1. 8.4 Visual Development

2. Syllabus Point - 12
Describe the role animal models have played in developing explanations of human brain development and function, including Hubel and Wiesel's experiments with monkeys and kittens.

3. = Critical Period Critical periods/ critical widows
These columns of cells are said to be formed during the critical period for visual development after birth
Adjacent columns receive stimulation from the same area of the retina in the right and left eye with the pattern repeated across the visual cortex
Visual cortex is made out of columns
Therefore it is a result of nurture rather than nature
There are times after postnatal development where the nervous system has to obtain specific experiences to develop
Critical periods/
critical widows =
BUT this not the case now…
Another BUT…
Newborn monkeys have these columns suggesting they are determined through genetics not environment
They found this out by injecting labelled tracers in the columns
Crowley and Katz showed that columns in the visual cortex are developed before critical period

4. Evidence of Critical Period through Medical Observation
Cataract
After two weeks when the bandage came off he had permanently impaired vision
So our eyes do develop during the critical period
Cataract is the clouding often lens of an eye and affects the amount of light getting into the retina
His eyes were bandaged
If cataracts are not removed
before the age of 10 -
Permanently impairment of the child’s
ability to perceive
Shapes or form and face recognition
is a result
Italian boy who had a minor eye infection when he was a baby

5. Quick Question What is a Critical Period? (2 Marks)
What is another name for the critical period? (1 Mark)
Check with the previous slides

6. Animal Models and Research
The Positive side to animal models:
We gain knowledge on the critical period through animal models
Animal models are easy to :
Obtain
Breed
Have short life cycles
Only grow into a small adult size
E.G – Mice
Chickens
Zebra fish

7. What are the positives of using animal models?
Quick
Question
What are the positives of using animal models?

8. Newborn Animals
Light + Patterns = difficulty with object discrimination and pattern recognition
Raised in the light for the first 3-6 months
Darkness = difficulty with object discrimination and pattern recognition
Raised in the dark for the first 3-6 months

9. Newborn Animals: Hubel and Wiesel
Raising monkeys from birth – 6 months.
Depriving them of light in one eye
After 6 months – monkeys exposed to light and were blind in that eye
Deprivation of light in one eye
= Monocular deprivation

10. Quick
Question
How would the blindness be caused?

11. Newborn Animals: Hubel and Wiesel
How would the blindness be caused?
Although the retinal cells in the blind eye did respond to the light, the cells of the visual cortex did not respond to any visual input from the deprived eye

12. Newborn Animals: Hubel and Wiesel
Hubel and Wiesel’s Conclusion:
Deprivation for a single
week
during
period after
birth causes the deprived
eye’s visual
cortex failing to
Respond to light
Visual deprivation of both
eyes during
Critical window
Has less effect
Than one eye deprived
Deprivation in adults has
no effect as everything has
developed
already
in the critical period

13. During the Critical Period
At birth there are lots of overlaps between the territories of different axons – in adults there are less
During the critical period there is further visual development

14. During the Critical Period
Dendrites and synapses from the light stimulated eye take up more territory in the visual cortex
After light deprivation the columns with axons are narrower than those for the light receiving light
So, visual stimulation is required for the refinement of the columns and so…
…for full development of the visual cortex

15. During the Critical Period
Synapses of another neurone sharing the target cell is weakened
Neurone fires into target cell
They release less neurotransmitter
If this happens repeatedly the synapse that are not firing will be cut back

16. During the Critical Period
Only the synapses on the axons receiving light will fire in the visual cortex where neurones of both eyes overlap
So when one eye is deprived of light
The axons will not be stimulated
Synapses from light deprived eye will be weakened and eventually lost

17. Quick Question Can you order these?
Axons from the visually deprived eye do not pass impulses to the cells in the visual cortex
There is a lack of stimulation in one eye
Axons from the non-deprived eye pass impulses to the cells in the visual cortex
Inactive synapses are eliminated
Synapses made by active axons are strengthened

18. Quick Answers Did You Get it Right? The order is:
There is a lack of stimulation in one eye
Axons from the non-deprived eye pass impulses to the cells in the visual cortex
Synapses made by active axons are strengthened
Axons from the visually deprived eye do not pass impulses to the cells in the visual cortex
Inactive synapses are eliminated

19. 8.5 Making Sense of what we see

20. Syllabus Point - 13
Consider the methods used to compare the contributions of nature and nurture to brain development, including evidence from the abilities of newborn babies, animal experiments, studies of individuals with damaged brain areas, twin studies and cross-cultural studies

21. What is Visual Perception?
It is not only the creation of an image but also knowledge and experience as the brain interprets sensory information from the retina
Label the
Retina ->

22. Did You Get it Right?

23. Depth Perception
Close Objects: What is stereoscopic vision? Cells in visual cortex which allow us to compare the view from one eye to the other and the visual field which is seen through different angles

24. Depth Perception Distant Objects
For images more that 30m away: images on both retinas are very similar so visual cues and past experiences are used when interpretation these images
What other things help us to judge depth?
Overlaps of objects
Changes in colour

25. Cross-Cultural Studies
Carpeted World Hypothesis: If we live in an area dominated by stripes And right angles We are more likely To perceive depth cues differently than those in a circular culture

26. Cross-Cultural Studies
What can you see?

27. Cross-Cultural Studies

28. Cross-Cultural Studies

29. Cross-Cultural Studies

30. Cross-Cultural Studies

31. Cross-Cultural Studies
The MÜLLER-LYER illusion
Which Line is Longer?

32. Cross-Cultural Studies
Both Lines
are the same length

33. Cross-Cultural Studies
Were YOU fooled by these visual illusions?
-People who live in a carpeted world are usually
fooled by visual illusions while those who do not live in a carpeted world are rarely fooled by them

34. Cross-Cultural Studies
However, some believe that it is not the experience of the person but their genetic differences in pigmentation which causes some greater difficulty to detect contours resulting to them being less vulnerable to illusions.

35. Cross-Cultural Studies+ =
Low retinal pigmentation
Lighter people
Good contour detection.
And so, are more easily caught out by the illusion

36. Depth cues in other Cross-Cultural Studies
Individuals from different cultures were shown a picture with depth cues such as:
Overlaps
Object size
Linear perspectives

37. Depth cues in other Cross-Cultural Studies
What they found:
All children had difficulties to interpret depth cues and 3D pictures
BUT
By 11 years old most European children could interpret 3D while some Bantu & Ghanaian children couldn’t

38. Depth cues in other Cross-Cultural Studies
What does this mean?
Depth Cues in Pictures are not innate and must be learned
* Innate – inborn. Someone being born with such a characteristic

39. Newborn Babies Did you know?
Awwh!
Did you know?
Within 24 hours of you little sibling being born they could distinguish between your voice and face, your mums and dads voice and face

40. & Newborn Babies Babies are born short-sighted but can see up to 30cm
They prefer stripes or other patterns
Before crawling they can distinguish between a
&

41. Newborn Babies and Visual Cliff
In a classic experiment babies were encouraged to walk across a table of glass with patterns below it to create an appearance of a steep drop
Poor Babyyy

42. Newborn Babies and Visual Cliff
The Result:
The babies were reluctant to walk across
Visual depth perception was innate – they were aware of the drop even if they had no previous stimulus themselves.

43. Newborn Babies and Visual Cliff
There is always someone who argues back:
‘But some perception development has already taken place since birth and so the reliability of the experiment decreases – Ha’
No! But, the test was also done n chicks and kid goats who were born walking and also refused to cross the cliff. So visual depth perception is innate!