Blakemore and Cooper (1970) - Visual Development

• background


  → neuroplasticity ;

  • the brain changes in response to external stimuli
  • e.g. environmental experiences

  → neurons ;

  • brain // nerve cells ,, differences neurons can have specialist functions
  • e.g. motor or sensory neurons

  → visual cortex ;

  • part of the brain that plays an important role in processing visual information ,, located at the back of the skull

  → monocular ;

  • relating to one eye

  → binocular ;

  • relating to both eyes
• aim

  → the aim of the study was to test whether kittens raised in an environment consisting of only horizontal or vertical stripes would develop normal vision

  • the researchers therefore wanted to test if brain plasticity occurs due to experiences rather than due to nature
• method ; design

  → study was a lab experiment ,, taking place in a controlled artificial environment

  → the participants in the study was newborn kittens who were immediately placed into a dark room.

  → at 2 weeks of age ,, the kittens were then randomly placed into one of the two conditions for five hours a day ;

  • IV - this was either a horizontal // vertical environment
  • DV - whether kittens raised in a horizontal environment could detect vertically aligned objects and vice-versa
• method ; procedure

  → newborn kittens immediately placed in a dark environment

  → at 2 weeks old ,, they were randomly placed in either a horizontal or vertical environment (a cylinder with black and white stripes of different width) for 5 hours a day

  → kittens has to wear a wide collar so they couldn't see anything other than the stripes

  → after 5 months ,, the kittens were moved from their dark cage to a well-lit ,, furnished room to see how they behaved once exposed to a 'normal' environment
• controls

  → the cylinders were identical ;

  • i.e. same length // diameter with the same floor and cover (only difference was the IV - the type of stripes)

  → the kittens spent the same amount of time each day in the cylinders (5 hours)

  → any time they were not in the cylinder ,, all kittens were kept in the dark

  → all kittens wore a collar so that all they could see was the stripes they were exposed to
• results ; behavioural ~ 2

  → all kittens showed behavioural blindness ; they couldn't detect objects or contours that were aligned in the opposite way to their previous environment. the horizontal-raised kittens couldn't see vertical lines ,, and the vertically-raised kittens couldn't see horizontal lines

  → only a horizontally-reared kitten would respond to a sheet of Perspex like this - a vertically-raised kitten would show no response

  → only a vertically-reared kitten would respond to a rod that was shaken in front of them like this - a horizontal-raised kitten would show no response
• results ; behavioural ~ 1


  → all cats showed visual impairment ,, and didn't show 'normal' behaviours such as visual placing

  → the cats didn't show a 'startle' response when an object was thrust towards them ,, but did show fear when they reached the edge of a table they were walking on

  → however ,, after about ten hours' exposure to the well-lit room ,, these deficits disappeared and they began to show visual placing ,, startle responses and would jump easily from a chair to the floor
• results - neurophysical 


  → the neurons in the visual cortex of a normal cat would be distributed in this (in both horizontal and vertical directions)

  • however ,, the horizontal-raised kittens (left) has no neurons in the vertical orientation ,, and the vertically-raised kittens (right) has no neurons in the horizontal orientation. these distributions are completely abnormal

  
• conclusion

  → this study provides evidence for plasticity in the brain ,, as the neurons in the visual cortex changed according to the stimulation they had received

  • i.e. the environment the kittens had been raised in

  → however ,, we have to be cautious when generalising this conclusion to human brains

  • are the differences between humans' and cats' brain just quantitative (i.e. different in size) ,, or are the brains qualitatively different?
• evaluation ; STRENGTH

  → RESEARCH METHOD ;

  • As this was a laboratory experiment, the kittens’ environments were highly controlled and therefore causal conclusions can be made. The study has levels of internal validity - we can infer that the IV (environment) directly caused visual impairment and neurophysiological damage (DV). 
  • The study could also be easily replicated in order to test the reliability of the findings (although this wasn’t done) = high in reliability
• evaluation ; WEAKNESS ~ 1

  → ETHICAL CONSIDERATION ;

  • exposing animals to a dark room for two weeks and then up until 5 months of age a visually depriving environment, could be considered to be psychologically harmful for the kittens. However, B&P reported no distress from the animals. Furthermore, the study complied with the ethical guidelines for animal research. It could also be argued that any harm to the animals were outweighed by the usefulness of this research
• evaluation ; WEAKNESS ~ 2

  → SAMPLING BIAS ;

  • B&P would argue that due to some physiological similarities between cats and humans, we can generalise results to humans. However, critics would argue against this due to obvious differences between the species. Furthermore, as the sample was very small (only 2 cats’ neurophysiology was examined) we may not be even able to generalise to other cats!