RUNNING HEAD: The development of verb argument structure When do children develop knowledge of verb argument structure? Evidence from verb bias effects in a structural priming task Michelle Peter1a Caroline F. Rowland1 Franklin Chang1 University of Liverpool Ryan Blything2 University of Manchester 1Department of Psychological Sciences, Institute of Psychology, Health & Society, University of Liverpool, Eleanor Rathbone Building, Liverpool, L69 7ZA, UK. 2Max Plank Child Study Centre, School of Psychological Sciences, University of Manchester, Manchester, M13 9PL, UK. a Corresponding author: Michelle Peter, Department of Psychological Sciences, Institute of Psychology, Health & Society, University of Liverpool, Eleanor Rathbone Building, Liverpool, L69 7ZA, UK. Email: Michelle.Peter@liv.ac.uk. Telephone: +44 151 794 1401. Abstract The structural priming paradigm is a powerful way of constraining theories about how children’s knowledge of verb-argument structure develops. Using a priming task that capitalises on verb bias effects and on a phenomenon called prime surprisal, we tested two accounts of syntactic development: one by Thothathiri & Snedeker [Thothathiri, M. & Snedeker, J. (2008a). Syntactic priming during language comprehension in three- and four-year-old children. Journal of Memory and Language, 58, 188-213] that claims that children have abstract knowledge about syntax before they learn the lexical links to these structures from verbs, and another by Chang, Dell, and Bock [Chang, F., Dell, G. S., & Bock, K. (2006). Becoming syntactic. Psychological Review, 113, 234-272] that proposes that children acquire abstract and lexical knowledge simultaneously. We assessed structural priming and the lexical boost across development. We also investigated whether the bias of the target verb influences structural priming across development, and whether the priming effect is stronger when there is a mismatch between prime verb bias and prime structure (prime surprisal).Children (aged 3-4 years and 5-6 years old) and adults heard and produced double-object dative (DOD) and prepositional-object dative (PD) primes with DOD- and PD-biased verbs. All participants heard both the same verb in the prime and target (e.g., gave-gave), and also a different verb (e.g., gave-sent). All age groups demonstrated significant evidence of structural priming, but only adults showed increased priming when the prime and target shared a verb (the lexical boost). Both children and adults produced more DOD responses with DOD-biased verbs (e.g., give) than with PD-biased verbs (e.g., bring), and priming was stronger when there was a mismatch between the prime verb’s bias and its structure (prime surprisal). These results show that, like adults, children’s knowledge of verb syntactic preferences influences their structure choice. We conclude that early syntax is lexically-grounded and that the lexical boost is not a reliable measure of verb-structure links. Keywords: structural priming, syntactic development, verb bias, lexical boost, prime surprisal. When do children develop knowledge of verb argument structure? Evidence from verb bias effects in a structural priming task Structural priming is a powerful way of measuring what adults know about syntactic structure. A number of priming studies have shown that, despite having the ability to be linguistically creative, adult speakers tend to repeat the syntactic structure of the sentences that they have recently encountered (Bock, 1986b). This effect is not contingent on non-syntactic factors such as the prosody of sentences or the thematic roles played by arguments, nor does it rely on the repetition of words across sentences - although the priming effect is often larger when prime and target sentences share a verb (the lexical boost; Pickering & Branigan, 1998). Thus, the phenomenon of structural priming is widely interpreted as evidence that adults have abstract representations of syntax that are stored independently of lexical items (e.g., Bock & Loebell, 1990; Cleland & Pickering, 2006; Noppeney & Price, 2004). Recently, the priming paradigm has helped us to learn more about children’s syntactic representations. These studies have been particularly useful in informing us about the way in which children’s knowledge of syntactic structure is similar to (and differs from) that of adults. For example, Shimpi, Gámez, Huttenlocher, and Vasilyeva (2007) found that children as young as three years old, who heard and repeated passive prime sentences, were more likely to describe target pictures using a passive rather than an active structure. Similar results were reported in a more recent study by Messenger, Branigan, McLean, and Sorace (2012). Evidence of abstract structural priming in children has also been demonstrated in language comprehension; Thothathiri and Snedeker (2008a) reported that children’s interpretation of target dative sentences was influenced by prior processing of dative prime sentences that contained a different verb. The fact that these finding hold even when prime and target do not share any lexical items, suggests that, like adults, children as young as three years old possess verb-general abstract syntactic representations that they employ during both production and comprehension. Thus, the results from the child literature are fairly consistent: children appear to have abstract knowledge of syntax from early on in development. However, priming studies in the acquisition literature tend to focus only on this question of what type of syntactic knowledge children have at the early stages of the acquisition process. While this approach is a useful way of distinguishing between early abstraction and item-specific theories (e.g., Fisher, 2002a; Pinker 1984; Valian, 1986 vs. Pine, Lieven & Rowland, 1998; Tomasello, 1992; 2000), it does not tell us much about how children’s knowledge of syntactic structure develops. Given that children cannot start with an adultlike knowledge of the particular syntactic structures used in their language, all theories need to incorporate acquisition mechanisms that enable children to interpret their own particular input to build knowledge of syntax. Studying how children’s responses to priming tasks change over development allows us to examine not only what knowledge children bring to the language learning task, but also how acquisition mechanisms interact with the input to build mature linguistic knowledge. Recently, Rowland, Chang, Ambridge, Pine, and Lieven (2012) used a structural priming task to investigate just this. Using a paradigm designed to test structural priming across development, they reported significant structural priming effects in both children (aged 3-4 years and 5-6 years) and adults. All age group produced more double-object dative (DOD) responses after a DOD prime than after a prepositional-object dative (PD) prime even when the prime and the target included different verbs (e.g., give-send). From the fact that there were no significant differences across development, the authors concluded that three year olds, like older children and adults, have already built abstract syntactic representations of English dative constructions. However, when prime and target sentences shared a verb, the pattern of priming differed across development; unlike adults, children did not show a lexical boost effect. The adults demonstrated a substantially larger priming effect when there was verb overlap compared to when the prime and target verbs were different (a significant lexical boost of 34%). However, the effect was only marginal in the 5-6 year olds (10%) and non-existent in the 3-4 year olds. In other words, the repetition of verbs across sentences did not act to enhance the priming effect for the youngest age group in the same way that it did for adults. These results have implications for our understanding about the relationship between abstract and lexical knowledge across development. One possible explanation is that the lexical boost is absent in the youngest children because adults and children differ in the way in which they have linked the verb lexicon to knowledge of syntactic structure. For the adults in Rowland et al.’s (2012) study, the presence of the lexical boost suggests that syntactic structure choice is influenced, not only by the activation of the prime structure, but by activation of the verb used in the prime. This occurs because, in adult representations, there are connections between verbs and syntactic structure in the form of argument structure links that specify the syntactic structures in which verbs can occur (see Pickering & Branigan, 1998). However, in three-year olds, these verb-structure links may not exist, or, at least, may not be strong enough yet to influence syntactic choices in a priming paradigm. Thothathiri and Snedeker (2008a) have suggested that children may first build abstract representations of syntactic structures (e.g., the dative structure), and only later establish links between these representations and individual verbs, building knowledge of the argument structure constraints of verbs slowly as experience with each individual verb accumulates. On this view, children’s syntactic representations are initially wholly abstract, and the lack of a lexical boost in the youngest age group is due to an absence of any links between verbs and structures. An alternative explanation, however, is that the lexical boost is the wrong tool to make inferences about the relationship between verbs and syntactic structure. On this model, the lexical boost does not stem from a lack of knowledge of verb argument structure but from a limitation in explicit memory.. According to Chang, Dell, and Bock (2006), structural priming occurs as a consequence of an error-based learning mechanism. In their Dual-path model, which provides an account of structural priming, the difference (or error) between predicted and actual sentences is used to makes gradual weight changes in the connections between syntactic representations. Because the model conceptualizes structural priming in terms of the same learning mechanism that drives syntax acquisition, these weight changes enable the model to learn syntactic structure whilst developing representations based on the structural properties of verbs. In this way, Chang et al. predict that verb-structure links develop in parallel with the development of syntactic knowledge. Lexical boost effects, however, are too large to result from these types of changes; they result, instead from the speaker’s explicit awareness of the repetition of lexical items across prime and target sentences (Chang, Janciauskas, & Fitz, 2012). On this model, lexical overlap simply acts as a cue in the retrieval of the explicit memory of the prime structure and, given that explicit memory increases with age (Naito, 1990; Sprondel, Kipp, & Mecklinger, 2011), the boost increases in line with the ability to form, store, and retrieve explicit memories. Thus, the lexical boost is small (or even absent) in young children not because children do not have verb-structure links, but because they are less efficient at retrieving an explicit memory trace of the prime sentence. In sum, there are two possible reasons for why children and adults respond differently in lexical boost paradigms; one that suggests that children’s knowledge of verb-structure links has yet to develop, and one that suggest that it develops in parallel with knowledge of syntactic structure, but that the lexical boost is the wrong place to look for these links in children. In order to distinguish between these two theories, and determine what children know about verb argument structure, we thus need to use a different method to establish whether children’s and adults’ knowledge of verb argument structure influences their syntactic structure choice. In the current study, we did this using a modified structural priming method; one that capitalises on verb bias effects in priming studies and on a phenomenon called prime surprisal. Verb bias and prime surprisal Although many dative verbs can occur in both prepositional and double object datives (e.g., I gave him a cake/I gave a cake to him), most of these verbs will tend to occur more often in one structure than another. For example, give tends to occur more often in double object than prepositional dative structures (Campbell & Tomasello, 2001; Gries & Stefanowitsch , 2004a). These syntactic preferences (or preferred argument structure constraints) affect how adults behave in priming studies. For example, in a corpus analysis of English dative verbs, Gries (2005) found that target verbs strongly associated with one structure resisted being primed into another structure. In another study by Coyle and Kaschak (2008), priming effects were found to be larger when the target verb was not strongly associated with one structure (i.e., when they were equi-biased). In other words, an adult’s knowledge of a verb’s preferred argument structure (i.e., whether this verb occurs more often in a DOD or a PD structure) influences how easily it is to prime that adult to produce the verb in that structure. Studying the effect of verb bias on priming provides us with a different way of tapping into a participant’s knowledge of the links between verbs in the lexicon and syntactic structure. We know that adults’ knowledge of a verb’s preferred argument structure influences their structure choice during a priming task. If children have also established these links (as predicted by Chang et al, 2006), then we should expect to see evidence of target verb bias effects across development. However, if children have not yet linked verbs with their argument structure preferences (as predicted by Thothathiri and Snedeker, 2008a), then only adults, and perhaps older children, should demonstrate target verb bias effects during a structural priming task. In addition, related research has suggested that the identity of the prime verb plays an important role in the size of the priming effect, such that priming is stronger when the bias of the prime verb makes its occurrence in a particular prime structure unexpected – an effect termed prime surprisal (Chang et al., 2006). For example, Jaeger and Snider (2007) found that adults were more strongly primed when DODbiased prime verbs were presented in a PD prime structure and Bernolet and Hartsuiker (2010) reported stronger priming when primes with PD-biased verbs were presented in a DOD-structure in Dutch. In other words, the more unexpected (or surprising) a verb is in a prime sentence, the more likely participants are to be primed. Not only do these results demonstrate that adult speakers store information about verb syntactic preferences, but they also suggest that adults make predictions about prime sentences based on their knowledge of these preferences. When these predictions are not met (i.e., when a verb is presented in an unexpected structure), prime surprisal works to boost the priming effect (Chang et al., 2006).We can exploit this to assess children’s knowledge of verb-structure links. If, like adults, children have created links between verbs and syntactic structure, then verb-structure mismatches during a structural priming task should also lead to prime surprisal effects in children. But, if they have not yet formed these verb-structure links, then we should only expect to see evidence of prime surprisal effects in adults. The current study In this study, we capitalise on verb bias and prime surprisal effects to test two accounts of how children develop knowledge of verb argument structure. One possibility is that children have abstract knowledge about syntax before they learn verb argument structure links between syntactic structures and individual verbs (Thothathiri & Snedeker, 2008a). On this view, we should see abstract structural priming across development but, because children have not yet created the links between verbs and the structures in which these verbs can occur, only adults should demonstrate evidence of lexical boost, target verb bias effects and prime surprisal. Another possibility is that children acquire abstract and lexical knowledge simultaneously, but that the lexical boost is not a reliable measure of verb-structure links (Chang et al., 2006). This account also predicts abstract structural priming across development and a lexical boost that increases with age. However, on this account, we should see target verb bias effects and prime surprisal across development since this account predicts that children acquire both abstract syntactic representations and knowledge of verb argument structure simultaneously from early on. The current study used a modified version of the priming paradigm used by Rowland et al. to test for structural and verb-specific priming effects in young children (3-4 years), older children (5-6 years), and adults. Children and adults heard and repeated DOD and PD prime sentences containing DOD- (give and show) and PD-biased verbs (bring and send) before producing target sentences with these verbs. First, we assessed whether we could replicate the findings of Rowland et al. by examining structural priming and the lexical boost across development. To do this, we observed whether participants produced more DOD- target sentences after DOD primes than after PD primes when verbs in the prime in the target were different (e.g., give-send), and then observed whether this priming effect increased when the prime and target verb were the same (e.g., give-give). Second, we tested whether children, like adults, show verb bias effects in priming tasks by exploring whether the size of the priming effect was influenced by the bias of the target verb. Third, we assessed whether children, like adults, demonstrate evidence of prime surprisal. To do this we explored the priming effect was stronger when prime verb bias and prime syntactic structure were mismatched (e.g., DOD-biased verb in a PD structure). Method Participants A total of 183 participants were tested. One hundred and twenty-three monolingual English-speaking children were recruited from nurseries and schools in the Liverpool area. Sixty-three of these children (32 females) were aged between five and six years old (mean age 5;8, age range 5;0-6;11) and 55 children (33 females) were aged between three and four years old (mean age 4;0, age range 3;04;11). An additional five children from the 3-4 year old age group were tested but produced eight or more (over half) non-target responses during the task and so were excluded from the final analysis. A further 60 monolingual English-speaking adults (42 females) were recruited from the University of Liverpool student participation pool. Participants were tested individually in either their classroom/nursery or in the language development laboratory at the University of Liverpool. Design and Materials Design. The study was presented in the form of a bingo game and used a 3 x 2 x 2 x 2 x 2 mixed design. Age (3-4 year olds/5-6 year old/adults) was the betweensubjects variable1. The four within-subjects variables were Prime Type (DOD and PD), Verb Match (same verb and different verb), Prime Bias (DOD- and PD-biased) and Target Bias (DOD- and PD-biased). The dependent variable was the proportion 1 Although descriptive analyses are presented by age-group, age was coded in months as a continuous variable (3.5 years/5.5 years/20 years) since it is not possible to compare three categorical factors within a mixed effects model. of dative responses that were DODs – a ratio of DOD responses over the sum of DOD and PD target responses. Visual stimuli. Sixty-four video cartoon animations were created in Anime Studio Pro and were presented in E-Prime 2.0. The cartoons included three pairs of donor and recipient characters that are familiar to young British children and have proper noun names: Tigger and Piglet, Dora (the Explorer) and Boots, and Bob (the Builder) and Wendy. A further three pairs of donor and recipient characters were referred to with determiner+noun NPs: the prince and the princess, the king and the queen, the boy and the girl. Donor and recipient characters were always paired together (e.g., Wendy was always paired with Bob, and the prince was always paired with the princess). A further five characters acted as objects and were referred to with nondefinite determiner+noun NPs: a cat, a baby, a fish, a puppy, a rabbit. All of the characters were animate to prevent animacy contrasts between the object and recipient influencing syntactic structure, since DOD sentences tend to occur with animate recipients and inanimate objects. Thirty-two of the animations depicted transfer actions that can be described with dative sentences. Thirty-two others were used as fillers and depicted noncausal actions that can be described with an intransitive sentence. Eight of the animations that were used as fillers were also used in a practice session. Each prime picture was always paired with a target picture that included different characters from those in the prime. Animations also depicted the direction of motion of transfer actions from right-to-left equally as often as they were transferred from left-to-right to control for the possibility that direction of transfer could influence structure choice. Bingo cards were created to match each video cartoon animation. Four bingo boards were created on which to place the cards during the ‘game’. Two of these boards included a grid of four squares that were used in a practice session before the actual experiment. The other two boards were used in the experiment and contained nine squares. Sentence stimuli. The four verbs used in this study – give, show, send, and bring are dative verbs that have been shown to be familiar in both structures to young children in the DOD and PD structure (Campbell & Tomasello, 2001; Gropen et al., 1989). Ninety-six different sentences and 32 verb stems were created to describe the 64 video cartoon animations. Thirty-two of these sentences described thirty-two different cartoon animations (eight DOD sentences for each verb). These were used as primes and depicted transfer actions using a DOD structure (e.g., Dora gave Boots a rabbit). A further thirty-two prime sentences described the same transfer actions but used the PD structure (e.g., Dora gave a rabbit to Boots). Thirty-two target verb-stems (eight verb-stems for each verb) were created (e.g., the boy brought...) in addition to thirty-two filler sentences which used an intransitive structure (e.g., the princess jumped). Each verb was presented eight times per participant: four times in the prime sentence (twice in the PD structure and twice in the DOD structure) and four times in the target verb-stem. Each participant was exposed to 16 prime-target pairs, interspersed with 16 filler-filler pairs. Fillers were used to minimize priming effects between pairs. Overall each participant was presented with, and produced, 64 sentences in total. No participant was asked to produce the same prime sentence twice and all participants were exposed to an equal number of prime-target pairs from each of the prime conditions. We explored both lexically-specific and lexically-independent priming as a within-subjects variable. Therefore participants were exposed to sentences in which verbs were repeated across primes and targets and also sentences where the verbs in primes and targets were different. Pairs of characters appeared equally as often in prime and target sentences and to avoid lexical overlap (other than that of the verb), characters in primes were always different to the characters in the targets with which they were paired. Furthermore, primes that contained determiner noun phrases (e.g., the princess) were always followed by targets with proper noun phrases (e.g., Wendy) and vice versa. Sentences were always presented in the past tense to avoid phonological overlap of the regular progressive (–ing) ending. Three of the verbs were irregular (gave, sent, brought) to avoid repetition of the regular past tense (-ed) ending. To control for sentence-specific preferences, 12 counterbalance groups were created to ensure that: 1) sentences that appeared as a DOD prime in one counterbalance group appeared as a PD prime in another and vice versa; 2) all characters in both prime and target sentences appeared equally as often with each verb, and 3) each prime verb was paired with itself and the three remaining verbs equally often in target sentences. All sentences across counterbalanced groups were presented semi-randomly to ensure that participants could not predict the structure of consecutive prime sentences. This also enabled us to ensure that characters appearing in a filler-filler pair would not have appeared in the preceding target sentence or in the following prime sentence. Procedure Children. The experiment used a confederate-scripting dialogue method adapted from Pickering and Branigan (1998) by Rowland et al. (2012). The experiment was conducted in the form of a bingo game in which the experimenter and the child took it in turns to describe cartoon animations on a laptop computer to a confederate. The experimenter introduced all of the characters involved in the task to the child by showing them a selection of bingo cards on which these characters appeared. Once happy that the child knew the names of the characters, the experimenter explained the game to the child. The experimenter and child sat in front of the computer side-by-side, while the confederate sat opposite. The confederate was unable to see the cartoons on the screen. The experimenter’s description of the cartoon on the left-hand side of the screen served as a prime for the child. The child was asked to repeat the prime sentence, addressing a hand puppet held by the confederate. The experimenter explained that the puppet could not see the screen and needed the child to tell them what was happening. The child was next instructed to produce a target sentence by describing a cartoon animation on the right-hand side of the screen. A stemcompletion technique was used to ensure that the target sentence contained the target verb but the child was instructed to produce the entire target sentence. For example, after describing a prime animation using the verb gave (e.g., The king gave a baby to the queen) and having the child repeat this sentence, the experimenter would, then say “Wendy showed...”, encouraging the child to produce either, “Wendy showed a rabbit to Bob” or “Wendy showed Bob a rabbit”. After each sentence the confederate looked to see if he/she had the bingo card corresponding to that cartoon. If he/she did, the correct bingo card was given to the experimenter or child as appropriate. Each dative prime-target pair was immediately followed by an intransitive filler-filler pair. The first person to fill the bingo grid with bingo cards was the winner of the game and the experiment was designed so that the participant always won. Before running the experiment using the nine-squared bingo board, a practice session using the four-squared board was carried out to ensure that the children understood the task. Adults. The procedure for adult participants was identical to the procedure for child participants except that adults were informed that they were serving as controls in an experiment designed for children. Additionally, they received explicit instructions to repeat the prime and produce the entire target sentence and did not have to direct their speech towards a hand puppet. Coding Target responses were recorded by the experimenter using the response coding function of E-Prime 2.0. The experiment was also audio-taped, allowing the first author to listen back to and then transcribe and code the data. Many of the young children and some of the older children needed prompting from the experimenter to produce the prime and the entire target sentence correctly. Some of them, however, only produced partial target responses (e.g., they completed the stem without including the target verb). In order to capture these partial target responses, we employed three levels of coding: lax, intermediate, and strict. To qualify for lax coding, the prime sentence had to be repeated correctly but the participant might have received help to do this. In addition, the participant may not have produced the target verb or the entire target utterance, but instead just completed the target stem. To qualify for intermediate coding, the prime sentence had to be repeated correctly with the participant needing minimal help to do this. In addition, the entire target utterance was produced, but prompting to do this was needed more than once. To qualify for strict coding, the prime and target sentence had to be produced correctly with no more than one prompt. A target response was considered a DOD if it contained the correct target verb followed by two noun phrases, and a PD if it contained the correct target verb followed by a noun phrase and a prepositional phrase headed by ‘to’. Responses coded as ‘other’ were those where, a) the participant failed to repeat the prime correctly (even after help), b) the participant produced the incorrect target verb and, c) the target sentence included the preposition ‘at’ rather than ‘to’. Preliminary analysis revealed that all coding schemes produced a virtually identical pattern of results, and so the following analyses are reported only on the strictly-coded data.2. 2 Under the lax coding scheme, 3-4-year olds, 5-6-year olds, and adults produced 0.13%, 0.03%, and 0.01% ‘other’ responses respectively. Under the intermediate coding scheme, 3-4-year olds, 5-6-year olds, and adults produced 0.22%, 0.05%, and 0.03% ‘other’ responses respectively. Under the strict coding scheme, 3-4-year olds, 5-6-year olds, and adults produced 0.24%, 0.07%, and 0.03% ‘other’ responses respectively. Results The aims of the present study were: 1) to replicate Rowland et al. (2012) to assess structural priming and the lexical boost across development, 2) to explore whether the bias of the target verb influences structural priming across development, and 3) to investigate whether a mismatch between prime verb bias and prime structure influences structural priming (prime surprisal) across development. 1. Structural priming and the lexical boost across development Our first aim was to investigate whether we would find abstract structural priming and a lexical boost across all three age groups. Using a production-to-production priming paradigm, we tested lexically-independent and lexically-specific priming. The mean proportion of DOD responses after DOD and PD primes in the same verb and the different verb conditions was calculated. Structural priming was demonstrated by a greater proportion of DOD responses after DOD primes than after PD primes. Evidence of a lexical boost would be demonstrated by a bigger priming effect in the same verb condition than in the different verb condition. % of dative target responses that were DODs Fig. 1. Mean proportion of DOD responses after DOD and PD primes when primes and targets were different (different verb) and the same (same verb) (error bars indicate standard error) 0.8 0.7 0.6 0.5 After DOD 0.4 After PD 0.3 0.2 0.1 0 3-4 5-6 Different verb Adults 3-4 5-6 Adults Same verb Figure 1 demonstrates the mean proportion of dative responses that were DODs after PD and DOD primes for each age group and verb condition (same/different). Table 1 reports the size of the priming effect for each age group and verb match condition (calculated as a percentage of DOD responses produced after DOD primes minus the percentage of DOD responses produced after PD primes) and also as Cohen’s d. These data indicate that the structural priming effect was largest in the adults (27%). Comparison of the same and different verb conditions shows that verb overlap boosted the structural priming effect (by 23%) for the adults, but not at all for the children. Table 1. Size of priming effect – calculated both as the percentage of DODs produced in each prime condition (difference score) and effect size (Cohen’s d) Age 3-4 5-6 Adults Different verb Same verb Difference Score Standard error Cohen's d Difference score Standard error Cohen's d 0.15 0.14 0.27 0.049 0.030 0.048 0.45 0.42 0.90 0.03 0.06 0.50 0.041 0.023 0.044 0.08 0.17 1.86 The results were analysed with a logit mixed effect (maximal) model as these models are well suited to analyzing binary dependent measures and allow us to model both random subject and item effects together (Baayen, Davidson, & Bates, 2008; Jaeger, 2008). The model included as fixed effects: a) Verb match condition (same/different verb); b) Age (3-4 year olds/5-6 year olds/adults) and c) Prime type (DOD, PD). Age was centred to reduce multi-collinearity (Neter, Wasserman, & Kutner, 1985) and other factors were effect/sum coded (Wendorf, 2004). Participant was included as a random effect. The dependent variable was the proportion of DOD structures produced – a ratio of DOD responses over the sum of DOD and PD target responses. The results revealed a main effect of Prime Type; β = 1.26 (SE = 0.11), z = 11.51, p < .001, indicating that the participants produced more DOD responses after DOD primes than after PD primes. There was also a main effect of Age; β = 0.11 (SE = 0.02), z = 6.37, p < .001, so the likelihood of producing DOD targets increased with age. An interaction between Prime Type and Age; β = 0.09 (SE = 0.01), z = 6.24, p < .001, showed that, overall, the size of the priming effect increased with age. There was also a main effect of Verb match condition; β = -0.21 (SE = 0.11), z = - 1.99 p < .01, indicating that more DOD responses were produced in the same verb condition than in the different verb condition. There was no interaction between Prime type and Verb match condition, suggesting that the priming effect did not increase when verbs in the prime and target were the same. However, these results should be considered in the light of the three-way interaction found between Prime type, Age and Verb match condition, β = 0.12 (SE = 0.03), z = 4.18, p < .001. This finding indicates that while, on the whole, there was no lexical boost, the priming effect was greater when there was verb overlap for some of the age groups. To explore the interaction further, we conducted three models on each age group. 1.1. Analyses by age Three separate logit mixed effect models were run on each age-group. The 3-4 year olds demonstrated a main effect of Prime type only, β = 0.77 (SE = 0.21), z = 3.68, p < .001, no effect of Verb match condition and no interaction. There was no significant difference between the proportion of DOD responses after DOD primes produced by 3-4 year olds in the same (31%) and different (35%) verb condition. In other words, they did not demonstrate a lexical boost. Likewise, the 5-6 year olds showed a main effect of Prime type only, β = 0.85 (SE = 0.19), z = 4.54, p < .001, and no effect of Verb match condition or interaction; they too showed no lexical boost. In contrast, analysis of the adults’ data revealed a main effect of Prime type; β = 2.02 (SE = 0.16), z = 12.49, p < .001, Verb match condition; β = -0.32 (SE = 0.16), z = -2.07, p = .04, and also a significant interaction between Prime type and Verb match condition; β = 1.30 (SE = 0.31), z = 4.13, p < .001. This means that, unlike the children, the adults produced significantly more DOD responses after DOD primes in the same (76%) verb condition than in the different (70%) verb condition. Thus, there was a large lexical boost effect in the adults. 2. The effect of target verb bias on structural priming across development Our second aim was to investigate both how the target verb bias influenced the participants’ choice of syntactic structure overall, and whether it influenced the size of structural priming across development. Fig. 2. Mean proportion of DOD responses when prime and target verbs were and the same with (a) DOD-biased target verbs and (b) PD-biased target verbs (error bars indicate standard error) (a) % of dative target responses that were DODs 0.9 0.8 0.7 0.6 After DOD 0.5 After PD 0.4 0.3 0.2 0.1 0 3-4 5-6 Adults Different verb, DOD-biased target 3-4 5-6 Adults Same verb, DOD-biased target % of dative target responses that were DODs (b) 0.8 0.7 0.6 0.5 After DOD 0.4 After PD 0.3 0.2 0.1 0 3-4 5-6 Adults Different verb, PD-biased target 3-4 5-6 Adults Same verb, PD-biased target As before, we ran a logit mixed effect model to analyse the data. This time the model included as fixed effects: a) Verb match condition (same/different verb); b) Age (3-4 year olds/5-6 year olds/adults); c) Prime type (DOD, PD) and d) Target bias (DODbiased, PD-biased). Again, age was centred to reduce multi-collinearity. There were no interactions between Prime type and Target bias, suggesting that the amount of priming was not affected by the bias of the target verb. However, the bias of the target verb did affect the participants’ choice of syntactic structure overall. The results revealed a main effect of Target bias; β = -1.10 (SE = 0.11), z = -9.80, p < .001, which indicates that more DOD responses were produced with DOD-biased target verbs than with PD-biased target verbs overall. There was also an interaction between Target bias and Age; β = -0.03 (SE = 0.01), z = -1.84, p = .07, caused by the fact that the effect of target verb bias increased with age. There was a three-way interaction between Target bias, Age and Verb match condition, β = 0.07 (SE = 0.03), z = 2.48, p = .01. This suggests that more DOD responses were produced with DOD-biased target verbs than with PD-biased target verbs and this effect varied across both age groups and verb conditions. 2.1. Analyses by age To analyse the three-way interaction further, three separate logit mixed effect models were run on each age-group. The 3-4-year olds demonstrated a main effect of Prime type, β = 1.02 (SE = 0.26), z = 3.86, p < .001, and a main effect of Target bias only; β = -2.03 (SE = 0.40), z = -5.06, p < .001. So, while the size of the priming effect was not influenced by the bias of the target verb, 3-4-year olds produced more DOD responses with DOD-biased target verbs- than with PD-biased target verbs overall. Likewise, 5-6-year olds showed a main effect of Prime type, β = 0.95 (SE = 0.20), z = 4.67, p < .001, and a main effect of Target bias; β = -1.44 (SE = 0.23), z = -6.23, p < .001 (see Figure 3). They also showed a main effect of Verb match condition; β = -0.44 (SE = 0.22), z = -2.02, p < .05, indicating that more DOD responses were produced when there was no verb overlap (since this is not relevant to our predictions, we do not consider it further). In the adults, there was a main effect of Prime type, β = 2.53 (SE = 0.24), z = 10.62, p < .001, of Target bias; β = 1.59 (SE = 0.22), z = -7.38, p< .001, and of Verb match condition, β = -0.47 (SE = 0.19), z = -2.40, p < .01. There was also an interaction between Target bias and Verb match condition, β = 1.44 (SE = 0.38), z = 3.83, p< .001 and between Prime type and Verb match condition, β = 1.18 (SE = 0.45), z = 2.64, p< .001. However, as with the children, there was no interaction between Target bias and Prime type, indicating that Target verb bias affected the number of DODs produced overall, but not the size of the priming effect. In sum, children and adults were more likely to produce DODs with DOD-biased verbs (and thus more likely to produce PDs with PD biased target verbs). However, the bias of the target verb did not affect the size of the priming effect. 3. The effect of prime verb bias on structural priming across development Lastly, we investigated the effect of prime verb bias on structural priming. Specifically, we explored whether children and adults are sensitive to prime surprisal by testing whether the priming effect was bigger when there was a mismatch between prime verb bias and prime structure. Fig. 3. Mean proportions of DOD responses when prime verb bias and prime structure were the same (match), and when prime verb bias and prime structure were different (mismatch) with (a) DOD-biased target verbs and (b) PD-biased target verbs (error bars indicate standard error) (a) % of dative target responses that were DODs 1 0.8 0.6 After DOD 0.4 After PD 0.2 0 3-4 5-6 Adults Match, DOD-biased target 3-4 5-6 Adults Mismatch, DOD-biased target (b) % of dative target responses that were DODs 0.6 0.5 0.4 After DOD 0.3 After PD 0.2 0.1 0 3-4 5-6 Adults Match, PD-biased target 3-4 5-6 Adults Mismatch, PD-biased target To analyse the data, two variables were created: ‘mismatch’, in which the prime verb occurred in an unexpected structure (e.g. a DOD biased verb in a PD structure), and ‘match’, in which the prime verb occurred in a match structure (a DOD biased verb in a DOD structure). Using a logit mixed effect model, analyses were conducted on a subset of the dataset that only included data from the different verb condition. Data from the same verb condition was not included because the ‘match’ effect would be confounded by a lexical boost effect. For example, in the ‘match’ condition, when the prime verb is PD-biased, the target verb will always be a PD-biased verb (sent or brought) which could increase the priming effect. The logit mixed effect model included as fixed effects: a) Age (3-4 year olds/5-6 year olds/adults); b) Prime type (DOD, PD); c) Prime bias match (match, mismatch), and d) Target bias (DOD-biased, PD-biased). Again, age was centred to reduce multi-collinearity. The results revealed main effects of Prime type; β = 1.61 (SE = 0.23), z = 6.98, p < .001, Age; β = 0.14 (SE = 0.02), z = 6.26, p < .001, and Target bias; β = -1.43 (SE = 0.21), z = -6.71, p < .001. There was also a significant interaction between Prime type and Prime bias match; β = 0.88 (SE = 0.43), z = 2.06, p < .05, indicating that, overall, structural priming was greater when the prime verb bias and prime structure were mismatched (i.e., prime surprisal increased the priming effect). There was no interaction between Prime type, Prime bias mismatch and Target bias, indicating that the bias of the target verb did not influence prime surprisal. However, there was a three-way interaction between Prime type, Age and Prime bias match; β = -0.09 (SE = 0.04), z = -2.08, p = 0.037. Inspection of Figure 3 (a and b) shows that this threeway interaction resulted from the prime surprisal effect decreasing with increasing age. In other words, a mismatch between prime bias and structure was less surprising for adults than for children. 3.1. Analyses by age Three separate analyses were run to further explore the interaction between Prime type, Age and Prime bias match. For the 3-4 year olds, there was a significant interaction between Prime type and Prime bias match; β = 3.50 (SE = 1.45), z = 2.41, p < .05, indicating prime surprisal increased the size of the structural priming effect for this age-group. There was also a significant interaction between Prime type and Prime bias match for the 5-6 year olds; β = 2.28 (SE = 0.77), z = 2.98, p < .001, so prime surprisal also increased the amount of structural priming for this age-group. However, the adult data revealed only marginal interaction between Prime type and Prime bias match; β = -1.41 (SE = 0.73), z = -1.94, p < .1, showing that the strengthening effect of prime surprisal on structural priming decreased with age. In other words, adults were less sensitive to prime surprisal than children. Results summary Both children and adults demonstrated significant structural priming; they all produced more DOD sentences after DOD primes than after PD primes when prime and target verbs were different. However, only adults showed increased priming when prime and target sentences shared a verb. Thus, consistent with recent findings (Rowland et al., 2012), the lexical boost increased with development. The results also revealed verb bias effects across development: 1) both children and adults produced more DOD responses with DOD-biased target verbs (e.g., give) than with PD-biased target verbs (e.g., bring) and this effect was larger in adults than in children, 2) priming was stronger when there was a mismatch between the prime verb’s bias and its structure (prime surprisal), with this effect decreasing across development. Discussion In this study, we used a priming paradigm to test for structural and verb-specific priming effects in young children (3-4 years), older children (5-6 years), and adults. Our aim was to test two accounts of how children develop knowledge of verb argument structure. One is that children develop abstract knowledge about syntactic structure first, and then learn the lexical links between these structures and verbs that constitute verb argument structure knowledge (Thothathiri & Snedeker, 2008a). On this view, we predict abstract structural priming across development but a growing lexical boost with age. Crucially, we also predicted that only adults should be affected by the argument structure preferences of particular verbs (target verb bias) and by prime surprisal. An alternative account, however, proposes that children acquire abstract and lexical knowledge simultaneously, but that the lexical boost is not a reliable measure of verb-structure links (Chang et al., 2006). This account also predicts abstract structural priming across development and a lexical boost that increases with age. However, it also predicts that, once we see structural priming effects, we should also see target verb bias and prime surprisal effects since children acquire both abstract and verb-specific knowledge together from early on. To test these accounts, we first assessed whether we could replicate the findings of Rowland et al. (2012) that showed structural priming effects are present across development, but that a lexical boost that grew with age. Second, we tested whether children, like adults, are influenced by the argument structure bias of the target verb. Third, we examined whether children, like adults, demonstrate evidence of prime surprisal. In our study we replicated the findings of Rowland et al. (2012). We found evidence for structural priming across development, in that young children, older children, and adults were significantly more likely to produce DOD sentences (e.g., Wendy gave Bob a rabbit) after hearing and repeating DOD primes (e.g., The boy sent the girl a fish) than after PD primes (e.g., The boy sent a fish to the girl). These results support Rowland et al.’s conclusion that, by the age of three, young children have built some form of abstract syntactic representations for the English dative constructions, which enable them to generalise across similarly-structured sentences. Our findings also fit with other studies reporting evidence for abstract priming in three-year-olds (e.g., Bencini & Valian, 2008; Messenger et al., 2012; Shimpi et al., 2007). Like Rowland et al., we also observed a lexical boost that increased with development: adults showed increased priming (23%) when the verb in the prime matched the verb in the target, but 3-4-year old and 5-6-year old children did not. In other words, although structural priming effects were apparent across development from age three to adulthood, the lexical boost was only apparent in adults. Given that we replicated the results of Rowland et al. (2012), our second aim was to compare the predictions of two differing explanations of how children develop knowledge of verb argument structure. We did this in two ways. First we tested whether participants’ responses were influenced by the bias of the target verb across all three ages. We found that they were. Although the target verb bias did not affect the size of the priming effect for either children or adults, all age-groups produced more DOD responses with DOD-biased target verbs (give, show) than with PDbiased target verbs (bring, send). In other words, children as young as three years were influenced by the alternation biases of the four dative verbs used in this study. Second, we tested whether children and adults were influenced by prime surprisal. Again, we found significant effects across all three age group. Priming effects were stronger when there was a mismatch between the prime verb’s bias and the prime structure (prime surprisal). In other words, the bias of the prime verb had an effect on the size of the priming effect across all three ages. Both of these findings are difficult to explain in terms of a theory that assumes that the acquisition of abstract syntactic knowledge happens prior to, and in isolation from, the acquisition of verb’s argument structure constraints (e.g., Thothathiri & Snedeker, 2008a). Instead, our results the results support a model in which children develop knowledge about syntactic structure at the same time as they learn about the argument structure preferences of particular verbs. This model is the connectionist model of syntactic processing and development called the Dual-path model (Chang, Dell, & Bock, 2006). The model has a dual-pathway architecture which separates conceptual-lexical and syntactic learning into separate meaning and sequencing pathways. This architecture is argued to be critical for learning isolable syntactic structures (Chang, 2002). Syntactic knowledge is learned within the sequencing pathway through an errorbased learning algorithm that is applied to next-word prediction. For example, the model might predict that after the word the, the next word should be boy. But, if the next word is actually girl, then the mismatch between the prediction and the actual next word (the error) is used to change the weights in the model so that it better predicts girl after the. Since the weights are initially random, at first, the model might not predict the next word correctly. With time, the model learns syntactic categories which subsequently combine into syntactic structures that allow it to predict sets of words (e.g., ‘the’ is followed by a noun: ‘boy’, ‘girl’, ‘cat’...). Because the model is building syntactic knowledge from individual words, knowledge of which verbs can occur in which structure (verb argument structure) develops at the same time as knowledge of syntactic structure. In other words, the model develops knowledge about verb argument structure using the same error-based learning mechanism that it uses to develop knowledge of syntactic structure. As a result, the model predicts that effects of target verb bias will be seen as soon as we see evidence of structural priming, because children acquire syntactic information about the argument preference of particular verb at the same time as they are building up knowledge of syntactic structure. In addition, a mismatch between the prime verb and the prime structure (e.g., a PD-biased verb in a DOD biased structure) leads to more error in prediction and thus a greater weight change in the model’s representation for that syntactic structure (e.g., the DOD). A greater weight change means a greater likelihood of the model choosing the same syntactic structure for its own subsequent production, which leads to an increased priming effect. Explaining the developmental pattern of target verb bias and prime surprisal In sum, our findings support an account like that of Chang et al. (2006) in which it is assumed that early syntactic representations are lexically-grounded. However, there are two findings in our data that remain to be explained. First, the effect of target verb bias increased over development: adults were more strongly influenced by the bias of the target verb than children. Conversely, the effect of prime surprisal decreased over development; adults were less influenced by the bias of the prime verb than children. This apparent contradiction is difficult to explain because both effects are assumed to stem from the same source; the participants’ knowledge of a verb’s preferred argument structure, which both influences the choice in production of the target and generates the expectation that creates primes surprisal. We speculate here that both results could stem from the dynamics of the learning process. The growth of the target verb bias over development can be explained by the way that children use verb-structure pairs in the input to adjust their internal verbstructure links in their language network. If children learn verb biases over time, their representations moment-by-moment represents the evidence they have so far accumulated from the input. However, daily probabilities of verb-structure pairs do not always match the long term probabilities. This means that early on in the learning process, while the child is building up evidence, her representations are likely to be less stable. For example, although the verb throw may have an overall bias towards the PD frame, it is likely that there will be days in which children only hear throw in the DOD. Early on in the learning process, these instances would weaken the PD bias of her representation of the verb throw. Thus, learning target verb biases is a gradual process of accumulating evidence over time which can be temporarily derailed by random fluctuations in the input. This can explain why target verb bias increases with development in this study. The decrease in prime surprisal over development can be explained by changes in the magnitude of the learning rate. Priming in the Chang et al. model is due to error-based learning, which is influenced by a learning rate parameter. The error between the predicted next word and the actual next word is the error signal (akin to surprisal) and the influence of this error signal on the model’s representations is modulated by the learning rate. Thus if the learning rate is higher early in development, the effect of surprisal on priming will be larger earlier in development. In other words, we might see greater prime surprisal early in development because the child is learning at a faster rate than the adult. There is independent motivation for using higher learning rates early on in connectionist models (all of the versions of the Dual-path model use higher learning rates early in development; Chang, 2002; 2009; Chang et al. 2006). In connectionist models, weights are initially randomized, and a small learning rate means that learning makes only small changes to these weights. The result is that models learning a complex set of representations tend to fail to converge on the target representations (e.g., sequences of abstract syntactic categories) within an appropriate amount of time. Using large, initial learning rates and reducing them over development allows the model to escape from these local minima and discover the right representations. For example, Chang et al. (2006) started his model with a learning rate of 0.25 for 10,000 patterns and then gradually lowered this learning rate to 0.05 after another 30,000 patterns. In Chang et al.’s model, if we test priming early on when the learning rate is 0.25, the effect of surprisal will be larger than if we test it later on when the learning rate is 0.5. In this way, a decrease in learning rate over development leads to a decrease in prime surprisal effects over development. To clarify how these two effects could arise within a developmental account of language acquisition, we developed a simple dynamic systems model of verb bias acquisition. In this model, we assumed that children get 100 inputs for two verbs (A, B), which were coded as 1 for PD and 0 for DOD (variable pd). Verb A occurs in PD 80% of the time and verb B occurs in PD 20% of the time. We then set the learning rate parameter to start at 0.1 and reduce to 0.01 in 100 steps. The model is governed by four equations. The first equation updates the PD bias for the verb V that is inputted by adjusting the previous PD bias for that verb by the error between the previous bias and the present input (PD = 1, DO = 0), multiplied by the learning rate. The second equation updates the bias for the other verb to be unchanged from the previous time step. The third equation set the initial bias to a uniform random number between 0 and 1. The fourth equation sets the PDCHOICE variable to be set to the bias of the verb that is being used at each point in time. These equations were used to generate each random child: 1) BIASV,T = BIASV,T-1 + ( PDINPUTT - BIASV,T-1 ) * LRATET if verb matches V 2) BIASV,T = BIASV,T-1 if verb mismatches V 3) BIASV,0 = UniformRandom (0, 1) 4) PDCHOICET = BIASV,T if verb is V To see how this model would explain the results in this study, we generated two random children (child 1 and child 2). The initial bias (at time 0) is a random number between 0 and 1 and hence child 2 has an initial bias of 0.85 for verb B, which is a bias for the DOD. But since verb B occurs in the PD 20% on average, over development, the bias gradually decreases until the child matches the adult’s baseline bias. On the other hand, verb B in child 1 is already close to the adult level (0.3) at the start of development. However, due to the random run of PDs early in development, the bias is moved first towards PD before returning to the adult level. Fig. 4. Development of target verb bias for two verbs (A and B) over 100 exemplars for two children Figure 4 shows that early verb bias might not match adult biases and that the gradual learning of adult biases can explain the growth of the target bias in our study. The figure also demonstrates effects of the learning rate. The learning rate starts off high and reduces over development, which means that early verb biases are affected more substantially by the identity of each prime structure (i.e., vertical displacement is greater). For example, for Verb A, Child 2 starts off with a bias of 0.98 but, once the first DOD is experienced, the bias drops by 0.08 because the learning rate is high. Later in development, biases change by only 0.01 because the learning rate is lower. This explains why prime surprisal effects are larger earlier in development. The dynamic systems model helps us understand how a model that allows verbstructure representations to change over development could provide an explicit account of the behavioural changes in this study. Although models which incorporate changes in learning rate over development are generally motivated by model-specific assumptions (e.g., avoiding local minima), we can link these assumptions to more general issues with the literature on the critical/sensitive period. For example, language learning ability is strongly associated with the age that language learning starts, even when the amount of input is controlled (Johnson & Newport, 1989; Lenneberg, 1967; Mayberry, 2007), which supports the view that the learning rate may change over age. Furthermore, there are many different phenomena in vision, auditory, and general cognition that have different sensitive periods (e.g., Crawford, Harwerth, Smith, & von Noorden, 1996; Daw, 1994; Katz and Shatz, 1996; Weisel & Hubel, 1965; Kral & Sharma, 2012), which suggests that the learning rate changes may be governed by neural mechanisms that are present across multiple brain areas (e.g., myelination, axon elaboration, synapse elimination, Knudsen, 2004). Since a complete model of language must be able to explain better learning abilities early in development, the same mechanisms that support that phenomenon could also explain the larger surprisal effects early in development in the present study. Conclusion Exploring the effect of verb syntactic preferences on priming in three age groups has allowed us to begin to build a theory of verb-syntactic development in which the role of the input as well as prior linguistic knowledge is considered. We observed evidence of abstract structural priming across development and, although only adults showed evidence of a lexical boost, both children and adults were sensitive to verb bias effects in the form of target verb bias and prime surprisal effects. We suggest that the lexical boost is not a reliable tool for making inferences about verb-syntactic development and propose that children acquire abstract knowledge of structure whilst also learning the lexical links to these structures from verbs. We also tentatively suggest that this process is best explained by a model that uses an errorbased learning mechansim with a variable learning rate. Acknowledgements Financial support for this research was supported by a faculty-funded doctoral studentship awarded to Michelle Peter by the University of Liverpool. We wish to thank the schools and children who took part in this study, and to the students who helped to collect the data. Thanks also go to the audiences at the AMLaP conference (Riva del Garda, Italy) in September, 2012 and at BUCLD in November, 2012 for their helpful comments on an earlier version of this paper. Appendix A A1. Experimental items Prime sentences before the slash are presented in the DOD structure; those after the slash are in the PD structure. The four prime verbs are given in parentheses. Target stems used the same combination of agent, verb, beneficiary, and theme as prime sentences (e.g., the target stem, “Piglet GAVE...” was designed to elicit either Piglet gave Tigger a puppy or Piglet gave a puppy to Tigger). 1. The king (GAVE/ SHOWED/ BROUGHT/ SENT) the queen a baby/ a baby to the queen 2. The boy (GAVE/ SHOWED/ BROUGHT/ SENT) the girl a fish/ a fish to the girl 3. Wendy (GAVE/ SHOWED/ BROUGHT/ SENT) Bob a puppy/ a puppy to Bob 4. Dora (GAVE/ SHOWED/ BROUGHT/ SENT) Boots a rabbit/ a rabbit to Boots 5. The prince (GAVE/ SHOWED/ BROUGHT/ SENT) the princess a baby/ a baby to the princess 6. The king (GAVE/ SHOWED/ BROUGHT/ SENT) the queen a cat/ a cat to the queen 7. Piglet (GAVE/ SHOWED/ BROUGHT/ SENT) Tigger a puppy/ a puppy to Tigger 8. Wendy (GAVE/ SHOWED/ BROUGHT/ SENT) Bob a rabbit/ a rabbit to Bob A2. Filler items 1. Boots was flying 2. The princess jumped 3. Piglet and Tigger bounced 4. The king and queen waved 5. Tigger was washing 6. The prince was rocking 7. Piglet waved 8. The cat was swinging 9. Dora was flying 10. Bob was swinging 11. The princess and the cat were rocking 12. Dora and Boots waved 13. Bob was flying 14. The prince jumped 15. Tigger was rocking 16. The queen waved 17. The king and queen bounced 18. Piglet jumped 19. Wendy was flying 20. Dora was washing 21. The boy waved 22. Boots pointed at Dora 23. Wendy and Bob jumped 24. Dora was swinging 25. The girl waved 26. Wendy pointed at Bob 27. Boots was washing 28. Piglet was rocking 29. The cat bounced 30. 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