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Infant speech segmentation and the role of the emergent lexicon

Final Activity Report Summary - ISS (Infant speech segmentation and the role of the emergent lexicon)

The two major objectives of this study were to determine
1. whether 11-month-old infants segmented familiar words from connected speech; and
2. whether early favoured babbling patterns or Vocal motor schemes (VMS) had an effect on speech perception.

In order to achieve the first project objective included 24 11-month-old and 12-month-old infants which were tested using the head turn preference paradigm to contrast passages containing trochaic words, i.e. words with strong-weak stress, likely to be familiar to infants, such as tummy and tickle, with rare words, e.g. tangy, piffle. The words were inserted near the beginning or the end of sentences spoken by a female speaker in a manner typical of infant-directed speech. The carrier sentences were identical for the familiar and the rare words. Looking times were recorded for orientation towards the two types of passages.

Infants of both ages showed evidence of segmenting previously known words from passages, even though the effect was stronger at 12 than at 11 months of age. The relatively weak effect at 11 months, despite earlier evidence of 7.5-month-old infants' success in segmenting words trained in the laboratory, suggested a need for more ecologically valid tests in order to trace the course of naturalistic word learning capacities.

In order to achieve the second objective, 24 infants were followed longitudinally to determine each infant's favoured babbling patterns or VMS. 14 of these infants were tested in the perception phase of the study. The results of these head turn experiments were unequivocal with respect to the relation between the number of VMS and the infant looking preferences. Infants with one VMS responded with longer looks to passages with inserted nonsense words which had the VMS that they produced, while infants with two VMS displayed longer looking times to the passages that contained the consonant that they were not yet consistently producing.

Since the transition from one to two VMS typically occurred as a matter of weeks at most, the infants' categorical attention shift away from consonants that they produced towards those that they were about to produce was remarkable. Contrary to the accepted notion that perception always preceded production, this result strongly argued for production initiating a perceptual shift towards 'noticing' contrasts that paved the way for further phonetic development.