Blakemore and Cooper

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  • Blakemore and Cooper
    • Aim
      • to investigate the development of the primary visual cortex in cats and find out if some of its properties such as orientation selectivity are innate or learned.
    • Background
      • Neuroplasticity= the growth of new synaptic pathways in response to demands from the environment.
      • Tufts University of Veterinary Medicine in Boston: human and cat brains are very similar, they both have folded cerebral cortices with similar lobes.
      • Visual info in cats is processed by the lateral geniculate nucleus of the thalamus (LGN) and relayed to the V1 where neurons are attuned to respond to every visual field. They are neurones which electively respond to lines and edges of every orientation. (Hubel and Wiesel, 1962)
      • Hirsch and Spinelli (1970) reported that early visual experience can change neural organisation in kittens, finding that that neurons only responded to information received from one eye and only to the orientation that eye had percieved.
    • Research method + design
      • Lab
      • Independent measures design
        • IV: horizontal/vertical environment   DV: their visuo-motor behaviour at 5mnths onwards, once placed in a normal environment (whether they could see the orientation they had not been exposed to)
    • Sample
      • Kittens were randomly allocated to one of the two conditions. 2 were used to study neuro-physiological effects by implanting electrodes in the V1 region of the brain.
    • Procedure
      • The kittens were housed from birth in a completely dark room. From the age of 2 weeks they were put in a special apparatus for about 5hrs a day.
        • The kitten stood on a clear glass platform halfway up a cylindrical container; the entire inner surface of which was covered with black and white stripes of different widths in either a vertical or horizontal orientation.
          • The top and bottom edges of the drum were outside of its field of vision. It could not even see its body as it wore a black cone that restricted the kittens visual field to a width of about 130 degrees. The environment was lit by a spotlight at the top of the cylindrical container.
            • This routine stopped when the kittens were 5mnths old; according to Hubel and Weisel this is after the critical period for normal physiological development of V1. The kittens were then taken for several hours each week from their dark cage to a small, well-lit room, furnished with tables and chairs.
              • Their behaviour was observed and recorded in response to visual stimuli in their environment. This was measured using two tasks.
                • 1) A sheet of thick Perspex with thick black and white lines, either horizontal or vertical in orientation, was held up infront of the kitten. The experimenters then observed to see if they produced a startle response to the object showing they had percieved it.
                  • 2) a tick was shaken in front of the kitten either held horizontally or vertically. They observed to see if the kitten tried to catch and chase the rod, demonstrating they had percieved it.
                • at 7 and a half months, 2 of the kittens (1 reared in horizontal and 1 in vertical) were anaesthetised so their neurophysiology could be examined (preferred orientation of neurones in the v1)
    • Findings
      • Regardless of which condition the kitten was in they were initially extremely visually impaired.
        • They guided themselves mainly by tough and response to feeling the edge of an object normally, showing that other senses were not impaired.
          • the kittens quickly recovered from many of the deficiencies and within 10 hours of normal vision showed startle responses and visual placing and would jump with ease from a chair to the floor [neuroplasticity]
            • however, some deficient were permanent: kittens were clumsy when trying to track an object (follow movement) and they often reached for objects out of reach (issue with depth perception)
              • **** kittens raised in a horizontal environment don't startle in response to the Perspex with vertical lines (and vice versa). Kittens raised in a horizontal environment didn't try to catch or chase the stick in response to it being held vertically and shaken (and vv)
                • the 2 cats who were operated on showed abnormal neurophysiological development. The horizontal conditioned cat had neurones which selectively responded to horizontal orientation, and v so their brain could not process any edges r lines in their environment which were oriented different to the orientation of the lines the kitten had been raised in.
                  • No neurons which responded to any line within 20 degrees of a vertical orientation for a cat raised in the horizontal environment. There was no region of silent neurones found.
                    • Unlike Hirsch and Spinelli (1970), who had shown different visual stimuli to each eye of their cats, B+C found that the majority of neurons (75%) responded to binocular information (visual info received from both eyes).
    • Conclusion
      • Visual experiences in the early life of kittens can modify their brains and have profound perceptual consequences

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