B - Blakemore and Cooper Flashcards
Background
Hirsch and Spinelli (1970) reported that early visual experience can change neural organisation in kittens. They reared kittens with one eye viewing vertical stripes, the other horizontal and found that, out of 21 neurones with elongated receptive fields all were monocularly driven, and in all but one case the orientation of the receptive field dosely matched the pattem experienced by that eye. Blakemore and Cooper therefore began a related project and this study is a preliminary report of their findings.
Their approach is slighty different to that of Hirsch and Spinelli in that they allowed kittens normal binocular vision in an environment consisting entirely of horizontal or vertical stripes. (Monocular vision is vision in which each eye is used separately whereas binocular vision is vision in which both eyes are used together).
Aim
The aim of this study was therefore 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 (as suggested by Hubel and Wiesel) or learned.
Method/Design
This was a laboratory experiment which used an independent measures design.
The independent variable (IV) was whether the kittens were reared in a horizontal or a vertical environment.
The dependent variable (DV) was their visuomotor behaviour once they were placed in an illuminated environment te. whether the horizontally raised kittens could detect vertically aligned objects and/or if the vertically raised kittens could detect horizontally aligned objects
Sample
Kittens (studied from birth until this report was compiled) were randomly allocated to one of the two conditions. Two of the kittens (one reared in a horizontal and one in a vertical environment) were used to study neurophysical effects.
Procedure
The kittens were housed from birth in a completely dark room.
From the age of two weeks they were put into a special apparatus for an average of about five hours per day. The kitten stood on a dear glass platform inside a tall cylinder the entire inner surface of which was covered with high contrast black-and-white stripes, either vertical or horizontal. There were no comers to its environment, no edges to its floor and the upper and lower limits to its world of stripes were a long way away. It could not even see its body as it wore a wide black collar that restricted its visual field to a width of about 130 (The kittens did not seem upset by the monotony of their surroundings and sat for long periods inspecting the walls of the tube.)
This routine was stopped when the kittens were 5 months old (well beyond the ‘critical period” in which total visual deprivation causes physiological deficits, Hubel & Weisel, 1970).
The kittens were then taken for several hours each week from their dark cage to a small, well-lit room, fumished 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 reared in the vertical environment) were anaesthetised so their neurophysiology could be examined.
Results
Regardless of whether the kittens had been exposed to vertical or horizontal stripes, they were initially extremely visually impaired: Their papillary reflexes were normal but they showed no visual placing when brought up to a table top and no starte response when an object was thrust towards them.
They guided themselves mainly by touch. They were 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.
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 horizon tal stripes followed the rod if it was held horizontally t.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.
However, some of their defects were permanent:
They always followed moving objects with very clumsy, jerky head movements. They often tried to buch things moving on the other side of the room, well beyond their reach.
The neurophysiological examination showed:
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 honzontal environment so there was distinct orientation selectivity, showing the kittens suffered from “physical blindness”.
About 75% of cells in both cats were dearly binocular and in almost every way the responses were like that of a normal kiten
The distributions of preferred onentation were however totally abnormal: not one neurone had its optimal orientation within 20 of the inappropriate axis and there were, in total, only twelve within 45 of it. This anisotropy (the property of being directionally dependent) was significant at p: 0.00001: chi squared test.
No obvious large regions of ‘slent cortex corresponding to the missing dortical columns were observed/found.
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.
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.
Method Evaluation
P- A strength of a lab experiment is that it enables a high level of control.
E- This is a strength as it enables control over extraneous variables, increasing internal validity, researchers can be more confident in inferring cause and effect.
E- In this study the kittens were put in a dark room from birth, then from 2 weeks they were only exposed to either vertical or horizontal environments. Due to the strict control over the environment, we can infer that the IV (environment) caused visual impairment and neurophysiological damage (DV).
P-A weakness of a lab experiment it they are low ecological validity.
E-As the environment is highly controlled it does not reflect behaviours that would be found in a real life and behaviours cannot be generalised beyond the study.
E-It is unlikely that kittens or humans would only be exposed to one direction of lines in the early years of life therefore the results are only relevant to the situation the researchers created for the kittens.
Data: Quantitative and Qualitative
The study collected quantitative data, meaning it could make easy comparisons between the vertical and horizontal conditions
75% of neurons in both cats were binocular as normal cat, however their sensitivities were different and abnormal.
In each cat no neurons had preferred orientation within 20 degrees of the opposite orientations of the lines in their rearing environment and only 12 were with 45 degrees.e.g in horizontally reared kitten they would have neurons respond around the vertical axis
- Qualitative data was also collected as they watched
- Their startle responses - showed no startle response and bumped into things around the room. The horizontally raised kitten ignored the rod shaken at them if it was presented vertically and the vertically raised kitten ignored a shaken rod that was presented horizontally.
- They showed no visual placing- they didn’t stretch paws out when brought to a table only once they’d felt it.
Ethics *** Be careful here as ethical guidelines are different for animals than pets
Blakemore and Cooper was ethically sound as there was no reported distress from the animals and the ethics committee for research on animals approved it .
The key guidelines with animals are:
Use as few as possible and inflict as little distress – which they did as they only used 2 kittens and anesthetised them
Use a species as undeveloped as possible – they chose kittens over primates -Kittens are less likely to suffer than primates, so that’s a good thing A mammal really needed to be used in this study for it to be generalisable. Would a mouse have done as well - possibly, but perhaps its brain is too different to humans to be sure to generalise from it.
It could also be argued that any harm to the animals were outweighed by the usefulness of this research.
Reliability
The study could be easily replicated in order to test the reliability of the findings
They had identical visual environmentsCylinders were the same diameter and lengthThe were illuminated above the spotlightThe same floor and coverThe spent the same time in the apparatusThe reminder of time they were in darknessWore a collar so they could not see their own paws and used normal binocular vision.
However they only used 2 kittens therefore it is difficult to establish consistency in the findings.
Sampling bias
Blakemore and Cooper 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. The physiological differences betweenthe cat’s brain and a human brain plus theyoung age of the kittens would make thedata difficult to generalise, despite theminor similarities
Furthermore, as the sample was very small (only 2 cats’ neurophysiology was examined) we may not be even able to generalise to other cats.
Validity
High internal validity due to high levels of control over extraneous variables and direct manipulation of the IV to measure the effect on the DV.
The use of both behavioural and neurophysiological measures shows that research has high validity as both measures show how the development of the kittens brain has been influenced by the environment.
