Questions: Developmental Plasticity and Sensitive Periods

Question 1

After a kitten has one eye occluded throughout its sensitive period for visual development, the cortical representation of the occluded eye is permanently reduced even after the occlusion is removed. This best demonstrates that:

• A. Monocular deprivation causes irreversible damage to the retina and optic nerve of the deprived eye
• B. Visual cortex development requires surgical alignment of both eyes during the sensitive period
• C. Experience-dependent competition during the sensitive period shapes cortical organization, so skewed input produces lasting structural bias
• D. Sensitive periods close through neuron death, which permanently eliminates the capacity for reorganization

Answer: (C)

Wiesel and Hubel's finding was that the deficit is entirely cortical and entirely caused by competitive experience — not retinal damage (option A) or surgical factors (option B). The open eye out-competed the occluded eye for cortical territory through activity-dependent synaptic strengthening and pruning. Option D is incorrect: sensitive periods close through regulatory mechanisms such as changes in GABA/glutamate ratios and molecular brakes on plasticity, not wholesale neuron death.

Question 2

A child who experienced early language deprivation is identified at age 6. Which statement best reflects what developmental plasticity research predicts about intervention?

• A. Intervention is unlikely to help because the sensitive period for language is closed by age 6
• B. The child can make meaningful gains from rich language input, though not as efficiently as during the peak window in early infancy
• C. The child's language ability will normalize completely given sufficient intervention because neural plasticity remains equal across the lifespan
• D. Only phoneme discrimination is permanently lost; vocabulary and grammar can be fully recovered at any age

Answer: (B)

Sensitive periods close at different rates for different functions. Phoneme sensitivity to non-native contrasts is largely fixed by 12 months, but vocabulary acquisition continues for decades and broader language plasticity extends substantially into middle childhood. A 6-year-old with early deprivation can still make meaningful gains — the sensitive period has tapered but not fully closed for many language functions. Option A overstates closure; option C ignores differential plasticity; option D reverses which language functions are most and least plastic.

Question 3

Phoneme sensitivity to non-native sound contrasts — such as the English /r/-/l/ distinction for Japanese speakers — is substantially reduced by 12 months of age, illustrating that some sensitive periods close very early in development.

• T. True
• F. False

Answer: True

This is a well-established finding. Infants universally discriminate phoneme contrasts from all languages at birth, but by around 10–12 months their perceptual sensitivity has narrowed to the contrasts of the language(s) they have been exposed to. This early closure of the phoneme-sensitivity window is one of the clearest demonstrations of a domain-specific sensitive period driven by experience-dependent neural organization.

Question 4

Developmental plasticity means the brain is uniformly reorganizable throughout the lifespan, with sensitive periods representing primarily a quantitative peak in this baseline capacity rather than a qualitatively different mode of development.

• T. True
• F. False

Answer: False

Sensitive periods involve qualitatively different developmental dynamics, not just elevated baseline plasticity. During sensitive periods the brain actively expects specific inputs and uses them to build foundational circuits through synaptic overproduction, competitive pruning, and structural remodeling. Outside sensitive periods these processes are regulated differently. The absence of expected input during a sensitive period does not simply leave a gap — it redirects development toward alternative structures that may be suboptimal for the expected function.

Question 5

Why is the absence of expected input during a sensitive period considered actively harmful to development rather than simply a missed opportunity?

Model answer: During sensitive periods the developing brain expects certain inputs and uses them to construct functional circuits. When expected input is absent, development does not pause — it is redirected. Alternative circuits compete for and capture the cortical resources that would have been used for the expected function, often in ways that are suboptimal and difficult to remediate later. By the time the input is restored, the cortical territory may already be organized around something else.

The Wiesel-Hubel monocular deprivation studies illustrate this: the deprived eye's cortical columns are not left empty and waiting — they are captured by the active eye. The deficit is structural reorganization, not mere absence of growth. This is why early intervention is valuable not just because it happens first, but because it finds the brain in a maximally reorganizable state before alternative circuits become entrenched.