young children’s failure to generalize when exposed to the...
TRANSCRIPT
Running Head: CONSERVATIVE LEARNING
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Young children’s failure to generalize when exposed to the same input as older learners:
An advantage in language learning
Jeremy K. Boyd
Adele E. Goldberg
July 14, 2009
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Abstract
The present study tested adults (M=22;4), seven-year-olds (M = 7;6), and five-year-olds (M =
5;2) on instances of a novel construction that showed different degrees of lexical overlap with
exposure items. Adults and seven-year-olds performed consistently at above-chance levels,
regardless of lexical overlap. Five-year-olds, on the other hand, were more conservative. They
were above chance when test items were identical to exposure items and when test items
consisted of new novel verbs paired with the same noun phrases seen during exposure, but not
when test items showed no lexical overlap with exposure items. Additionally, unlike adults and
seven-year-olds, five-year-olds showed no evidence of having mastered the novel construction’s
linking rules. Thus, young learners are less likely to generalize abstract argument structure
constructions when exposed to the same systematic input as older learners. These results are
interpreted, in light of the widespread idiosyncrasy and narrow generalizations that exist in
languages, as providing possible insight into the early learner’s advantage in language
acquisition.
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1. Introduction
Children have been known to put diapers on their heads and marbles in their mouths, but
in other ways they are clearly less than fully creative. Imagine a young child brought to an
elaborate carnival that boasts a dizzying array of games, newly rearranged each day. Dauntingly,
the rules for each game vary from booth to booth, and no one is able to instruct the child as to
how to play. Instead, adults and older children are busy playing the games themselves, skipping
from booth to booth, and playing games at multiple booths simultaneously; their reactions
convey a deep involvement in the games, as they often grin broadly, weep openly, or laugh
heartily.
Young children would no doubt be intrigued and would want to play these games as well.
But learning to anticipate the rules of each game would require watching and listening carefully
again and again. Some understanding of the carnival would come quickly; an impression of the
sights and sounds, tacit knowledge of the physical layout of their favorite booths or knowledge
of which ones had the longest lines. But only slowly would most children be able to venture out
and toss their first ring. Most likely, young children would initially stand close by their parents,
trying to comprehend their parents’ intents and imitate their strategies. And it would take some
time, perhaps years, before they were equipped to adopt more efficient rules for any of the
games.
Language is not a carnival, but it does involve a dizzying array of conventional language
games or constructions, each with its own quirks of form and function (Austin, 1962;
Wittgenstein, 1953). To have adult-like competence in a language is to know how to use those
constructions, producing and comprehending new combinations without conscious effort in
contextually appropriate ways. Just as a child at a carnival may quickly glean in broad strokes
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information about the layout of a carnival, a child learning a language learns early on many
features of her language. A large body of work in artificial grammar learning, for example,
indicates that infants are able to detect formal and statistical regularities that they are exposed to
(Gomez & Gerken, 1999; Marcus, Vijayan, Bandi Rao, & Vishton, 1999; Saffran, Aslin, &
Newport, 1996; Saffran, 2003). And young children also pick up on the meanings of individual
utterances with surprising alacrity (cf. Tomasello, 2003). By the age of three, children are
typically able to converse about tickling, hugs and cotton candy.
There has been an ongoing debate about how long it takes children to acquire abstract
constructions, with some arguing for very early learning and others arguing that productive
representations appear quite late, at around 3.5 years (e.g., Naigles, 1990; Tomasello, 2000).
Recent work indicates that 2-year-old children have some general understanding of the English
transitive construction’s form and function, and are able to identify which scenes reversible
transitive utterances with novel verbs correspond to (Fernandes, Marcus, Di Nubila, &
Vouloumanos, 2006; Gertner, Fisher, & Eisengart, 2006). However, by two years of age,
children have witnessed tens of thousands of transitive utterances, so it is not necessarily
surprising that they may have formed a tentative generalization (Abbot-Smith, Lieven, &
Tomasello, 2008). Evidence that the generalization is tentative comes from a study that
replicated Gertner et al.’s findings, but only when toddlers were first exposed to familiar
transitives during a practice session, as they were in Gertner et al.’s experiment (Dittmar, Abbot-
Smith, Lieven, & Tomasello, 2008a). Without the preceding training, 2-year-old children showed
no evidence of sensitivity to a generalized transitive construction. The Gertner et al. result is thus
not inconsistent with a plethora of other evidence demonstrating that children’s early syntactic
representations are more or less item-based.
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Study after study has shown that during their early conversations, children tend to
produce only minor variations of the formulations that they have witnessed in the input. They
readily substitute I for you or my dog for your cat, but they also largely tend to avoid more
creative extensions and combinations of patterns (Akhtar & Tomasello, 1997; Baker, 1979; Bates
& MacWhinney, 1982; Braine, 1976; Brooks & Tomasello, 1999; Dittmar, Abbot-Smith, Lieven,
& Tomasello, 2008b; Ingram & Thompson, 1996; Lieven, Pine, & Baldwin, 1997; MacWhinney,
1982; Savage, Lieven, Theakston, & Tomasello, 2003; Schlesinger, 1982; Tomasello, 1992;
Tomasello, 2000; Tomasello, 2003). If a two year old child, for example, learns a novel verb by
hearing it used in an intransitive construction, they themselves are highly likely to use it only
intransitively, without creatively causitivizing it. As children get older, however, they are
increasingly more likely to do what adults would do: creatively turning It pilked into He pilked it,
if pilking is what he did to it. The idea that young children’s generalizations may be more
tentative or partial, or may need more contextual support than adults’ is supported by much work
in non-linguistic category formation (Fisher & Sloutsky, 2005; Munakata, 2001; Munakata,
McClelland, Johnson, & Siegler, 1997; Rovee-Collier, 1997).
Why children are conservative with language is still an open question. It may be that their
early failure to generalize reflects a lack of sufficient data: perhaps learners need a massive
number of exemplars before they are able to generalize. Alternatively, young children may be
more tentative with their generalizations than adults, even when exposed to the same input.
1.1 The benefits of hugging the data without generalizing
Children’s apparent lack of full generalization early on may serve them well. Much
recent work in linguistics has observed that far from being a system of simple, elegant rules,
adult linguistic competence requires detailed, partially idiosyncratic, often probabilistic
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knowledge of grammatical patterns (Bresnan, Cueni, Nikitina, & Baayen, 2007; Bybee, 1995;
Fisher, 2002; Goldberg, 2006; Lakoff, 1970; Langacker, 1988). There are in fact thousands of
collocations, prefabricated utterances (“prefabs”), idioms and minor constructions that often
buck the trends of a language in unexpected ways (Culicover, 1999; Jackendoff, 2002). Take, for
example, the minor pattern in English that involves the combination of a preposition and a bare
count noun as in the examples below:
(1) She went to bed.
(2) She stayed in bed.
(3) She came from school.
(4) He was at dinner.
(5) She left for work.
(6) He was in hospital. (British)
Normally (non-generic) count nouns require determiners, so the form of this construction is
clearly unusual. Moreover, no modification of the bare noun is allowed:
(7) *She went to big bed. (Cf. She went to the big bed).
The construction also requires a special interpretation. One does not go to prison as a warden,
but only as a prisoner. People do not go to bed in order to stand on the bed, as they might if they
were going to the bed. The construction conveys that a stereotypical activity associated with the
nominal referent is involved. But the [P N] pattern is not productive, and attempts to generalize it
would lead learners astray. For example, American English speakers do not go to hospital,
although British English speakers do. And neither group can go *to bath, *to computer, or *to
kitchen, even though there exist stereotypical activities associated with these places.
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Another interesting distributional pattern involves a small but open set of adjectives
including asleep, afloat, and alive. These adjectives resist appearing prenominally in attributive
position, as is evident in the examples in (8):
(8) a. ??the/an asleep child
b. ??the/an afloat ship
c. ??the/an alive monster
Other semantically similar or phonologically similar adjectives show no such dispreference for
attributive position:
(9) the sleeping child
(10) the adult monkey
See Boyd and Goldberg (in prep.) for experimental studies that demonstrate that this pattern is
partially productive. It is motivated by the diachronic history of many of the adjectives as
prepositional phrases (e.g., asleep comes from the Old English PP on sleep). As prepositional
phrases, it made sense that they would not occur attributively. Today’s speakers, no longer aware
of the historical origin of these adjectives, implicitly recognize and respect their unusual
distributional pattern. But a learner who was too quick to generalize might use all adjectives
attributively on the one hand, or she might erroneously assimilate semantically or phonologically
similar items to the minor pattern exhibited by asleep, afloat, and alive.
As a final example, consider the many a night + SAI construction exemplified in (11):
(11) Many a night have I wept into a salad bowl full of frosted flakes.
http://www.spectremusic.com/chat/archives/001620.html
The form of this construction is unusual in that it combines a plural quantifier (many) with a
singular determiner (a); the construction also involves subject-auxiliary inversion, a marked
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word order pattern in English. The function of this construction is likewise quite particular. A
corpus search of 2000 examples on Google reveals that the construction involves first person
pronoun subjects 99% of the time (when compared with 2nd or 3rd person pronouns). The choice
of auxiliary is also restricted in that no instances of the future marker will occurred in any of
instances collected (see Berson & Goldberg, in prep., for details). There is a strong statistical
preference, therefore, for the construction to convey subjective (speaker-centered) reflections
about past events. A speaker who was to generalize the construction too broadly would likely be
led astray, possibly producing infelicitous instances such as the following:
(12) ??Many an afternoon will she take me to the zoo.
Constructions that show limited generalization are not hard to come by (e.g., Lakoff,
1970; Goldberg, 2006, Chapter 3). Moreover, fixed idioms and collocations abound as well
(Pawley & Syder, 1983; Wray, 2002). Learners who generalize broadly on the basis of little data
would clearly be in danger of overgeneralizing each of these cases. More prudent learners who
hug the data initially will ultimately learn the language more accurately. This idea may well play
a role in explaining the finding that there is an advantage to being exposed to a language from an
early age (e.g., Newport, 1990).
1.2 Why are children more conservative learners?
As noted in the introduction, young children do not appear to generalize as broadly as
adults; instead they are conservative. Why children are conservative, however, remains unclear.
Have they simply not been exposed to a sufficient number of exemplars to enable them to
generalize? Much previous research might lead to this conclusion, because most of the work
demonstrating children’s early conservatism has involved constructions that are, to varying
degrees, familiar from the ambient language; for example, much work has been done on the
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English transitive construction (see Tomasello, 2000 for an overview). We know that the
tendency to generalize is increased by exposure to varied exemplars (e.g., Bybee, 1985, 1995), so
children and adults may not be different in their tendency to generalize. Better generalization by
adults may simply be due to the fact that they have had more exposure to the requisite data.
On the other hand, it is possible that children are more tentative with linguistic
generalizations than adults even when exposed to the same input. Intriguingly, there exists some
evidence that suggests that adults readily generalize on the basis of remarkably little data. In a
series of experiments, adult participants were exposed to a wholly novel argument structure
construction, which involved both a novel form a novel abstract meaning. Participants saw only
sixteen video clips of the novel construction, and exposure lasted a total of three minutes. The
novel construction included novel verbs so that knowledge of verbal meaning could not be used
to learn the construction’s meaning. In a subsequent forced-choice comprehension task, adults
and older children (M = 6;4) were able to associate new instances of the novel construction with
its meaning significantly more often after training than in a control condition in which they
watched the same video without sound. They were also able to distinguish the novel construction
from instances of the transitive construction involving new novel verbs (Casenhiser & Goldberg,
2005; Goldberg, Casenhiser & Sethuraman, 2004). These experiments indicate that adults and
older children can learn tentative construction-level generalizations over items quickly, on the
basis of little input.
More recent work using similar methods has demonstrated that the learning by adults is
quite specific and robust. Both SOV and OSV orders can be learned and distinguished from one
another. Moreover, undergraduates are willing to use the novel construction in production tasks,
with some evidence of retention over a 7-day delay (Boyd, Gottschalk, & Goldberg, 2009).
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Goldberg, Casenhiser and White (2007) includes additional control conditions that rule out
spurious explanations for above-chance performance in this paradigm. It seems that for adults,
minimal exposure to a novel construction is sufficient for the formation of generalizations that go
well beyond the specific exemplars encountered in the input. Adults and older children thus
readily form abstract and general constructional representations. What is unclear, however, is
whether younger children are able to do the same.
2. Experiment
Do learners at varying ages form an abstract constructional category with equal ease
when given the same exposure? If generalization is entirely input-driven—that is, if
generalization of a pattern depends solely on being exposed to a critical mass of input exemplars
of that pattern (Marchman & Bates, 1994; Tomasello, 2000)—then learners at varying ages
should perform similarly when their knowledge of the construction is tested. It is possible,
though, that generalization will not be equivalent across age groups. Specifically, in light of their
documented conservative behavior during the course of normal language development, younger
children may hug the input data more closely than adults: they may behave in a manner that is
consistent with the acquisition of lexically-specific representations, but not general
representations.
As a means of testing for item-specific versus general constructional representations, the
present experiment manipulates the novelty of the items that participants are tested on. Based on
previous results (Boyd et al., 2009; Casenhiser & Goldberg, 2005), we predict that adults and
older children will perform at high levels, even when test items are high in novelty. Younger
children, on the other hand, may show decrements in performance as novelty increases.
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2.1 Participants
Eighteen five-year-olds (age range: 4;6-5;9; M = 5;2), 18 seven-year olds (age rage 6;9 to
8;1; M = 7;6), and 18 undergraduates (age range: 18;5 to 43;0; M = 22;4) took part in the
experiment. An additional eight five-year-olds and one seven-year-old were tested, but their data
were not included for reasons explained in the results section. Five-year-olds were recruited from
summer recreational programs in the Princeton area, and seven-year-olds were recruited from
local afterschool programs. Each child was given a children’s book in exchange for participation.
Adults were either recruited through the use of online advertisements, in which case they
received a $12 payment for participation, or through the Princeton University Department of
Psychology subject pool, in which case they received course credit.
2.2 Novel Construction
We created a novel construction that describes APPROACH events in which one person
moves towards another person. The construction has the form NP1NP2V, where NP1 denotes the
individual who is moving (the agent), NP2 denotes the individual who is being moved towards
(the goal), and V is a novel verb that can be construed to encode a manner of motion. For
example, The doctor the construction worker feigos denotes an event in which a doctor crawls
towards a construction worker.
All instantiations of the construction contained two definite English NPs (e.g., the doctor
and the construction worker) followed by a verb with an -o suffix, and a present or past tense
marker (e.g., feigos, feigoed). The presence of determiners and inflectional markers served to
make NPs and verbs simpler to identify, although we assume that by five years old, children
have learned what NPs and verbs are. Our interest is in whether they are able to generalize the
clausal construction. The -o suffix was used to facilitate recognition of the construction: previous
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research has shown that verb markings that correlate with the meaning of a construction make
recognition more accurate (Casenhiser & Goldberg, 2005).
2.3 Exposure Trials
Participants were familiarized with 16 different exemplars of the construction during an
approximately three minute exposure block. Since a number of studies have suggested that
children have an easier time learning abstract categories when they are given input samples with
less variability (Casasola, 2005; Casenhiser & Goldberg, 2005; Goldberg, Casenhiser, &
Sethuraman, 2004; Maguire, Hirsh-Pasek, Golinkoff, & Brandone, 2008), we sought to reduce
variability during exposure in two ways. First, all of the exposure sentences featured just two
NPs—the doctor and the construction worker. These were balanced so that each one occurred as
NP1 half of the time, and as NP2 the other half. Second, the frequency distribution of the five
verbs that appeared in the exposure sentences was skewed in favor of a single verb. Eight of the
sixteen exposure sentences featured the verb moopo, while the remaining eight were evenly
divided among four other verbs: keybo, feigo, suuto and vako.
The 16 exposure sentences were embedded in short, 10-second movies that depicted their
meanings. Each movie showed an agent approaching a goal, and used a voiceover that featured
an exposure sentence with a present tense verb, followed by the same sentence with a past tense
verb. For example, if a movie showed a doctor hopping towards a construction worker (see
Figure 1), then the sentence The doctor the construction worker vakos would be heard
simultaneously with the hopping motion. After the hopping had ended, the sentence The doctor
the construction worker vakoed would play.
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2.4 Test Trials
In order to determine whether participants had learned anything during exposure, we
administered a forced choice comprehension task involving 12 holistic trials and four linking
trials. Both types of trials required participants to listen to a voiceover sentence, then pick out
which of two simultaneously-played movies depicted its meaning. Holistic trials are described in
detail in the following section; linking trials are described in §2.4.3.
2.4.1 Holistic Trials
Holistic trials were designed to determine whether participants recognized that the
NP1NP2V construction had a general APPROACH meaning that was disjoint from the meaning of a
more common construction type—the intransitive. Participants’ task was to listen to a sentence,
and then to indicate which of two simultaneously played movies it referred to.
The movie pairs that made up holistic trials depicted two types of events: one movie
showed an agent character approaching a goal character (as in exposure trials), while the other
showed the same two characters performing a repetitive intransitive motion in synchrony, e.g.
Figure 1. An example exposure trial. The agent (the doctor) approaches the goal (the construction worker) while a present tense NP1NP2V description plays (left). After the approach event has concluded (right), a past tense NP1NP2V description plays.
“The doctor the construction worker vakoed.” “The doctor the construction worker vakos.”
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clapping. These movie pairs were combined with different kinds of voiceover sentences to
produce subtypes to the holistic trial category—approach trials and intransitive trials. Approach
trials featured NP1NP2V voiceovers that described the approach movie in a movie pair. A correct
answer on an approach trial was therefore a point to the approach movie. Intransitive trials on the
other hand, featured intransitive sentences that described the intransitive movie in a movie pair.
This means that a correct answer on an intransitive trial was a point to the movie showing
synchronous repetitive intransitive motion. Figure 2 gives an example of the way in which
different types of voiceover sentences were combined with holistic trial movies to create either
approach trials or intransitive trials.
2.4.2 Novelty
In addition to testing whether participants could identify approach scenes if and only if
they heard instances of the NP1NP2V construction, we also wanted to assess the effects of
Figure 2. Holistic trial movies were combined with different voiceovers to create either approach trials, or intransitive trials. In an approach trial, the above movies were combined with an exemplar of the NP1NP2V construction—The princess the basketball player pookos—and a correct response was a point to the movie on the right, which shows a princess hopping on one foot towards a basketball player. In an intransitive trial, the same movies were combined with an intransitive sentence—The basketball player and the princess are zorping—and a correct response was a point to the movie on the left, which shows the basketball player and the princess clapping their hands. No participant saw the same movie pair combined with more than one sentence.
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novelty on participants’ ability to correctly interpret the construction. To this end, we
manipulated the amount of novelty that was present in approach trials.
Three levels of novelty were used—no novelty, novel verb, and all novel. For trials with
no novelty, the target movie and its associated voiceover sentence were simply repeated from
exposure. For trials with a novel verb, the target movie showed the same characters from the
exposure block—i.e., the construction worker and the doctor—enacting a novel manner of
approach, which was labeled in the voiceover with a new novel verb form. In trials that were all
novel, the target movie involved characters that had not been seen during exposure enacting a
novel manner of approach. These trials were accompanied by voiceovers in which none of the
constituents in the NP1NP2V exemplar had ever been heard during the course of the experiment.
Of interest was how the amount of novelty in the approach movie and voiceover sentence
affected performance. We hypothesized that increased familiarity would generally be associated
with better performance, and that increased novelty would be associated with worse
performance.
Overall, subjects were tested on six approach trials and six intransitive trials. The six
approach trials were further subdivided according to novelty, with two no novelty trials, two
novel verb trials, and two all novel trials.
2.4.3 Linking Trials
Good performance is possible on holistic trials given only a general understanding of the
NP1NP2V construction. On approach trials, for example, a participant who knows only that two
initial NPs are associated with the meaning APPROACH could correctly pick out approach movies.
But have participants acquired knowledge of the NP1NP2V construction that is more detailed
than this? Specifically, do they know that the construction’s first NP encodes the agent, and that
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its second NP encodes the goal? In order to answer this question, participants were tested on four
linking trials immediately following the 12 holistic trials. Linking trials were identical to holistic
trials, with one caveat. Whereas in holistic trials participants chose between approach movies
and intransitive movies, in linking trials they chose between two approach movies in which the
agent and goal roles were reversed. For example, if the voiceover sentence was The construction
worker the doctor gippos (see Figure 3), then the trial featured one movie in which the
construction worker approached the doctor (the target movie), and another where the doctor
approached the construction worker (a distractor).
2.5 Procedure
Participants were tested individually. A practice block was followed by an exposure
block, and then a test block. The practice block consisted of six trials that familiarized
participants with the testing procedure by having them match exemplars of known construction
types (involving familiar verbs) with one of two simultaneously-played movies. The exposure
block consisted of 16 exposure trials, played in different random orders for each participant. The
instructions for the exposure block simply asked participants to pay attention to what they would
“The construction worker the doctor gippos.”
Figure 3. A linking trial. Knowledge of the NP1NP2V construction’s linking rules is needed to determine which of the two individuals mentioned in the stimulus sentence is the agent, and which is the goal. Above, the correct response is to the left.
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see and hear. The test block was broken down into four sub-blocks. The first three sub-blocks
each contained two approach trials randomly intermixed with two intransitive trials. In sub-block
one, the approach trials had no novelty; in sub-block two they featured novel verbs; in sub-block
three all constituents were novel. The fourth sub-block consisted of four randomly-ordered
linking trials.
All test trials looped indefinitely until a response was made. Participants were instructed
to watch the pair of clips as many times as necessary before picking one. Children pointed to
their choice, which the experimenter then recorded with a button press. Adults pressed the button
themselves. Test materials were balanced for target side, with half of the target movies appearing
on the left, and half on the right. Test trials were also counterbalanced across participants for
target movie. For the trial shown in Figure 2, for example, half of all participants viewed the two
movies while hearing The princess the basketball player pookos, while the other half heard The
basketball player and the princess are zorping. Use of the first voiceover sentence makes the
approach movie the target; use of the second makes the intransitive movie the target. This sort of
counterbalancing served to reduce the possibility that some specific combination of voiceover
sentences with movie pairs would skew our results.
2.6 Results
Over the course of testing, we noticed that eight child subjects showed no response
variability in the first three test sub-blocks. In particular, six five-year-olds picked the
intransitive movie on every trial, and one five-year-old and one seven-year-old picked the
approach movie on every trial. This sort of behavior suggests strategic responding in which
children decided to consistently pick a certain type of movie without taking into account a
semantic interpretation of the voiceover sentences, as instructed. These participants were
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consequently excluded from further analysis, along with another five-year-old whose poor
performance in the practice block suggested an inadequate understanding of the task. This left us
with analyzable data from 18 participants in each of the three groups.
For these participants, we calculated their proportion of correct responses on approach
trials (broken down according to novelty), as well as on linking and intransitive trials. Group
means are shown in Table 1 for approach and linking trials, and in Table 2 for intransitive trials.
Table 1: Mean Proportion of Correct Responses (SD) on the Novel Construction
5-year-old 7-year-old Adult No Novelty .83** (.30) .97** (.12) 1.0**(0.0) Novel V .69* (.42) .78** (.35) .97** (.12) All Novel .50 (.42) .86** (.29) 1.0** (0.0) Linking .53 (.30) .88** (.23) .97** (.12)
Table 2: Mean Proportion of Correct Responses (SD) on Intransitives
Trial Type (with reference to distractor) 5-year-old 7-year-old Adult
No Novelty .81** (.30) .94** (.16) 1.0** (0.0) Novel V .75** (.35) .92**(.19) 1.0** (0.0) All Novel .75** (.35) .86**(.33) 1.0** (0.0)
Did variations in novelty have an effect on approach trial performance? To answer this
question, each participant’s approach trial means were entered into a mixed two-by-three
ANOVA, with age (five-year-old vs. seven-year-old vs. adult) as a between-participants variable,
novelty (no novelty vs. novel verb vs. all novel) as a within-participants variable, and the
proportion of correct responses as the dependent measure.
Results showed a significant main effect of novelty on approach trials, F(2, 102) = 7.36,
p < .01, reflecting the fact that performance generally declined as novelty increased (no novelty:
94%; novel V: 81%; all novel: 79%), as well as a main effect of group, F(2, 51) = 10.05, p <
.001, and a significant interaction of group and novelty, F(4, 102) = 3.80, p < .01, which together
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indicated that the novelty effect was predominantly localized to the five-year-old group, as seen
in Figure 4.
To follow up on the significant group-by-novelty interaction, a series of one-tailed t-tests
was run to determine whether performance in each of the conditions shown in Figure 4 was
above a chance baseline—i.e., greater than 50% correct. These tests indicate that all three groups
were above chance on approach trials with no novelty (five-year-olds: t(17) = 4.76, p < .0001;
seven-year-olds: t(17) = 17.00, p < .0001; adults: 100% correct), and on trials with novel verbs
(five-year-olds: t(17) = 1.94, p = .034; seven-year-olds: t(17) = 3.34, p < .01; adults: t(17) =
17.00, p < .0001). When trials had no lexical overlap with exposure sentences, however, five-
year-olds were not above chance, t(17) = 0.0, p = 1, but seven-year-olds and adults were (t(17) =
5.33, p < .0001 and 100% correct, respectively).
Figure 4. Approach trial results. Whereas adult performance on approach trials was at ceiling regardless of novelty (see the dark gray bars), both child groups showed decrements in performance as novelty increased (see the light gray and white bars). In fact, five-year-olds were just above chance on trials involving a novel verb, and were no different than chance on trials that had no lexical overlap with exposure items. Error bars indicate the SEM.
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This outcome suggests that the two older groups developed general constructional
representations that allowed them to accurately interpret exemplars of the construction,
regardless of their novelty. Five-year-olds’ performance, on the other hand, suggests that they
were operating with more item-specific representations. These representations allowed for
above-chance performance when dealing with exemplars that had been seen in the input, and
when interpreting exemplars that differed only minimally from the input (i.e., in the novel verb
condition), but did not allow for above-chance performance when test items had no lexical
overlap with items from the input.
On intransitive trials, we found that all groups performed significantly above chance,
without regard to the novelty of the distractor approach movies (five-year-olds: (t(17) = 4.56, p <
.001; seven-year-olds: t(17) = 9.03, p < .0001; adults: 100% correct). Moreover, children’s
performance was not significantly modulated when distractor novelty was taken into account,
F(2, 68) = .80, p =.45. This finding indicates that the five-year-old children understood the task.
Moreover, five-year-olds’ performance on intransitives did not suffer a decline across test
blocks, which militates against the possibility that their poorer performance as novelty increased
on the approach trials was due to increased fatigue or distraction as the experiment wore on.
The second question that we were interested in answering concerned the specificity of the
knowledge that participants gained from exposure to the NP1NP2V construction. Good
performance on holistic trials indicates that a general association between the NP1NP2V form
and APPROACH semantics has been learned. It does not, however, demonstrate that participants
know that NP1 links to the agent role, and NP2 to the goal role. To determine whether linking
rules had been learned, we calculated the proportion of correct responses in each group on
linking trials (see Table 1), and found that adults and seven-year-olds were significantly above
CONSERVATIVE LEARNING
21
chance, (adults: t(17) = 17.00, p < .0001; seven-year-olds: t(17) = 6.89, p < .0001), whereas five-
year-olds were not, t(17) = 0.40, p = .35.
Overall then, while adults and older children had little difficulty on either of the trial
types that were designed to test for knowledge of the NP1NP2V construction, the learning
demonstrated by five-year-olds was much more limited. Given the same amount of exposure to
the construction as adults, there was no evidence that five-year-olds had developed the sort of
abstract representation that would allow them to correctly interpret constructional exemplars that
had no lexical overlap with exposure exemplars. Similarly, there was no evidence that five-year-
olds had learned the construction’s linking rules. Their performance on trials involving the novel
construction thus stands in contrast to their performance on intransitive trials, which were always
statistically above chance, and further, provide evidence against the existence of fatigue effects
in the experiment.
3. Discussion
The findings of the present study demonstrate that younger children are less likely to
generalize than older learners when exposed to the same systematic input. This suggests that
children’s failure to generalize a given construction in many previous experiments may not be
due simply to a lack of exposure to enough exemplars of that construction. Instead, we
hypothesize that young children fail to generalize because they are less adept at detecting
patterns in the input. Item-based behavior is thus the result of younger children’s relative
inability to detect more abstract generalizations in language, perhaps because of their tendency to
be distracted from abstract structural similarity by surface dissimilarity (Gentner & Medina,
1998). Before, however, addressing the causes of the younger children’s item-based behavior in
more detail, we seek to rule out some alternative interpretations of the current data.
CONSERVATIVE LEARNING
22
3.1 Alternative Interpretations
One might argue that above chance performance on approach trials in the present
experiment does not reflect actual learning about the NP1NP2V construction. Instead, both
children and adults may have adopted a strategy in the first three test sub-blocks whereby they
simply favored approach movies, without regard for the meaning of the voiceover sentences that
they heard. Recall that one child—whose data was subsequently excluded from analysis—
actually chose approach movies on every trial. In order to rule out the possibility that other
participants executed a more nuanced version of this strategy wherein they probabilistically
(instead of deterministically) favored approach movies, performance on intransitive trials is
relevant. Recall that all groups performed significantly above chance when considering
intransitive trials, without regard to the novelty of the approach distractor. In particular,
children’s performance was not significantly modulated when distractor novelty was taken into
account. This outcome is inconsistent with the notion that good approach trial performance was
due to strategic responding, and instead suggests that participants picked movies—as
instructed—based on a semantic interpretation of the voiceover sentences.
Another possible strategy involves associating intransitive sentences and intransitive
movies, then matching exemplars of the NP1NP2V construction to approach movies based on a
process of elimination. If for example, a participant is able to predict that the movie on the left in
Figure 2 should be described with an intransitive structure like The basketball player and the
princess are Ving, then they know that if they hear an NP1NP2V structure, it probably refers to
the movie on the right. Note that this strategy, like the one outlined above, does not require any
actual knowledge of the NP1NP2V construction. Again, however, the data rule this possibility
out. This process-of-elimination hypothesis incorrectly predicts that children’s performance
CONSERVATIVE LEARNING
23
should be insensitive to novelty manipulations. Yet our results demonstrate that younger
children’s performance on approach trials shows a linear decline, such that when target movies
and voiceover sentences are entirely novel, they are no longer performing at an above chance
level (see Figure 4). Older children also show better performance on old items than on those that
contain novelty. These patterns are straightforwardly explained by the hypothesis that children’s
knowledge of the NP1NP2V construction is in some respects item-based. As test items show less
lexical overlap with exposure items, children are increasingly unsure about whether to interpret
them as descriptions of approach movies, or descriptions of intransitive movies.
Note also that both of these strategies are additionally ruled out by 7-year-old and adult
performance on linking trials. Always choosing approach movies, or matching the NP1NP2V
construction to approach movies based on a process of elimination incorrectly predicts at chance
performance when the target and distractor movies both show approach events. Adults and older
children, however, were well above chance on linking trials—an outcome that indicates they
have learned the specific linking rules.
Finally, we address the fact that our test item blocks were ordered and the five year olds
did progressively worse on later trials involving the novel construction. While it is normally
legitimate to keep order constant in a between-subjects design such as ours, it is possible that
five-year-olds had less stamina than older children or adults, and that this is responsible for their
poorer performance as the experiment went on. However, the entire experiment took 12-15
minutes, of which approximately five minutes was devoted to the entire set of testing trials. This
short time span with kindergarten-aged children argues against an explanation based on
increasing fatigue. Moreover, as noted above, the fact that intransitive trials—which were
interspersed with holistic trials in each of the first three test sub-blocks—showed no decrement
CONSERVATIVE LEARNING
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over time, also argues against the notion that the five-year-old data pattern is due to fatigue.
Instead, intransitive performance suggests that five-year-olds remained attentive to the task
throughout.
When our results are put into a larger context, we find that they are not unexpected. The
following section reviews some relevant work about young children’s ability to generalize.
3.2 Previous indications that younger children tend to miss generalizations
The finding that young children are more conservative despite having the same input is
reminiscent of other findings in research on children’s memory and cognition (Brainerd &
Mojardin, 1998; Brainerd & Reyna, 2004; Brainerd, Reyna, & Ceci, 2008). False recall and
recognition of sentences that are semantically equivalent, but formally different from exposure
sentences appears to increase steadily between 5 and 11 years of age. Older children and adults
are more likely to “fill in” gaps in their experience, while younger children are less likely to do
so. In one paradigm, for example, a list of words is generated by compiling a set of associates for
a target word: the word doctor, for example, could be used to generate the related words nurse,
sick, hospital, ill, patient, cure, stethoscope, and surgeon. After exposure to the list of related
words, participants were asked whether the original (non-occurring) word, doctor, had appeared
in the list. Adults are more likely than children—quite likely, in fact—to falsely recall that they
had seen doctor in the original list (Brainerd & Reyna, 2004; Fisher & Sloutsky, 2005). This is
arguably evidence that adults are responding based on a higher-level category—whether or not
the probe word is a member of the semantic field exemplified by the associates of doctor—
whereas children are responding in an item-based fashion, based on the words that were actually
present in the input.
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25
In related work, it has been shown that children have more trouble with systematic
“reversal shifts” than adults do (Brainerd, Reyna, & Forrest, 2002). For example, if participants
are exposed to instances that exemplify a pattern (e.g., all blue objects are labeled “winners” and
all red objects are labeled “losers”), adults show an advantage when they need to reverse the
pattern (making all blue objects losers, and all red objects winners), as compared with when they
have to learn an entirely new rule (e.g., all square objects are winners, and all circular objects are
losers). The advantage occurs because adults presumably learn abstract, color-based categories
for the labels, and a reversal shift requires these categories to be relabeled, which is significantly
easier than learning entirely new shape-based categories. In contrast, children show no advantage
for reversal shifts (Brainerd & Reyna, 2004; Tighe, Tighe, & Schechter, 1975)—a finding that
suggests that they are performing the task in an item-based fashion, by associating each
individual object with a label, rather than categorizing objects.
Overall then, there is a significant body of results from linguistic and non-linguistic tasks
that demonstrate that children often fail to learn or use abstract categories in their behavior.
Moreover, the results just discussed are crucially similar to our experimental findings in that they
demonstrate that children’s responses have an item-based character, even when children are
exposed to input that is sufficient for category formation in adults. This suggests that the
differences between child and adult behavior cannot solely be due to differences in the amount of
input that each group receives.
3.3 Children are Sometimes Ready Generalizers
The results reported here at first blush appear to be at odds with recent work that has
suggested that in certain types of situations, children are more likely to generalize than adults
(Hudson Kam & Newport, 2005, in press; Singleton & Newport, 2004). For example, a deaf
CONSERVATIVE LEARNING
26
child, referred to as Simon, who was exposed to obligatory motion classifiers in ASL only 70%
of the time by his parents, generalized the use of the classifiers to 90% of appropriate contexts,
resulting in use that was indistinguishable from native signers (Singleton & Newport, 2004).
Similarly, in an experimental study, hearing children who were taught an artificial language that
used a determiner only 60% of the time, showed a tendency to streamline the pattern either by
always producing the determiner, or more often, by omitting the determiner. Adults, on the other
hand, were more likely to match the probabilities witnessed in the input, producing the
determiner approximately 60% of the time (Hudson Kam & Newport, 2005).
How can children be at once more conservative than adults and more likely to generalize
than adults? There are likely several factors at play in determining whether generalization occurs.
The one that is most relevant in the present context is the idea that a pattern must be implicitly
recognized in order to be generalized.
Clearly, learners have to detect a generalization in order to take advantage of it. Children
arguably generalize in Newport and colleague’s experimental studies because the pattern of
determiner use was easy to detect. In order to be considered generalizers, children needed only to
use the high-frequency, lexically specific determiner generally or not at all. Indeed, other studies
that have investigated children’s knowledge of concrete morphological patterns have also found
quite early generalization (Dąbrowska & Szczerbiński, 2006; Dąbrowska & Tomasello, 2008).
The patterns required for more abstract construction-learning are less easy to detect,
however, in that they require children to extend abstract constructions that depend on word order
and abstract meaning. In order to recognize English argument structure constructions, for
example, children have to overlook concrete differences in the various verbs and arguments
involved; they need to recognize the common word order and extremely abstract function.
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Younger children may not be capable of recognizing a fully abstract pattern as readily; without
the shared commonality (in arguments, in the present study) new instances are not easily
assimilated to the exemplars witnessed during exposure. Indeed, studies of children’s use of
these more abstract constructions have consistently shown a conservative bias (see Tomasello
2000 for an overview of many such studies involving the transitive construction).
There are other factors—beyond the ability to recognize the patterns involved—that
likely lead children and adults to respond as they do in Newport and colleagues’ set of very
interesting studies. We believe the following additional premises are required:
(i) Unconditioned variation is harder to retain than conditioned variation (since
conditioning factors serve to make variation predictable).
(ii) Learners attempt to learn the input veridically; if it contains probabilistic
variation, they will attempt to produce probabilistic variation.
(iii) Producing one form (generalization) is easier than producing many forms
(variation).
The first premise states that predictable variation is easier to retain than unpredictable
variation. In Newport’s studies, the variation in the input was unpredictable; that is, the variation
was unconditioned or ‘inconsistent’: the determiner (or classifier) appeared or did not appear,
without being conditioned by a differing semantic interpretation or by different accompanying
nouns. Thus, children’s tendency to generalize (or to omit the recalcitrant determiner altogether)
may have stemmed from being unable to predict when the determiner should appear. In support
of this idea is the fact that when the unconditioned variation was made quite complex, with one
determiner appearing 60% of the time and sixteen other determiners appearing 2.5% of the time
each, adults also tended to generalize, boosting the probability of the high-frequency determiner
CONSERVATIVE LEARNING
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(Hudson Kam & Newport, in press, Experiment 1). At the same time, when this very complex
variation was made predictable (conditioned), in that each of the 17 determiners always appeared
only with certain nouns, the complex but conditioned variation was learned by adults (Hudson
Kam & Newport, in press, Experiment 2). Thus, it seems that when learners are unable to predict
variation (because it is unconditioned), they are likely to use some default strategy (e.g., “I’m
going to stick with the one determiner that I can remember” or “Just forget those crazy little
words, I have no idea what they’re doing”). Understandably, with their better short-term memory
and metacognitive skills, adults have an easier time keeping track of unconditioned probabilistic
variation and reproducing it veridically. But when the language gets too complex, even adults
rely on a simpler generalization.
In order to explain why children more readily generalize in Newport’s studies than adults
do, we need to focus on what it is that participants are trying to do. Most likely, all participants
are attempting to reproduce the input veridically. If the input is probabilistic, the target response
is probabilistic (see Premise ii).
The third premise is that generalization is easier than variation, which explains why the
default strategy is to generalize when a pattern is recognized. This is in some sense trivial: all
other things being equal, repeating a pattern is less effortful than producing several unrelated
patterns. Repeated actions, whether linguistic or non-linguistic, become routinized and therefore
require less effort. Evidence of this comes from both studies indicating that repetition or
familiarity leads to increased perceptual fluency (Bornstein & D'Agostino, 1994), and from
studies that demonstrate structural and lexical priming and a tendency to perseverate more
generally (Ramage, Bayles, Helm-Estabrooks, & Cruz, 1999). The reason that learners do not
ultimately generalize or simplify a language completely, using only a single construction, stems
CONSERVATIVE LEARNING
29
from Premise (ii): they aim to reproduce the target language veridically, together with the fact
that ultimately, of course, multiple constructions exist because communication is improved by
being able to utilize various constructions with differing functions. That is, constructions
collectively provide the expressive power of a language.
To summarize, extant findings are consistent with the idea that both children and adults
are subject to a tendency to generalize and a tendency to reproduce the input veridically. But it is
only possible to generalize a pattern if there is some (implicit) recognition of the pattern. Adults
clearly have better working memory and better metacognitive skills, so they are more likely to
implicitly or explicitly recognize a pattern when one exists.
Conservatism, or hugging of the data, results from cases in which children fail to
implicitly recognize a pattern. Intriguingly, due to the fact that there is much idiosyncrasy in
language and the fact that many generalizations that exist are quite narrow, data-hugging is
prudent, and may well play a role in explaining why young learners learn languages better.
4. Conclusion
We have presented clear evidence that younger children are more conservative when
learning a novel abstract argument structure construction than older learners are, despite being
exposed to the exact same input. Young children tend to rely quite closely on the input data
without taking liberties with it.
We have also argued that this tendency to be conservative may facilitate language
learning insofar as language is rife with minor patterns and narrow generalizations. This
suggestion is very much in the spirit of Newport’s “Less is More” hypothesis (1990; see also
Elman, 1993) in the sense that we suggest that children’s lack of sophistication happens to lead
to more accurate language learning. In particular, we suggest that the failure to recognize abstract
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commonalities inhibits children from generalizing rampantly, as they might otherwise have a
tendency to do. Once language is recognized to involve a network of related but partially
idiosyncratic constructions, the ability to avoid rampant generalization can be seen to be
advantageous.
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31
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