Summarize this article

Summary needs 600 words

1.General research question

2.Experiments 1 & 2: methods and findings ( actual data should be included )

3.Conclusions/implications

Isolated words enhance statistical language learning in infancy

Casey Lew-Williams1, Bruna Pelucchi1,2, and Jenny R. Saffran1
1Department of Psychology and Waisman Center, University of Wisconsin-Madison, USA
2Department of Evolutionary Biology, University of Ferrara, Italy

Abstract
Infants are adept at tracking statistical regularities to identify word boundaries in pause-free
speech. However, researchers have questioned the relevance of statistical learning mechanisms to
language acquisition, since previous studies have used simplified artificial languages that ignore
the variability of real language input. The experiments reported here embraced a key dimension of
variability in infant-directed speech. English-learning infants (8–10 months) listened briefly to
natural Italian speech that contained either fluent speech only or a combination of fluent speech
and single-word utterances. Listening times revealed successful learning of the statistical
properties of target words only when words appeared both in fluent speech and in isolation; brief
exposure to fluent speech alone was not sufficient to facilitate detection of the words’ statistical
properties. This investigation suggests that statistical learning mechanisms actually benefit from
variability in utterance length, and provides the first evidence that isolated words and longer
utterances act in concert to support infant word segmentation.

Introduction
For 15 years, infant statistical learning has been a focus of research in the area of cognitive
development. Many researchers have shown that infants have a prodigious and domain-
general ability to track statistical patterns in their environments (e.g. Aslin, Saffran &
Newport, 1998; Fiser & Aslin, 2002; Kirkham, Slemmer & Johnson, 2002; Pelucchi, Hay &
Saffran, 2009; Saffran, Aslin & Newport, 1996). Given sequential events X and Y, infants
are highly sensitive to the probability that event X will transition to event Y (and vice versa).
This sensitivity to transitional probabilities (TPs) has been robustly demonstrated in several
auditory and visual domains. For example, when exposed to continuous speech with no
pause-defined cues to word boundaries, infants can segment words by noting which
syllables occur together with the most consistency.

A majority of these studies have assessed learning using highly simplified artificial
languages. While the materials used in statistical language studies typically afford a great
deal of experimental control, they fail to capture many of the dimensions of variability that
characterize infant-directed speech (though see Pelucchi et al., 2009; Singh, Nestor &
Bortfeld, 2008; Thiessen, Hill & Saffran, 2005). This has led several researchers to suggest
that statistical learning mechanisms cannot handle the complexities of real language, and to
question the hypothesis that statistical learning launches infants into language acquisition
(Johnson & Tyler, 2010; Yang, 2004). Here, we aimed to capture a significant source of
variability in infant-directed speech – the presence of both isolated words and longer

© 2011 Blackwell Publishing Ltd.
Address for correspondence: Casey Lew-Williams, Waisman Center, Infant Learning Lab, 1500 Highland Ave., Room 501,
University of Wisconsin-Madison, Madison, WI 53705-2280, USA; lewwilliams@wisc.edu.

NIH Public Access
Author M

anuscript

Dev Sci. Author manuscript; available in PMC 2012 February 16.

Published in final edited form as:
Dev Sci. 2011 November ; 14(6): 1323–1329. doi:10.1111/j.1467-7687.2011.01079.x.

N
IH

-P
A

A
uthor M

anuscript
N

IH
-P

A
A

uthor M
anuscript

N
IH
-P
A
A
uthor M
anuscript

utterances – to assess the degree to which statistical learning abilities are well matched to the
structure of early language input.

Natural speech is replete with pauses, which in some cases provide valuable cues to the
locations of word boundaries. Corpus analyses show that while caregivers often produce
long, uninterrupted strings of words, they also produce much shorter utterances, such as
words in isolation. These single-word utterances, which by definition have pauses at their
edges, are a salient feature of infant-directed speech. Brent and Siskind (2001) found that
9% of caregiver utterances consisted of isolated words, of which 27% occurred two or more
times in neighboring utterances (e.g. See the doggie over there? Doggie!). Fernald and
Morikawa (1993) found similar proportions: an average of 9% of utterances spoken by
American and Japanese mothers were single content words. Other researchers have
estimated similar or even higher proportions of isolated words (Aslin, Woodward,
LaMendola & Bever, 1996; Siskind, 1996; van de Weijer, 1998). Researchers disagree about
whether this is a substantial proportion of early language input. But viewed through a wide
lens, the presence of isolated words seems more impressive: by combining estimates of total
language exposure by Hart and Risley (1995) and of isolated word exposure by Brent and
Siskind (2001), we can estimate that a child may hear up to 4 million isolated word tokens
by their fourth birthday.

Given these numbers, isolated words could be expected to play a role in early language
acquisition. At the perceptual level, many studies have demonstrated that after hearing
words in sentences, infants can recognize them when they appear in isolation (e.g. Jusczyk
& Aslin, 1995; Jusczyk & Hohne, 1997; Pelucchi et al., 2009). Conversely, after hearing
words in isolation, infants can recognize them when they appear within sentences (e.g. Gout,
Christophe & Morgan, 2004; Houston & Jusczyk, 2000; Jusczyk & Aslin, 1995). Of
particular interest are findings demonstrating that caregivers’ use of isolated words is linked
to later vocabulary development. Brent and Siskind (2001) found that 75% of 18-month-
olds’ first words had previously appeared in isolation in mothers’ speech, and moreover, that
the frequency of hearing a word in isolation (but not the frequency of hearing a word
overall) was a unique predictor of later word use (see also Ninio, 1992).

Given the presence of isolated words in infant-directed speech, what is their role in
statistical learning? To date, we do not know whether these acoustically demarcated units
have any effect on infants’ computations of statistically coherent syllable sequences, or more
broadly speaking, whether statistical learning mechanisms can help infants make sense of
natural speech that contains a mix of isolated words and longer utterances. Do isolated
words offer a shortcut for word segmentation, such that infants do not need to track TPs in
natural speech? Alternatively, perhaps the presence of isolated words facilitates the
detection of TPs in fluent speech.

To address this issue, we tested 8- to 10-month-old English-learning infants’ abilities to
segment words from natural Italian speech that either did or did not contain isolated words.
In Experiment 1, infants were tested in one of two conditions. In the Fluent Speech
condition, infants heard a set of Italian sentences abbreviated from the materials used in a
previous study of statistical learning (Pelucchi et al., 2009, Experiment 3). Two types of
target words were embedded within the sentences: high-TP words (TP = 1.0), where the
component syllables never appeared elsewhere in the corpus, and low-TP words (TP =
0.33), where the component syllables recurred within many other words in the corpus. This
brief, pause-free familiarization was designed to minimize the likelihood that infants would
be able to learn enough about high- vs. low-TP words. In the Fluent Speech + Isolated
Words condition, infants heard the same target words within sentences, and also heard the
target words spoken in isolation between sentences. Critically, this condition was designed

Lew-Williams et al. Page 2

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

such that successful learning of the words’ statistical properties required infants to integrate
their experience hearing fluent speech and isolated words.

After familiarization with the Italian speech, infants were tested on their listening times to
high- and low-TP words using the Headturn Preference Procedure. If infants cannot detect
the words’ statistical coherence based on a very short exposure to fluent speech alone, then
we would expect listening times to be equivalent for both types of target words in the Fluent
Speech condition. In the Fluent Speech + Isolated Words condition, the same results would
emerge if infants relied on isolated words alone, since all target words appeared in isolation
with the same frequency. However, we predicted an interaction between condition and the
type of target word. If infants can integrate statistical information gained from hearing
words in isolation and in fluent speech, then we would expect listening times to differ for
high- and low-TP words in the Fluent Speech + Isolated Words condition.

Experiment 1
Method

Participants—Participants were 40 healthy, full-term infants with a mean age of 9.5
months (range = 8.3–10.9). Infants were from monolingual English-speaking households,
and had no prior exposure to Italian or Spanish. Parents reported no pervasive
developmental delays and no history of hearing or visual problems. Infants were randomly
assigned to the Fluent Speech condition (10 female, 10 male) or the Fluent Speech +
Isolated Words condition (10 female, 10 male). Eleven additional infants were tested but not
included in analyses due to fussiness (10) or inattentiveness (1).

Speech stimuli—Infants were familiarized with natural, infant-directed Italian speech that
either did or did not contain isolated tokens of target words (see Figure 1). In the Fluent
Speech condition, infants heard grammatically correct and semantically meaningful
sentences adapted from a previous study of statistical learning (Pelucchi et al., 2009,
Experiment 3). Sentences were recorded by a female native speaker of Italian at a rate of
approximately six syllables per second, presented at approximately 60 dBSPL. Embedded
within the sentences were four bisyllabic target words: casa, bici, fuga, and melo (English
translations: house, bike, escape, and apple tree). The target words appeared with equal
frequency during familiarization, but their internal TPs differed. For half of the infants in
this condition, casa and bici were high-TP words: their component syllables (ca, sa, bi, and
ci) always appeared in the contexts of the words casa and bici. Thus the internal TPs of
these words were 1.0. For these infants, fuga and melo were low-TP words: the initial
syllables (fu and me) appeared 33% of the time in the words fuga and melo, but 67% of the
time else-where in the speech (always in stressed position). Thus the internal TPs of fuga
and melo were 0.33. The other half of the infants heard a different, counterbalanced
familiarization, with casa and bici as low-TP words and fuga and melo as high-TP words.

In Pelucchi et al. (2009), infants successfully discriminated high-TP from low-TP words
after receiving 18 exposures to each target word. Importantly, in the present experiment,
infants received just 12 exposures to each target word. This reduction was designed to
decrease the likelihood that infants would successfully segment target words when hearing
only fluent speech.

In the Fluent Speech + Isolated Words condition, infants received only six exposures to each
target word within sentences, with 12 additional occurrences of the initial syllables of low-
TP words. Each target word was also presented three times in isolation, yielding a total of
nine exposures to each target word. Additional filler sentences were interspersed in order to
match familiarization length across conditions. In order to mimic caregiver use of isolated

Lew-Williams et al. Page 3

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

words (Brent & Siskind, 2001), each isolated word appeared between sentences, bordered by
300-ms pauses, and always followed a sentence that contained the same target word. Test
items for both conditions consisted of the four target words (two high-TP, two low-TP); the
tokens were identical to the single-word utterances used in the Fluent Speech + Isolated
Words condition.

Procedure—The experiment consisted of a familiarization phase (90 sec) and a test phase
(approximately 3 min), using the Headturn Preference Procedure. Infants were seated on a
caregiver’s lap within a double-walled, sound-attenuated booth, equipped with a center light
and two side-lights. Infants heard speech stimuli while parents listened to unrelated speech
over headphones. The experimenter coded infant head-turns outside of the booth via a
closed-circuit camera using a button-box connected to a computer. During familiarization,
infants heard Italian speech from laterally placed speakers. The lights flashed contingently
on infants’ looking behavior. Each test trial was initiated when infants looked to a flashing
center light, at which point the experimenter signaled the center light to extinguish and one
of the side-lights to begin flashing. When infants looked at the side-light, an isolated token
of a high- or low-TP word was repeated until infants looked away for 2 s or 20 s had
elapsed. Side of stimulus presentation was counterbalanced, and the experimenter was blind
to test-item presentation. Infants’ looking time was calculated automatically using custom-
designed software. During the test, each high- and low-TP word was repeated on three trials,
randomized by block, for a total of 12 test trials.

Results and discussion
Looking times were analyzed in a 2 × 2 mixed ANOVA with condition (Fluent Speech,
Fluent Speech + Isolated Words) as a between-subjects factor, and test item (high-TP, low-
TP) as a within-subjects factor (see Figure 2).1 Looking times revealed a significant main
effect of test item, F(1, 38) = 4.3, p < .05, ηp2 = .10, suggesting that infants listened significantly longer to high-TP words than to low-TP words. Analyses also showed a significant interaction between condition and test item, F(1, 38) = 7.8, p < .01, ηp2 = .17. Bonferroni-corrected post-hoc comparisons (p < .025) revealed that infants in the Fluent Speech condition listened equally to high- and low-TP words, t(19) = .5, p = .6, d = .09, but that infants in the Fluent Speech + Isolated Words condition listened significantly longer to high-TP words, t(19) = 3.2, p < .005, d = .53. Given this very brief exposure, infants failed to learn enough about the words’ statistical properties to successfully discriminate the test items in the absence of isolated words. However, the presence of single-word utterances facilitated infants’ detection of the statistical properties of those words in fluent speech.

Infants’ successful discrimination of high- and low-TP words in the Fluent Speech +
Isolated Words condition is particularly striking given the frequency with which infants
were exposed to target words across conditions. Infants in this condition received just nine
exposures to each target word, while infants in the Fluent Speech condition received 12
exposures. Even with fewer opportunities to track statistical properties of Italian speech,
infants integrated information gained from hearing words in isolation with statistical
information available in fluent speech. Critically, infants heard high- and low-TP words
equally often in isolation. If they had attended only to isolated words, we would expect no
difference in looking to each word type, since all target words would have an identical TP of
1.0. Thus, attention to the statistical coherence of syllables was required for infants to
successfully discriminate high- from low-TP words.

1In both Experiments 1 and 2, performance did not vary by gender and did not differ across the two counterbalanced corpora. Thus,
these factors were not included in the main analyses.

Lew-Williams et al. Page 4

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

An alternative explanation for these findings is that the presence of isolated words simply
made the speech more engaging. We know that infants prefer listening to speech with
variability in pitch (Cooper & Aslin, 1990; Fernald & Kuhl, 1987), and that pitch variability
heightens infants’ ability to track sequential statistics (Thiessen et al., 2005). It is thus
possible that variability in utterance length heightened infants’ interest in listening to the
Italian familiarization. This may have resulted in an increased ability to detect statistical
properties of target words from fluent speech alone, regardless of the contribution of isolated
words. To test this alternative hypothesis, infants in Experiment 2 listened to a combination
of fluent Italian speech and isolated words, but there was no phonological overlap between
the words presented in fluent speech and isolation. If variability alone enhances
performance, then infants should continue to show successful discrimination in Experiment
2. However, if the crucial factor is the phonological overlap between the isolated words and
the fluent speech, then infants should fail to discriminate between the test items in
Experiment 2.

Experiment 2
Method

Participants—Participants were 20 healthy, full-term infants (10 female) with a mean age
of 9.4 months (range = 8.4–10.8). Six additional infants were tested but not included in
analyses due to fussiness (4) or inattentiveness (2).

Speech stimuli and procedure—Materials and procedures were comparable to the
Fluent Speech + Isolated Words condition from Experiment 1. In both experiments, there
were nine exposures to the target words casa, bici, fuga, and melo during the familiarization
(90 s). In the previous experiment, infants heard each target word six times in fluent speech
and three times in isolation; however, in Experiment 2, all nine exposures were in fluent
speech, and infants heard different Italian words in isolation: pane, dono, tema, and socio.
Like the target words, these unrelated isolated words were bisyllabic and conformed to a
strong–weak stress pattern. Crucially, however, these isolated words did not overlap with the
target words.

Results and discussion
Listening times in Experiment 2 were compared to listening times in the Fluent Speech +
Isolated Words condition from Experiment 1 in a 2 (condition) × 2 (test item) mixed
ANOVA. Analyses revealed a significant interaction, F(1, 38) = 5.6, p < .025, ηp2 = .13, suggesting that listening times to high- and low-TP words differed in the two conditions. A paired-samples t-test showed that infants did not show a significant difference in listening times to high- and low-TP words in Experiment 2, t(19) = .3, p = .8, d = .07 (see Figure 2). The lack of discrimination suggests that isolated words do not simply enhance attention to the speech stream. Rather, caregiver use of isolated words seems to play a role in helping infants detect statistical regularities related to those words in otherwise pause-free speech.

General discussion
The usefulness of statistical learning mechanisms in explaining early language learning is
dependent upon infants’ abilities to organize the variability inherent in real speech. We
focused here on a particularly salient source of variability in caregiver speech – the presence
of both isolated words and longer utterances – and provided the first evidence that isolated
words and longer utterances act in concert to facilitate infant word segmentation. In two
preferential-listening experiments, English-learning infants received brief exposure to
Italian. When hearing high- and low-TP target words in a brief corpus of fluent speech

Lew-Williams et al. Page 5

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

alone, infants did not demonstrate that they learned enough about the words’ statistical
properties to distinguish between them. However, infants who heard a similarly brief corpus
containing target words both in fluent speech and in isolation successfully detected the
coherence of their component syllables. This finding indicates that statistical learning
mechanisms may in fact benefit from variability in utterance length. The only way that
infants could have discriminated high- from low-TP words in this condition was through the
interaction of fluent speech and isolated words.

The industry of studies on statistical language learning was built on the premise that pauses
do not reliably occur between words, posing a difficult puzzle of word segmentation to
young language learners. Previous research shows that infants are highly adept at
discovering statistical regularities in pause-free speech (Saffran et al., 1996), and that
embedding words in sentences has many other benefits in early language learning, by
helping infants recognize words faster (Fernald & Hurtado, 2006), anticipate subsequent
words (Lew-Williams & Fernald, 2007), discover grammatical categories (Mintz, 2003), and
produce multiword speech (Bannard & Matthews, 2008).

Isolated words – which by definition are acoustically demarcated from other utterances by
moments of silence – may also have positive consequences for language learning (Peters,
1983; Pinker, 1984). Using computational or adult experimental data, previous researchers
have demonstrated that isolated words facilitate the discovery of word boundaries in fluent
speech (Brent & Cartwright, 1996; Conway, Bauerschmidt, Huang & Pisoni, 2009; Dahan &
Brent, 1999; van de Weijer, 1998). Descriptions of this process converge on a common
premise: words spoken in isolation become perceptually familiar, ‘pop out’ when heard in
fluent speech, and provide a means of segmenting adjacent words in fluent speech.
Similarly, infant studies suggest that highly familiar words, such as the infant’s name or the
family’s word for mother, provide useful cues to the boundaries of the words adjacent to
them (Bortfeld, Morgan, Golinkoff & Rathbun, 2005), and even help infants in challenging
artificial language tasks (Mersad & Nazzi, 2010). However, this hypothesis has not yet been
tested using actual isolated words with infant learners.

The experiments reported here offer a new perspective on how a combination of isolated
words and longer utterances may support early word segmentation. Words heard in isolation
are relatively familiar and recognizable when heard in fluent speech, and they enhance
infants’ abilities to detect the statistical properties of syllable sequences in the global
language input. Importantly, isolated words are not likely to be essential for language
learning, and they do not simply replace the need for infants to compute the locations of
word boundaries in fluent speech. But isolated words are a prevalent feature of caregiver
speech, and even a minimal number of exposures to words in isolation may confer
advantages in early statistical learning. This research thus complements and extends
previous work on the importance of infant-directed speech (Brent & Siskind, 2001;
Gleitman, Newport & Gleitman, 1984; Kemler-Nelson, Hirsh-Pasek, Jusczyk & Cassidy,
1989; Singh, Nestor, Parikh & Yull, 2009; Thiessen et al., 2005; Werker, Pons, Dietrich,
Kajikawa, Fais & Amano, 2007).

Isolated words appear to facilitate learning about statistical attributes of fluent speech.
However, both long sentences and isolated words are very much part of the statistical
landscape of speech, and their relationship is likely to be symbiotic: the distributions of
syllables in fluent speech could also help infants learn about the isolated words themselves.
While infants may treat a novel isolated word like casa as a single, unsegmented unit, they
may also oversegment, treating casa as two monosyllabic words. Recent computational
models of word segmentation have focused on this issue, examining the initial assumptions
that learners could make about the nature of words (Goldwater, Griffiths & Johnson, 2009).

Lew-Williams et al. Page 6

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

Generally, ideal learners tend to favor the most efficient segmentation strategies given the
input data, which in this case would be treating casa as a single word. But statistics are
needed to guide learners toward this correct interpretation. Over time, infants could
gradually determine that the component syllables ca and sa should be more tightly linked by
noting the regularity with which those syllables co-occur in the language environment. Thus,
while isolated words support statistical learning in long utterances, statistical features of
long utterances also help infants learn about the structure of isolated words.

While isolated words are particularly salient in the speech stream, they are just one in a
network of useful segmentation cues that may inform each other multidirectionally. It will
be important to discover how isolated words work together with other linguistic and domain-
general cues to signal the locations of word boundaries, such as lexical stress (Curtin, Mintz
& Christiansen, 2005; Johnson & Jusczyk, 2001), phrase-level prosody (Shukla, Nespor &
Mehler, 2007), sentence position (Seidl & Johnson, 2006), language-specific phonotactic
constraints (Brent & Cartwright, 1996), and concurrently presented visual information
(Cunillera, CQmara, Laine & Rodríguez-Fornells, 2010). Future studies should also aim to
understand how statistical learning mechanisms operate given other dimensions of
variability in infant-directed speech, such as the presence of multiple talkers in complex
turn-taking interactions. In some cases, as in the research on utterance length reported here,
variability does not pose a problem to the young learner, but in other cases, variability may
disrupt learning. Studies of the variability inherent in infant-directed speech will both
enhance and constrain accounts of early language acquisition, by allowing us to determine
the degree to which infant learning mechanisms are well matched to the structure of early
language input.

Acknowledgments
We would like to thank the participating families, the members of the Infant Learning Lab, and especially Rosie
Maier for her help with data collection. We also thank Michael Frank, Erik Thiessen, and anonymous reviewers for
comments on a previous version of this paper. This research was funded by grants from the Eunice Kennedy
Shriver National Institute of Child Health and Human Development to CLW (F32HD069094), JRS (R01HD0
37466), and the Waisman Center (P30HD03352). Additional funding was provided by a grant from the James F.
McDonnell Foundation to JRS, and an NICHD supplementary grant made possible by the American Recovery and
Reinvestment Act of 2009 (R01HD037466-09S1).

References
Aslin RN, Saffran JR, Newport EL. Computation of conditional probability statistics by 8-month-old

infants. Psychological Science. 1998; 9:321–324.
Aslin, RN.; Woodward, JZ.; LaMendola, NP.; Bever, TG. Models of word segmentation in fluent

maternal speech to infants. In: Demuth, K.; Morgan, JL., editors. Signal to syntax. Mahwah, NJ:
Erlbaum; 1996. p. 117-134.

Bannard C, Matthews D. Stored word sequences in language learning: the effect of familiarity on
children’s repetition of four-word combinations. Psychological Science. 2008; 19:241–248.
[PubMed: 18315796]

Bortfeld H, Morgan JL, Golinkoff RM, Rathbun K. Mommy and me: familiar names help launch
babies into speech-stream segmentation. Psychological Science. 2005; 16:298–304. [PubMed:
15828977]

Brent MR, Cartwright TA. Distributional regularity and phonotactic constraints are useful for
segmentation. Cognition. 1996; 61:93–125. [PubMed: 8990969]

Brent MR, Siskind JM. The role of exposure to isolated words in early vocabulary development.
Cognition. 2001; 81:B33–B44. [PubMed: 11376642]

Conway CM, Bauerschmidt A, Huang SS, Pisoni DB. Implicit statistical learning in language
processing: word predictability is the key. Cognition. 2009; 114:356–371. [PubMed: 19922909]

Lew-Williams et al. Page 7

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

Cooper RP, Aslin RN. Preference for infant-directed speech within the first month after birth. Child
Development. 1990; 61:1584–1595. [PubMed: 2245748]

Cunillera T, Cámara E, Laine M, Rodríguez-Fornells A. Speech segmentation is facilitated by visual
cues. Quarterly Journal of Experimental Psychology. 2010; 63:260–274.

Curtin S, Mintz TH, Christiansen MH. Stress changes the representational landscape: evidence from
word segmentation. Cognition. 2005; 96:233–262. [PubMed: 15996560]

Dahan D, Brent MR. On the discovery of novel wordlike units from utterances: an artificial-language
study with implications for native-language acquisition. Journal of Experimental Psychology:
General. 1999; 128:165–185. [PubMed: 10406104]

Fernald A, Hurtado N. Names in frames: infants interpret words in sentence frames faster than words
in isolation. Developmental Science. 2006; 9:F33–F40. [PubMed: 16669790]

Fernald A, Kuhl P. Acoustic determinants of infant preference for motherese speech. Infant Behavior
and Development. 1987; 10:279–293.

Fernald A, Morikawa H. Common themes and cultural variations in Japanese and American mothers’
speech to infants. Child Development. 1993; 64:637–656. [PubMed: 8339686]

Fiser J, Aslin RN. Statistical learning of higher-order temporal structure from visual shape sequences.
Journal of Experimental Psychology: Learning, Memory, and Cognition. 2002; 28:458–467.

Gleitman L, Newport M, Gleitman H. The current status of the motherese hypothesis. Journal of Child
Language. 1984; 11:43–79. [PubMed: 6699113]

Goldwater S, Griffiths TL, Johnson M. A Bayesian framework for word segmentation: exploring the
effects of context. Cognition. 2009; 112:21–54. [PubMed: 19409539]

Gout A, Christophe A, Morgan JL. Phonological phrase boundaries constrain lexical access II: Infant
data. Journal of Memory and Language. 2004; 51:548–567.

Hart, B.; Risley, TR. Meaningful differences in the everyday experience of young American children.
Baltimore, MD: Brookes; 1995.

Houston DM, Jusczyk PW. The role of talker-specific information in word segmentation by infants.
Journal of Experimental Psychology: Human Perception and Performance. 2000; 26:1570–1582.
[PubMed: 11039485]

Johnson EK, Jusczyk PW. Word segmentation by 8-month-olds: when speech cues count more than
statistics. Journal of Memory and Language. 2001; 44:548–567.

Johnson EK, Tyler MD. Testing the limits of statistical learning for word segmentation.
Developmental Science. 2010; 13:339–345. [PubMed: 20136930]

Jusczyk PW, Aslin RN. Infants’ detection of the sound patterns of words in fluent speech. Cognitive
Psychology. 1995; 29:1–23. [PubMed: 7641524]

Jusczyk PW, Hohne EA. Infants’ memory for spoken words. Science. 1997; 277:1984–1986.
[PubMed: 9302291]

Kemler-Nelson DG, Hirsh-Pasek K, Jusczyk PW, Cassidy KW. How the prosodic cues in motherese
might assist language learning. Journal of Child Language. 1989; 16:55–68. [PubMed: 2925815]

Kirkham NZ, Slemmer JA, Johnson SP. Visual statistical learning in infancy: evidence for a domain
general learning mechanism. Cognition. 2002; 83:B35–B42. [PubMed: 11869728]

Lew-Williams C, Fernald A. Young children learning Spanish make rapid use of grammatical gender
in spoken word recognition. Psychological Science. 2007; 18:193–198. [PubMed: 17444909]

Mersad, K.; Nazzi, T. When Mommy comes to the rescue of statistics. Poster presented at the Biennial
Meeting of the International Society for Infant Studies; Baltimore, MD. 2010.

Mintz TH. Frequent frames as a cue for grammatical categories in child directed speech. Cognition.
2003; 90:91–117. [PubMed: 14597271]

Ninio A. The relation of children’s single word utterances to single word utterances in the input.
Journal of Child Language. 1992; 19:87–110. [PubMed: 1551935]

Pelucchi B, Hay JF, Saffran JR. Statistical learning in a natural language by 8-month-old infants. Child
Development. 2009; 80:674–685. [PubMed: 19489896]

Peters, A. The units of language acquisition. New York: Cambridge University Press; 1983.
Pinker, S. Language learnability and language development. Cambridge, MA: Harvard University

Press; 1984.

Lew-Williams et al. Page 8

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

Saffran JR, Aslin RN, Newport EL. Statistical learning by 8-month-old infants. Science. 1996;
274:1926–1928. [PubMed: 8943209]

Seidl A, Johnson EK. Infant word segmentation revisited: edge alignment facilitates target extraction.
Developmental Science. 2006; 9:565–573. [PubMed: 17059453]

Shukla M, Nespor M, Mehler J. An interaction between prosody and statistics in the segmentation of
fluent speech. Cognitive Psychology. 2007; 54:1–32. [PubMed: 16782083]

Singh L, Nestor SS, Bortfeld H. Overcoming the effects of variation in infant speech segmentation:
influences of word familiarity. Infancy. 2008; 13:57–74. [PubMed: 21088702]

Singh L, Nestor SS, Parikh C, Yull A. Influences of infant-directed speech on early word recognition.
Infancy. 2009; 14:654–666.

Siskind JM. A computational study of cross-situational techniques for learning word-to-meaning
mappings. Cognition. 1996; 61:39–91. [PubMed: 8990968]

Thiessen ED, Hill EA, Saffran JR. Infant-directed speech facilitates word segmentation. Infancy. 2005;
7:53–71.

van de Weijer, J. Language input for word discovery. Nijmegen: Max Planck Institute for
Psycholinguistics; 1998.

Werker JF, Pons F, Dietrich C, Kajikawa S, Fais L, Amano S. Infant-directed speech supports phonetic
category learning in English and Japanese. Cognition. 2007; 103:147–162. [PubMed: 16707119]

Yang CD. Universal grammar, statistics or both? Trends in Cognitive Sciences. 2004; 8:451–456.
[PubMed: 15450509]

Lew-Williams et al. Page 9

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

Figure 1.
Subset of Italian stimuli from Experiment 1. In the Fluent Speech + Isolated Words
condition, participants heard both fluent speech and isolated words (left and right columns);
in the Fluent Speech condition, participants heard only fluent speech (two repetitions of the
sentences in the left column). High-TP words are italicized; low-TP words are bolded, as are
additional occurrences of the initial syllables of low-TP words. Only one of the two
familiarization corpora is shown in the figure. Filler sentences are omitted.

Lew-Williams et al. Page 10

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript

Figure 2.
Mean looking times to high-TP and low-TP words in Experiment 1 (Fluent Speech
condition, Fluent Speech + Isolated Words condition) and Experiment 2 (Fluent Speech +
Unrelated Isolated Words condition). Error bars represent standard errors of the mean.

Lew-Williams et al. Page 11

Dev Sci. Author manuscript; available in PMC 2012 February 16.
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript
N
IH
-P
A
A
uthor M
anuscript