Human infants' accommodation responses to dynamic stimuli

PURPOSE: A young infant's environment routinely consists of moving objects. The dynamics of the infant accommodative system are almost unknown and yet have a large impact on habitual retinal image quality and visual experience. The goal of this study was to record infants' dynamic accommodative responses to stimuli moving at a range of velocities. METHODS: Binocular accommodative responses were recorded at 25 Hz. Data from infants 8 to 20 weeks of age and pre-presbyopic adults were analyzed. A high-contrast image of a clown was moved between 20- and 50-cm viewing distances at four velocities (a step, 50 cm/s, 20 cm/s, and 5 cm/s). RESULTS: Most infants who had clear responses were able to initiate their response within a second of stimulus onset. The infants were able to discriminate the different stimulus velocities and to adjust their response velocities and durations in an appropriate fashion. CONCLUSIONS: The data indicate that by the third postnatal month infants are able to respond with latencies within a factor of two of adults' and that there is little immaturity in the motor capabilities of the accommodative system compared with the sensory visual system at the same age.