PERCEPTION OF LINGUISTIC RHYTHM BY NEWBORN INFANTS
11
look for an alternative explanation. For instance, follow-
ing adult subjects’ judgements in Exp. 3, one might argue
that Dutch sentences, containing more consonant clusters
and more frication, are less pleasant to listen to, and thus
keep the babies more excited. Such an interpretation would,
however, assume that stimuli that are less preferred provoke
more sucking, which would appear to be in contradiction
with the earlier studies’ interpretations. In the absence of
a good model of what provokes a baby’s sucks, the question
remains open12.
It is yet possible to provide an interpretation of the present
results in terms of genuine preference. Indeed, French can be
seen as closer to Dutch and English than to Japanese along
a number of dimensions. Regarding the most relevant one,
rhythm, objective acoustic/phonetic measures of rhythmic
properties suggest that French rhythm is much closer to that
of Dutch and English than to that of Japanese (Ramus et al.,
1999). Similar arguments could be made for syllable struc-
ture, intonation, size of the phonemic repertoire... It is thus
conceivable that Dutch and English sound more familiar to
the French newborn than Japanese. Native-language prefer-
ence might therefore be re-interpreted as preference for the
most familiar stimulus (along the dimensions that are rele-
vant to the baby).
Conclusion
The literature on infant speech perception has suggested
for years that newborns discriminate languages’ rhythmic
patterns. The evidence accumulated so far, although com-
pelling, has always left open the possibility that the dis-
criminations observed might be due to a sensitivity to into-
national differences. Here, using resynthesized stimuli, we
have shown that intonation is not necessary for newborns
to discriminate between Dutch and Japanese. This does not
strictly imply that intonation was not used by babies to dis-
criminate languages in previous experiments, but it makes
the "intonation hypothesis" more unlikely than ever, thereby
strengthening the "rhythm hypothesis".
The point of the present study is not, however, to deny
that intonation can be processed by newborns and play a
role in language acquisition (see for instance Guasti, Nespor,
Christophe, & van Ooyen, in press), but to show that rhythm
is sufficient for babies to discriminate languages, and there-
fore that they genuinely process rhythm. This in turn rein-
forces the plausibility of language acquisition scenarios that
rely on rhythm as a cue to other properties of language the
infant has to learn. Noticing the correlation between a lan-
guage’s rhythm type and the structure of its syllables, Ramus
et al. (1999) proposed for instance a detailed scenario of how
the early perception of rhythm might cue the acquisition of
syllable structure. It has also been proposed that procedures
that listeners use to normalize for speech rate are language-
specific, and indeed depend on the type of rhythm of a given
language (Pallier, Sebastian-Galles, Dupoux, Christophe, &
Mehler, 1998; Sebastian-Galles, Dupoux, & Costa, in press).
Since speech rate variability, like talker variability (see Exp.
1), is likely to be an obstacle to the extraction of relevant
linguistic units by the infant, an interesting hypothesis would
be that the perception of speech rhythm allows for an early
selection of the appropriate normalization strategy. The "syl-
lable structure" and the "normalization" hypotheses are ob-
viously independent and not exclusive. More generally, it is
conceivable that speech rhythm may allow infants to make
quite a large array of language-specific adjustments on their
phonological representations.
"Phonological bootstrapping" scenarios (Morgan & De-
muth, 1996) like those proposed above typically require three
lines of evidence: (a) a correlation between a perceptible
acoustic/phonological cues and a linguistic property to be
learnt, (b) evidence that the acoustic/phonological cues are
processed by infants sufficiently early, and (c) evidence that
infants actually use those cues in their acquisition of the lin-
guistic property. The first line of evidence typically comes
from linguistic and experimental studies like those of Ramus
et al. (1999), Pallier et al. (1998) and Sebastian-Galles et al.
(in press). The second line comes from perceptual studies
conducted on infants like the present one. Here, we have
shown that speech rhythm is indeed a cue that is processed by
newborns. The third line of evidence may be more difficult to
obtain, because the actual causes of observed developmental
changes are never certain. The proposed scenarios yet predict
that an impairment in speech rhythm perception may delay
or impair the infant’s acquisition of correct syllable structure
and/or speech rate normalization.
Such predictions may eventually be testable if suitable
neuropsychological cases are found. We speculate that
dyslexic children might provide us with such a case. Al-
though speech rhythm perception has never been specifically
tested in dyslexics, there is some evidence that they may have
trouble discriminating the rhythmic patterns of sequences of
tones (McGivern, Berka, Languis, & Chapman, 1991; Kujala
et al., 2000). Similarly, neither the representation of sylla-
ble structure nor speech rate normalization have been inves-
tigated in dyslexics. However, informal observations point at
particular difficulties with handling complex consonant clus-
ters, hence suggesting a possibly impoverished representa-
tion of syllables. Dyslexics, or alternatively other language-
impaired populations, might thus provide a critical test of the
hypothesized bootstrapping role of rhythm.
References
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Bertoncini, J., Floccia, C., Nazzi, T., & Mehler, J. (1995). Morae
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neonates. Language and Speech, 38, 311-329.
Bertoncini, J., & Mehler, J. (1981). Syllables as units in infant
perception. Infant Behavior and Development, 4, 247-260.
12 Note that this problem is not particular to the sucking behav-
ior. In studies using preferential listening techniques, preference
sometimes goes for the novel stimulus, and sometimes for the fa-
miliar one. No generalized account of infants’ preferences has been
proposed.