A child is born with a cataract in one eye. Corrective surgery is delayed until age 8. What outcome would developmental neuroscience predict for vision in that eye?
AFull recovery of normal visual acuity — the brain is plastic throughout childhood
BLikely permanent impairment of visual acuity in that eye, despite the corrected optics
CNo impairment — the other eye compensated, and the visual system will reallocate normally after surgery
DBetter-than-normal vision, because the eye was protected from overstimulation during development
The visual cortex has a critical period in early life when patterned input is required to develop normal acuity. Without visual input during this window, the cortex reallocates the territory devoted to that eye to the open eye — through competitive synaptic pruning. By age 8, this reorganization is largely complete. The surgery restores optical clarity but cannot undo the cortical rewiring that occurred during the missed window. The optics are fixed; the brain is not.
Question 2 Multiple Choice
A child is adopted at age 6 from severe language deprivation, compared to one adopted at age 1 from similar conditions. What would research on language development predict about their long-term outcomes?
ANo difference — with good schooling and language exposure, both will achieve native-like proficiency
BThe child adopted at age 6 will likely have more persistent grammatical deficits, as more of the sensitive period has elapsed
CThe child adopted at age 6 will recover faster because older children are more efficient learners
DBoth will have similar outcomes because sensitive periods only apply to second language acquisition, not first
Language acquisition has a sensitive period extending through middle childhood. Children deprived of language input until age 6 have lost part of this window. Research consistently shows earlier intervention leads to better grammatical outcomes — though vocabulary continues improving. Grammatical structure has an earlier and steeper cutoff than vocabulary, consistent with some aspects of language being closer to a strict critical period. The child adopted at age 6 will likely retain some persistent grammatical deficits.
Question 3 True / False
The defining difference between a critical period and a sensitive period is that a critical period requires appropriate input during a specific window — without it, the relevant capacity fails to develop properly and cannot be fully recovered later.
TTrue
FFalse
Answer: True
This is the precise definitional distinction. Critical periods are strict: the relevant neural circuits are actively wired and pruned based on incoming experience during the window. Without appropriate input, those circuits are repurposed or pruned away, making deficits largely permanent. Sensitive periods are softer: experience during the window has outsized effects, but the window is not a hard biological cutoff and some plasticity remains afterward.
Question 4 True / False
Because critical periods depend on neuroplasticity, they demonstrate that the brain remains equally plastic for that system throughout the lifespan.
TTrue
FFalse
Answer: False
This reverses the logic. Critical periods exist precisely because plasticity for a given system is HIGH during the window and then NARROWS afterward. Hubel and Wiesel's work showed the visual cortex is highly plastic during the critical period and much less so after it closes. Critical periods are evidence for declining, time-limited plasticity — not for constant lifelong plasticity. The 'critical' nature of the period is defined by the narrowing of plasticity that follows.
Question 5 Short Answer
What is the 'use it or lose it' mechanism that underlies critical periods, and why does it make early deprivation difficult to reverse later?
Think about your answer, then reveal below.
Model answer: During critical periods, neural circuits are shaped by competitive synaptic pruning: connections that receive input are strengthened; those that receive little input are weakened and eliminated. Cortical territory is allocated to active inputs at the expense of inactive ones. Once this pruning is complete, the circuits are largely fixed. If appropriate input never arrived, the cortical territory was repurposed — reallocated to other inputs. Later experience must compete against already-established circuits rather than simply filling vacant territory, making reversal very difficult.
This question targets the mechanistic basis of critical periods, not just their descriptive features. Understanding that 'use it or lose it' is about competitive allocation of cortical real estate — not just passive decay — explains why restoration of the missing input after the period often fails to restore normal function. The architecture has already been reorganized around the input that was present.