THE ACQUISITION OF COORDINATION AND RECURSION OF PPS : HOW TO FARE THE DEVELOPMENT OF THESE COMPUTATIONS ?

Recursion, a computation that is implemented by tucking a constituent into another, is widely or if it is an integral part of general cognitive resources and is called into action as an external factor. Naturally, an important element in this discussion is the knowledge of when recursion is acquired. This study wants to contribute to this wide investigation by focusing on the acquisition of one recursive instance – that of Prepositional Phrases (PPs) in Brazilian Portuguese. The results point to the age bracket of 4 years of age as the one in which recursion starts being meaningfully processed.


Introduction
A standard observation in linguistics is that an expression of a given syntactic, semantic or phonological category may become part of another expression if both hold the same category.This computation, named recursion, that is implemented by tucking a constituent into another, is widely recognized as a fundamental cognitive capacity.An interesting that is, if it lies in the underpinnings of language capacity (CHOMSKY, 2005;FITCH;HAUSER;CHOMSKY, 2005;HAUSER;CHOMSKY;FITCH, 2002) or if is an integral part of general cognitive resources and is called into action as an external factor (ARSENIJEVIC, HINZEN, explain the fact that recursion is supposed to be a major language principle found in all languages (cf.localized dispute in EVERETT, 2005EVERETT, , 2007;;NEVINS, PESETSKY, RODRIGUES, 2009), the second option makes it easier to understand the multiple characteristics that involve the implementation of recursion in different aspects and phrases of different languages.acquisition of recursion.How and when exactly do children start processing recursion?On one hand it does not seem to be present in children's earliest utterances (ROEPER; SNYDER, 2004SNYDER, , 2005;;ROEPER, 2011).Contrastingly, coordination appears as an earlier acquisition in language comprehension and production (PÉREZ-LEROUX et al., 2012).
The fact that coordination appears earlier is rather intuitive and can be explained by the simple fact that coordination is a straight-forward way to bypass computation by accounting for items that are sent to storage (for instance, short-term memory) the way they appeared, without any correlation or hierarchy between them.This simplicity is likely to be successeful for at least a few items.Nevertheless, when there is a number of items that starts challenging memory capacity, a safer cognitive decision is to resort to structure, which exponentially increases memory and processing capacities (MILLER, 1956).
If items are organized hierarchically, then embedding computation, that is recursion, is a processing resource that once deployed might bring a reduction to the cost of combinatory computation.It might be costly to start the recursive structure, for instance: There is a banana in the box on the tray.But after the computation is established, it might be easier to embed other PPs, for instance: on the chair, over the carpet (MAIA et al., 2013).
Clearly the evaluation of most economical choices can be readily attested in adult language, but how do children acquiring language implement these choices?
In order to verify children's processing of recursion, this study will focus on a highly recursive structure: prepositional phrases (PP) in Brazilian Portuguese.The aim here is to contrast PP recursion to PP coordination in acquisition.To do this, this research will try to assess children at the earliest moment that recursion of PPs becomes an available property of their grammar, so that coordination can be compared at this very point.
Since MAIA et al. (2013) attested a scale advantage in embedding multiple layers of PPs5 , this study also controlled for this possibility in children.That is, since the number of layers was a controlled factor it will be possible to verify if multiple embedding once deployed has processing advantages over coordination of several items, because it supposedly generates no extra computational cost, while coordination still requires reiteration and memory.

The test
An oral sentence picture matching test was produced to be applied to sixteen 3 y-o and sixteen 4 y-o children, following a between-subject distribution.Children heard a sentence and had to match it with one of two pictures: one depicted a situation of a coordinated list and the other depicted a situation of embedded nouns hierarchically organized.
The prosodic contour of phrases was controlled, using PRAAT platform6 , such that the only cue used for interpretation was syntactic.We left no pauses and suppressed all prosodic modulation, so that there were no biases that could confound participants.
Using a preferential looking paradigm, participants listened to test sentences either in the recursive or coordination condition.For instance, in the recursive condition: There is a banana in the box on the tray on the chair; and in the coordinated condition: There is banana in the box and on the tray and on the chair.At the same time, children were presented with two images displayed side-by-side on the computer screen.One image was associated with the coordinated representation of the sentence (e.g., three bananas: one placed in the box, another on the tray, and another one on the chair) and the other with the recursive representation of the sentence (e.g., only one banana on top of the three containers) (Figure 1).
Then, when listening to the test sentence, children had to point gestures from behind, so that the experimenters could have an after-test response control, besides the register taken down by the experimenter's assistant during the test.

Materials and Method
In this experiment, participants listened to test sentences either in 338 the recursive or coordination conditions For instance, in the recursive condition: There is a banana in the box on the tray on the chair; and in the coordinated condition: There is banana in the box and on the tray and on the chair.At the same time, children were presented with two images displayed side-by-side on the computer screen (Figure 1).One image (on the right) was associated with the coordinated representation of the sentence (e.g., three bananas: one was placed in the box; one, on the tray; and one, on the chair).The other image (on the left) was associated with the recursive representation of the sentence (e.g., only one banana on top of the three containers).Then, when listening to the test sentence in one of the experimental conditions (coordination vs. recursive), children had to point toward the image that best matched, in their opinion, the sentence they had just heard.When children clearly and resolutely pointed to one of the pictures, experimenters would count the response as relating to a coordinated or a recursive interpretation.Thus, if participants in each one of the two age groups were able to process and to correctly interpret the recursion of PPs, there would be more pointing toward the images representing the recursion, when they listened to the recursive sentences and more pointing responses toward the images representing coordination, when they listened to the coordinated sentences.
The number of recursive layers and that of coordinated items were also controlled for.There were sentences with to or three recursive layers and coordinated items, as it can be seen in the examples below: Recursive sentence with two embeddings

Tem gato na caixa na mesa
(There is cat in the box on the bed) Recursive sentence with three embeddings (There is pig in the bucket on the tray on the chair)

Tem maça na caixa e no balde
(There is apple in the box and in the bucket)

Tem cachorro na caixa e no balde e na cadeira
(There is dog in the box and in the bucket and on the chair)
Children were tested in two public preschools in Rio de Janeiro, and their parents signed an informed consent form.An additional eight children participated in the study, but were not included in the experiment (4), there were experimental problems (2), or there was some kind of fussiness during the experiment session in the school (2).

Stimuli
Eight pairs of experimental sentences were created from eight target words likely to be known by children, for example: banana, cat, apple, pig, cake, dog, sandwich, rabbit.For each target word, we recorded a pair of sentences: one was the coordinated version and the other was the recursive version.The coordinated version was recorded with the conjunction AND before each PP, for example: There is banana in the box and on the tray and on the chair.The recursive version was recorded without a pause between the PPs, for instance: There is banana in the box on the tray on the chair (c.f., Appendix 1, for stimuli's list).Although the sentences were carefully recorded, so that no additional cues, such as pauses, could be extracted from prosody, the sentences were uttered as if they were being spoken naturally to a child, in a child-direct speech way.The recording was done by a male Brazilian Portuguese speaker (the second author) who recorded the stimuli after a few sessions of practice in order to control for other extraneous factors (e.g., pauses, noises, pitch variations, etc.).In total, we created sixteen test sentences: eight in the recursive condition and eight in the coordination condition.Thus, we created two lists of stimuli, so that each version of a given sentence pair appeared in a different list.This means that a given child would listen to a given sentence only in a recursive or a coordination condition, but not in both,

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following a Latin square distribution.Each list contained four sentences recorded in the recursive version and four in the coordinated one, plus the participants were assigned to each list and the order of sentences presentation within each list was pseudo-randomized.

Procedure
Children were tested individually in their own preschool.During the experiment, participants were seated in front of a computer screen displaying the visual stimuli.
They were told that they were going to play a game in which they would listen to.
The experiment started by a practice session consisting in a pictures simultaneously presented to them (Figure 2).As soon as the participant gave two correct pointing responses in this practice session, the experimenter would start the test session.
Before the test session began, the experimenter would adjust headphones to the children's ears.The test session was composed of test sentences with a recursive structure and half with a coordinated structure counterbalanced between participants.
Each test trial started by an inspection period to provide the child enough time to look at the pair of images displayed on the screen.Each right side of the screen, and a neutral audio prompt was played at the same time, for instance: Hey, look!Do you see that?Both images were then silently presented on the screen, for 5 seconds.Then, these images would disappear, and the screen was blank for 500ms.Finally, the two images appeared again together on the screen, simultaneously to the auditory test sentence.Participants' task was to point toward the image that, in their opinion, matched the sentence they had heard.Each trial ended with the sound and illustration of clapping hands to stimulate the child's participation, regardless of whether the response was correct or not.The time course of each trial is described in Figure 3.

Results
Responses that correctly matched the target interpretation of the sentences (recursive in recursive condition, coordination in coordination condition) were scored as 1, and incorrect responses were scored as 0 (See Appendix 2).Thus, for each child and for each condition, we calculated the average scores of their responses and used them as the dependent measure in our analysis.
Because recursive and coordination responses in this task are complementary, we chose the proportion of pointing toward the recursive image as our dependent measure in the statistical analysis.
Figure 4 presents the average proportion of pointing responses toward the recursive and the coordination images for each condition (Recursive or Coordination) for both groups of children (3-year-old Vs.

4-year-old).
A one-way analysis of variance (ANOVA) was conducted with participants as random factor.This analysis included a within-subject factor Condition (Recursive, Coordination), and two between-subjects factor, List (List1, List2) and Group (3 year old, 4 year old).

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A main effect of Condition (F(1,34) = 6.38, p < .02)was observed.Taking all together, children pointed more toward the coordination image than to the recursive image when they heard the coordinated sentences.p = .055)indicating that while 4-year-old children pointed more toward the recursive image than toward the coordination image when they heard the test sentences with the recursive structure (and vice-versa for the test sentences with the coordinated structure), 3-year-olds always pointed more toward the coordination image for both conditions (recursive, coordination).Thus, the proportion of pointing responses toward the recursive image in the recursive condition was above chance for 4-yearolds (60%), but for 3-year-old children the average was below chance (40%), (t(34) = -3.164,p < .01).No other effect or interaction reached

Discussion
The main effect of the test points to the fact that the children tested at 3 and at 4 years of age appear to have the coordination interpretation available to them.One might argue that this test cannot properly disentangle coordination from a simple lexical effect: children might stock semantic contents of the items presented to them without really coordinating them.Nevertheless, even the simple adding of one layer of PP already entails a syntactic merge between a DP and a PP (a pencil in The fact that they recognize the coordinated condition in which there is a distribution of items, for instance: There is [a] banana in the box and on the tray and on the chair, shows that the structure entailed in the PP coordination is being at least partially realized.
As a contrast, the recursive condition is more complex and cannot be confounded with mere memory storage, because such sentences necessarily entail hierarchical structures that yield meaning on their own, 346 correctly matched to its corresponding sentence, that meant that the child knew that a single object was nested in two or three containers.That is, the distributive reading was blocked.
The recursive structure appeared to be meaningful to the children tested as of 4 years of age (Check the two last columns in Figure 4).Four year olds pointed more to the recursive pictures than to coordinated ones when they listened to recursive sentences.Thus, this test successfully computation to children.
factor, statistically speaking.Nevertheless, since 3 year-olds do not appear to use PP recursion meaningfully, and they were tested for layers together with 4 year-olds, another test focusing on 4 year-olds and multiple layers as a factor should be applied, in order to verify if their acquired computation seems to be similar to that of adults in this respect.
Currently, we are developing a semantic investigation of manner PPs, conveying different thematic roles, and we expect to get the very same results as those of the place PPs already tested here, since recursion is a syntactic computation and should not be hindered or facilitated by the semantic content of the phrase.We also intend to test acquisition of other recursive phrases in a similar fashion.
Most importantly, since 4 years of age is the moment that PP recursion seems to become available, several types of recursive computations must be tested involving other cognitive domains, so that it is possible to fare if recursion of PPs and of other linguistic structures, arising from interface effects, derive from more primitive properties than those In terms of more sophisticated perspectives, a desirable advancement, as much as it is hard to accomplish with children, is the use of online testing, that can discriminate between automatic and reasoned upon processes.

FIGURE 1 :
FIGURE 1: A pair of images shown in the experiment, originally in color.The participant would choose the image on the left if she had an interpretation of recursion (on the left: «There is a banana in the box, on the tray, on the chair»), or the one on the right for coordination (on the right: «There is a banana in the box, AND on the tray, AND on the chair»).

FIGURE 2 :
FIGURE 2: Participant during the test, pointing to the image on the right

FIGURE 3 :
FIGURE 3: The complete time course of each trial.

FIGURE 4 :
FIGURE 4: Proportion of pointing responses toward the Recursive image and the Coordination image after listening to the test sentences, with a recursive or a coordinated syntactic structure, for each group of participants.Error bars represent the standard error of the mean.