8.5.1 Critical period and visual development Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 8

The 20 questions

1. What is a critical period in the development of vision?

   • A window early in life when visual experience must occur for normal visual development to take place
   • A time when the lens becomes permanently fixed in shape, which stops any further change in focusing ability
   • A period when the eyes stop producing rhodopsin, which occurs at a fixed age in every mammal species
   • A time in adult life when vision can be fully repaired, after the visual system has finished maturing

2. Why is the critical period important for mammals?

   • It allows the eye to grow to adult size, which must happen before the visual cortex can start to develop
   • It provides time for the lens to change colour, which is needed before the animal can see colours clearly
   • It allows the retina to make new rods in adulthood, which replaces the rods lost during early life
   • It allows visual capacities such as binocular vision to develop fully, using sensory input from the eyes

3. Which experiment by Hubel and Wiesel is most closely linked to the critical period?

   • Recording the activity of a single rod cell in darkness only, which measured its response to a dim flash
   • Measuring the speed of nerve impulses in frog axons, which showed how fast impulses travel in unmyelinated nerves
   • Sewing one eye of a kitten shut during early development, which caused lasting loss of vision in that eye
   • Growing bacteria in a sterile culture, which tested how quickly the bacteria divided in a nutrient medium

4. A kitten has one eye closed for several months during early development. What is the most likely result?

   • The eye has reduced function because the visual cortex was not stimulated by it during the critical period
   • The kitten gains improved night vision in both eyes, because the closed eye supplies extra rods to the other eye
   • The kitten gains improved colour vision, because the closed eye develops stronger cone cells in the dark
   • The eye develops normally, since the visual cortex is able to form all the connections it needs without visual input

5. A student says that a child who is born blind in one eye cannot develop vision in that eye later in life, if the cause is not treated within the critical period. Which statement is best supported?

   • Incorrect, because the eye is not connected to the brain, so no treatment can affect its development at any age
   • Partly correct, because development of vision is most sensitive in the critical period, but some plasticity can persist
   • Correct, because the critical period cannot be changed at all in any species, so treatment must be given at the start
   • Incorrect, because vision never depends on experience, so the eye always develops normally whatever happens

6. Which structure in the visual pathway is most affected by lack of visual experience during the critical period?

   • The skin of the hands, which contains touch receptors and is not involved in vision at all
   • The small intestine, which absorbs nutrients from food and is not part of the visual pathway
   • The visual cortex, where experience during the critical period shapes the connections between neurones
   • The skeletal muscle of the leg, which controls movement and is not connected to the visual system

7. Which factor is necessary for the normal development of binocular vision?

   • Constant exposure to red light only, which strengthens the connections between the rods in both eyes
   • Both eyes receiving input that is roughly matched, so that the cortex can combine the two images
   • Only one eye being used throughout childhood, so that the other eye does not compete for the cortical space
   • Complete darkness during the first weeks, which allows the visual system to reset before light input begins

8. What is meant by visual deprivation in an experiment on the critical period?

   • Giving an animal extra light exposure, which increases the amount of visual input the animal receives
   • Removing the optic disc from the retina permanently, which stops all signals from reaching the brain
   • Preventing normal visual experience through one eye, for example by suturing the eyelid shut
   • Increasing the brightness of the environment, which saturates the rods and cones in both eyes

9. A researcher finds that kittens deprived of visual input during the critical period show poor depth perception as adults. Which conclusion is best supported?

   • Adult kittens cannot see at all after deprivation, which is why their depth perception is poor
   • Depth perception is unaffected by early experience, since adult perception depends only on the genes of the animal
   • Early visual experience is needed for normal depth perception to develop, since deprivation caused the deficit
   • Depth perception depends only on the colour of the retina, so the deprivation has no effect on the cortex

10. Which statement describes why the critical period may be considered a form of developmental plasticity?

    • The eyes shrink during this period, which changes the size of the image on the retina
    • The brain is most able to adapt its connections during this window, so experience has a strong effect
    • The brain cannot adapt at all during this window, so experience has no lasting effect on the connections
    • The brain is damaged permanently by all visual input, which is why plasticity is lost after the window

11. A study compares children who had cataracts removed early with those who had them removed late. Which result would support the idea of a critical period?

    • Children treated earlier showed better visual development than those treated later
    • Neither group was affected by the cataracts, so the condition has no effect on visual development at any age
    • Both groups developed equal vision regardless of timing, so the age of treatment does not matter
    • Late treatment led to better visual development than early treatment, since the brain adapts more slowly when young

12. What is the best evaluation of the claim that the critical period applies only to vision?

    • Incorrect, because critical periods have also been described for other systems, including language and hearing, though details differ
    • Incorrect, because critical periods do not exist in any system, since all development is fixed by the genes at birth
    • Correct, because no other system is affected by experience, so the critical period is unique to the visual system
    • Correct, because vision is the only sense that develops, and so no other system shows any form of critical period

13. Which statement best describes the outcome of Hubel and Wiesel's experiments on kittens with one eye deprived?

    • Most cortical neurones responded mainly to the open eye, showing reduced input from the deprived eye
    • The cortex stopped responding to both eyes, which showed that deprivation of one eye damages both sides
    • The deprived eye became more sensitive than the open eye, which showed that deprivation strengthens the connections
    • The cortex became equally responsive to both eyes, showing that deprivation had no effect on the connections

14. A child is born with a condition that blocks light from reaching the retina for the first months of life. Which outcome is most likely if treatment is delayed beyond the critical period?

    • No effect on vision at all, since the connections form correctly without any light input in early life
    • Full recovery of vision regardless of timing, since the visual cortex always develops normally once light is restored
    • Permanent visual impairment, because the connections in the visual cortex did not develop normally
    • Improved colour vision because of the blockage, since the retina compensates for the lack of light

15. Which pair correctly matches a process with its role in visual development?

    • Blood flow to the retina: sets the length of the critical period, since blood supply limits how long plasticity lasts
    • Lens focusing: determines the timing of the critical period, which ends when the lens reaches adult shape
    • Rhodopsin synthesis: controls the critical period directly, by setting the window length in the retina
    • Visual experience: strengthens connections in the visual cortex during the critical period

16. A researcher designs an experiment to test the critical period. Which control group is most appropriate?

    • Animals given normal visual experience throughout development, so they can be compared with deprived animals
    • Animals with no eyes at all, which cannot be used to test the effect of visual deprivation in any way
    • Animals whose visual experience is measured only in adulthood, which shows whether the adults can see normally
    • Animals kept in complete darkness as adults only, which tests the effect of light on adult vision only

17. Which statement describes the link between the critical period and neural plasticity?

    • Plasticity only occurs in the retina, so the brain cannot change its connections at any age
    • Plasticity increases steadily with age throughout life, reaching its highest point in old age
    • Plasticity is absent during the critical period, so the brain is fixed at that time
    • Plasticity is high during the critical period and falls as the brain matures

18. Which of the following would most likely extend the time over which visual plasticity remains high in an animal?

    • Removing the visual cortex, which would allow the rest of the brain to take over the visual function for longer
    • Exposing the animal to constant darkness only, which keeps the rods active and so extends the window for vision
    • Maintaining normal visual experience and enrichment during development, which supports the formation of connections
    • Keeping an eye permanently closed from birth, which would keep the window open for longer in the deprived eye

19. Which statement correctly describes evidence that a critical period exists for vision in mammals?

    • Visual deprivation has the same effect at all ages in every study, so no window of sensitivity exists
    • Visual deprivation in early life leads to lasting visual deficits, while the same deprivation in adulthood has much smaller effects
    • Animals raised in darkness develop better visual cortex connections, which is why deprivation helps vision
    • Adult animals lose all vision if their eyes are covered for one day, showing the window never closes

20. In a study of visual cortex development, which recording method would best show that individual neurones respond to a particular feature, such as the orientation of a line?

    • Counting the total number of rods in the retina of each animal at the end of the study
    • Measuring the body weight of each animal before and after a period of visual deprivation
    • Recording the firing of single cortical neurones while presenting stimuli with different orientations
    • Measuring the average blood pressure across the whole cortex during a long period of general darkness

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