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RESEARCH ARTICLE
Selective Cooperation in Early Childhood –
How to Choose Models and Partners
Jonas Hermes
1,2
*, Tanya Behne
1,2
, Kristin Studte
1
, Anna-Maria Zeyen
1
,
Maria Gräfenhain
3
, Hannes Rakoczy
1,2
1Institute of Psychology, University of Göttingen, Waldweg 26, D-37073 Göttingen, Germany, 2Leibniz
ScienceCampus Primate Cognition, Kellnerweg 4, D-37077 Göttingen, Germany, 3Department of Child and
Adolescent Psychiatry, Psychotherapy and Psychosomatics, University of Leipzig, Liebigstr. 20a, D-04103
Leipzig, Germany
*jonas.hermes@psych.uni-goettingen.de
Abstract
Cooperation is essential for human society, and children engage in cooperation from early
on. It is unclear, however, how children select their partners for cooperation. We know that
children choose selectively whom to learn from (e.g. preferring reliable over unreliable mod-
els) on a rational basis. The present study investigated whether children (and adults) also
choose their cooperative partners selectively and what model characteristics they regard as
important for cooperative partners and for informants about novel words. Three- and four-
year-old children (N = 64) and adults (N = 14) saw contrasting pairs of models differing
either in physical strength or in accuracy (in labeling known objects). Participants then per-
formed different tasks (cooperative problem solving and word learning) requiring the choice
of a partner or informant. Both children and adults chose their cooperative partners selec-
tively. Moreover they showed the same pattern of selective model choice, regarding a wide
range of model characteristics as important for cooperation (preferring both the strong and
the accurate model for a strength-requiring cooperation tasks), but only prior knowledge as
important for word learning (preferring the knowledgeable but not the strong model for word
learning tasks). Young children’s selective model choice thus reveals an early rational com-
petence: They infer characteristics from past behavior and flexibly consider what character-
istics are relevant for certain tasks.
Introduction
Cooperation is an essential social-cognitive skill that constitutes human society, is uniquely
human on its sophisticated levels and emerges in early childhood [1,2]. Young children already
engage in cooperative activities with adults and peers [3–5] and understand essential aspects of
joint collaboration: By 2 years, children engage in collaborative activities regardless of whether
or not a partner is needed to achieve a physical goal and are sensitive to whether or not a part-
ner intends to cooperate [6]. And from 3 years, children regard joint commitments of collabo-
rative engagements as binding [7] and coordinate two complementary roles in cooperative
PLOS ONE | DOI:10.1371/journal.pone.0160881 August 9, 2016 1/13
a11111
OPEN ACCESS
Citation: Hermes J, Behne T, Studte K, Zeyen A-M,
Gräfenhain M, Rakoczy H (2016) Selective
Cooperation in Early Childhood –How to Choose
Models and Partners. PLoS ONE 11(8): e0160881.
doi:10.1371/journal.pone.0160881
Editor: Rachel L Kendal, Centre for Coevolution of
Biology & Culture, University of Durham, UNITED
KINGDOM
Received: February 29, 2016
Accepted: June 21, 2016
Published: August 9, 2016
Copyright: © 2016 Hermes et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: This work was supported by the German
Science Foundation (Deutsche
Forschungsgemeinschaft, DFG), grant Ra-2155/1-1
(grant received by HR, TB, MG). Additionally the
authors acknowledge support by the Open Access
Publication Funds of the University of Göttingen. Both
funders had no role in study design, data collection
and analysis, decision to publish, or preparation of
the manuscript.
problem-solving [8]. However, successful cooperation not only depends on children fulfilling
the commitments they entered into with their partners, but also on the appropriate choice of
individuals to cooperate with. Although little is known about how children choose cooperative
partners, indirect evidence from previous research suggests that children are sensitive to a
cooperative partner’s intentions, as they are more reluctant to re-initiate a cooperative activity
with a previously unwilling partner than with a previously unable partner [6] and engage in
direct and indirect reciprocity by sharing selectively with those who had shared themselves [9].
And chimpanzees, too, choose cooperative partners that have proven competent in the past
[10]. This raises the question of how children (or apes) make such choices. Do they evaluate
relevant characteristics of potential partners and selectively choose who to collaborate with on
that basis?
What we do know, however, is that children are quite selective when it comes to the ques-
tion whom to learn from. Extensive recent work on children’s selective social learning has
shown that preschoolers do not just blindly pick up information from anyone indiscriminately,
but selectively request and endorse information from partners with certain characteristics (see
[11–14] for reviews). When learning the labels of novel objects, for example, children from age
3–4 prefer to learn from knowledgeable over ignorant, confident over unconfident, previously
reliable over unreliable and adult over peer models [15–17].
But it remains unclear on what social cognitive underpinnings this selectivity rests. Is it a
rational process, similar as it would be required for the reasonable choice of partners for a
cooperative activity? Do children systematically generalize from perceived model characteris-
tics (e.g. previous linguistic accuracy) to the expected usefulness of the model for specific future
problems (e.g. finding out names of novel objects)–much like adults would often reason (“She
was consistently accurate, so she seems reliable, so I should trust her when needing novel infor-
mation”)? Or is it a more heuristic and less systematic process, perhaps having to do with more
global impression formation in the style of halo-effects? Rather than perceiving some model as
reliable, or competent in some specific way, children might form very global impressions of
someone as simply positive across the board, leading to some very unspecific preference for
that person regardless of the problem at hand. So someone previously shown to be nice, say, or
a good singer, might be perceived as globally positive and therefore preferred for any task. A
third possibility, that young children simply extrapolate future behavior based on the past
track record of that specific behavior seems implausible in the light of many studies that have
found some transfer from one type of behavior shown by a model to predictions about or eval-
uations of another kind of behavior by that model [18–21].
The question of whether selective learning—as documented abundantly in 4-year-olds—is
based on rational inductive inferences or rather on global, heuristic impression formation is
still unresolved. But divergent findings suggest that preschoolers use both strategies in certain
situations: On the one hand there are results that seem to support global, halo-style impression
formation. For example, in some studies children expected models that previously were more
accurate to be nicer in future too [18], and previously stronger models to be more accurate
[22]. On the other hand, however, several studies have documented that children generalize
competences in a rational way. When, for example, confronted with a strong and a knowledge-
able model, preschoolers rationally choose between the two for knowledge-relevant or
strength-relevant problems [23]. Similarly, they differentiate between domains of knowledge:
when confronted with experts from different domains (e.g. toy labeler vs. toy fixer or doctor vs.
car mechanic), they direct questions reasonably to the according expert [24,25]. Preschoolers
have even shown to be flexible and context-sensitive in their model recruitments: while 4-year-
olds usually prefer adults over peers as a source for learning new words, such preferences can
be reversed when an adult model has previously proved unreliable [17]. Moreover, children
Selective Cooperation in Early Childhood
PLOS ONE | DOI:10.1371/journal.pone.0160881 August 9, 2016 2/13
Competing Interests: The authors have declared
that no competing interests exist.
trust adults over children for food questions (where adults usually know more) but trust chil-
dren over adults for toy questions (where children usually know more; see [26]).
In the present study, we intend to explore the cognitive underpinning of children’s selective
recruitment of social partners for cooperative activities using the paradigms established to
examine children’s epistemic trust.
The results from studies on epistemic trust indicate that children—at least under certain cir-
cumstances—choose models rationally. But obviously in this research, very clearly circum-
scribed tasks (such as learning words for novel objects) were used, that were quite clearly
connected to certain characteristics (accuracy, knowledge). The requirements for a cooperative
partner are however less clear cut. What would characterize a rational choice of a cooperation
partner? Our intuition is that for successful cooperation a much broader range of model char-
acteristics are diagnostic than for simple, circumscribed tasks, such as word learning. Thus for
a novel word learning task, for example, a model’s previous accuracy in object labelling is
clearly diagnostic and relevant whereas other characteristics such as a model’s relative strength
or weakness is not. However, in the case of real life interactions, co-operations in particular,
things are much more complex. Say you are moving house and have to move a heavy wardrobe
from one place to the next. Obviously, you would preferentially recruit a strong partner over a
weak one, but a much broader range of factors might be important, such as affiliation or a
potential partner’s knowledge or reliability, and perhaps many more. In contrast to the word
learning task, it is not simply a question of requesting or endorsing a piece of information, but
of interacting and coordinating with another person. Thus when recruiting partners and
choosing models based on their past track record, what kind of inferences and generalizations
are justified depends on the scope of model characteristics and on the scope of requirements of
the tasks involved.
Against this background, in the present study we tested whether the generalizations children
draw from a model characteristic vary as a function of different tasks. We expected that chil-
dren regard a broad range of characteristics as predictive for the choice of a cooperative part-
ner, whereas for the choice of an informant to learn labels for novel objects from only a narrow
range of characteristics, clearly connected to the problem (such as knowledgeability), should be
regarded as diagnostic.
To test this in the current study we employed a design similar to Fusaro et al. [22] in manipu-
lating the two characteristics labeling accuracy and strength. To explore the different scopes of
inferences that children draw from characteristics such as strength and word knowledge, Fusaro
et al. [22] confronted children with a good and a bad lifter (strength condition) or a good and a
bad labeler (accuracy condition) and later children chose between those models in a labeling
and a strength task and answered several trait and behavioral prediction questions. In the cur-
rent study we used a similar design to explore children’s assessment of potential cooperative
partners. Our focus here is on whether a broader range of characteristics is regarded as predic-
tive for cooperative tasks as compared to clearly circumscribed solitary tasks. In the current
study we therefore adopted the general design of Fusaro et al. [22], but instead of their pure
strength task, we developed cooperation tasks in which physically taxing activities needed to be
done together. For the more clearly circumscribed solitary task we used the established word
learning paradigm that has commonly been used in selective trust studies. Labeling accuracy
and physical strength were chosen as model characteristics because these do not obviously over-
lap and can be demonstrated in a way easily comprehensible for young children [22,23].
In the familiarization phase, participants thus saw contrasting pairs of models that differed
either in their physical strength (strong/weak) or in their labeling accuracy (accurate/inaccu-
rate). In the test phase children were then confronted with two types of problems: In word
learning tasks, participants were shown novel, unknown objects and chose from which model
Selective Cooperation in Early Childhood
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to endorse information about them. The word learning tasks were thus clearly connected to
labeling accuracy, but not to strength. In cooperation tasks, participants were confronted with a
problem that could only be solved by two people and that required both physical force and
skillfulness. The cooperation tasks were thus clearly connected to physical strength but not
directly to labeling accuracy. If participants regard a broad range of characteristics as relevant
for a cooperative partner and, in contrast, regard only clearly connected and circumscribed
characteristics as diagnostic for successful word learning, they would prefer both the strong
(over the weak) and the accurate (over the inaccurate) model for a cooperative task. In contrast,
for the word learning task, they would prefer the accurate over the inaccurate model but should
not systematically prefer the strong or the weak model.
First, in a pilot study we tested this intuition of rational selective choice of informants and
cooperative partners in adults and thereafter conducted an age-appropriate version for 3- and
4-year-old children. These age groups were specifically chosen because selective learning and
trust have often been found to emerge between the ages of 3 and 4 (e.g. [16,21]).
Ethics Statement
Both the pilot study and the main study were conducted in accordance with the Declaration of
Helsinki and the Ethical Principles of the German Psychological Society (DGPs), the Associa-
tion of German Professional Psychologists (BDP), and the American Psychological Association
(APA). They involved no invasive or otherwise ethically problematic techniques and no decep-
tion (and therefore, according to national jurisdiction, did not require a separate vote by a local
Institutional Review Board; see the regulations on freedom of research in the German Consti-
tution (§ 5 (3)), and the German University Law (§ 22)).
Pilot Study (Adults)
Participants
Fourteen adults (M= 22 years, age range: 19–29 years, 12 female) participated. They were
mostly undergraduate psychology students and were recruited through public announcements.
Design and procedure
After receiving information about the procedure and the main aim of the study (i.e.to compare
adults’and children’s responses) participants gave oral consent and were then tested individu-
ally in a quiet room. The adults were shown the material designed for the child study in an
adapted computerized version using pictures and short videos. The sessions lasted approxi-
mately 15 min and consisted of a familiarization phase showing the contrast between the two
puppets and two test blocks, one with cooperation tasks and one with word learning tasks
(with order of blocks systematically varied across participants). Participants wrote down their
answers to test questions on a pre-defined answer sheet.
The study followed a 2x2 design. The domain in which models were familiarized (strength
or accuracy) was varied between subjects whereas the type of test items (word learning and
cooperation) was varied within subject.
Familiarization phase. Participants were randomly assigned to one of two familiarization
conditions, the accuracy condition and the strength condition. In the accuracy condition partici-
pants saw four slides, in each of which two puppet models named a familiar object (e.g. a ball,
see S1 Table). One model consistently demonstrated knowledge by naming the objects accu-
rately in speech bubbles whereas the other model consistently demonstrated ignorance by
naming the objects incorrectly. In the strength condition, participants saw four slides in each of
Selective Cooperation in Early Childhood
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which two puppet models were confronted with a task requiring physical strength (see S2
Table). One puppet demonstrated strength—as indicated by the sentence “Max has no problem
in lifting this ...”typed beside him. The other puppet demonstrated weakness as indicated by
the sentence “Toni does not succeed in lifting this ...”typed beside him. After the familiariza-
tion phase two comprehension questions were asked. In the accuracy condition we asked who
said more/fewer names correctly while in the strength condition, we asked who has more/less
strength.
Test Blocks. In the word-learning test block (four trials) the participant saw a slide with a
picture of an unknown object (see S1 Fig) and was asked if she knew the object. Subsequently
both puppets labelled the objects with different novel labels using speech-bubbles and the par-
ticipant was asked to choose between the two labels.
In the cooperative test block (four trials) the participant saw a short video clip in which a
single experimenter introduced and explained the tasks each involving an unknown apparatus
(see S3 Table for pictures and details about the information provided). Each apparatus con-
tained hidden toy animals and two persons were required to cooperate in order to retrieve
them, with one of the roles requiring some physical force. For example, one apparatus was a
wooden box with a cord on the cover plate. The toy animals in the box could be retrieved if one
person pulled on the cord (requiring some force), while the other person took out the animals.
The participant was asked to choose a puppet to cooperate with. As these materials were
designed primarily for child participants in the main study, the adults were explicitly instructed
to imagine themselves in the physical (but not cognitive!) position of a small child when think-
ing about the cooperation problems.
Results and Discussion
The proportions of trials in which adults selected the strong/accurate puppet are illustrated in
Fig 1. A mixed ANOVA with type of task as within-subject factor and familiarization condition
as between-subject factor on the choice of the puppet with the positive characteristic resulted
in an interaction between type of task and familiarization condition (F(1,12) = 6.04, p<.05,
partial η
2
= .36) and no main effects. Comparisons of the adults’choice of the puppet with the
positive characteristic to chance level revealed that in the word learning tasks they preferred
the accurate puppet’s label in every single case, but they did not prefer the strong puppet’s
labels above chance (t(6) = 1.16, p= .29). In contrast, for the cooperation tasks they preferred
both the strong puppet (t(6) = 9.3, p<.01, d= 3.5) and the accurate puppet (t(6) = 2,5,
p<.05, d= .95) above chance.
Thus, adult participants regarded a broader range of characteristics as relevant for the
choice of a cooperative partner, but only clearly circumscribed characteristics as important for
word learning. The main study will tell whether 3- and 4-year-olds already show the same pat-
tern of rational selective inferences as adults do.
Main Study (Children)
Participants
Thirty-two 3-year-old children (M= 44 months, range: 39–47 months, 15 girls) and thirty-two
4-year-old children (M= 51 months, range: 48–55 months, 16 girls) were included in the final
sample. All children were native German speakers and they were recruited from a database of
parents who had volunteered to participate in studies on child development and came from
mixed socio-economic backgrounds. Parents gave their written consent for the participation of
their children. Fourteen additional children were excluded from analyses due to experimenter
Selective Cooperation in Early Childhood
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error (n= 4), failure to answer the comprehension questions after two repetitions (n=5)or
uncooperativeness/extreme shyness (n= 5).
Design and Procedure
Children were tested individually in a quiet room, either in their daycare center or in the Uni-
versity child lab. In the lab, children were tested without the accompanying parent being pres-
ent in the room during the test session. Each session was videotaped. For all children, the
session consisted of i) a warm-up ii) a familiarization phase showing the contrast between the
two models, and iii) two test blocks: one with cooperative tasks and one with word-learning
tasks.
The study followed a 2x2 design. The domain in which models were familiarized (strength
or accuracy) was varied between subjects whereas the type of test items (word learning and
cooperation) was varied within subject.
Fig 1. Adults’selection of the puppet with the positive characteristic. Adults’selection of the puppet with
the positive characteristic as a function of task and familiarization condition. Significantly above-chance
choice of the model with the positive characteristic (accurate/strong) is marked by asterisks (*p<.05 and **p
<.01, one-sample t-tests). +: no parametrical test was applicable due to a lack of variance. Error bars show
standard errors.
doi:10.1371/journal.pone.0160881.g001
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Warm-up. All testing was done by two experimenters, one who played the two puppets
that served as models and one who interacted with the child. Both experimenters played with
the child until she felt comfortable and then the two puppets were introduced. We decided to
use puppet models (as is typically done in research on selective trust) in order to assure a stan-
dardized procedure by restricting differences between the models to the manipulated aspect.
Familiarization phase. Children were randomly assigned to one of the two familiarization
conditions: The accuracy condition and the strength condition. In each condition children saw
two models. In the manipulation of accuracy we followed a standard procedure commonly
used in selective trust studies and we adopted this procedure for the manipulation of strength,
using similar methods as in Fusaro et al. [22]. In the accuracy condition, children saw the two
puppets label the same four familiar objects as in the pilot study (see S1 Table). For each one,
the puppets were asked in turn what the object (e.g., a ball) was called. One puppet demon-
strated knowledge by consistently naming the objects accurately (e.g. “This is a ball”). The
other puppet demonstrated ignorance by consistently naming the same objects inaccurately
(e.g. “This is a shoe”).
In the strength condition the puppets were confronted with the same four tasks requiring
physical strength as in the pilot study (see S2 Table). For example, a heavy suitcase was shown
and the puppets were each asked “Can you lift this suitcase?”One puppet consistently demon-
strated strength by succeeding in the tasks and saying “That’s easy, I’m good at that”, whereas
the other puppet demonstrated weakness by never succeeding and always saying “Ups, that’s
tough. I’m not good at that.”The assignment of puppets to positive and negative characteristics
was counterbalanced across subjects, and the order in which puppet acted/labeled was counter-
balanced across trials for each subject.
Comprehension questions. The same two comprehension questions as in the pilot study
were asked to assess whether the child understood the performance shown by the puppets. If at
least one comprehension question was answered incorrectly, the familiarization phase was
extended by repeating one or at most two familiarization trials followed by the same compre-
hension questions. If these were still not both answered correctly after the repetitions, the child
was excluded from analyses. Twelve children needed additional familiarization trials before
they provided correct judgments.
Test Blocks. Then all children participated in two test blocks, one with word-learning and
the other with cooperative tasks. The order of the task blocks was counterbalanced (across chil-
dren and conditions), as was the order of tasks within each block. Before the second test block,
there was a short reminder phase consisting of two further familiarization trials. The reminder
trials (for objects see S1 and S2 Tables) followed the same format as in the initial familiarization
and were followed by the same comprehension questions. In the reminder phase six children
needed one or two additional familiarization trials, before passing the comprehension check.
In total, 16 children needed one or more repetitions in the initial familiarization and/or in the
reminder familiarization phase. When these 16 children were excluded from analyses, the pat-
tern of results remained the same.
In the word-learning test block (four trials) the child was presented a picture of an unknown
object (see S1 Fig) and asked whether she knew what the object was called. If a child felt she
was required to answer and guessed a label for the object, this label was doubted by the experi-
menter saying “I don’t think that’sa(...)”. After the child was asked which puppet she would
like to ask for an object label, both puppets provided different novel labels for the object (in
counterbalanced order) and the experimenter repeated the labels provided by the puppets. As
the crucial test question, the child was then asked to choose between the two labels (e.g.
“[Name of puppet A] said that’s a Dreto. [Name of puppet B] said that’s a Taki. What do you
think this is, a Dreto or a Taki?”). Over the 4 trials, the proportion of trials in which children
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endorsed the label of the puppet with the positive characteristic (accurate/strong) was com-
puted as the basis for subsequent statistical analyses.
In the cooperative test block (four trials) the experimenter introduced the same unknown
apparatuses as in the pilot study to the child (see S3 Table). On each trial, the experimenter
explained the apparatuses and then asked the child with which puppet she would like to coop-
erate on the apparatus. Over the 4 trials, the proportion of trials in which children chose the
puppet with the positive characteristic (accurate/strong) was computed as the basis for subse-
quent statistical analyses.
Coding procedure and reliability
All test sessions were coded from videotape by one rater with respect to three types of
measures:
•Comprehension questions: Identification of the puppet with the positive and negative char-
acteristic by pointing to and/or naming the puppet (possible scores: 0–2).
•Cooperation task: Number of trials in which the child choses the puppet with the positive
characteristic as a partner by pointing to or saying the puppet’s name (possible scores: 0–4).
•Word learning task: Number of trials in which the child uses the label provided by the puppet
with the positive characteristic (possible scores: 0–4).
A second rater blind to the hypotheses of the study coded the videos of 12 randomly chosen
children. Inter-rater reliability was perfect for the comprehension questions (κ= 1.0) and very
good concerning children’s scores on the cooperation tasks (κ= .88) and on the word learning
tasks (κ= .77).
The datasets can be found in S1 Dataset (pilot study) and S2 Dataset (main study).
Results
Children’s choice patterns of the strong/weak or accurate/inaccurate puppets are depicted in
Fig 2. A mixed ANOVA with type of task as within-subject factor and familiarization condition
and age groups as between-subject factors on the choice of the puppet with the positive charac-
teristic yielded a significant interaction between type of task and familiarization condition (F-
(1,60) = 4.29, p<.05, partial η
2
= .07). No other interactions or main effects emerged.
Exploring children’s answer patterns more closely (see Fig 2), the same pattern of rational
selective inferences as in adults was revealed: Comparisons of children’s choice of the puppet
with the positive characteristic against chance level showed that in the word learning tasks they
preferred the accurate puppet’s labels (t(31) = 4.12, p<.01, d= .73), but not the strong pup-
pet’s labels (t(31) = 0.2, p= .84) above chance, whereas for the cooperation tasks they preferred
both the strong puppet (t(31) = 3.16, p<.01, d= .56) and the accurate puppet (t(31) = 2.64,
p<.05, d= .47) above chance.
Discussion
Preschoolers in this study selectively recruited models as cooperative partners and as infor-
mants in a systematical and rational way, and in basically the same way as the adults did: they
regarded multiple characteristics (strength and knowledge) as diagnostic for a good co-opera-
tive partner whereas they regarded only knowledge as diagnostic for a good informant about
novel object labels. These findings show that preschoolers’perception of others does not simply
rest upon global evaluation but that children this age infer characteristics in a rational way, and
flexibly adjust their criteria for selective recruitment of partners to the requirements of the
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situation. Children’s pattern of choices suggests that they considered cooperation (in contrast
to word learning) as a broader task, requiring more than just the direct physical characteristics
(such as strength) needed.
This flexible pattern of model choice, preferring models with certain characteristics for
some but not all tasks, is in line with previous research on selective trust where, for example,
children reversed their general preference to trust adults over peers when adults had proven
unreliable [17] or when children usually know more about the domain in question (i.e. toys,
see [26]). This study, together with other findings on selective trust (e.g. [23,24,27]), provides
converging evidence for the theoretical claim that children’s model choices are based on ratio-
nal inferences [28].
In the present study children were confronted with a circumscribed task for the domain of
knowledge (word learning task) and with a broader cooperation task for the domain of
Fig 2. Children’s selection of the more puppet with the positive characteristic. Children’s selection of
the puppet with the positive characteristic as a function of task and familiarization condition. Significantly
above-chance choice of the model with the positive characteristic (accurate/strong) is marked by asterisks
(*p<.05 and **p<.01, one-sample t-tests). Error bars show standard errors.
doi:10.1371/journal.pone.0160881.g002
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strength. Since the types of problems were not counterbalanced between domains—no simple,
circumscribed stength tasks and no cooperation tasks for which labeling was relevant were
administered—the present data cannot strictly rule out an alternative interpretation of the
results. In our initial interpretation we distinguished between problems that require differen-
tially broad scopes of characteristics. An alternative—potentially complementary—interpreta-
tion of the present results, however, distinguishes between characteristics, rather than
problems, of different scope: some characteristics (e.g. knowledge) might be predictive for a
wider range of problems (e.g. word learning and cooperation) whereas other characteristics
(e.g. physical strength) are predictive for only a limited set of problems directly linked to the
characteristic (e.g. physically taxing cooperative activities). This, however, marks a rather rich
interpretation in that it presupposes that children understand that characteristics can differ in
breadth and hence in inferential scope. Furthermore, recent results suggest that children gener-
ally draw similarly wide generalizations from strength and knowledge [23].
How can the present results be reconciled with seemingly diverging evidence, in particular
in a quite similar design by Fusaro et al. [22]? In that study children were confronted with a
good and a bad lifter (strength condition) or a good and a bad labeler (accuracy condition) and
later children chose between those models in a labeling and a strength task and answered sev-
eral trait and behavioral prediction questions. In Fusaro et al. [22], children generalized
strength widely, choosing the strong over the weak model in nearly all tasks, but generalized
narrowly from accuracy (only to labeling-relevant behavior and smartness). The different pat-
tern of model choices in the strength-related tasks of the current study was as predicted and
reflects the essential difference between these task and the one by Fusaro et al. [22]: Whereas in
Fusaro et al. [22] the strength task was exclusively connected to strength (i.e., lifting objects),
the cooperation tasks in the present studies were broader in their requirements, extending
beyond physical strength. The discrepancy in findings concerning the knowledge-related tasks
plausibly came about due to a crucial difference in the familiarization phase between both stud-
ies. In the present study, the strong vs. weak models were introduced as a minimal contrast
pair such that they only differed in the crucial respect whether or not they were able to lift
objects. In Fusaro et al. [22], in contrast, the two models differed not only in their ability to lift,
but also in the accuracy of their announcements: both uttered “I will lift this”before success-
fully/unsuccessfully trying to lift. The weak model was thus not only weak but also inaccurate
(in estimating her own capacities). This, in turn, would make broader inferences concerning
the contrast between the two models perfectly rational. In our study with the minimal contrast,
however, such broad inferences are in no way licensed.
One potential concern regarding the familiarization in the present study is that the manipu-
lations of strength and knowledge were not clearly symmetrical. The inaccurate model’s wrong
labels might have been perceived as bizarre and less excusable than the weak model’s failure in
e.g. lifting a suitcase, and this might have led to an avoidance of the inaccurate model across
the board. However, since in Fusaro et al. [22] the familiarization was similar to the present
study and children did not avoid the inaccurate model for strength tasks, it is most likely that
children’s preference for the accurate model in cooperation tasks in the present study indicates
that they regard a broader range of characteristics as relevant for cooperation as compared to
lifting.
One assumption, that both interpretations described above (the assessment of the differen-
tial scope of tasks and the assessment of the differential scope of characteristics) make, is that
in ascribing characteristics, children engage in two inferences. First, an inference from some
observed behavior (e.g. labeling/lifting something) to ascribing traits (”smart”/“strong”) to the
agent, and a second inference from the traits to predicting future behavior, such as perfor-
mance in a given task. In the light of established research on the development of trait
Selective Cooperation in Early Childhood
PLOS ONE | DOI:10.1371/journal.pone.0160881 August 9, 2016 10 / 13
understanding, our results (along with recent results on selective trust, see [23]) reveal surpris-
ingly early trait reasoning capacities in children—given that in prior research on trait reasoning
children showed rational behavior-to-behavior inferences only at a much later age [29,30]
whereas preschoolers showed indications of trait understanding only if the inferential chain
was split (e.g. only trait-behavior inferences, see [31]) or if indirect measures, such as their rea-
soning about mental states, were used [32]. We do not know yet what accounts for the differ-
ence between children’s reasoning about abilities in selective trust and about personality traits.
One potential difference between these inferences is that personality traits are more abstract
than the traits relevant in selective trust research. Children’s reasoning about traits with low
degrees of abstraction in selective trust scenarios might present a Zone of Proximal Develop-
ment for trait understanding, with later development towards successful reasoning about more
abstract traits.
Supporting Information
S1 Dataset. SPSS data file of the pilot study (adults).
(SAV)
S2 Dataset. SPSS data file of the main study (children).
(SAV)
S1 Fig. Novel objects used in the word learning test block.
(PDF)
S1 Table. Objects and incorrect object labels used in the accuracy familiarization condition.
(PDF)
S2 Table. Objects used in the strength familiarization condition and associated actions.
(PDF)
S3 Table. Apparatuses used in the cooperative test block and associated actions.
(PDF)
Acknowledgments
Thank you very much to Marlen Kaufmann and Konstanze Schirmer for help with recruiting
children and organizing the study. We also like to thank all children who participated as well as
their parents and preschool teachers.
Author Contributions
Conceived and designed the experiments: JH TB KS AZ MG HR.
Performed the experiments: JH KS AZ.
Analyzed the data: JH TB KS AZ MG HR.
Contributed reagents/materials/analysis tools: JH TB KS AZ MG HR.
Wrote the paper: JH TB KS AZ MG HR.
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