Which of the following reaches adult levels the soonest after birth?

• A. Contrast sensitivity
• B. CFF
• C. Vernier acuity
• D. Stereopsis

Answer: (B)

The main idea is that different visual functions mature at different rates after birth, with temporal processing maturing fastest. Critical flicker fusion reflects how quickly the visual system can follow changes in light over time, a function supported by early-developing retinal and magnocellular pathways. Because these pathways establish early, infants reach near-adult flicker fusion levels within the first months of life. In contrast, higher-level spatial and binocular functions—contrast sensitivity at higher spatial frequencies, Vernier (fine alignment) acuity, and stereopsis (depth from binocular disparity)—depend on more mature cortical processing and precise neural wiring, which develop more slowly. So, the earliest to reach adult levels is the ability to detect flicker at high frequencies, followed by gradual improvement in the other measures that require finer spatial detail and binocular coordination.