g., noun- versus verb-phrase). Take for example the sentence “The beautiful baby smiled at her mother” which consists of two intonational phrases, with a boundary between “baby” and “smiled”. It is possible to create strong statistical cues between syllables that fall within an intonational phrase, as would be present in any natural language, or between syllables that span an intonational phase boundary, which almost never occurs in natural languages. This design was implemented in Shukla, White, and Aslin (2011) using nonsense syllables as in Saffran et al. (1996), but organized into short sentences rather than continuous streams. A family of such sentences was presented to
6-month-olds as they watched a video
display depicting PD0325901 in vitro three salient objects. One of the objects consistently underwent motion Romidepsin supplier across trials while the other two objects never moved, thereby drawing infants’ attention to the single moving object. The key feature of the design, implemented across two groups of infants, was that there were syllables with strong statistical links (i.e., words) and syllables with weak statistical links (i.e., part-words), but in only one of the two conditions were the strongly linked syllables within an intonational phrase. Thus, if infants attended only to syllable statistics, regardless of their positioning with respect to intonational phrases, both groups would extract these word-candidates and map them onto the single object in the video display that was moving. However, if infants were constrained to extract syllable statistics when they fell within an intonational phrase, then only
infants in the group where the ends of words were aligned with the ends of intonational phrases would map these syllable statistics to the moving object. That is precisely the outcome reported by Shukla et al. The main reason for describing the Shukla et al. (2011) study is that it illustrates how the statistical-learning mechanism of young infants is constrained in a principled way to reduce the computational complexity faced by a naïve learner in the language domain. Intonational phrases Immune system are universal characteristics of natural languages that presumably do not themselves have to be learned because they are based on low-level durational and pitch cues. But the Shukla et al. study also illustrates a second important point about the implications of designing laboratory experiments to test infants. As noted earlier, it is natural for experimentalists to eliminate all but one source of information to determine whether it alone is sufficient for learning; that was the goal of the Saffran et al. (1996) study that focused on syllable statistics while eliminating prosodic and repetition cues that are present in natural language input.