hubel and wiesel


  they used single-cell recording to record the electrical activity of individual nuerons in the visual cortex of kittens. they found that neurons in the main part of kittens brains do not respond to the environment in a random way . they found that all the cells responding to one angle were grouped together in columns which shows that cells in the visual cortex are highly organised.
• background research- hirsch and spinelli


  rasied kittens in darkness, after 3 weeks were given daily sessions where one eye could only see vertical lines and the other horizontal.

  they found that cells linked to 'the vertical eye' now only responded to vertical lines and and cells linked with the 'horizontal eye' now only responded to horizontal lines. therefore, the visual cortex cells had been 'forced' to adapt to the kittens' unusual environment .
• what is brain plasticity?


  the brain's tendency to change and adapt as a result of learning and experience
• aim 1

  to look further at the physiological and behavioural effects of restricted early visual experience on the development of the cells of the visual cortex
• aim 2 - (nurture v nature)


  to consider whether brain development/plasticity occurs due to nurture rather than nature.
• what type of experiment and design was used?


  a lab experiment with an independent measures design
• what was the IV?


  whether the kittens were reared in a horizontal or vertical environment
• what was the DV?


  the behavioural and nuerophysical effects observed after being reared in a visually restricted environment
• what was the sample used?


  newborn kittens at the beginning of the study and mature cats of 5 months old when the behavioural testing began.
• how many cats' results were used?


  2 of the cats nuerophysical responses were reported
• how old were the cats at the point of nuerophysical testing?


  7.5 months old
• characteristics of the cylinder used


  kitten stood on a clear glass platform in a tall cylinder .

  the entire surface was covered with contrasting black and white stripes of varying widths.

  one cylinder had vertical stripes and the other horizontal.

  there were no corners anywhere nor edges.
• kittens collar worn + purpose


  the kitten wore a wide black collar to prevent it being able to see its body which would have introfuced new line orientations. the collar restricted the visual field to a width of about 130 degrees.
• cylinder dimensions


  cylinder was 2 metres high with a 46 cm diameter
• how long did the kittens spend in darkness?


  for the first 2 weeks of their lives they were in a completely dark room and were allowed normal binocular vision
• what happened after 2 weeks?


  they were placed in the cylinder for an average of 5 hours a day. the rest of the time was still spent in the dark room.
• what did blakemore and cooper report about the kittens response to the environment


  the kittens did not seem upset by the restricted environment . they sat for long periods of time inspecting the walls of the tube
• why was this routine stopped at 5 months?

  this was shown to be well beyond the critical period for visual development
• what would have happened if it was stopped previous to 5 months old?


  under 5 months old, visual experience causes physiological changes to the visual system . if the kitten had been exposed to normal visual stimulation within this period , recovery may have been possible. therefore it was necessary to ensure the critical period had passed.
• what happened after 5 months?


  they were taken to another room for severla hours a week. the room was small, well -lit and had chairs adn tables. the cast visual experiences were observed
• how was the possible extraneous variable of astigmatism controlled?


  to prevent possible blurred vision explaining the cats' behavioural difficulties the cats were given contact lenses, spectacle lenses and 3mm artifical pupils, which ensured that the 'reflective state' of the eye was corrected
• what happened in the behavioural testing?


  the cats initial responses to the new visual world were observed before any learning could take place. further observations were made over the following weeks as they learned to 'see' the new visual environment
• how were cats anaesthesised for nuerophysical testing?


  at 7.5 months the cats were anaesthesised using nitreous oxide and and temporarily paralysed using succinyl choline.
• how was activity in the primary visual cortex tested?


  using micropipettes filled with sodium chloride . this micropipette allowed researchers to record activity in single nuerons in the primary visual cortex
• how was this controlled


  thin bright slits or edges were shown on a screen 114cm from the cat, the brightness of the background of the stripes was carefully controlled . one long cut was made into the medial edge of the post lateral gyrus . every single nueron was tested
• where else was the electrode inserted


  in other positions in Brodmann's area 17 - therefore this exploration covered many cortical columns
• behavioural assessment- results 1

  (temporary/permanent deficits)


  temporary deficits- visual placing reflex was not shown immediately- within 10 hours this reflex had recovered and the cats could jump from floor to table

  
  

  permanent deficits- cats often reached out to touch something that was actually quite far away
• behavioural assessment - results 2


  when shown a long black rod held vertically and shaken , teh cat raised with vertical stripes would watch it, run to it and play with it. if the rod was then held horizontally the other cat would do the same but the first one completely ignored it .
• neurophysiological assessment -results 1


  in both cats, 75% of the cells were clearly binocular and in almost every way responded as a normal animal would
• neurophysiological assessment- results 2


  abnormal responses to lines of certain orientations -

  in the horizontal cat the cells in the visual cortex did not respond to lines within 20 degrees of the vertical orientation and only 12 of the 52 neurons (columns) responded within 45 degrees of the vertical orientation. (vertical lines were not seen)
• neurophysiological assessment - results 3


  the anisotropy was signfiicant, at p<0.00001 (using chi squared)
• conclusion 1 - nature/nurture


  nature (the visual cortex) may adjust itself as it matures in response to visual experience, aka, nature (brain) is modified by nurture (experience) so that the biological system fits the demands of the environment
• conclusion 2- nervous system


  in this study cells seemed to change from their preferred innate orientation towards the orientation that was common in experience . this suggests that the unused parts of the nervous system didn't simply degenerate but adapted to match the actual visual input experienced.
• research method strength


  lab experiment - close control of extraneous variables eg artifical eye lenses worn.
• how is it shown that a lab experiment was used?

  clear IV and DV used

  close control
• research method weakness


  artificial environment may act as an extraneous variable. may be that the distress caused by the experience affected the devlopment of kittens/cats . this means the effects of visual deprivation observed may not generalise to everyday experiences
• sampling strength


  use of animals not humans improves ethics and allows a useful insight into brain plasiticty to be created which otherwise couldn't happen with human infants
• sampling weakness


  can't generalise to a wider human population. humans visual system is far more complex than cats despite both being mammals and some some similariites between visual systems. reduces population valdidity.
• validity evaluation


  internal validity - can infer that the IV causes the DV

  lab experiment improves validity

  low population validity - lack of generalisability
• reliability strength


  standardised procecures used in lab environment , eg all same size cylinders, kittens always left for 5 hours in speical environment