The Ontogeny of Lexical Networks

Abstract

Although the semantic relationships among words have long been acknowledged as a crucial component of adult lexical knowledge, the ontogeny of lexical networks remains largely unstudied. To determine whether learners encode relationships among novel words, we trained 2-year-olds on four novel words that referred to four novel objects, which were grouped into two visually similar pairs. Participants then listened to repetitions of word pairs (in the absence of visual referents) that referred to objects that were either similar or dissimilar to each other. Toddlers listened significantly longer to word pairs referring to similar objects, which suggests that their representations of the novel words included knowledge about the similarity of the referents. A second experiment confirmed that toddlers can learn all four distinct words from the training regime, which suggests that the results from Experiment 1 reflected the successful encoding of referents. Together, these results show that toddlers encode the similarities among referents from their earliest exposures to new words.

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Psychological Science
24(10) 1898 –1905
© The Author(s) 2013
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DOI: 10.1177/0956797613478198
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Research Article
Ever since Quine (1960) pointed out the complexity of
mapping a new label to its proper referent, a large litera-
ture has emerged concerning how children learn words.
Most of this research, however, assumes that the goal of
word learning is to map a word to its correct referent or
category of referents. Although mapping is a crucial com-
ponent of word learning, a tremendous amount of addi-
tional information comes along with hearing a new word.
Imagine a child hearing a novel animal labeled for the
first time: “That’s a dog!” Obviously, the child needs to
learn the label-referent mapping. However, he or she
could also encode useful information about other nearby
objects (such as a leash or a ball), the background con-
text (e.g., a park vs. a kitchen), or the similarity between
this new animal and his or her pet cat.
If the full complexity of the perceptual and semantic
input available to young children is considered, word learn-
ing becomes a multidimensional problem that extends
beyond label-referent associations. It has been shown that
skilled language users exploit this rich structure; adult
semantic knowledge is not organized like a dictionary of
label-referent pairings. Instead, the lexicon is a complex
semantic network that represents relationships among
words (e.g., McClelland & Rogers, 2003; McNamara, 2005;
Steyvers & Tenenbaum, 2005). This has been demonstrated
most clearly with the semantic priming paradigm, in which
participants are faster to respond to a target word if it is
related to a prime word than if it is not. Adults show
semantic priming effects for many types of lexical-seman-
tic relationships, including feature overlap, thematic role
similarity, and verb-noun relationships (e.g., McNamara,
2005; Neely, 1991).
Despite extensive research on adult semantic knowl-
edge, little is known about the ontogeny of lexical net-
works. In particular, how do lexical-semantic relationships
emerge over the course of word learning? Lexical knowl-
edge continues to develop throughout childhood (Carey,
478198PSS
XXX10.1177/0956797613478198Wojcik, Saffran
Semantic Relationships
research-article
2013
Corresponding Author:
Erica H. Wojcik, University of Wisconsin–Madison, Department of
Psychology, 1202 W. Johnson St., Madison, WI 53703
E-mail: ehwojcik@wisc.edu
The Ontogeny of Lexical Networks: Toddlers
Encode the Relationships Among Referents
When Learning Novel Words
Erica H. Wojcik and Jenny R. Saffran
University of Wisconsin–Madison
Abstract
Although the semantic relationships among words have long been acknowledged as a crucial component of adult
lexical knowledge, the ontogeny of lexical networks remains largely unstudied. To determine whether learners encode
relationships among novel words, we trained 2-year-olds on four novel words that referred to four novel objects,
which were grouped into two visually similar pairs. Participants then listened to repetitions of word pairs (in the
absence of visual referents) that referred to objects that were either similar or dissimilar to each other. Toddlers listened
significantly longer to word pairs referring to similar objects, which suggests that their representations of the novel
words included knowledge about the similarity of the referents. A second experiment confirmed that toddlers can
learn all four distinct words from the training regime, which suggests that the results from Experiment 1 reflected the
successful encoding of referents. Together, these results show that toddlers encode the similarities among referents
from their earliest exposures to new words.
Keywords
word learning, lexical development, semantic networks, cognitive development, language development, learning
Received 7/17/12; Revision accepted 1/17/13

Semantic Relationships 1899
1985) and into adulthood (Ameel, Malt, & Storms, 2008),
so it is possible that representations of lexical relation-
ships emerge later in the word-learning process. However,
infants are sensitive to statistical relationships among
newly learned words (e.g., Lany & Saffran, 2011), and
adults can track multiple levels of statistical information
in parallel (Romberg & Saffran, 2013; Yurovsky, Yu, &
Smith, 2012). It is thus possible that from their earliest
exposures to new words, young children encode not
only label-referent associations but also the relationships
among the referents. Recent studies have demonstrated
that by 21 months of age, infants show semantic priming
effects for highly familiar words (Arias-Trejo & Plunkett,
2009). However, it is not known whether young children
encode the relationships among the referents of novel
words as they begin to learn those words, or alterna-
tively, if individual word representations need to be
robust before these connections are encoded. The cur-
rent study was designed to address these issues.
There are many facets of semantic relatedness that
might be encoded by young learners, such as functional
or thematic similarity. In the current study, we focused on
visual similarity because it is an early organizing feature
in nonlinguistic categorization (e.g., Behl-Chadha, 1996;
Quinn, Eimas, & Rosenkrantz, 1993; Sloutsky, 2003). The
fact that 2-year-olds attend to shapes during word learn-
ing suggests that visual characteristics are prioritized (i.e.,
Samuelson & Smith, 2005). Semantic priming studies also
suggest that visual similarity is a component of adults’
lexical representations (Schreuder, Flores d’Arcais, &
Glazenborg, 1984; Yee, Ahmed, & Thompson-Schill,
2012). We thus chose to begin our investigation of the
ontogeny of lexical relationships by manipulating the
visual similarity of novel referents.
In our first experiment, 2-year-olds learned four novel
words that referred to four novel objects grouped into
two visually similar pairs. Although participants were
ostensibly taught object labels, the similarity structure of
the referents provided them with another type of infor-
mation that they could incorporate into their representa-
tions of the novel words. We then tested participants
using an auditory task previously developed to examine
toddlers’ knowledge of the relationships among highly
familiar words (Willits, Wojcik, Seidenberg, & Saffran,
2013). The question of interest was whether listening
preferences for pairs of novel words would be affected
by the visual similarity of the referents of those words in
the absence of the referents themselves.
Experiment 1
Experiment 1 was designed to investigate whether tod-
dlers encode the similarity structure among objects in
a small artificial lexicon. Toddlers show sensitivity to
semantic relationships among familiar words by 21 months
of age (Arias-Trejo & Plunkett, 2009) and can activate this
knowledge in the absence of visual referents by 24 months
of age (Willits et al., 2013). Because our task required the
activation of novel lexical representations, we tested a
slightly older age group (26- to 28-month-olds).
Participants were first trained on four label-object
pairs. Crucially, each object was visually similar to one
other object and distinct from the other two (see Fig. 1).
We then investigated whether toddlers were sensitive to
the similarities among the referents of the words they had
just learned. To do so, we compared participants’ listen-
ing times for word pairs that referred to similar objects
versus listening times for word pairs that referred to dis-
similar objects. This method allowed us to examine tod-
dlers’ nascent lexical representations in the absence of
visual referents, thus tapping into the encoded represen-
tations of the words they had just learned.
Method
Participants. Participants were 32 full-term monolin-
gual English learners (16 male, 16 female) with a mean
age of 27.0 months (range = 25.11–28.4). Eight additional
toddlers were excluded from the analyses because of
fussiness (n = 7) or an average looking time greater than
2 standard deviations from the mean (n = 1).
Stimuli. The training stimuli consisted of four novel
labels (tursey, coro, blicket, pif), each paired with a single
novel object image. Although the objects were all different,
they were organized into two visually similar pairs: two
were blue ovals, and two were red stars (see Fig. 1). Label-
object pairings were counterbalanced across participants.
Fig. 1. The four novel objects that participants were trained on in the
two experiments. Each object was visually similar to one other object
and distinct from the other two. A novel label was paired with each
object.

1900 Wojcik, Saffran
Each test trial consisted of repetitions of a word pair
(e.g., tursey, coro, tursey, coro . . . ). Eight trials contained
word pairs that labeled visually similar objects, and eight
contained word pairs that labeled visually dissimilar
objects. Counterbalancing ensured that word pairs
referred to similar objects for half of the toddlers and to
dissimilar objects for the other half of the toddlers.
Referents were not displayed during the test phase.
Procedure. Toddlers were seated on a caregiver’s lap in
a sound-attenuated booth; the caregiver wore blacked-
out glasses and listened to music over headphones. Three
monitors were used: The training trials were presented
on a center monitor, and two side monitors were posi-
tioned 90° to the left and to the right, respectively. The
training phase (2.5 min) began with the four objects dis-
played in a grid for 10 s. During each subsequent training
trial (6 s), a single object was displayed on either the left
or the right side of the screen and was labeled twice:
“Look at the __! There’s a __!” or “See the __! This is a __!”
The first two trials used familiar objects (ball and shoe) to
introduce the format. The next four blocks each included
four novel-object trials, with each label-object pair pre-
sented once per block (randomized).
The test phase immediately followed training. Each of
the 16 test trials began with a central attention-getter
paired with music. Once the toddler looked to the center
monitor, the neutral visual stimulus (a spinning pinwheel)
began to play on one of the two side monitors. When the
toddler looked to that side, a word pair was repeated
from speakers mounted directly below the monitors until
the infant looked away for more than 2 s or for a total of
20 s. Half of the trials consisted of repetitions of word
pairs with similar referents, and the other half consisted of
repetitions of word pairs with dissimilar referents. Each
block of four trials included two similar-object and two
dissimilar-object trials. After the experiment, parents filled
out the MacArthur-Bates Communicative Development
Inventories (CDI; Short Form Level II; Fenson et al., 2000).
Results and discussion
The question of interest was whether toddlers’ listening
times to word pairs were influenced by the visual similar-
ity of their referents (in the absence of those referents).
Thus, we compared listening times to word pairs that
referred to similar or dissimilar objects. A paired-samples
t test revealed a significant effect of trial type (similar
object vs. dissimilar object), t(31) = 3.91, p < .001, η
2
=
.331. Toddlers preferred to listen to labels referring to
similar objects (7.99 s, SE = 0.50) compared with labels
referring to dissimilar objects (6.54 s, SE = 0.38; see Fig.
2). We also calculated a preference score for each toddler
by subtracting his or her mean listening time on
dissimilar-object trials from his or her mean listening time
on similar-object trials. Of the 32 participants, 25 had a
positive preference score, which indicates that they lis-
tened longer on similar-object trials than on dissimilar-
object trials (see Fig. 3).
The results of Experiment 1 suggest that when tod-
dlers are learning new words, they do not just learn the
associations between labels and their referents; they also
encode relationships among the referents. The visual
similarity of the referents affected which word pairs tod-
dlers preferred to listen to in the absence of the referents
themselves. Because the label-object pairings were coun-
terbalanced across participants, the pattern of results can-
not be due to idiosyncratic preferences for some labels or
label pairings over others. The information that toddlers
encoded about the visual similarities among referents
affected their behavior in an auditory test.
However, there is an alternative hypothesis that could
explain these results without recourse to the encoding of
the similarity structure of the referents. It is possible that
the toddlers failed to learn the four unique label-object
pairs during training. Instead, they may have categorized
the similar objects together, treating their labels as syn-
onyms, or they simply may not have learned the words
robustly enough to distinguish among the visually similar
referents. For example, if tursey and coro referred to the
two blue ovals, it could be that toddlers treated the labels
as interchangeable or were confused about which word
Visually Dissimilar Visually Similar
Object Type
Mean Looking Time (s)
0
2
4
6
8
10
Fig. 2. Results from Experiment 1: mean looking time as a function of
whether spoken words referred to visually dissimilar or visually similar
objects. Error bars show standard errors.

Semantic Relationships 1901
referred to which object. If the data reflect this alternative
hypothesis, and toddlers underlearned the lexical struc-
ture provided in Experiment 1, the results do not address
our original hypothesis concerning the encoding of simi-
larity structure among the referents but instead simply
reflect category learning (blue ovals vs. red stars). To
tease apart these two hypotheses, we conducted a sec-
ond experiment designed to determine whether the
training procedure from Experiment 1 resulted in the
specific learning of all four label-object pairs.
Experiment 2
In this experiment, we used the same training procedure
as in Experiment 1. However, instead of assessing lexical
representations using an auditory task as in Experiment
1, we tested word-learning outcomes with a looking-
while-listening task (see Fernald, Zangl, Portillo, &
Marchman, 2008). We investigated whether toddlers
could learn all four label-object pairs as distinct lexical
entries given the training regimen from Experiment 1. If
so, this would support our original interpretation of the
results of Experiment 1: namely, that toddlers’ listening
preferences reflect their newly acquired knowledge
about the similarity structure of the referents.
Method
Participants. Participants consisted of a new sample of
24 full-term, monolingual English learners (11 male, 13
female) with a mean age of 27.8 months (range = 26.11–
28.12). Seven additional toddlers were excluded from the
analysis because of inattentiveness (n = 4) or experi-
menter error (n = 3). The remaining participants were
comparable with the Experiment 1 participants in their
expressive MacArthur-Bates CDI scores (64 vs. 67.2,
respectively, out of a possible score of 100), t(54) = 0.52,
p = .61.
Stimuli and design. The training stimuli were identi-
cal to those used in Experiment 1. On each of the 16 test
trials, two of the novel objects were displayed, one on the
bottom left and one on the bottom right of the screen.
Toddlers heard a prerecorded sentence directing them to
one of the objects. Half of the test trials contrasted similar
novel objects (i.e., either the two blue ovals or the two
red stars). The other half contrasted dissimilar objects
(i.e., one blue oval and one red star). These two trial
types allowed us to examine the robustness of the tod-
dlers’ representations of the novel words. In particular,
successful word recognition on the similar-object trials
required participants to have encoded the fine-grained
details differentiating two perceptual neighbors, whereas
successful word recognition on the dissimilar-object trials
did not.
Procedure. The training procedure was identical to that
in Experiment 1. The test phase began with two trials
using familiar objects (shoe and dog); these trials were
intended to orient participants to the task. Next, partici-
pants viewed the novel-object trials in four blocks of four
trials each. The test trials began with two objects pre-
sented in silence (1.5 s). Participants then heard one of
the objects labeled in a sentence frame (“Where’s the __?”
or “Find the __.”). This was followed by an attention-
getting phrase, such as “Can you see it?” or “Do you like
it?”, and 1 s of silence.
Each test block consisted of one trial for each label.
The blocks consisted of two similar-object trials and two
dissimilar-object trials. The target picture (i.e., the picture
that was labeled) was presented equally on the left and
right side within blocks, and each of the object pictures
was displayed an equal number of times on the left and
Listening-Time Preference Score (s)
8
6
4
2
0
–2
–4
Fig. 3. Results from Experiment 1: scatter plot showing mean listening-
time preference scores. Preference scores were calculated by subtract-
ing each participant’s mean listening time on dissimilar-object trials
from his or her mean listening time on similar-object trials.

1902 Wojcik, Saffran
right throughout the test phase. Trial order was counter-
balanced across participants. After the experiment, the
parents filled out the MacArthur-Bates CDI (Short Form
Level II; Fenson et al., 2000).
Results and discussion
The primary question was whether participants could
learn four distinct word-referent pairs, given that each
object was highly similar to one other object. Looking
behavior was coded frame by frame (see Fernald et al.,
2008). For each 33-ms frame, we calculated the propor-
tion of trials on which toddlers were looking to the target
picture.
To determine whether toddlers successfully learned
the word-referent pairs, we compared looking behavior
before and after the audio presentation of the target
word. If participants learned the word, the proportion of
looking time to the target object after hearing its label
should increase. A baseline window (from 450 ms to
2,450 ms) represented prelabeling behavior. The target
window started at 2,750 ms, beginning 300 ms after the
noun onset to allow for the planning of eye movements
(Fernald et al., 2008), and was 1,500 ms in duration. We
calculated the mean proportion of looks to the target for
each toddler across frames during the baseline and target
windows. Trials were excluded if there were more than
10 consecutive frames in which the participant was not
attending to the stimuli (32 out of 386 total were
excluded).
A paired-samples t test was used to compare looking
during the baseline and target windows. Participants
looked significantly more to the target object during the
target window than during the baseline window, t(23) =
4.78, p < .001 (see Table 1). This suggests that the tod-
dlers learned the novel words. However, as noted previ-
ously, there were two types of test trials: dissimilar-object
trials, in which toddlers had to locate the target given one
of the blue objects and one of the red objects, and simi-
lar-object trials, which required a decision between either
two blue or two red objects. It is possible that the overall
learning effect was driven by the easier dissimilar-object
trials.
Follow-up analyses were conducted to examine the
dissimilar-object and similar-object trials separately. A
paired-samples t test comparing the baseline and target
windows for the dissimilar-object trials revealed that the
participants looked significantly more to the target object
during the target window than during the baseline win-
dow, t(23) = 3.28, p < .005. We found the same pattern for
the more challenging similar-object trials, t(23) = 3.06,
p < .01 (see Fig. 4 and Table 1). To compare performance
on the two trial types, we calculated difference scores for
each subject by subtracting baseline-window accuracy
from target-window accuracy for both similar- and dis-
similar-object trials. A paired-samples t test comparing
those difference scores revealed no significant difference
between trial types, t(23) = 0.41, p = .69. These results
suggest that our participants’ representations of the novel
words were robust and included sufficient detail to per-
mit learners to distinguish between the visually similar
referents.
The results from Experiment 1 left open the possibility
that toddlers did not learn distinct label-referent associa-
tions for the visually similar objects; they could have
encoded only the broad visual features and treated the
Table 1. Results From Experiment 2: Mean Proportion of
Looks Infants Made to the Target Object in the Baseline and
Target Windows
Trial type Baseline window Target window
All .50 (.009) .60 (.022)
Dissimilar object .51 (.018) .62 (.031)
Similar object .49 (.013) .59 (.025)
Red star .47 (.028) .61 (.041)
Blue oval .50 (.025) .61 (.032)
Note: Standard errors are given in parentheses.
.3
.4
.5
.6
.7
.8
.9
1.0
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
Proportion of Looks to Target
Time (ms)
Dissimilar Trials
Similar Trials
Target Window
Fig. 4. Results from Experiment 2: mean proportion of looks infants
made to the target object as a function of time and trial type. The verti-
cal line marks the beginning of the target window (300 ms after the
onset of the spoken word, to take into account eye movement plan-
ning; Fernald, Zangl, Portillo, & Marchman, 2008). Error bars show
standard errors.

Semantic Relationships 1903
similar-object labels as synonymous at test. A separate
word-comprehension task was needed to ensure that
toddlers could learn the four distinct words from our test-
ing regime. The results from Experiment 2 demonstrate
that the toddlers formed a strong enough representation
of the visual object associated with each word to be able
to distinguish it from a visually similar neighbor. This
finding supports the hypothesis that the participants in
Experiment 1 learned the novel words as distinct lexical
items and encoded the relationships between them. The
results from Experiment 1, therefore, are likely due to
successful encoding of the relationships among similar
referents during the word-learning process.
General Discussion
When people think about word learning, they tend to
focus on how children acquire the mapping between
sounds (or signs) and their referents. However, it has
been shown that the links among meanings underpin
people’s conceptual knowledge (see McClelland &
Rogers, 2003). The current study was designed to take a
first step toward understanding the ontogenesis of the
associations composing a semantic network by looking
at what toddlers learn about semantic relationships dur-
ing their initial exposure to new words.
In Experiment 1, we investigated whether toddlers
encode the relationships among word referents when
learning novel words. Participants were taught four novel
words that referred to four novel objects consisting of
two visually similar pairs. Toddlers listened significantly
longer to word pairs labeling visually similar referents
than to pairs of labels for visually dissimilar referents in
the absence of the referents themselves. Because the
only difference between the pairs of words was the simi-
larity of their referents, these results suggest that early
lexical representations include information about the
similarity structure of the words’ referents, even for words
toddlers have just learned.
To examine the possibility that the results did not
reflect the encoding of word relationships, but instead
the conflating of labels for visually similar items, we
exposed the participants in Experiment 2 to the same
training regimen. We found that the toddlers successfully
learned the four novel word-referent pairings as distinct
lexical entries. Together, our two experiments suggest
that although toddlers learn novel word-referent associa-
tions, they also encode the relationships among these
words.
Our findings are particularly striking because the train-
ing procedure is similar to what is used in most tradi-
tional word-learning studies; it was not designed to
highlight the relationships among the referents. The
training provided ostensive labels for four novel objects,
but toddlers learned more than just this one type of asso-
ciation. They also took into account other relationships,
such as those among the referents.
The demonstration that early lexical representations
include information about visual similarity among the ref-
erents can be construed as the referential analog to the
neighborhood density effects observed for the sounds of
words (e.g., Hollich, Jusczyk, & Luce, 2002). According to
this view, young learners encode the visual overlap
among the referents of different words much as they
encode the auditory overlap of their labels. If this is the
case, then what is known about early lexical representa-
tions can inform the study of early semantic representa-
tions. For example, Hollich et al. (2002) found that
17-month-olds acquired words forms from dense neigh-
borhoods (i.e., words that sound similar to many other
known words) more readily than words from sparse
neighborhoods. Because our results show that toddlers
encode information about visual relationships among ref-
erents, it is possible that novel objects with many similar
neighbors are more easily learned than those in a sparse
visual neighborhood. In fact, results from a connectionist
model looking at semantic growth suggest that novel
words that are semantically associated with many known
words are acquired more quickly than novel words with-
out many semantic associations (Hills, Maouene, Riordan,
& Smith, 2010). With the results from the current studies
in hand, researchers can use findings from the auditory
domain to advance the understanding of how semantic
relationships interact with word learning.
The current results can also help to expand how peo-
ple think about the word-learning literature. The majority
of word-learning tasks used with infants and young tod-
dlers involve brief training sessions designed to expose
participants to novel words, often on a two-dimensional
screen. Because of this stripped-down artificial situation,
it is unclear whether participants’ resulting knowledge is
wordlike. In these lab settings, infants may just be form-
ing an association between a sound and a picture.
Although this type of association is an important compo-
nent of word learning and knowledge (e.g., Smith & Yu,
2008; Vouloumanous & Werker, 2009), lexical representa-
tions are much richer than just associations between
labels and objects. Thus, it is important to determine the
character of novel word representations acquired in
experimental paradigms. The current study demonstrates
that during toddlers’ first encounters with novel words,
they are encoding more than just the label-object associa-
tions. In fact, even in the stripped-down environment of
a computerized word-learning experimental paradigm,
novel word representations include information concern-
ing the relationships among words. Our findings thus
provide evidence that when researchers employ tradi-
tional word-learning paradigms that teach new words in

1904 Wojcik, Saffran
short training sessions, they are indeed investigating
novel lexical entries, not just label-object associations.
More broadly, the results from this study show the
importance of expanding the study of word learning
beyond just the study of how young children learn which
labels go with which referents. Researchers can draw
from what is known about adult lexical representations to
investigate when and how toddlers acquire that knowl-
edge. For example, it is known that skilled language users
are sensitive to many other types of relationships beyond
the visual similarity of referents. Adults’ semantic knowl-
edge includes the functional relationships between words
(such as “broom” and “floor”; Moss, Ostrin, Tyler, &
Marslen-Wilson, 1995). It would be interesting to teach
toddlers different kinds of novel words, such as those
with overlapping functional or conceptual representa-
tions, to determine which types of relationships are
encoded in early lexical entries. Similar questions emerge
for words across multiple syntactic categories, in which
relationships among words might be somewhat more
abstract. By manipulating the structure of the artificial
lexicon, research can begin to further tease out the type
of information encoded by young word learners—along
with the dimensions of similarity that toddlers fail to
encode. Indeed, given the richness of early linguistic, con-
ceptual, and social environments, it is just as important to
discover which types of information learners ignore as to
discover which types of information they encode.
Researchers have just begun to explore early semantic
networks in young children. Notably, the auditory task
used in the current study is quite different from other
behavioral methodologies that have been used previ-
ously, such as the intermodal-preference-procedure (IPP)
priming task (e.g., Arias-Trejo & Plunkett, 2009). One
benefit of our auditory task is that it allows researchers to
test word knowledge in the absence of visual referents;
this was necessary for the present research because pre-
senting the toddlers with the referents would have pro-
vided them with the exact information that we were
trying to assess. Because the auditory task is novel, we
hope to further explore this methodology, in conjunction
with other techniques, such as the IPP priming task, to
uncover both the mechanisms behind our effect and the
characteristics of young children’s semantic networks.
Word learning is not just about mapping a label to its
referent and making the appropriate extensions to other
similar referents. Children must also learn how different
words are semantically related to each other. Adults
know many important relationships among words, and
this connectedness is a crucial component of people’s
semantic and linguistic systems. Investigating the emer-
gence of these relationships will help researchers more
fully understand the early word-learning process. By
demonstrating that young children encode the visual sim-
ilarity of referents during word learning, this study con-
tributes to an understanding of word learning and
presents a paradigm that can be used to further investi-
gate early encoding of semantic relationships and how
this knowledge interacts with early word learning.
Author Contributions
E. H. Wojcik and J. R. Saffran both developed the study concept
and design. Testing, data collection, data analyses, and inter-
pretation were performed by E. H. Wojcik under the supervi-
sion of J. R. Saffran. Both authors drafted and revised the
manuscript.
Acknowledgments
We thank the families who participated in the experiments as
well as the members of the Infant Learning Lab, specifically
Casey Lew-Williams, Brianna McMillan, and Hillary Stein. We
also thank Jill Lany, Casey Lew-Williams, and Katharine Graf
Estes for their comments on previous versions of this
manuscript.
Declaration of Conflicting Interests
The authors declared that they had no conflicts of interest with
respect to their authorship or the publication of this article.
Funding
This work was funded by a National Science Foundation
Graduate Research Fellowship to E. H. Wojcik and by grants
from the National Institute of Child Health and Human
Development (to J. R. Saffran; R37HD037466), the Waisman
Center (P30HD03352), and the James F. McDonnell Foundation
(to J. R. Saffran).
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