The critical period for susceptibility of human stereopsis.

PURPOSE To define the critical period for susceptibility of human stereopsis to an anomalous binocular visual experience. METHODS Random dot stereoacuity was measured in 152 children with a history of onset of either infantile or accommodative strabismus before 5 years of age. In each of these populations and in the combined population, the critical periods for susceptibility of stereopsis are described using four-parameter developmental weighting functions. RESULTS In children with infantile strabismus, the critical period for susceptibility of stereopsis begins at 2.4 months and peaks at 4.3 months. In children with accommodative esotropia, the critical period for susceptibility of stereopsis begins at 10.8 months and peaks at 20 months. When the data are combined across the two populations, the critical period begins soon after birth and peaks sharply at 3.5 months but shows continued susceptibility to at least 4.6 years. CONCLUSIONS An anomalous binocular visual experience during early infancy severely disrupts stereopsis, yet the critical period for susceptibility of stereopsis extends through late infancy and early childhood and continues to at least 4.6 years of age.