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Abstract:
Dramatic improvements occur in spatial vision during the
first year of life. However, by one year of age, vernier acuity,
discrimination based on relative position sensitivity, is still
much worse than grating acuity, the ability to detect fine details.
We used steady-state visual evoked potentials (VEPs) to examine the
neural processing underlying vernier acuity and grating acuity
during development. We determined the full developmental sequences
of both types of acuity by testing 73 healthy children between the
ages of 1 month and 15 years of age. The grating acuity stimulus
consisted of sinewave gratings alternating with a luminance-matched
unpatterned field at a temporal frequency of 5 Hz. The vernier
acuity stimulus was comprised of squarewave gratings with offsets
appearing and disappearing (5 Hz) within each grating bar.
Individuals' thresholds were estimated by extrapolating the first
harmonic amplitude functions to zero microvolts. Grating acuity
achieved full maturity by 5-6 years of age, but vernier acuity did
not reach adult levels until 12-14 years of age. While grating
acuity improved gradually to adult levels, vernier acuity plateaued
in early childhood, then exhibited a late rapid phase of
development between 6 and 12 years of age. These divergent
developmental sequences of visual detection and discrimination
suggest separate underlying mechanisms. The data will be discussed
within the context of sensitive periods for perceptual
development.
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