In two experiments, a manual search task explored 12- to 14-month-old infants' representations of small sets of objects. In this paradigm, patterns of searching revealed the number of objects infants represented as hidden in an opaque box. In Experiment 1, we obtained the set-size signature of object-file representations: infants succeeded at representing precisely 1, precisely 2, and precisely 3 objects in the box, but failed at representing 4 (or even that 4 is greater than 2). In Experiment 2, we showed that infants' expectations about the contents of the box were based on number of individual objects, and not on a continuous property such as total object volume. These findings support the hypothesis that infants maintained representations of individuals, that object-files were the underlying means of representing these individuals, and that object-file models can be compared via one-to-one correspondence to establish numerical equivalence.

Young infants construct models of the world composed of objects tracked through time and occlusion. To date little is known about the degree to which these models are sensitive to the material makeup of the represented individuals. Two experiments probed 8-month-olds' ability to represent different kinds of entities: rigid, cohesive objects, flexible, cohesive objects, and non-rigid, non-cohesive portions of sand. In Experiment 1, infants represented an array of two rigid, cohesive objects hidden behind a single screen, but failed to represent hidden arrays of two flexible objects or two portions of sand. In Experiment 2, entities were hidden behind two screens instead of one, thereby reducing the information processing demands of the task. In that case, infants succeeded in representing arrays of both types of object stimuli, but again failed to represent the portions of sand. It is argued that (1) the processes by which infants individuate and track entities are sensitive to material kind, (2) rigid cohesive objects occupy a privileged status in this system, and (3) early knowledge about objects and substances has a quantificational aspect. q 2002 Published by Elsevier Science B.V.

We present data from a preferential looking method to investigate when infants have mapped singular and plural markers in English onto the semantic distinction between singleton sets and sets with more than 1 individual. Twenty- to 36-month-old children heard sentences that marked number in 1 of 2 ways: (a) redundantly with verb morphology, lexical quantifiers, and noun morphology (“Look, there ARE SOME blicketS”/“Look, there IS A blicket”) or (b) only with noun morphology (“Look at the blicketS”/“Look at the blicket”). Twenty-four-month-old infants, but not 20-month-old infants, looked at the screen that matched the carrier sentence with respect to singular–plural distinction when number was expressed on the verb, on the noun, and with quantifiers. Detailed looking-time analyses suggest that the arrays begin to be differentiated on the child’s hearing are or is. Twenty-four-month-olds failed when number was marked on the noun alone, whereas 36-month-olds suc-Correspondence should be addressed to Sid Kouider, Laboratoire de Sciences Cognitives et

This study investigates children's ability to use language to guide their choice of individuation criterion in the domains of objects and events. Previous work (Shipley, E. F., & Shepperson, B. (1990). Countable entities: developmental changes. Cognition, 34, 109 -- 136.) has shown that children have a strong bias to use a spatio-temporal individuation strategy when counting objects and that children will ignore a conflicting linguistic description in favor of this spatio-temporal bias. Experiment 1 asked children (3-, 4-, and 5-year-olds) and adults to count objects and events under different linguistic descriptions. In the object task, subjects counted pictures of familiar objects split into multiple pieces (as in Shipley, E. F., & Shepperson, B. (1990). Countable entities: developmental changes. Cognition, 34, 109 -- 136.) and described either using an appropriate kind label (e.g. "car") or the general term "thing". In the event task, subjects watched short animated movies consisting of a goal-oriented event achieved via multiple, temporally separated steps. The events were described either with an appropriate telic predicate targeting the goal (e.g. "paint a flower") or with an atelic predicate targeting the steps in the process (e.g. "paint") and the subjects' task was to count the events. Relative to adults, children preferred a spatio-temporal counting strategy in both tasks; there was no difference among the three groups of children. However, children were able to significantly change their counting strategy to follow the linguistic description in the event but not the object task. Experiment 2 extended the object task to include counting of other types of non-spatio-temporal units such as sub-parts of objects and collections. Results showed that children could ...

Four experiments investigated whether 12-month-old infants use perceptual property information in a complex object individuation task, using the violation-of-expectancy looking time method (Xu, 2002; Xu & Carey, 1996). Infants were shown two objects with di#erent properties emerge and return behind an occluder, one at a time. The occluder was then removed, revealing either two objects (expected outcome, if property di#erences support individuation) or one object (unexpected outcome). In Experiments 1--3, infants failed to use color, size, or a combination of color, size, and pattern di#erences to establish a representation of two distinct objects behind an occluder. In Experiment 4, infants succeeded in using cross-basic-level-kind shape di#erences to establish a representation of two objects but failed to do so using withinbasic -level-kind shape di#erences. Control conditions found that the methods were sensitive. Infants succeeded when provided unambiguous spatiotemporal information for two objects, and they encoded the property di#erences during these experiments. These findings suggest that by 12 months, di#erent properties play di#erent roles in a complex object individuation task. Certain salient shape di#erences enter into the computation of numerical distinctness of objects before other property di#erences such as color or size. Since shape di#erences are often correlated with object kind di#erences, these results converge with others in the literature that suggest that by the end of the first year of life, infants# representational systems begin to distinguish kinds and properties.

Thepr2/#5 ofcompar2(5U cognition benefitsfre commonmeasur# acrur species. We re2O4 her on five experFO2(5 using the violation of expectancy looking timemeasur with frh2O4P5--2( rh2O macaques (Macaca mulatta), each designed to build oncurO4/ knowledge concerge2 spontaneousrontaneous24OF ofnumber Each subject, tested in only oneexperP mental condition, watched as eggplantswer placed behind ascrFP one at a time,after which thescrU/ wasr2444/ r2444/52 an outcome thateither matchedor did not match the number placed therd Subjects lookedlonger at impossible than possible outcomes in 1 3, 1 small + 1 small bigor 2small, 2 1 3, and 2 1 or 4 conditions. They failed in 2 or 3or 5 and in 1 3 conditions. Thispatter ofr2#/---- closely matches thatobser## acrr sever# prer## studies of human infants. The data allow us to test amongfour di#er4F prer4F# concer#52 thefor5U and content of the mentalrnt rntal2#F----/ under#F---- looking in these exper454O2( Object filer2#+U#U2(4OUU-- ar favor over (i) low-levelpervel245 rrvel245##U2(4 (ii)r)25O5P+2(4#P-- of continuousvartinuo such as volumeor sure2F are and (iii) analog magnitudernitude25PF+P2 ofnumber We conclude by consider4# exactly how the objecttrect25 systemrstem25 in these andother rherF exper2O4P # does and does notrt24UU++ number and how it might be oneevolutionar prolut sor of the human specific system ofnumber rberU2(F4/P2r # 2003 Published byElsevier Science (USA).

A manual search paradigm explored the development of English singular–plural comprehension. After being shown a box into which they could reach but not see, infants heard verbal descriptions about the contents of the box (e.g., “There are some cars in the box ” vs. “There is a car in the box) ” and were then allowed to reach into the box. At 24 months of age, but not at 20 months, infants ’ search patterns were influenced by verbal number markings. However, verbal number marking did not influence search behavior when plurality was signaled by noun morphology alone. These data converge with parental reports and preferential looking studies concerning the developmental course of mastery of English plural marking and show that infants can create a mental model of the number of objects on the basis of singular–plural morphology alone.

Using the violation-of-expectancy method, we investigated 10-month-old infants’ ability to rely on dynamic features in object individuation processes. Infants were first familiarized to events in which two different objects repeatedly appeared and disappeared, one at a time from behind a screen; at test, the screen was removed, revealing either one or two objects. In Experiment 1, one self-moving non-rigid agent and one inert object were involved in each trial, while in Experiment 2 two different agents were presented. Infants preferred to look at one-object outcomes in Experiment 1, but they did not show any preference for one- or two-object outcomes in Experiment 2. The results suggest that infants can use dynamic information to detect agents in complex individuation tasks before they can rely on shape or surface features. We propose that the sortals AGENT and INERT OBJECT appear in development before 12 months without a substantial contribution of linguistic experience. These findings may motivate a revision of current theories on the development of kind-based individuation and object files.

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