PERCEPTION OF LINGUISTIC RHYTHM BY NEWBORN INFANTS
therefore insufficient to disentangle the role of rhythm and
intonation. This concern is addressed in the next two experi-
ments.
Experiment 3: sasasa with
artificial intonation
Materials and Method
Stimuli
In previous experiments testing language discrimination
by adults on the basis of rhythm only (Ramus & Mehler,
1999; Ramus et al., submitted), sentences were resynthe-
sized following the flat sasasa manner: all consonants were
mapped to /s/ and all vowels to /a/, and in addition the orig-
inal F0 contour of the sentence was ignored and replaced by
a constant F0. Thus all differences concerning intonation or
syllable structure were eliminated, preserving only rhythmi-
cal differences between the two languages.
When testing babies, an additional concern is to keep them
awake and active in the experiment. In this respect, flat
sasasa stimuli are potentially problematic. Both their low
phonetic diversity and their monotonous intonation are sus-
ceptible to provoke boredom or distress in infants, and/or
to induce them to process the stimuli as non-speech. We
thus felt we had to improve the attractiveness of our stimuli,
while still adequately testing our hypotheses. Considering
that newborns are known to react normally to low-pass fil-
tered speech (Mehler et al., 1988; Nazzi et al., 1998), we as-
sumed that phonetic diversity was not a necessary condition,
but we chose to preserve some variability in the intonation.
Therefore, we decided to resynthesize the same 40 sen-
tences as before using a sasasa phonetic mapping, i.e., to
map all consonants to /s/ and all vowels as /a/. However,
instead of applying a flat intonation to each sentence, we ap-
plied artificial intonation contours. Five intonation contours
inspired from French sentences were designed and each was
applied to 4 of the Dutch and 4 of the Japanese sentences.
All contours included a regular declination towards their end,
in order to be more easily adapted to sentences of different
lengths; they are illustrated in Figure 4. Thus, the resynthe-
sized sentences incorporate both within-sentence and within-
language intonational variability, but no differences in into-
nation between the two languages.
A potential criticism of this method is that there might be
an interaction between intonation and rhythmic structure, so
that the five contours selected might be more adapted to the
rhythmic structure, say, of Dutch, than to that of Japanese.
This would then introduce a difference between the two sets
of sentences that would not be a rhythmic difference, strictly
speaking. In order to investigate this possibility, we have
conducted the following preliminary experiment on adult
subjects.
Judgement by adult subjects of sentences resynthesized
with an artificial intonation. Twelve participants were re-
cruited and tested in a quiet room. They were 4 men and
8 women, with a mean age of 34 years, and of various native
Figure 4. Intonation contours used in Exp. 3.