Vernier Acuity in Human Infants: Rapid Emergence Shown in a Longitudinal Study

BACKGROUND: Vernier acuity was measured longitudinally for comparison with published results on early stereopsis development. METHODS: Thirty-seven human infants were tested using forced-choice preferential looking. These included 29 pilot infants (9 or 12 weeks of age) and eight infants tested longitudinally (9 weeks to 11 to 15 weeks of age). RESULTS: At 9 weeks, Vernier acuity was about 40 minutes of visual angle, compared with a typical adult value of less than 10 arc sec of visual angle. Vernier acuity improved rapidly immediately after emergence, doubling within about 10 days. After age 11 weeks, Vernier acuity remained constant, at 1000 arc sec (17 min) of visual angle, until testing ended. CONCLUSION: Vernier acuity developed over a time course different from published data on stereoacuity. Vernier acuity emerged significantly sooner, whereas stereopsis improved most quickly at an age when Vernier acuity was changing most slowly. It is unlikely that a single critical immaturity limits infant performance on both visual tasks.