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In press: Developmental Science
THREE-MONTH-OLD INFANTS ATTRIBUTE GOALS TO A NON-HUMAN AGENT
Yuyan Luo
University of Missouri
Address correspondence to Yuyan Luo, Department of Psychological Sciences, University of Missouri, Columbia,
MO 65211, USA; phone: (573) 882-0429; fax: (573) 882-7710; email: [email protected].
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Abstract
The present research examined whether 3-month-old infants, the youngest found so far to engage in goalrelated reasoning about human agents, would also act as if they attribute goals to a novel non-human agent, a selfpropelled box. In two experiments, the infants seemed to have interpreted the box’s actions as goal-directed after
seeing the box approach object-A as opposed to object-B during familiarization. They thus acted as though they
expected the box to maintain this goal and responded with increased attention when the box approached object-B
during test. In contrast, when object-B was absent during familiarization and introduced afterwards, the infants’
responses were consistent with their having recognized that they had no information to predict which of the two
objects the box should choose during test and therefore responded similarly when the box approached either object.
However, if object-B was absent during familiarization and object-A was in different positions but the box persistently
approached it, thus demonstrating equifinal variations in its actions, the infants again acted as though they attributed
to the box a goal directed towards object-A and expected the box to maintain this goal even when object-B was
introduced and hence responded with prolonged looking when the box failed to do so during test. These results are
consistent with the notion that (a) infants as young as 3 months appear to attribute goals to both human and nonhuman agents and, (b) even young infants can use certain behavioral cues, e.g., equifinal variations in agents’
actions, to make inferences about agents’ goals.
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There is now considerable evidence of infants’ understanding about agents’ goals (e.g., Bíró & Leslie, 2007;
Gergely, Nádasdy, Csibra, & Bíró, 1995; Luo & Baillargeon, 2005; Meltzoff, 1995; Woodward, 1998). However, the
nature and development of such an understanding remains controversial. Some suggest that experience with self
and others allows infants to first interpret human agents’ actions that are familiar to them as goal-directed (e.g.,
Meltzoff, 1995, 2005; Tomasello, Carpenter, Call, Behne, & Moll, 2005; Woodward, 2005). Others propose that an
innate abstract computational system, a psychological-reasoning system, guides infants’ goal-related understanding
(e.g., Csibra & Gergely, 2007; Johnson, 2000; Leslie, 1994, 1995; Luo & Baillargeon, 2007; Premack, 1990).
Therefore, infants seem to attribute goals to any individual they identify as an agent, whether human or non-human,
and appropriate behavioral cues embedded in agents’ actions enable infants to perceive these actions as goaldirected. Both views have gained support from numerous studies.
Woodward and colleagues report findings consistent with the humans-first view (e.g., Sommerville,
Woodward, & Needham, 2005; Woodward, 1998, 2009). In a ground-breaking study, Woodward (1998) found that
infants at 5 to 6 months encoded a human agent’s repeated actions of grasping an object as goal-directed. However,
when the agent was replaced with an inanimate object, the infants did not respond as such. Woodward (1998)
concluded that 5- to 6-month-olds appear to attribute goals to human but not to non-human agents.
Further results reveal the importance of experience, especially infants’ first-person action experience in their
intentional understanding. Due to young infants’ limited experience, certain actions are clearly goal-directed to them,
while others are ambiguous (Woodward, Sommerville, & Guajardo, 2001). Six-month-olds do not encode an agent
contacting an object with the back of her hand, an unfamiliar action, as goal-directed (Woodward, 1999). With
development, infants’ own abilities to perform certain actions help them perceive these actions in others as goaldirected (Woodward, 2005; Woodward & Guajardo, 2002). Twelve-month-olds seem to interpret a person looking at
an object as goal-directed, but not 7- and 9-month-olds (Woodward, 2003), presumably because older infants are
more experienced with encoding the relationship between one’s gaze and the target object, as infants’ gaze-following
abilities develop between 9 and 12 months (e.g., Butterworth & Jarrett, 1991; Corkum & Moore, 1998; D'Entremont,
Hains, & Muir, 1997).
Additionally, even first-hand action experience acquired in a laboratory facilitates infants’ goal-attribution.
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Sommerville et al. (2005) extended the Woodward (1998) task to 3-month-olds, the youngest to have participated in
looking-time studies on goal attribution. The infants, who typically cannot grasp an object (Needham, Barrett, &
Peterman, 2002), responded as though they identified a human agent’s hand grasping an object as goal-directed in
the habituation task, if they first acquired “grasping” experience by wearing Velcro mittens to “swipe at” objects (the
agent in the habituation task also wore a mitten). Positive results were not obtained, however, when the infants
participated in the looking-time task first or alone.
The all-agents view that infants appear to engage in psychological reasoning about human and non-human
agents has also gained increasing support. For example, Luo and Baillargeon (2005) found that 5-month-olds seem
to attribute goals to a non-human agent, a self-propelled box. They reasoned that the infants in Woodward (1998) did
not respond as though they attributed goals to inanimate objects because they did not perceive these objects as
agents: each object’s end was hidden from view, making it unclear whether its actions were self-generated or not. In
their experiments, infants were therefore given unambiguous evidence of agency. They first watched orientation
events in which the box moved back and forth in the center of an apparatus; it was clearly self-propelled. Similar to
Woodward (1998), infants then watched a familiarization event in which the box approached a cone but not a cylinder.
Following familiarization, the locations of the two objects were reversed. During test, the box approached either the
cone (old-goal event) or the cylinder (new-goal event). Infants looked reliably longer at the new- than at the old-goal
event. These and control results suggested that infants’ responses were consistent with their having categorized the
self-propelled box as an agent and attributed to it a goal directed towards the cone during familiarization, and that
infants seemed to have expected the agent to maintain this goal during test and hence responded with prolonged
looking to the new-goal event. Besides, infants responded similarly when a short but not a long handle was attached
to the box. The short handle always remained fully visible so that the box was still a self-propelled agent. However,
the end of the long handle was always hidden from view, as in the inanimate-objects experiments of Woodward
(1998). In this ambiguous situation, infants no longer perceived the box as an agent. These results demonstrate that
infants also behave as though they attribute goals to non-human agents and thus add to many other reports on
infants’ psychological understanding about non-human agents (e.g., Csibra, 2008; Gergely et al., 1995; Johnson et
al., 2008; Kuhlmeier, Wynn, & Bloom, 2003; Surian, Caldi, & Sperber, 2007).
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Csibra, Gergely, and colleagues propose that certain behavioral cues help infants encode goals underlying
agents’ actions, such as the outcomes brought by agent’s actions, or equifinal variations in agent’s actions (e.g.,
Csibra, Bíró, Koós, & Gergely, 2003; Csibra & Gergely, 2007; Gergely & Csibra, 2003). For example, after watching a
human agent touch an object with the back of her hand and move the object – the agent’s action therefore produces
an effect – 6-month-olds act as if they interpret this unfamiliar action as goal-directed (Jovanovic et al., 2007; Király,
Jovanovic, Prinz, Aschersleben, & Gergely, 2003). Furthermore, although 9-month-olds do not perceive an agent’s
looking at an object as goal-directed, they seem to identify the goal directed toward the particular object if the agent
inspects it from different angles in three fixations, thus demonstrating equifinal variations in her looking behavior
(Johnson, Ok, & Luo, 2007).
According to researchers supporting the humans-first view, experience with human agents, especially firsthand action experience, plays an important role in infants’ intentional understanding of others, although they disagree
on the age at which infants first encode others’ actions as goal-directed and the mechanisms involved (e.g., Meltzoff,
2005; Tomasello, 1999; Woodward, 2009). This view predicts that very young infants should first perceive humans’
but not other agents’ actions in terms of goals. The only study to date with 3-month-olds involved human agents
(Sommerville et al., 2005). In this study, these young infants’ everyday experience failed to help with their goalrelated understanding about others; they perceived others’ mittened grasping action as goal-directed only after they
themselves had had active “grasping” experiences with objects. If such self-produced goal-directed actions initially
led infants to perceive goals underlying human agents’ actions only, then these young infants should be unable to
deal with situations involving non-human agents.
Conversely, the all-agents view predicts that from the beginning, infants should act as if they can reason
about all agents’ actions in terms of goals when provided with appropriate cues to agency and intention. Therefore,
even 3-month-olds, the youngest to have been tested in goal-related studies, should attribute goals to a novel nonhuman agent, i.e., a self-propelled box, as in Luo and Baillargeon (2005), and this goal-attribution could also be
facilitated by behavioral cues such as equifinal variations in the agent’s actions. The present research tested these
predictions in Experiments 1 and 2, respectively. Positive evidence would lend support to the all-agents view. More
importantly, comparisons of Sommerville et al. (2005) and the present study would enlighten us on what information
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enables young infants to encode an entity’s goals. This in turn would shed further light on how to synthesize the two
theoretical views to better characterize early intentional understanding. We will return to this issue in General
Discussion.
Experiment 1
Infants were assigned to a two-object or a one-object condition (see Fig. 1), as in Experiment 1 of Luo and
Baillargeon (2005). The procedure of the two-object condition is described above. The one-object condition was
identical except that during familiarization, only the cone was present. Results similar to Luo and Baillargeon (2005)
were expected. Infants in the two-object condition should look reliably longer at the new- than at the old-goal event.
Conversely, since infants in the one-object condition were not given information to predict the box’s choice between
the two objects when the cylinder was added during test, they should not differentiate between the two events in
which the box contacted either the cone or the cylinder and hence should look about equally at both events. This
condition aimed to address potential difficulties with the two-object condition, e.g., that infants formed an association
between the box and the cone during familiarization and responded to disruption of this association in the new-goal
event, because this alternative would predict that infants in the two conditions would respond similarly.
Method
Participants
Twenty-four healthy, full-term infants (range = 2 months, 16 days to 4 months, 8 days; M = 3 months, 9
days), 12 male and 12 female, participated. Twelve infants, 6 male and 6 female, were randomly assigned to the twoobject (M = 3 months, 12 days) or the one-object (M = 3 months, 6 days) condition. Fifteen infants were excluded for
fussiness (6), looking for 95% or more of the maximum looking time allowed (60 s) in both test trials (5), looking time
difference between the two test trials that was more than 2.5 SDs from the mean (1), drowsiness (1), inattentiveness
(1), or observer errors (1).
Apparatus
The apparatus consisted of a wooden display box, 114 cm high, 104 cm wide, and 47 cm deep, that was
mounted 76 cm above the room floor. The infant faced an opening 54 cm high and 101 cm wide in the front of the
apparatus; between trials, a curtain consisting of a muslin-covered frame, 61 cm high and 104 cm wide, was lowered
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in front of the opening. The side walls of the apparatus were painted white, and the floor was covered with grey
granite-pattern contact paper. The back of the apparatus was made of grey foam core board; at the bottom of the
back wall was an opening 1.5 cm high and 101 cm wide that was filled with black fringe. Two muslin-covered
windows, 31.5 cm high and 30 cm wide, were created in the left and right walls of the apparatus and were used to
introduce or remove the box, cone, and cylinder between trials.
The cardboard box, 5.5 cm high, 18 cm wide, and 15.5 cm deep, was covered with green contact paper.
Attached to the back lower edge of the box was a metal rod, 1 cm in diameter and covered with the same grey
granite-pattern contact paper as the apparatus floor. The rod extended through the fringe-filled opening at the bottom
of the back wall. An experimenter used a wooden handle at the end of the rod behind the back wall to move the box;
the handle fit into a linear groove in the apparatus floor with adjustable stops so that the box could travel the
designated path in each trial. Because the rod was not visible to the infants, the box appeared to move on its own.
The cone and cylinder were made of polyvynil chloride pipes. The cone consisted of a cylinder, 16.5 cm
high and 11.5 cm in diameter, and a conical top 9 cm in slant height. It was covered with white contact paper
decorated with pastel dots. The cylinder, 20.5 cm high and 11.5 cm in diameter, was painted yellow and decorated
with blue stripes.
Procedure
Infant sat on a parent’s lap, facing an apparatus resembling a puppet stage. Parents were instructed to
close their eyes during test and not interact. Two naïve observers monitored the infant's looking behavior by viewing
infants through peepholes in large cloth-covered frames on either side of the apparatus. Looking times recorded by
the primary observer were used. Interobserver agreement for 25 of the 36 infants in the two experiments averaged
88% per trial per infant.
All infants first received two orientation trials in which the box moved back and forth across apparatus,
starting from the left in the first trial and from the right in the second trial. Each movement cycle lasted 6-s and cycles
repeated until the trial ended when the infant looked away for 2 consecutive seconds after having looked for at least
3 cumulative seconds, or for 60 cumulative seconds.
Next, infants received five familiarization trials appropriate for their condition. Each trial involved a 3-s pre-
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trial (in which the box moved to stop against the cone) and a main-trial (in which the box paused in this position until
the trial ended). Each familiarization main-trial ended when the infant looked away for 2 consecutive seconds after
having looked for at least 2 cumulative seconds, or for 60 cumulative seconds.
All infants then received a display trial with the two objects in reversed positions; the box was absent. This
trial ended when the infant looked away for 2 consecutive seconds after having looked for at least 5 cumulative
seconds, or for 60 cumulative seconds.
Finally, all infants received two test trials in which the box moved to contact the cone (old-goal event) or the
cylinder (new-goal event) during the pre-trial and paused in this position until the trial ended during the main-trial. Half
of infants saw the new-goal event first; and half saw the old-goal event first. Each test main-trial ended when the
infant looked away for 2 consecutive seconds after having looked for at least 5 cumulative seconds, or for 60
cumulative seconds.1
In both experiments, infants were attentive during the 3-s pre-trials of familiarization and test, means ranging
from 2.0 to 2.6 seconds; infants’ looking times between conditions during orientation, familiarization, and display were
not reliably different, all Fs(1, 22) < 3.78, ps > .064. Preliminary analyses of Experiment 1 test data revealed no
significant interaction among condition, event, sex and/or order of test trials, all Fs(1, 16) < 2.93, ps > .10; data were
therefore collapsed across sex and order in subsequent analyses.
Results
Infants’ test main-trial looking times (see Fig. 2) were analyzed by means of a 2 x 2 ANOVA with condition
(two- or one-object) as a between-subjects factor and event (new- or old-goal) as a within-subject factor. The
analysis yielded a significant condition x event interaction, F(1, 22) = 6.96, p < .025. Planned comparisons revealed
that infants in the two-object condition looked reliably longer at the new-goal (M = 33.1, SD = 23.6) than at the oldgoal (M = 16.4, SD = 11.5) event, F(1, 22) = 6.19, p < .025, Cohen’s d = 0.8, whereas infants in the one-object
condition looked about equally at the events (new-goal event: M = 22.7, SD = 22.7; old-goal event: M = 31.1, SD =
21.9), F(1, 22) = 1.55, p > .22, d = -0.4.2 Examination of individual infants’ looking times confirmed these results. Nine
of the twelve infants in the two-object condition looked longer at the new-goal than at the old-goal event, Wilcoxon
signed-ranks T = 13, p < .05, whereas only four of the twelve infants in the one-object condition did so, T = 23,
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p > .20.
The results suggested that in the two-object condition, infants seemed to have categorized the box as an
agent and interpreted its actions during familiarization as goal-directed. They appeared to expect the box to continue
acting on the goal object during test and hence responded with prolonged looking when this expectation was
violated. In the one-object condition, although infants might still perceive the box’s actions as goal-directed, they had
no information to help them predict during test, which of the two objects the box should choose, and hence
responded similarly when the box approached either one. These results extend those of Luo and Baillargeon (2005)
to 3-month-olds and demonstrate that infants this young also act as if they attribute goals to a novel non-human
agent, thus supporting the all-agents view of intentional understanding.
However, it is possible that in the one-object condition, the introduction of the cylinder after familiarization
had confused infants, leading to negative results. Experiment 2 addressed this possibility.
Experiment 2
Experiment 2 was similar to the one-object condition, except that during familiarization, the cone was placed
in the left or the right corner; the box still moved to contact it in each trial (see Fig. 3; different-positions condition).
Therefore, equifinal variations of the box’s actions were presented; it went through different paths to contact the cone.
Given that equifinality is a powerful cue for eliciting infants’ goal-related interpretation of agents (e.g., Bíró & Leslie,
2007; Csibra, 2008; Johnson, Ok et al., 2007; Jovanovic et al., 2007; Király et al., 2003), it should make clear that the
box’s goal drove it to always pursue the cone during familiarization. If so, infants should behave as though they
expect the box to again act on this goal even with the cylinder added and hence look reliably longer at the new- than
at the old-goal event. Positive results in Experiment 2 would thus render alternative interpretations of the one-object
condition data less likely. Had infants been confused by the addition of the cylinder after familiarization, they should
have responded similarly in Experiment 2 and the one-object condition.
Method
Participants
Another 12 infants (range = 2 months, 21 days to 3 months, 27 days; M = 3 months, 2 days), 6 male and 6
female, participated in Experiment 2. Seven infants were excluded for looking time differences between the two test
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trials that were more than 2.5 SDs from the mean (3), looking for 95% or more of the maximum looking time allowed
(60 s) in both test trials (2), being distracted (1), or drowsiness (1).
Apparatus and Procedure
Experiment 2 was identical to the one-object condition, with one exception: the cone was in the right corner
during the first, second, and fifth familiarization trials and in the left corner during the third and fourth familiarization
trials; the box always started from the center, moved to contact the cone, and paused until the trial ended.
Preliminary analyses of Experiment 2 test data with those of the one-object condition revealed no significant
interaction among condition, event, sex and/or order, all Fs(1, 16) < 1.53, ps > .23; data were therefore collapsed
across sex and order in subsequent analyses.
Results
The infants’ looking times in Experiment 2 were compared to those of the infants in the one-object condition
of Experiment 1. Infants’ test main-trial looking times (see Fig. 2) were analyzed by means of a 2 x 2 ANOVA with
condition (different-positions or one-object) as a between-subjects factor and event (new- or old-goal) as a withinsubject factor. The analysis yielded a significant condition x event interaction, F(1, 22) = 6.35, p < .025. Planned
comparisons revealed that infants in the different-positions condition looked reliably longer at the new-goal (M = 38.8,
SD = 21.6) than at the old-goal (M = 23.8, SD = 12.1) event, F(1, 22) = 5.24, p < .05, d = 0.7, whereas those in the
one-object condition did not differ reliably in their looking times at the two events, F(1, 22) = 1.63, p > .21, d = -0.4.3
Examination of individual infants’ looking times in the different-positions condition confirmed these results; nine of the
twelve infants looked longer at the new-goal than at the old-goal event, T = 13, p < .05.
These results suggested that infants acted as if they had realized that the box had a goal directed toward
the cone, since it persistently moved itself to contact the cone even when the cone was in different positions across
familiarization. They thus seemed to expect the box to continue approaching the cone during test and responded with
heightened interest when the box approached the newly-introduced cylinder. These positive results ruled out lowlevel interpretations of the one-object condition data. Together with previous findings (e.g., Bíró & Leslie, 2007;
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Csibra, 2008; Johnson, Ok et al., 2007), these results also make clear that equifinal variations in agents’ actions help
infants encode goals underlying these actions.
General discussion
The present results suggest that 3-month-old infants, the youngest to have been tested in goal-related
studies, seem to attribute goals to the actions of a novel non-human agent. These results are thus consistent with the
all-agents view that infants’ intentional understanding is rooted in a specialized psychological-reasoning system,
which is activated whenever infants attempt to make sense of actions of individuals they identify as agents, even an
unfamiliar self-propelled box. Furthermore, these results suggest that even young infants use specific behavioral
cues, equifinality in this case, to interpret agents’ goal-directed actions.
Sommerville et al. (2005) attributed 3-month-olds’ failure to view a human agent grasping objects as goaldirected to lack of first-person action experience. Why did the infants in the present research readily attribute goals to
the non-human agent moving to contact an object? One possibility is that the infants were given richer behavioral
information about the agent than those of Sommerville et al. (2005). In Sommerville et al. (2005), infants simply saw
the agent’s arm and hand reach to an object during habituation. In the present research, infants first watched the box
move back and forth in the center during orientation. They then saw the box move to contact the cone in the corner
during familiarization. Therefore, the box changed its behavior from orientation to familiarization, which helped infants
realize that the box did so to pursue its goal object, the cone. Support for this comes from studies by Johnson and
colleagues (Johnson, Shimizu, & Ok, 2007; Shimizu & Johnson, 2004) in which 12-month-olds saw a self-propelled
“blob” approach object-A rather than object-B during habituation. Next, the objects’ positions were reversed, and the
blob approached either object-A (old-goal event) or object-B (new-goal event). Infants looked reliably longer at the
new- than at the old-goal event when the blob started each habituation trial facing forward and then turned to face
object-A, but not when it was already facing object-A before moving toward it. These results suggest that evidence
that an object changes its behavior, even a subtle change such as a simple turn, to pursue an object, elicits infants’
intentional understanding.
In Sommerville et al. (2005), 3-month-olds did not see changes in the agent’s actions in the looking-time
task. They clearly did not use their previous knowledge about other people’s behavior to understand this particular
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agent’s actions and goals. Their success in the action-first condition shows the importance of firsthand experience. It
was also noted by the authors that behavioral cues such as the action-effect co-occurrence and equifinality were
present in infants’ mitten-wearing experience. Therefore, it is possible that 3-month-olds, without firsthand experience,
would still act as if they attribute goals to a human agent’s unfamiliar actions if they were given rich behavioral
information about the agent as in the present research, for example, when the agent’s actions were enhanced with
the aforementioned cues.
In the present research, three cues were used: self-propulsion, changes of behavior to achieve a goal, and
equifinality. These cues signaled to infants that the self-propelled box was an intentional agent. Recent results
suggest that self-propulsion alone is insufficient: infants do not view a self-propelled object following a fixed path to
contact another object as an agent (Csibra, 2008; Johnson, Shimizu et al., 2007; Kamewari, Kato, Kanda, Ishiguro, &
Hiraki, 2005; Shimizu & Johnson, 2004). However, positive results were obtained when the object engaged in
contingent interaction with an experimenter before it moved towards another object (Johnson et al., 2008; Johnson,
Shimizu et al., 2007; Shimizu & Johnson, 2004), thus revealing yet another cue to agency.
The present results provide evidence for the all-agents view by demonstrating that infants as young as 3
months also seem to attribute goals to non-human agents. Therefore, young infants do not engage in intentional
understanding about human agents only. An innate psychological-reasoning system may guide infants’ interpretation
of all agents. However, this is not to say that infants’ experience with self and others plays little role in their
understanding. In fact, many types of experiences can be at work to facilitate infants’ attribution of goals to nonhuman agents. For instance, 3-month-olds might have seen other non-human agents’ actions, or these young infants
might have had firsthand experience of moving themselves to come into contact with a goal object. These could all
have aided them to make sense of the self-propelled box’s actions in the present research.
Therefore, in order to paint a clearer picture of early intentional understanding, Bíró and Leslie (2007)
offered a “cue-based bootstrapping” approach. They propose that infants initially attend to featural information and/or
behavioral cues to identify agents and to interpret agents’ actions. With learning and experience, infants need fewer
and fewer cues to infer that an entity’s behavior is driven by intentions. Given infants’ exposure to other people and
their own actions, they can still encode goals underlying human agents’ actions even when there are minimal cues
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(e.g., Woodward, 1998), but when agents and/or their actions are unfamiliar or ambiguous, additional information
becomes critical for infants to make inferences about agents and their goals and intentions (e.g., Johnson, Ok et al.,
2007; Jovanovic et al., 2007; Király et al., 2003; Luo, 2010). Thus, an innate predisposition to attend to cues of
agency and intention, as well as prior knowledge and experience, may work together in infants’ psychological
understanding.
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Acknowledgments
This research was supported by research funds from the University of Missouri. I thank Renée Baillargeon,
György Gergely, Kris Onishi, Kristy vanMarle, and two anonymous reviewers for helpful comments. I am also grateful
to the University of Missouri Infant Cognition Laboratory for their help with the data collection, and the parents and
infants who participated in the research.
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Footnotes
1. As in Luo and Baillargeon (2005), whether the infants saw the new-goal or the old-goal event first during test was
counterbalanced, but which object, the cone or the cylinder, was the goal or which side the goal object was on during
familiarization was not. Because the one-object condition served as a control for the two-object condition and the
different-positions condition as a control for the one-object condition, it seemed unnecessary to do so. For example,
the two-object and the one-object conditions were similar except for whether or not the cylinder was present during
familiarization. Any preferences resulted from the imbalanced design should have affected both conditions and might
have led to similar looking patterns. However, as will become clear, the infants’ looking behavior was influenced by
their different interpretations of the agent’s actions across conditions; they seemed to attribute goals to the agent in
the two-object and the different-positions condition but not in the one-object condition. This was supported by the
reliable condition by event interactions in each experiment.
2. Although the differences were not reliable, there was a tendency for infants in the two-object condition to look
longer during orientation and familiarization and to look shorter during display than those in the one-object condition.
The test data in Experiment 1 were therefore subjected to an analysis of covariance (ANCOVA); the factors were the
same as in the ANOVA, and the covariates were infants’ mean looking times during orientation and familiarization
and their looking times during display. The results replicated those of the ANOVA: the condition x event interaction
was significant, F(1, 19) = 5.88, p < .05; and planned comparisons confirmed that infants in the two-object condition
looked reliably longer at the new- than at the old-goal event, F(1, 19) = 7.00, p < .025, whereas those in the oneobject condition did not do so, F(1, 19) = 2.03, p > .17.
3. The test data of the different-positions condition in Experiment 2 and those of the one-object condition in
Experiment 1 were subjected to an analysis of covariance (ANCOVA) as in Experiment 1. The results replicated
those of the ANOVA: the condition x event interaction was significant, F(1, 19) = 7.02, p < .025; and planned
comparisons confirmed that infants in the different-positions condition looked reliably longer at the new- than at the
old-goal event, F(1, 19) = 6.34, p < .025, whereas those in the one-object condition did not look reliably differently at
the two events, F(1, 19) = 2.36, p > .14.
20
Figure Captions
Figure 1. Schematic drawing of the orientation, familiarization, display, and test events of the two-object and oneobject conditions in Experiment 1.
Figure 2. Mean looking times of the infants in Experiments 1 and 2 during the test trials. Error bars represent
standard errors. An asterisk (*) indicates a statistically significant difference between infants’ looking times at the two
test events.
Figure 3. Schematic drawing of the orientation, familiarization, display, and test events of the different-positions
condition in Experiment 2.
Two-object Condition
One-object Condition
Orientation Event
Orientation Event
Familiarization Event
Familiarization Event
Display
Display
New-goal Test Event
New-goal Test Event
Old-goal Test Event
Old-goal Test Event
Different-positions Condition
Orientation Event
Familiarization Event
or
Display
New-goal Test Event
Old-goal Test Event