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RESEARCH ARTICLES
◥
COGNITIVE DEVELOPMENT
Observing the unexpected
enhances infants’learning
and exploration
Aimee E. Stahl*and Lisa Feigenson
Given the overwhelming quantity of information available from the environment,
how do young learners know what to learn about and what to ignore? We found that
11-month-old infants (N= 110) used violations of prior expectations as special
opportunities for learning. The infants were shown events that violated expectations
about object behavior or events that were nearly identical but did not violate
expectations. The sight of an object that violated expectations enhanced learning
and promoted information-seeking behaviors; specifically, infants learned more
effectively about objects that committed violations, explored those objects more,
and engaged in hypothesis-testing behaviors that reflected the particular kind of
violation seen. Thus, early in life, expectancy violations offer a wedge into the
problem of what to learn.
Humans are capable of remarkable achieve-
ments, from learning a language to design-
ing skyscrapers and mastering calculus.
These achievements would be impossi-
ble without learning. Yet, as many the-
orists have noted, the problems of when learning
should occur, and what should be learned at all,
are highly underdetermined (1,2). In an environ-
ment that is dynamic and complex, how can a
learner know which aspects of the world to at-
tend to and learn from, and which to ignore?
Without a filter for determining when and what
to learn, or a teacher to provide guidance (3), in-
formation overload can, in practice, make learn-
ing impossible.
At the same time, some aspects of the world
appear to be represented even prior to learn-
ing. These cognitive primitives, sometimes col-
lectively called “core knowledge,”can be observed
in newborn creatures (4,5) and emerge across
diverse rearing conditions (6) and cultures (7).
But far from obviating the need for learning,
core knowledge may be a foundational under-
standing from which learning begins. One way
this could be so is if core knowledge offers a
wedge into the hard problems of knowing when
and what to learn. If a learner has a basic rep-
ertoire of core expectations about the world,
then detecting a violation of these expectations—
a conflict between what was predicted and what
is observed—mightsignalaspecialopportunity
for learning.
Acluethatcoreknowledgemayinfactguide
early learning comes from infants’behavior
in tests of preverbal cognition. Across hun-
dreds of studies, infants respond when basic
expectations are violated, including expecta-
tions generated by core knowledge (8). For ex-
ample, infants look longer when a ball appears
to pass through a wall than when it is stopped
by the wall, suggesting a core understanding of
object solidity (9), and they look longer when
an object hidden in one location is revealed in
a different location, suggesting a core under-
standing of object continuity (10). Seeing sur-
prising events like these can trigger increases
in infants’looking, as well as alterations in
facial expression (11), pupil dilation (12), and
changes in cerebral blood flow or brain electri-
cal activity (13,14). These various responses
have been taken to indicate the detection of a
discrepancy between what was expected and
what is observed, and have been documented
across many knowledge domains. Infants de-
tect violations when, for example, a hidden ob-
ject vanishes (15), when 5 + 5 = 5 (16), and when
a social entity approaches someone mean rath-
er than someone nice (17). Responses to such
surprising physical, numerical, and social events
have been invaluable in efforts to character-
ize the roots of human cognition. Yet it re-
mains unknown what purpose these surprise
responses serve and what the cognitive conse-
quences of experiencing an expectancy viola-
tion might be.
Here we tested the hypothesis that, early in
life, violations of core expectations signal a spe-
cial opportunity for learning. First we asked
whether infants more effectively learn new in-
formation about objects thatviolate expectations
than about objects that accord with expectations
(experiments 1 to 3). Then we asked whether in-
fants preferentially seek information from objects
that violated expectations, and whether their ex-
ploratory actions test plausible explanations for
an observed violation (experiment 4).
Infants’learning about objects that
violated expectations
In experiments 1 to 3, we showed infants an
event whose outcome either was expected be-
cause it accorded with core knowledge of object
behavior or was surprising because it violated
core knowledge, using events modeled on those
in many previous studies. Then we taught infants
something new about the object that had par-
ticipated in the event, and finally we measured
how well they learned this new information.
Three aspects of our design were crucial. First,
we ensured that events that violated core knowl-
edge differed minimally from events that ac-
corded with core knowledge, by perceptually
matching the events in all respects except for
their outcomes. Second, we ensured that any
observed learning enhancement was caused by
experiencing a violation of core expectations,
rather than by longer perceptual exposure to
objects that violated expectations, by match-
ing the duration of infants’looking across out-
come types. Third, we ensured that infants were
learning something genuinely new by teach-
ing them information that could not have been
known beforehand and that could not have
been acquired just by seeing the objects them-
selves (i.e., we taught infants an object’s hidden
property).
In experiment 1, 11-month-old infants saw
an event that either accorded with or violated
object solidity or spatiotemporal continuity,
two core physical principles to which young
infants have consistently shown sensitivity
(18–20)(N= 40; movies S1 to S4). In the so-
lidity event (Fig. 1A), infants saw an object (a
toy car for half the infants; a ball for the other
half) roll down a ramp and pass behind a
screen. A solid wall, partially visible above the
screen, clearly blocked the object’s path. In-
fants then saw the screen removed to reveal
either that the object had been stopped by the
wall, thereby according with expectations about
solidity (Knowledge-Consistent outcome, n=10),
or that the object appeared to have passed
through the wall, thereby violating expecta-
tions about solidity (Knowledge-Violation out-
come, n= 10). In the spatiotemporal continuity
event (Fig. 1B), a separate group of infants saw
two screens placed on an empty stage. The ex-
perimenter hid an object (a ball for half the
infants; a block for the other half) behind the
left screen, then lifted both screens to reveal
either that the object was still behind the left
screen, thereby according with expectations
about continuity (Knowledge-Consistent out-
come, n= 10), or that the object was now behind
the right screen, thereby violating expectations
about continuity (Knowledge-Violation outcome,
n=10).
Unlike previous studies designed to measure
differences in infants’looking to expected versus
RESEARCH
SCIENCE sciencemag.org 3APRIL2015•VOL 348 ISSUE 6230 91
Department of Psychological & Brain Sciences, Johns
Hopkins University, Baltimore, MD 21218, USA.
*Corresponding author. E-mail: astahl4@jhu.edu
on April 2, 2015www.sciencemag.orgDownloaded from on April 2, 2015www.sciencemag.orgDownloaded from on April 2, 2015www.sciencemag.orgDownloaded from on April 2, 2015www.sciencemag.orgDownloaded from
violation events, here we gave all infants the
same limited visual exposure to the Knowledge-
Consistent and Knowledge-Violation outcomes;
all infants had just 10 s to encode the event out-
come. A univariate analysis of variance (ANOVA),
with looking time to the event outcome as the de-
pendent variable and event type (Solidity or Con-
tinuity) and outcome type (Knowledge-Consistent
or Knowledge-Violation) as fixed factors, showed
no main effect of outcome type [F(1,36) = 0.002,
P= 0.96] (18) (table S1), which was as predicted
given the short encoding window in our de-
sign. Thus, any subsequent differences in learn-
ing cannot be attributed to longer perceptual
exposure to the object in the Knowledge-Violation
events.
Immediately after this 10-s exposure to the
outcome of the Knowledge-Consistent or the
Knowledge-Violation event, we taught all in-
fants new information about the object in the
event. The experimenter demonstrated that the
object had a hidden auditory property (e.g., it
squeaked) by moving it up and down while the
sound played synchronously from a hidden
central location for 12 s. Our dependent mea-
sure was infants’learning of this object-sound
mapping. In the test trial, infants saw the tar-
get object from the preceding event and a new
distractor object resting silently on the stage
(baseline; 5 s). For half the infants, the ball was
the target and either the car or the block was
the distractor; this was reversed for the other
half. Then the experimenter moved both ob-
jects up and down simultaneously while the
previously taught sound (e.g., squeaking) played
from a hidden central location (mapping test;
10 s). For each infant we calculated a learning
score by determining the proportion of time
that infants looked at the target object (relative
to the new distractor object) during the base-
line, then subtracting this value from the pro-
portion of time they looked at the target object
during the mapping test, when the taught
sound played (table S1). If infants had success-
fully learned the object-sound mapping, they
should increase the proportion of time they
looked at the target object when the sound played;
such auditory-visual “matching”is the pattern
typically observed in studies of infants’mapping
abilities (21).
We found that infants’learning of the object-
sound mapping depended on whether they had
just seen a Knowledge-Consistent or a Knowledge-
Violation event. A univariate ANOVA, with learn-
ing score as the dependent variable and event
type (Solidity or Continuity) and outcome type
(Knowledge-Consistent orKnowledge-Violation)
as fixed factors, yielded only a significant main
effect of outcome type [F(1,36) = 10.691, P=0.002,
partial h
2
= 0.229]. Infants’learning scores were
significantly greater after Knowledge-Violation
events than after Knowledge-Consistent events
(Fig. 2A). We then compared infants’learning
scores to chance (zero). Infants showed no evi-
dence of learning after events consistent with
object solidity [t(9) = –1.088, P= 0.31] or con-
tinuity [t(9) = 1.62, P= 0.14] but showed sig-
nificant learning after violations to object solidity
[t(9) = 3.092, P= 0.01] and spatiotemporal con-
tinuity [t(9) = 3.715, P= 0.005] (18)(Fig.2Aand
table S1).
In experiment 2, we asked whether this pat-
tern reflected actual learning or simply indicated
greater attention to objects that had violated
expectations. As in experiment 1, infants saw
an object violate the core principle of solidity
(n= 10) or continuity (n= 10) and were then
taught that the object had a hidden auditory
property (e.g., it squeaked). However, during
the mapping test, we played an entirely novel
sound (e.g., rattling). This time, infants did not
increase their proportion of looking to the tar-
get object when the novel sound played after
violations of either solidity [t(9) = 1.453, P=
0.18] or continuity [t(9) = 0.036, P=0.97](table
S1). A univariate ANOVA, with learning score
as the dependent variable and event type (So-
lidity or Continuity) and sound type (taught
sound from the Knowledge-Violation condition
of experiment 1 or novel sound from experiment
2) as fixed factors, yielded only a significant main
effect of sound type. Infants’learning scores
were significantly greater when the taught sound
played in the mapping test (experiment 1) than
when the novel sound played (experiment 2)
[F(1,36) = 5.349, P= 0.03, partial h
2
= 0.129]
(18). This confirms that infants’performance
in experiment 1 reflected successful learning
of an object property, rather than heightened
visual preference for an object that had violated
expectations.
In experiment 3, we asked whether viola-
tions of expectation enhance learning specif-
ically about objects that violated expectations,
rather than about anything that might follow
a violation. We showed infants (n= 10) the
continuity violation from experiment 1, with an
object (i.e., ball) hidden behind the left screen
but revealed behind the right. After the object
was revealed in the surprising location, the
experimenter reached in with a new object (i.e.,
a block) and demonstrated that it had a hid-
den auditory property (e.g., it squeaked). We
then measured infants’learning about this
new object. As in experiment 1, we calculated
learning scores by determining the proportion
of time that infants looked at this new object
(relative to a distractor object) during the si-
lent baseline, then subtracting this value from
the proportion of time they looked at it dur-
ing the mapping test, when the taught sound
played. We found that infants did not map
the sound to the new object in the mapping
test; their learning scores did not differ from
chance [t(9) = 0.074, P= 0.94] (table S1). An
independent-samples ttest confirmed that
this pattern differed significantly from that
of experiment 1, in which infants were taught
about the very object that had violated con-
tinuity [t(18) = 2.126, P=0.048] (18). Hence,
violations of expectation enhanced learning
only for the object involved in the violation
event, not for unrelated objects. Further, in-
fants’failure to learn about the new object
shows that the enhanced learning in experi-
ment 1 was not due to general arousal or nov-
elty. When taught about an object that was
completely perceptually novel (because it had
never been seen before) but did not violate
any expectations, infants showed no evidence
of learning.
92 3APRIL2015•VOL 348 ISSUE 6230 sciencemag.org SCIENCE
Knowledge-
Consistent
Knowledge-
Consistent
Knowledge-
Consistent
Knowledge-
Violation
Knowledge-
Violation
Knowledge-
Violation
Fig. 1. Knowledge-Consistent and Knowledge-Violation outcomes in experiments 1 to 4. (A) Solidity events (movies S1 and S2). (B) Continuity events
(movies S3 and S4). (C) Support events (movies S5 and S6).
RESEARCH |RESEARCH ARTICLES
Infants’exploration and hypothesis
testing after violations of expectation
Our finding that violations shaped infants’
learning in a targeted way, enhancing learn-
ing only about objects relevant to the observed
violation, raises a further question about the
nature of the new information learned. In ex-
periments 1 to 3, the new information taught
to infants was arbitrary, in the sense that it did
not clearly causally relate to the surprising vio-
lations (because the sound made by an object
does not offer a direct explanation for its be-
havior). Besides enhancing learning for such
arbitrary mappings [like those acquired by
nonhuman animals (22)], do violations of ex-
pectation privilege the learning of particular
kinds of information that are relevant to the
nature of the surprising event? When an ob-
servation conflicts with prior knowledge, an
effective learning strategy would be to seek
evidence that could explain the discrepancy be-
tween what was predicted and what is observed.
Older children engage in this kind of hypothesis
testing, performing targeted actions to support
or rule out possible explanations for an event
(23,24). But it is unknown whether preverbal
infants actively test hypotheses about events,
especially events involving violations of core
knowledge.
In experiment 4, we first asked whether in-
fants (N= 40) preferentially seek information
from an object that violated expectations over
an object that did not. Infants saw an event
that either accorded with or violated the prin-
ciples of object solidity or (extending our in-
quiry to another principle) object support (18)
(movies S5 and S6). The solidity events were
identical to those in experiment 1 (Knowledge-
Consistent outcome, n= 10; Knowledge-Violation
outcome, n= 10) (Fig. 1A). In the support event
(Fig. 1C), infants saw an object (e.g., car) either
pushed along a surface while remaining com-
pletely supported, thereby according with expec-
tations about support (Knowledge-Consistent
outcome, n= 10), or pushed over the surface
edge without falling, thereby violating expect-
ations about support (Knowledge-Violation out-
come, n=10)(25). As before, we limited infants’
visual exposure to the event outcomes; a uni-
variate ANOVA, with looking time to the eve nt
outcome as the d ependent variable and event
type (Solidity or Support) and outcome type
(Knowledge-Consistent orKnowledge-Violation)
as fixed factors, showed no main effect of
outcome type [F(1,36) = 0.794, P=0.379](18)
(table S2).
After infants saw the outcome of the solid-
ity or support event, we gave them two objects
to freely explore for 60 s: the target object
from the preceding event (e.g., car) and a new
distractor object (e.g., ball; for half the infants
the car was the target and the ball was the
distractor, and for the other half this was re-
versed). We calculated infants’exploration pre-
ference scores by subtracting the amount of
time they explored the new distractor object
from the amount of time they explored the tar-
get object (table S2). We predicted that infants
who had seen a Knowledge-Consistent event
would show no preference, whereas infants who
had seen a Knowledge-Violation event would
prefer to explore the object that h ad just vio-
lated their expectations. A univariate ANOVA,
with infants’exploration preference score as
the dependent variable and event type (Solid-
ity or Support) and outcome type (Knowledge-
Consistent or Knowledge-Violation) as fixed
factors, yielded a significant main effect of out-
come type [F(1,36) = 5.933, P=0.02, partial h
2
=
0.14]: Infants who had seen the Knowledge-
Violation event explored the target object more
than infants who had seen the Knowledge-
Consistent event. We then compared infants’
SCIENCE sciencemag.org 3APRIL2015•VOL 348 ISSUE 6230 93
-30 -20 -10 0 10
-30
-
20
-
10
0
10
Exploration Score
Prefer Distractor Object Prefer Target Object
Learning Score
Map to Distractor Object Map to Target Object
Infant exploration following:
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
-2
-1.
5
-
1
-0.5 0 0.5
1
1.
5
2
Action Tendency Score (z-score)
More Dropping More Banging
Infant behavior following:
Knowledge-Violation
Event (Solidity)
Knowledge-Consistent
Event (Solidity)
Knowledge-Violation
Event (Support)
Knowledge-Consistent
Event (Support)
Knowledge-Violation
Event (Solidity)
Knowledge-Consistent
Event (Solidity)
Knowledge-Violation
Event (Support)
Knowledge-Consistent
Event (Support)
-0.3 -0.2 -0.1 0 0.1 0.2 0.3
Knowledge-Violation
Event (Solidity)
Knowledge-Consistent
Event (Solidity)
Knowledge-Violation
Event (Continuity)
Knowledge-Consistent
Event (Continuity)
20 30
Infant learning following:
Fig. 2. Results from experiments 1 and 4. (A) Infants’learning after Knowledge-Consistent and
Knowledge-Violation events in experiment 1. Bars represent average learning scores (proportion of
looking at target object during mapping test minus proportion of looking at target object during
baseline). (B)Infants’exploration after Knowledge-Consistent and Knowledge-Violation events in
experiment 4. Bars represent looking at and/or touching the target object minus looking at and/or
touching the new distractor object. (C) Infants’exploratory behaviors on the target object after
Knowledge-Consistent and Knowl edge-Violation even ts in exper iment 4. Ba rs represe nt infant s’
z-scored object-banging behaviors minus z-scored object-dropping behaviors. All error bars rep-
resent SEM.
RESEARCH |RESEARCH ARTICLES
exploration preference scores to chance (zero).
Collapsed across the solidity and support events,
infants who had seen a Knowledge-Consistent
event explored the target and distractor objects
equally [t(19) = –1.128, P= 0.27], whereas in-
fants who had seen a Knowledge-Violation event
preferred to explore the target object [t(19) =
2.395, P=0.027](18) (Fig. 2B and table S2).
Infants who saw a violation event showed
enhanced interest in the violation object, pre-
ferring to explore it over a new object. Because
details of infants’exploratory behaviors might
reveal an even richer interplay between knowl-
edge and exploration, we next asked whether
infants explored the target object qualitatively
differently depending on which violation they
had seen. We analyzed two common exploratory
behaviors, each relevant to one of the presented
events: banging an object (relevant to testing
object solidity) and dropping an object onto
the table or floor (relevant to testing object sup-
port). Because dropping an object takes longer
than banging an object, we converted the fre-
quency of these behaviors into zscores to en-
able direct comparison (table S2). To calculate
infants’tendency to bang versus drop objects,
we subtracted each infant’sz-scored dropping
frequency from their z-scored banging fre-
quency. A univariate ANOVA, with action tenden-
cy score on the target object as the dependent
variable and event type (Solidity or Support)
and outcome type (Knowledge-Cons istent or
Knowledge-Violation) as fixed factors, yielded
a significant interaction between event type
and outcome type [F(1,36) = 9.43, P= 0.004,
partial h
2
= 0.208] (Fig. 2C). An independent-
samples ttest revealed that infants who had
seen an object appear to pass through a wall
(Knowledge-Violation solidity event) banged
that object more than they dropped it, relative to
infants who had seen the same object stopped by
the wall (Knowledge-Consistent solidity event)
[t(18) = 2.378, P= 0.029]. By contrast, infants
who had seen an object appear to hover in mid-
air (Knowledge-Violation support event) did
the reverse: They dropped the object more than
they banged it, relative to infants who had seen
the same object fully supported (Knowledge-
Consistent support event) [t(18) = –2.045, P=
0.056] (18) (Fig. 2C and table S2). This double
dissociation in infants’behavior—wherein in-
fants who saw a solidity violation tended to ac-
tively bang the target object, whereas infants who
saw a support violation tended to drop it—shows
that infants tailored their exploratory actions to
the type of violation seen.
The infants’banging and dropping of the
new distractor object that had not participated
in the solidity or support event did not differ
across event types or outcomes. A univariate
ANOVA, with action tendency score on the dis-
tractor object as the dependent variable and
event type (Solidity or Support) and outcome
type (Knowledge-Consistent or Knowledge-
Violation) as fixed factors, yielded no significant
interaction [F(1,36) = 0.062, P=0.80].Critical-
ly, a repeated-measures ANOVA that examined
action tendency scores across object type (tar-
get or distractor), event type (Solidity or Sup-
port), and outcome type (Knowledge-Consistent
or Knowledge-Violation) yielded a significant
interaction among these three factors [F(1,36) =
4.95, P= 0.032, partial h
2
= 0.12] (18); infants
performed differential actions only after Knowl-
edge-Violation events and only on the objects
that had committed the violation. This dissoci-
ation in infants’actions on just the target object
reveals two senses in which infants’behaviors
were highly directed: They focused on the entity
that had violated expectations, and they were
relevant to the nature of the observed violation.
Thus, infants’behaviors are not merely reflexive
responses to the novelty of surprising outcomes
but instead reflect deeper attempts to learn
about aspects of the world that failed to accord
with expectations.
Conclusions
Our findings show that infants’learning is
changed when their expectations are violated.
Much as scientists faced with unexpected pat-
terns of data are propelled to think harder, run
further experiments, or change their methods of
inquiry, untutored preverbal minds are sensitive
to conflict between the predicted and the ob-
served, and use this conflict as a scaffold for
new learning.
In our experiments, we tested learning after
violations of expectations drawn from core knowl-
edge of object behavior—knowledge that is avail-
able from early in life, is universal across human
cultures, and is present in other species. The
existence of these foundational expectations has
beenusedtoargueforthepresenceofrichinnate
knowledge in infants; given our finding that vio-
lations of these expectations lead to enhanced
learning, early knowledge and early learning
are mutually reinforcing. In addition,expectancy
violations involving other types of knowledge
are also likely to be important in learning. Chil-
dren form new expectations by tracking expe-
rienced contingencies (26), by receiving others’
testimony (27), and by using abstract knowl-
edge to form probabilistic predictions about
events they have never observed (28). Some of
these sophisticated behaviors have been inter-
preted in terms of Bayesian inferences that gen-
erate knowledge by weighing new evidence
against prior beliefs (29,30). Our findings accord
well with such a framework and suggest ave-
nues to explore how violations detected in dif-
ferent domains of prior knowledge, or using
different kinds of new evidence, shape explo-
ration and learning throughout the life span
and across species.
Together, our experiments reveal that when
infants see an object defy their expectations,
they learn about that object better, explore that
object more, and test relevant hypotheses for
that object’s behavior. Seen through this lens,
the decades of findings that infants look longer
at surprising events suggest not only that in-
fants are equipped with core knowledge about
fundamental aspects of the world but also
that this knowledge is harnessed to empower
new learning even in infancy. Thus, core knowl-
edge is not an alternative to learning but is
instead a key ingredient in driving learning
forward.
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ACKNO WLED GME NTS
Supported by NSF Graduate Research Fellowship DGE-1232825
(A.E.S.). We thank J. Halberda for comments; J. Taggart,
S. Folsom, M. Santoru, C. Veazey, G. Lisandrelli, and K. Grubb
for assistance with data collection and coding; and J. Garmon
for construction of the experimental apparatus. Data can be
found on the Harvard Institute for Quantitative Social Sciences
dataverse (DOI: 10.7910/DVN/29315).
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