8.4 Visual Development

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.

= 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

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

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

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

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

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

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

Quick Question How would the blindness be caused?

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

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

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

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

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

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

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

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

8.5 Making Sense of what we see

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

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 ->

Did You Get it Right?

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

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

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

Cross-Cultural Studies What can you see?

Cross-Cultural Studies

Cross-Cultural Studies

Cross-Cultural Studies

Cross-Cultural Studies

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

Cross-Cultural Studies Both Lines are the same length

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

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.

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

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

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

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

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

& 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 &

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

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.

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!