Blakemore & Copper

• Background:

  The physical structure of the brains of humans and cats is

  very similar: both have cerebral cortices with similar

  lobes, both have grey and white matter.

  Kittens’ brains have a neuroplasticity.

  Hirsch and Spinelli (1970) reported that early visual

  experience can change neural organisation in kittens.

  Vertical eye responded to vertical objects and horizontal

  eye to horizontal objects.

  Their approach is slightly different in that they allowed

  kittens normal binocular vision in an environment

  consisting entirely of horizontal or vertical stripes
• Aim: To investigate the development of the primary visual cortex (in cats) and to find out if some of its properties such as orientation selectivity are innate or learned.
• Research method:

  • lab exp
  • independent measures
• IV: whether the kittens were reared in a horizontal or vertical environment
• DV: visuomotor behaviour once placed in an illuminated environment
• Method:

  • Kittens studied from birth were randomly allocated to one of the two conditions and were housed from birth in a completely dark room. From two weeks they were put into a tall cylinder for an average of about five hours per day.
  • The kitten stood inside the cylinder the entire inner surface of which was covered with high contrast black-and-white stripes, either vertical or horizontal.
• Method pt2:

  • The cats wore a wide black collar that restricted its visual field to a width of about 130 degrees The routine stopped at 5 months old The kittens were taken for several hours each week from their dark cage to a small, well-lit room, furnished with tables and chairs.
  • Their visual reactions were observed and recorded/noted. At 7.5 months, two of the kittens (one reared in the horizontal and one in the vertical environment) were anaesthetised and their neurophysiology was examined.
• Results:

  • They were initially extremely visually impaired: they showed no visual placing when brought up to a table top and no startle response when an object was thrust towards them. They guided themselves mainly by touch.
  • frightened when they reached the edge of the surface they were standing on. They showed ‘behavioural blindness’ in that the kittens raised in the horizontal environment could not detect vertically aligned objects and vice versa.
• Results pt2:

  • Only the eyes of the kitten brought up in vertical stripes followed a rod held vertically and only the eyes of the kitten reared in horizontal stripes followed the rod if it was held horizontally i.e. both kittens remained blind to contours perpendicular to the stripes they had lived with.
  • The kittens quickly recovered from many of the deficiencies and within a total of about 10 hours of normal vision they showed startled responses and visual placing and would jump with ease from a chair to the floor.
• Results pt3:

  • Some of their defects were permanent: They always followed moving objects with very clumsy, jerky head movements. They often tried to touch things moving on the other side of the room, well beyond their reach.
• Results pt4:

  • No evidence of severe astigmatism, which might have explained the behavioural responses. Horizontal plane recognition cells did not ‘fire-off’ in the kitten from the vertical environment and vertical plane cells did not ‘fire-off’ in the kitten from the horizontal environment so there was distinct orientation selectivity, showing the kittens suffered from ‘physical blindness’. About 75% of cells in both cats were clearly binocular and in almost every way the responses were like that of a normal kitten.
• Conclusion:

  • Visual experiences in the early life of kittens can modify their brains and have profound perceptual consequences.
  • A kitten’s visual cortex may adjust itself during maturation to the nature of its visual experience.
  • A kitten’s nervous system adapts to match the probability of occurrence of features of its visual input.
• Conclusion pt2:

  • Brain development is determined by the functional demands made upon it, rather than pre-programmed genetic factors.
  • The environment can determine perception at both a behavioural and physiological level – at least in cats.
  • It is questionable as to whether results can be generalised to humans.