Our brain helps us find our way in the world. The sensory cortex allows us to process information from the environment, and the motor cortex allows us to respond to that information. But is the way we perceive the world around us innate? Or do we learn what external information means as we develop? If we miss a sensory experience, will it permanently affect us? Blakemore and Cooper (1970) explored how the visual cortex develops in cats.
- We are going to explore the Blakemore and Cooper (1970) study.
- First, we will examine how the environment impacts brain development.
- Then, we will discuss experiments on animals in psychology, highlighting the ethical issues and brain structure differences.
- Following on, we will explore Blakemore and Cooper’s (1970) impact of early visual experience on brain development study, and discuss the results before providing an evaluation and a summary.
Fig. 1 - Blakemore and Cooper (1970) wanted to investigate how visual deprivation affects kittens.
How does the Environment Impact Brain Development?
While it is difficult to separate the effects of environment from biology in humans, Blakemore and Cooper (1970)1 attempted to separate these two aspects in cats by subjecting kittens to visual deprivation during critical developmental stages. The results of their experiment help us better understand how the environment affects brain development.
Before Blakemore and Cooper did their study, Hirsh and Spinelli (1970) conducted a study to determine how changing the early visual environment of kittens affects their brain structure during development.
Impact of Early Visual Experience on Brain Development – Early Evidence in Psychology
Hirsch and Spinelli (1970) found early evidence that early visual experiences affect brain development and lead to psychological impairments. They raised kittens by restricting all visual stimuli to vertical lines for one eye and horizontal lines for the other. They found that receptive fields exposed only to horizontal lines became sensitive only to horizontal lines, while detection of vertical lines was impaired, and vice versa.
These results suggest a lack of appropriate environmental stimuli can lead to significant brain impairments.
Experiments on Animals in Psychology
Why do psychologists choose to conduct experiments on animals? Some animals have a similar brain structure to humans. So by studying their brain structure, we can understand more about ours without having to perform invasive experiments on humans.
Ethics
While it is not ethical to deprive humans of visual experience and put them at risk of long-term psychological impairment, conducting such an experiment on animals is ethical because of the potential benefits of understanding human biology.
Brain Structure
Although cats and humans are quite different, our brain structure is similar. Like humans, the cat's brain has a visual cortex, where visual information is processed. Neurons in the visual cortex are selective for lines with certain orientations, i.e., some neurons fire selectively on horizontal lines, others on lines at a certain angle, and still others on vertical lines (Hubel & Wiesel, 1962).
We know that humans also have neurons in the visual cortex that are selective to line orientation. Suppose the lack of visual experience with horizontal lines in the early development of cats can lead to pruning (degradation) of the neurons that respond to these lines and blind them to horizontal stimuli.
In that case, we can predict that a similar process would occur in humans.
Early evidence of the influence of the environment underscores the role of brain plasticity. Some evidence suggests this process is particularly important in early development. Children’s brains are more plastic, more capable of learning, and more likely to rewire themselves to recover from brain damage.
Brain plasticity refers to the brain’s ability to change its connections, functions, and structure in response to external influences (environment) or internal changes (brain damage).
Blakemore and Cooper (1970): Impact of Early Visual Experience on Brain Development
Blakemore and Cooper (1970) wanted to investigate further how the visual cortex develops in cats, particularly whether the function of recognising lines of a particular orientation is innate or learned. They wanted to understand the effects of limited visual experience on cats physiologically and behaviourally and the brain’s plasticity.
Fig. 2 - How does a limited visual experience affect cat brain development?
Blakemore and Cooper (1970): Research Design
Blakemore and Cooper conducted a controlled laboratory experiment. An independent design (between participants) was used. Kittens were randomly assigned to one of two experimental conditions, i.e., they were raised in either horizontal stripes (black and white) or vertical stripes (black and white) environments.
To measure the effects of this restricted environment on the kittens’ brain structure and function, they were placed in a furnished room after five months of age. Their behaviour was observed to see if they could recognise objects of different orientations. In addition, one kitten from each condition was randomly selected to have its brain examined under anaesthesia.
Blakemore and Cooper (1970): Procedure
For the first two weeks after birth, kittens were housed in a completely dark room. After that, the kittens were placed in a cylinder for five hours a day, consisting only of horizontal or vertical lines, which lasted for five months.
- By placing the cats in a cylinder, they were not exposed to any corners or edges.
- The inside of the cylinder (horizontal or vertical, black and white stripes) was all they could see during their time there, as they were given a wide black collar that prevented them from looking at themselves.
- The stripes were below and above the kittens, standing on a transparent glass platform inside the cylinder.
After five months, the cats were taken out of their darkroom for a few hours each week to explore a small furnished room containing objects with different orientations (e.g., tables and chairs). Experimenters observed and recorded their behaviour.
Two months after the experimental condition ended (the cats were then seven and a half months old), one from the vertical condition and one from the horizontal condition were anaesthetised. The changes in their brain structure were examined.
Fig. 3 - A timeline of the Blakemore and Cooper (1970) study shows how the study was conducted.
According to Hubbel and Wiesel (1972), susceptibility to neural pruning in response to sensory deprivation is highest during the first three months of cats’ development. Exposing cats to the restricted visual environment in the experimental condition for five months ensures that the effects on the cats’ brain cells will be noticeable.
The Blakemore and Cooper's (1970) Kitten Experiment: Results
When the cats were placed in the furnished room, their vision appeared significantly impaired. They could not detect edges or objects oriented in the opposite direction than that they had previously been exposed to. Objects thrown at the kittens would not frighten them, but they still showed fear responses when approaching an edge of a surface.
Kittens raised in a horizontal environment could not follow a vertically moving pole and vice versa. The cats were unable to show visual placement. Visual placement is a reflex that refers to automatically lifting one’s feet to reach a surface when approaching it.
For example, when cats were brought near a table, they did not move their legs to reach it.
The cats used the sense of touch to compensate for their visual impairment and to navigate their surroundings. The cats’ pupillary reflexes remained normal, indicating that their ability to adapt to brightness levels was not affected.
Recovery
After spending ten hours in the normal environment, the kittens partially recovered and began to show startled responses, object recognition, and visual placement.
- It was still difficult for the kittens to follow objects moving in a different direction than the direction they had been raised.
- Difficulties with spatial and depth perception persisted as the cats attempted to touch objects that were far out of their reach.
Neuropsychological Examination
In kittens exposed to a vertical environment, there were no neurons with a preferred orientation for horizontal lines or even lines with orientation within 20 degrees of horizontal. The opposite result was observed in kittens exposed to a horizontal environment.
The neurons did not disappear, as the authors found no evidence of ‘silent’, inactive parts of the cortex. Still, they changed their preferred orientation to match the early environment. Most cells were binocular (binocular cells enable depth perception) and showed correct responses.
Blakemore and Cooper (1970): Evaluation
Blakemore and Cooper conducted a laboratory experiment. They controlled extraneous variables (exposure to edges and corners, time the cats spent in the cylinder, etc.) and manipulated only the orientation of the strips to which the cats were exposed. Experimenters could then draw causal conclusions about the effects of visual experience on brain development. A standardised procedure was used that will allow for future replications.
Although the study did not protect the kittens from harm, the researchers claimed that the kittens showed no signs of distress when placed in the cylinders. The study followed appropriate ethical guidelines for animal research and has led to important implications for understanding human brain function and brain plasticity.
Regarding the neuropsychological study, only the brains of two cats were examined, limiting the generalisability of the results. Our ability to generalise these results to humans is also controversial.
However, the similar brain structure and potential for plasticity in humans and cats allow us to make some generalisations about how our brain cells are affected and can adapt to environmental factors.
Blakemore and Cooper: Summary
Early visual experiences have a significant impact on brain structure and function. The visual cortex was impaired in kittens raised in a limited visual environment. The lack of lines of a particular orientation led to adjustments in the preferred orientations of neurons in the visual cortex. Brain function adapted to the requirements of the kittens’ limited environment.
Blakemore and Cooper - Key takeaways
- Hirsch and Spinelli (1970) found evidence of early visual experience's influence on kittens' brain development.
- Researchers conduct animal studies because animals may have brain structures similar to that of humans. Brain plasticity is the ability of the brain to change its connections, functions, and structure in response to external influences (environment) or internal changes (brain damage).
- Blakemore and Cooper (1970) conducted a controlled laboratory experiment to investigate how the early visual environment affects the development of the visual cortex in cats, specifically whether the function of recognising lines of a particular orientation is innate or learned.
- Blakemore and Cooper (1970) found that the cat's vision appeared significantly impaired when the cats were placed in a furnished room. They could not detect edges or objects oriented in the opposite direction than that they had previously been exposed to, amongst other visual impairments.
- Limitations of the study by Blakemore and Cooper (1970) include the generalisation of the results to humans, particularly the neuropsychological findings from the sample of only two cats. However, it was a laboratory experiment that controlled for extraneous variables, rendering it reliable.
References
- BLAKEMORE, C., COOPER, G. Development of the Brain depends on the Visual Environment. Nature 228, 477–478 (1970). https://doi.org/10.1038/228477a0
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