br Conclusions br Conflict of interest

Conclusions
Conflict of interest
Acknowledgments This work was supported by a Human Frontiers Science Program Young Investigator Grant nr. RGY 0073/2014, the LABEX EFL (ANR-10-LABX-0083>) and the ANR grant nr. ANR-15-CE37-0009-01 awarded to Judit Gervain. We thank the staff of the maternity of the Robert Debré Hospital for their help with participant recruitment. We also thank Lionel Granjon for his help with the stimuli, and Katie Von Holzen for her help with the permutation tests.
Introduction One pillar of linguistic competence is lexico-semantic knowledge. Apart from modality-independent semantic knowledge about objects and concepts this requires a lexicon containing word-forms and a tight link between both representations (Gupta and Tisdale, 2009). While word-forms are generally arbitrary, they order continine show quite specific regularities within a given language, in that languages differ substantially with regard to their phoneme inventory and the way in which phonemes are combined to yield well-formed lexical candidates (Chomsky and Halle, 1965; Trask, 1996). As an example neither the English word/NECK/nor the Slovak word/KRK/have any inherent relation to the respective body part but while the corresponding German word/HALS/could qualify as a lexical candidate in English,/KRK/cannot. It violates the ‘phonological grammar’ (Jacquemot et al., 2003) of English (and German). Such phonotactic constraints regulate lexical access (Vitevitch et al., 1999; Vitevitch, 2003), aid segmentation of the auditory stream (Brent and Cartwright, 1996; McQueen, 1998) and have been shown to play an important role in language acquisition in infants (Friederici and Wessels, 1993; Jusczyk and Aslin, 1995; Jusczyk, 1999; Gervain and Mehler, 2010). The acquisition of native phonotactic rules can be conceived to follow the trajectory of increasingly sophisticated sensitivity to subtle differences in the auditory input. At birth infants are exquisite ‘differentiators’: they are sensitive to basic acoustic features of speech (Telkemeyer et al., 2011), prefer their mother’s over other female voices (DeCasper and Fifer, 1980) and native over non-native stress patterns (Mehler et al., 1988); newborns attend more to speech than to non-speech sounds (Vouloumanos and Werker, 2007), show greater cerebral activation for forward versus reversed speech (Dehaene-Lambertz et al., 2002; Pena et al., 2003), distinguish phonemes (Mahmoudzadeh et al., 2013) and may even perceive phonotactic universals pertaining to sonority profiles (Gomez et al., 2014). Within the first year of life the endowment with such universal, ‘inborn’ discriminative capacities sets the basis for a gradual perceptual attunement to specific features of the native language(s) (Naatanen et al., 1997). There is ample evidence for such ‘perceptual narrowing’, extending beyond the linguistic domain (for a review see Maurer and Werker, 2014). With regard to phonetic attunement, vowel (Cheour et al., 1998) and consonant (Werker and Tees, 1984) differentiation have been shown to increasingly narrow down to those relevant in the native language between 4 and 10 months. Notably this seems to include both, a decrease in sensitivity to non-native and an increase in sensitivity to native contrasts (Kuhl et al., 2006). Regarding phonotactics behavioral work has shown an impact of native regularities on word segmentation at 9 months (Friederici and Wessels, 1993), but sensitivity to a native/non-native contrast may be present even earlier (Obrig et al., 2010). In sum, sensitivity to phonotactic and prosodic regularities in the incoming speech stream helps the infant to segment word-forms in a ‘bottom-up’ fashion (Gervain and Mehler, 2010). This supplies lexical candidates to be linked to conceptual knowledge, traditionally assumed to emerge after the 1st birthday. Notably however, increasing lexical knowledge in turn fosters statistical learning of phonotactic frequency distributions in the native language. Recent work suggests that such top-down cues for novel word-form learning may be available quite early. Evidence for ‘true word knowledge’ has been reported at 6 months (Bergelson and Swingley, 2012), and training of word-object pairs may establish ‘proto-words’ already at 3 months (Friedrich and Friederici, 2015). Irrespective of what qualifies as a ‘true word’ (Nazzi and Bertoncini, 2003), even very basic lexical knowledge can support segmentation in a ‘top-down’ fashion at 6 months (Bortfeld et al., 2005). Instead of assuming acquisition of substantial word-form knowledge a prerequisite to proceed to lexico-semantic acquisition, it therefore seems more intuitive to postulate mutual interaction between both capacities during language acquisition. As yet work on the interaction between ‘bottom-up’ statistical phonological learning and the influence of emerging lexical knowledge on the acquisition of native phonotactic constraints is scarce (Swingley and Aslin, 2007; Yeung et al., 2014). The present study targets this as a part of a larger project investigating different age groups and different training scenarios.