Assignment

Statistical Learning by 8-Month-Old Infants
Jenny R. Saffran; Richard N. Aslin; Elissa L. Newport
Science, New Series, Vol. 274, No. 5294. (Dec. 13, 1996), pp. 1926-1928.
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infection of ~nurinecells (15)and transgenic
mice expressing human CD4 (16) and provides a rationale for transgenic approaches to
developing animal models of HIV disease.
REFERENCES AND NOTES
I. F. Cocchi et a/.,Science 270, 1811 (1995).
2. Y. Feng, C. C. Broder, P. E. Kennedy, E. A. Berger,
ibid. 272, 872 (1996).
3. M. Samson, 0.Labbe, C. Mollereau,G. Vassart, M.
Parmentier, Biochemistry 35, 3362 (1996); C. J.
Raport, J. Gosling, V. L. Schweckart, P. W. Gray, I.
F. Charo, J. 6/01, Chem. 271, 17161 (1996).
4. H. Choe et a/.,Cell 85, 1135 (I996); B. J. Doranzet
a/.,ibid., p. 1149.
5. T. Dragic eta/.,Nature 381, 667 (1996); H. Deng et
a/.,ib@, p. 661;G.Akhatibetal.,Science 272, 1955
( I996).
6. S. Gartner eta/.,Science 233, 215 (1986).
7. R. Atchison eta/., unpubl~shedobservatons.
8. L. Boring et a/.,J. Bioi. Chem. 271, 7551 (1996).
9. We cloned cDNAs encoding human or murineCCR5
nto the expressionvector pcDNA3 (Invitrogen)after
engneering the FLAG epitope Into the NH,-termnus
as descrbed (13).Expresson of each construct was
determned by FACS w~than antbody to FLAG (antiFLAG) (Boehringer Mannhem), and relative expression for each (see below)was calculated as the percentage of cells expressng human CCR5 on the cell
surface normalizedto the expresson of hCCR5 (defined as loo%), w~thstandard errors of the mean.
The mean fluorescence intensty of the postve cells
from any sngle sample nevervariedfrom the average
by more than 30% in a single experiment.Therefore,
neither the relative number of postve cells nor the
absolute expression levels w~thintransfected cells
explains the differences in coreceptor activity. C~Imeric receptors were prepared by the overlap polymerase chain reactlon (PCR) method (17). hCCR5
(HHHH), human CCR5 (100% relative expression);
mCCR5 (MMMM), murlne CCR5 (126 2 49%);
HMMM, NH,-terminus of human CCR5 [am~noacids
(aa) 1 to 321 fused to murlne CCR5 (aa 35 to 354)
(77 ? 22%): MHHH, NH,-termnus of murne CCR5
(aa 1 to 34) fused to human CCR5 (aa 33 to 352)
(73 -t 17%);MHMM, extracellular loop 1 and a portion of transmembranedomain 3 of humanCCR5 (aa
86 to 118) replacing the corresponding segment of
the murlne receptor (aa 88 to 120) (37 -t 22%);
MMHM, extracellular loop 2 and adjacent porions of
human CCR5 (aa 134 to 210) replacing the corresponding regon of the murine receptor (aa 136 to
212) (81 2 30%); MMHH, NH,-term~nal half of
mCCR5 (aa 1 to 162) fused to the COOH-termnal
half of hCCR5 (aa 161 to 352) (80 -t 39%).
10. I. F. Charo et a/., Proc. Nati. Acad. Sci. U.S.A. 91,
2752 (1994).
11. C. Franci, L. M. Wong, J. Van Damme, P. Proost, I. F.
Charo, J. /mmuno/. 154, 6511 (1995).
12. We cloned cDNAs encoding human CCR2B or chimeras into the expresson vector pCMV4 (18) after
engineeringthe FLAG epitope into the NH,-terminus
as described (13).Express~onof each construct (see
below)was determned as descrbed earlier. Chimeric receptors were prepared by the overlap PCR
method (17). 5555, human CCR5 (100% relat~ve
expression);2222, human CCR2B (87 ? 2%);5222,
NH,-termnus of CCR5 (aa 1 to 32)fused to CCR2B
(aa 45 to 360) (27 -t 5%); 2555, NH,-terminus of
CCR2B (aa 1 to 44) fused to CCR5 (aa 33 to 352)
(108 ? 17%);2255, CCR2B (aa 1 to 136) fused to
CCR5 (aa 124 to 352) (119 -t 33%).
13. F. S. Monteclaro and I. F. Charo, J. Biol. Chem. 271,
19084 (1996); F. S. Monteclaro et ai., unpubl~shed
observations.
14. J. Gosling eta/., unpubshed observat~ons.
15. P. J. Maddon eta/., Cell 47, 333 (1986).
16. P. Loreset a/.,AIDS Res. Hum. Retroviruses8,2063
(1992).
17. S. N. Ho, H. D. Hunt, R. M. Horton, J. K. Pulen, L. R.
Pease, Gene 77, 51 (I989).
18. S. Andersson, D. L. Davis, H. Dahlback, H. Jornval,
D. W. Russell,J. Biol. Chem. 264, 8222 (1989).
19. M. A. Godsmth, M. T. Warmerdam, R. E. Atchison,
M. D. Miller, W. C. Greene,J. Virol. 69, 4112 (1995).
20. COS-7 cells were transfected w~th2 p,g of pasmid
DNA per well in a six-well plate as descrbed (19).
DNA samples consisted of appropriate combinatons of 0.5 p,g of a human CD4 expression plasmd
[pCD4Neo (19)l or pla~nvector, and 1 5 p,g of a
chemokine receptor-expressng plasmd or plain
vector. About 30 hours after additon of DNA, the
medium in each we was replaced with 1.0 ml of
medium contanng HV-I Ba-L (-1 00 to 170 ng of
p24 per sample; source: NH ADS Reagent Repository, passaged on prlmary human macrophages).About 10 hours later, an additona 1.0 ml
of medium was added to each well. After 30 hours,
the cells were recovered from the dish as described
(19) and analyzed with a FacScan (Becton Dickinson). Stainincl for intracvto~lasmicHV-1 w24 was
(Coulter Immunology)and goat ant-mouse fuorescein sothocyanate (FTC)-conjugated secondary
ant~body(Becton Dick~nson).Cells were further
sta~nedwith phycoerythr~n(PE)-conjugated antlCD4 (Becton Dcknson).Appropriate controls ndcated that the appearance of double-positve cells
(FTC + PE) was dependent on cotransfection with
both CD4 and human CCR5 expression plasmids
and on the presence of HIV-I Ba-L.
21. H. Arai and I. F. Charo, J. 6/01, Chem. 271, 21814
(I996).
22. We acknowledge the adv~ceof M. Warmerdam
(transfecton-nfectionassay),E. Welder (FACS studies),and L. Borng, H. Ara~,and R. Speck (scientf~c
interpretation). We appreciate the ass~stanceof
J. Carrolland M. Cenceros In the preparation of ths
manuscript. Supported In part by NIH grant
HL52773 (I.F.C.)and by Pfzer (M.A.G.).
carr~edout ~7ththe Fix and Perm reagents (Caltag
Laboratories), with a monoclonal antibody to p24 24 September 1996; accepted 24 October 1996
Statistical Learning by 8-Month-Old Infants
Jenny R. Saffran, Richard N. Aslin, Elissa L. Newport
Learners rely on a combination of experience-independent and experience-dependent
mechanisms to extract information from the environment. Language acquisition involves
both types of mechanisms, but most theorists emphasize the relative importance of
experience-independent mechanisms. The present study shows that a fundamental task
of language acquisition, segmentation of words from fluent speech, can be accomplished by 8-month-old infants based solely on the statistical relationships between
neighboring speech sounds. Moreover, this word segmentation was based on statistical
learning from only 2 minutes of exposure, suggesting that infants have access to a
powerful mechanism for the computation of statistical properties of the language input.
During early development, the speed and
accuracy with which an organism extracts
environmental information can be extremely important for its survival. Some
species have evolved highly constrained
neural mechanisms to ensure that environmental information is properly interpreted,
even in the absence of experience with the
environment (1). Other species are dependent on a period of interaction with the
environment that clarifies the information
to which attention should be directed and
the consequences of behaviors guided by
that information (2). Depending on the
developmental status and the task facing a
particular organism, both experience-independent and experience-dependent mechanisms may be involved in the extraction of
information and the control of behavior.
In the domain of language acquisition,
two facts have supported the interpretation
that experience-independent mechanisms
are both necessary and dominant. First,
highly complex forms of language production develop extremely rapidly (3).Second,
the language input available to the young
child is both incomplete and sparsely repDepartment of Brain and Cognitve Sciences, Unversity
of Rochester, Rochester, NY 14627, USA.
resented compared to the child’s eventual
linguistic abilities (4). Thus, most theories
of language acquisition have emphasized
the critical role played by experience-independent internal structures over the role of
experience-dependent factors (5).
It is undeniable that experience-dependent ~nechanis~nsare also required for the
acquisition of language. Many aspects of a
particular natural language must be acquired from listening experience. For example, acquiring the specific words and phonological structure of a language requires
exposure to a significant corpus of language
input. Moreover, long before infants begin
to produce their native language, they acquire information about its sound properties
(6). Nevertheless, given the daunting task
of acquiring linguistic information from listening experience during early development, few theorists have entertained the
hypothesis that learning plays a primary
role in the acquisition of more complicated aspects of language, favoring instead
experience-independent mechanisms (7).
Young humans are generally viewed as
poor learners, suggesting that innate factors are primarily responsible for the acquisition of language.
Here we investigate the nature of the
SCIENCE VOL. 274 13 DECEMBER 1996
experience-dependent factors involved in
language acquisition. In particular, we ask
whether infants are in fact better learners
than has previously been assumed, thus potentially reducing the extent to which ex-
~erience-indevendentstructures must be
rnaterial that serves as a potential learning
experience. They are subsequently presented with two types of test stimuli: (i) items
that were contained within the familiarizaword stimuli (18), with longer listening
times for nonwords (Table 1). This noveltv
preference, or dishabitllation effect, ind(-
cates that 8-month-olds recoenized the diftion rnaterial and (ii) items that are highly
similar but (by some critical criterion) were
not contained within the familiarization
material. During a series of test trials that
immediately follows familiarization, infants
control the duration of each test trial by
their sustained visual fixation on a blinking
light (14). If infants have extracted the
crucial information about the familiarizau
ference between the novel and the familiar
orderings of the three-syllable strings. Thus,
8-month-old infants are capable of extracting serial-order information after only 2
posited. The results demonstrate that infants uossess ~owerfulmechanisms suited to
learning the types of structures exemplified
in linguistic systems. Experience may therefore play a more important role in the aclnin of listening experience.
Of course, simple serial-order information is an insufficient cue to word boundquisition of language than existing theories
suggest.
One task faced by all language learners is
the seglnentation of fluent speech into
words. This process is particularly difficult
because word boundaries in fluent s~eech
aries. The learner must also be able to extract the relative freauencies of co-occurtion items, they may show differential durations of fixation (listening) during the
two types of test trials (15). We used this
procedure to determine whether infants can
acquire the statistical properties of sound
sequences from brief exposures.
In our first experiment, 24 8-month-old
infants from an American-English language
environment were familiarized with 2 min
of a continuous speech stream consisting of
four three-syllable nonsense words (hereafter, “words”) repeated in random order
(16). The speech strealn was generated by a
speech synthesizer in a monotone fernale
voice at a rate of 270 syllables per minute
(180 words in total). The synthesizer provided no acoustic information about word
rence of sound pairs, where relatively low
transitional probabilities signal word
boundaries. Our next experiment examined
whether 8-month-olds could oerform the
are marked inconsistently by discrete acoustic events such as pauses (8). Although it
has recently been demonstrated that
8-month-old infants can segment words
more difficult statistical computations required to distinguish words (that is, recurrent syllable sequences) from syllable strings
spanning word boundaries (that is, syllable
sequences occurring more rarely). To take
an English example, pretty#baby, we wanted
to see if infants can distinguish a word-
– from fluent speech and subsequently recognize them when presented in isolation (9),
it is not clear what information is used by
infants to discover word boundaries. This
problem is complicated by the variable
acoustic structure of speech across different
languages, suggestiAg that infants must discover which, if any, acoustic cues correlated
with word boundaries are relevant to their
D
internal syllable pair like pretty from a wordexternal syllable pair like ty#ba.
Another 24 8-month-old infants from
an American-English language environment were familiarized with 2 min of a
continuous s~eechstrealn consisting of
native language (10); there is no invariant
acoustic cue to word boundaries present in
all languages.
One important source of information
that can, in principle, define word boundboundaries, resulting in a continuous strealn
of coarticulated consonant-vowel syllables,
with no pauses, stress differences, or any
other acoustic or prosodic cues to word
boundaries. A sample of the speech strealn
is the orthographic string bidakupadotigolabubidaku. . . . The onlv cues to word boundu
three-syllable nonsense words similar in
structure to the artificial language used in
our first experiment (19). This time, however, the test items for each infant consisted
of two words and two “vart-words.” The
part-words were created by joining the final
svllable of a word to the first two svllables of
aries in any natural language is the statistical information contained in seauences of
sounds. Over a corpus of speech there are
measurable statistical regularities that disaries were the transitional probabilities between syllable pairs, which were higher
within words (1.0 in all cases, for example,
bida) than between words (0.33 in all cases,
another word. Thus, the part-words contained three-svllable seauences that the in- ”
tinguish recurring sound sequences that
comprise words from the more accidental
fant had heaid duringLfamiliarization but
statisticallv, over the corvus, did not correspond to words (20). These part-words
could onlv be iudped as novel if the infants
sound sequences that occur across word
boundaries (11). Within a language, the
transitional probability from one sound to
the next will generally be highest when the
two sounds follow one another within a
word, whereas transitional orobabilities
for example, kupa).
To assess learning, each infant was presented with repetitions of one of four threesvllable strings on each test trial. Two of
, ” –
had learned the words with sufficient specificitv and comoleteness that seauences L.
these three-syllable strings were “words”
from the artificial language presented during familiarization, and two were three-syllable “nonwords” that contained the same
syllables heard during familiarization but
crosskg a word ‘boundary were reiatively
ilnfamiliar.
Despite the difficulty of this word versus
part-word discrimination, infants showed a
significant test-trial discrimination between
the word and part-word stimuli (21), with
longer listening times for part-words (Table
1). T~ILIS, 2 min of exposure to concatenated speech organized into “words” was suffispanning a word boundary will be relatively
low (12). For example, glven the sound
sequence pretty#baby, the trans~t~onal probability from pre to ty 1s greater than the
transitional probability from ty to ba. Previously, we showed that adults and children
can use information about transitional
not in the order in which they appeared as
words (17).
The infants showed a significant testtrial discrimination between word and nonprobabilities to discover word boundaries in
an artificial language corpus of nonsense
words presented as continuous speech, with
no acoustic cues to word boundaries (13).
We asked whether 8-month-old infants
can extract information about word boundTable 1. Mean tlme spent llstenlng to the famlllar
nonwords)and experlment 2 (wordsversus pat–wc
times.
and novel stimuli for experlment 1 (words versus
3rd~)and signlflcance tests comparing the listening
Mean listening tlmes (s)
Experiment Matched-pairs t test
Famlllar ltems Novel ltems
aries solely on the basis of the sequential
statistics of concatenated s~eech.We used
the famillarization-preference procedure developed by Jusczyk and Aslin (9). In this 1 7.97 (SE = 0.41) 8.85 (SE = 0.45) t(23) = 2.3, P < 0.04
2 6.77 (SE = 0.44) 7.60 (SE = 0.42) t(23) = 2.4, P < 0.03
procedure, infants are exposed to auditory
SCIENCE VOL.274 13 DECEMBER 1996 1927
cient for 8-month-old infants to extract
information about the sequential statistics
of syllables. Moreover, this novelty preference cannot be attributed to a total lack of
experience with the three-syllable sequences forming part-words, as was the case with
the nonwords in the first experiment. Rather, infants succeeded in learning and remembering particular groupings of threesyllable strings-those strings containing
higher transitional probabilities surrounded
by lower transitional probabilities.
The infants’ performance in these studies is particularly impressive given the impoverished nature of the familiarization
speech stream, which contained no pauses,
intonational patterns, or any other cues
that, in normal speech, probabilistically
supplement the sequential statistics inherent in the structure of words. Equally impressive is the fact that 8-month-old infants in both experiments were able to
extract information about ‘sequential statistics from only 2 min of listening experience. Although experience with speech
in the real world is unlikely to be as
concentrated as it was in these studies,
infants in more nak~ralsettings presum-
, ably benefit from other types of cues correlated with statistical information.
Our results raise the intriguing possibility that infants possess experience-dependent mechanisms that may be powerful
enough to support not only word segmentation but also the acquisition of other aspects of language. It remains unclear whether the statistical learning we observed is
indicative of a mechanism specific to language acqu~sitionor of a general learning
mechanism applicable to a broad range of
distributional analyses of environmental input (22). Regardless, the existence of computational abilities that extract structure so
rapidly suggests that it is premature to assert
a priori how much of the striking knowledge base of human infants is primarily a
result of expertence-independent mechanisms. In particular, some aspects of early
development may turn out to be best characterized as resulting from innately biased
statistical learning mechanisms rather than
innate knowledge. If this is the case, then
the massive amount of experience gathered
by infants during the first postnatal year
may play a far greater role in development
than has previously been recognized.
REFERENCES AND NOTES
1. Certain species-spec~ficsk~llsdevelop w~thoutany
experiential input, nclud~ngbat echolocat~on[E.
Gould, Dev. Psychobioi. 8, 33 (197511 and cricket
song [R. Hoy, Am. Zool. 14, 1067 (1974)l.
2. Examples of behaviors mediated by early experience
are imprint~ng[E. Hess, imprinting (Van Nostrand,
New York, 1973);M. Leon, Physioi. Behav. 14, 311
(1975)l and suckl~ngresponses n newborn rats [M
H Te~cherand E M Blass, Science 198, 635
(1977)l.
3 These mlestones have been wel-documented both
in English [for example, R Brown, A First Language
[Harvard Univ. Press, Cambridge, MA, 197311 and
cross-ingu~st~cally[for example, E Lenneberg, Biologicai Foundations of Language [Wiley, New York,
1967); D. Slob~n,Ed., vols. 1 to 3 of The Crosslinguistic Study of LanguageAcquisition (Erlbaum,Hsdale, NJ, 1985, 1987, 199211
4. This “argument from the poverty of the stmulus”
remains w~delyaccepted [for example, N. Chomsky,
Aspects of the Theory of Syntax (MIT Press, Cambridge, MA, 1965); S Crain, Behav. Brain Sci. 14,
597 (199111.
5. D. B~ckerton,Behav. Brain Sci 7, 173 (19841, N.
Chomsky, Rules and Representations (Columbia
Univ, Press, New York, 1981);J. Fodor, Modularity
of Mind (MT Press, Cambrdge, MA, 1983),L. Gleitman and E. Newport, in Language: An Invitation to
Cognitive Science, L Gleitman and M. Liberman,
Eds (MIT Press, Cambridge, MA, 19951, pp. 1-24
6. Examples ncude vowel structure [P K. Kuhl, K. A
W~lliams,F. Lacerda, K N. Stevens, B Lindblom,
Science 255, 606 (1992)],phonotactics [P Jusczyk,
A. Frieder~ci,J. Wesses, V. Svenkerud, A. Jusczyk,
J. Mem. Lang. 32, 401 (1993)],and prosodc structure [P. Jusczyk, A. Cutler, N. Redanz,ChildDev. 64,
675 (199311.
7 Exceptions Include research on prenatal exposure
to maternal speech [A. DeCasper, J.-P. Lecanuet,
M.-C. Busnel, C. Granier-Deferre, R. Maugeais, infant Behav. Dev. 17, 159 (1994)] and early postnatal preferences [J, Mehler et a/, Cognition 29, 149
(1988)l
8 R. Cole and J. Jakimk, n Perception and Production
of Fluent Speech, R Cole, Ed. [Erlbaum, H~lsdale,
NJ, 19801, pp 133-163.
9, P Jusczyk and R Asl~n,Cognitive Psycho1 29, 1
(I995)
10. A. Chr~stophe,E Dupoux,J. Bertoncini,J. Meher, J.
Acoust. Soc. Am 95, 1570 (1994);A. Cutler and D
Carter, Comput. Speech Lang. 2, 133 (1987)
1I.Z Harris, Language 31, 190 (1955); J Hayes and
H. Clark, n Cognition and the Development of Language, J Hayes, Ed. (Wiley, New York, 1970).See
M Brent and T. Cartwright [Cognition 61, 93
[ l996)l for a dscussion of related statstcal cues to
word boundares
12. The transitional probability of
frequency of XY
‘IX = frequency of x
13. J Saffran, E. Newport, R. Aslin, J Mem, Lang 35,
606 [1996);,R Tunck, S Barrueco,Psychol.
Sci., n press.
14. Each infant was tested ndvidualy whle seated on
the parent’s lap in asound-attenuated booth. Synthetic speech was generated off-line by the MacinTalk system and stored on disk at a sampng rate
of 22 kHz for on-line playback through an Audiomedia board in an Apple Quadra 650 computer. An
observer outside the testng booth montored the
infant’s looking behav~orw~ththe use of a color
video system, using a buttonbox connected to the
computer to intate trials and score head-turn responses. Both the parent and the observer listened
to masking music over headphones to eliminate
bias. Dur~ngthe 2-mn fam~liarizationphase, the
infant’s gaze was f~rstdirected to a bllnkng Ight
located on the front wall of the test~ngbooth, and
then the sound sequence was presented from two
loudspeakers located on the s~dewalls The infant’s gaze was drected to one of two blinkng
Ights on these side walls during fam~liarization,but
there was no relat~onbetween lights and sound.
Immediately after fam~liarization,12 test trials were
presented (six words and SIX nonwords). Each test
trial began with the central blinking hght When the
observer s~gnaledwith a button press that the n –
fant had fixated on the central ight, one of the two
side blink~nglights was turned on and the center
light was ext~nguishedWhen the nfant faced the
sde light (a head turn of at least 30″ n the directon
of the Ight), the three-syllable test strlng was
played and repeated until the infant looked away
from the light for 2 s or until 15 s of looking had
occurred. The observer smply recorded the direct~onof the Infant’s head turn, and the computer
measured ookng t~mes,determ~nedwhen the 2-s
ookaway crlterlon had been met, and controlled
the randomization and presentaton of stmul. Cumulatve look~ngtme across each of the two types
of test trals provded the measure of preference.
15 The drect~onof the f~xatonpreference depends on
the degree of famlarity wth the stmuli. If the Infants
have become hghy famliar w~ththe stmuli, they
show d~shabituat~onbehavior, preferr~ngthe novel
stimu.
16. Two counterbalanced stimulus cond~tionswere
generated. For each condition, 45 tokens of each
of four trisyllabc nonsense words (conditon A: tupiro, golabu, bidaku, and padoti; condition B:
dapiku, tiiado, burobi, and pagotu) were spoken n
random order to create a 2-min speech stream,
w~ththe stpuaton that the same word never occurred twce In a row.
17. Test stirnull, tupiro, goiabu, dapiku, and tilado. In
condton A, the first two strings were words and the
last two strings were nonwords (the trans~t~onal
probabllt~esbetween the syllables in the nonwords
were all zero relat~veto the exposure corpus, as
these syllable palrs had never occurred durng famliarizat~on).In cond~t~onB, the first two strings were
nonwords and the last two strings were words. Ths
between-subjects counterbalanced design ensured
that any observed preferences for words or nonwords across both conditions would not be artifacts
of any general preferencesfor certain syllablestrings.
Each of the four test strings were presented [repeated with a 500-ms Interval between test strngs) on
three differenttrials, resutng n a total of 12test trals
per Infant.
18 There were no signficant differences betweenthe infants n conditon A and conditon B: t(22) = 0 31. The
data from the two groups were thus combined for the
other analyses.
19 Condit~onA words pabiku, tibudo, goiatu, and daropi, condt~onB words, tudaro, pigoia, bikuti, and
budopa
20 Test st~muli:pabiku, tibudo, tudaro, and pigoia. In
conditon A, the frst two strngs were words and
the second two strings were part-words. For example, the part-word pigola spanned the word
boundary between daropi#goiatu and thus was
heard dur~ngexposure In cond~tionB, the frst two
strlngs were part-words and the second two
strlngs were words The part-words were thus
three-syllable sequences that the infants had heard
during the course of the exposure period. The diff~cultyof ths test dscrminaton can be seen by
comparing the trans~tionalprobabillt~esbetween
the syllables in the words (1.0 between syllables 1
and 2 and between syllables 2 and 3) to the transitonal probabilites between the syllables n the
part-words (0.33between syllables 1 and 2 and 1.O
between syllables 2 and 3)
21. There were no signifcant d~fferencesbetween the
Infants In conditon A and condtion B: 1122) = 0 49.
The data from the two groups were thus combined
for the other analyses
22. For example,this same general mechanismcould be
used to find an object, such as a human face, in the
environment.
23 We thank J. Galipeau, J Hooker, P Jusczyk, A.
Jusczyk, T. Mntz, K Ruppert, and J. Sawusch for
ther help with varlous aspects of ths research, and
P, Jusczyk, S. Pollak, M. Spivey-Knowton, and M.
Tanenhaus for their helpful comments on a previous
draft Supported by an NSF predoctoral felowsh~p
(J.R.S.), NSF grant SBR9421064 (R.N.A.),and NIH
grant DC00167 [E.L.N.). The parents of all particlpants gave Informed consent.
10 May 1996; accepted 30 September I996
1928 SCIENCE VOL. 274 13 DECEMBER 1996