Perceptual narrowing of linguistic sign occurs in the 1st year of life.

Over their 1st year of life, infants'"universal" perception of the sounds of language narrows to encompass only those contrasts made in their native language (J. F. Werker & R. C. Tees, 1984). This research tested 40 infants in an eyetracking paradigm and showed that this pattern also holds for infants exposed to seen language-American Sign Language (ASL). Four-month-old, English-only, hearing infants discriminated an ASL handshape distinction, while 14-month-old hearing infants did not. Fourteen-month-old ASL-learning infants, however, did discriminate the handshape distinction, suggesting that, as in heard language, exposure to seen language is required for maintenance of visual language discrimination. Perceptual narrowing appears to be a ubiquitous learning mechanism that contributes to language acquisition.