The overall shapes of the significant diversity components from the lexical decision and naming studies are similar. For example, leftward diversity plays the same facilitative role in both tasks (with a possibly reduced contribution of leftward as-modifier diversity for
naming. This could mean that the lexical representations of nouns are in general better discriminated from preceding context: one learns better when one can compare a token to the incremental expectations generated immediately prior. Such a pattern of effects could be supported by standard error-based learning (e.g., Fine & Jaeger, 2013), and fits well with prior work. For example, Baayen (2010) finds that more diverse lexical contexts to the left of a target word correlate with faster reaction times. Similar interpretations apply to the prepositional measures of Baayen et al. (2011) and (largely) prepositional measures of Lester and Moscoso del Prado Martín (2015; prepositions by definition stand to the left of the noun).
main differences: the loadings of general modifiers, rightward as-head and rightward as- modifier distributions are reversed, leading to opposite effects on response times. The
difference in relationships means the following: (a) general modifier diversity inhibits lexical decision but facilitates naming; (b) rightward as-modifier diversity inhibits lexical decision but facilitates naming; (c) rightward as-head diversity facilitates lexical decision but inhibits naming. Points (a) and (b) suggest inhibition in lexical decision for nouns whose total as- modifier diversity mainly comes from the rightward direction. Inspection of the rightward as-modifier distributions shows that the categories with the greatest frequencies in the rightward as-modifier direction are active and passive sentential subjects. Perhaps the general indeterminacy of the subject role in English, which can assume many thematic functions relative to the verb, leads to a processing response that slows access until more information (i.e., from the main verb) becomes available. Increased indeterminacy at the syntactic level could exacerbate the conservativism of this approach. This “slowing of the clock” could burn into the system to produce slower responses to nouns in isolation.
The facilitation of rightward as-head diversity in comprehension may reflect the inverse of the rightward as-modifier diversity. I have proposed that the latter arises from a
conservative processing strategy, based on the naturalistic standard of processing in context, which states, “when nouns project a more uncertain array of possible integrations with upcoming heads. suppress access until more information becomes available.” Apparently, the strategy reverses for nouns that show greater uncertainty for how upcoming material may be bound to them. Under these circumstances, the noun is accessed more quickly, possibly to support the rapid integration of upcoming modifiers given expectations that the noun will be further elaborated. This situation mirrors that of the as-modifier distributions in that both
prioritize the head as a means of settling the parse. Again, through repeated experience with contextualized processing, these strategies may tune the links between nouns and syntactic nodes to produce the observed effects in isolated and minimally syntactic contexts. The effect reverses in picture naming, which could be due to challenges specific to production, namely, the fact that speakers must commit to only one out of several possible continuations at each “choice point” in the utterance (e.g., Jaeger, 2010; Kuperman & Bresnan, 2012). One such choice point would be the decision of whether to elaborate a noun phrase with
additional rightward structures (e.g., relative clauses or prepositional phrases). Some
evidence suggests that when speakers face more choices for how to encode an utterance, they take longer to initiate the utterance (Hwang & Kaiser, 2014; Myachykov, Scheepers, Garrod, Thompson, & Fedorova, 2013; but cf. Ferreira, 1996). This effect has been attributed to planning: more choices require more careful, hence longer planning latencies. Perhaps this effect also plays out at the lexical level, such that words that introduce more possibilities for structural elaboration require more careful planning. Importantly, this effect would have to hold even when no such continuation is pursued. Interestingly, the effect was only observed for the syntactic naming task, suggesting that planning-oriented syntactic effects requires that the speaker intends to produce an overtly syntactic structure.
The above discussion demonstrates a deeper level of complexity in the nature of syntactic-distributional effects than has previously been proposed. The specific details regarding how each layer of syntactic organization impacts processing, and how these layers relate to one another remains unclear. I have proposed several possible explanations for the effects observed in the studies presented here, but ultimately future research is needed to unravel this complex tapestry of relationships. Nevertheless, several general conclusions are
warranted. First, adults are highly sensitive to the purely syntactic distributions of words, even after information attributable to other distributional sources has been carefully stripped away (cf. Baayen et al., 2011). Moreover, this sensitivity surfaces in behavior, that is, in response latencies (cf. Linzen et al., 2013). Second, the behavioral response to syntactic distributions is differentiated according to hierarchy and word order. Finally, the shape of the response depends on the task, specifically whether one is reading or speaking, and whether the word is processed in isolation or within a syntactic context. Properly controlled (e.g., within carefully orthogonalized experimental designs), these measures have great potential for illuminating how experience shapes lexical representation and processing.
D. Word Learning in Children
In Chapter 4, I explored the genesis of the syntactic effects that were observed in adult lexical processing. Most research on distributional effects in adults assume that they arise during language learning, either through the accumulation of exemplars in memory (e.g., Bybee, 2010; Goldberg, 2006), “burnt-in” patterns of activation (e.g., Plaut & Booth, 2000) or through discrimination learning (e.g., Baayen et al., 2011; see Rescorla and Wagner, 1972). I therefore expected that the first appearance of words in child speech would be supported by the diversity and typicality of the syntactic relationships in which they appear. Some evidence from the inflectional morphology suggests that more diverse inflectional distributions lead to earlier acquisition. For example, Baayen, Feldman, and Schreuder (2006) find a negative correlation between inflectional entropy and subjective age-of- acquisition ratings. When children begin to master these inflectional distributions, they also begin to produce more tokens of words that belong to those paradigms (Stoll et al., 2012). I
hypothesized that similar learning mechanisms would apply at the syntactic level, such that more diverse distributions would support earlier acquisition. I further predicted that more typical syntactic distributions would support earlier acquisition. Nouns that meet the expectations for the syntactic behavior the class as a whole should (a) be experienced more often in the environments that best fit the communicative needs of speakers and (b) allow for analogical extension into novel environments based on the behavior of other nouns. Point (b) receives additional empirical support from the results on priming in adult lexical decision. As a first step, I tested these predictions using the overall syntactic distributions, ignoring hierarchy and word order. Results confirmed the hypotheses, but revealed an unexpected temporal offset. The diversity and typicality effects overlapped in time, but diversity preceded typicality, and typicality extended beyond diversity. Thus, nouns are first learned through repeated exposure in diverse contexts. Given a certain threshold of experience, class-wide expectations begin to emerge, something like the accumulation of a Bayesian prior. Further research is needed to see what role, if any, hierarchy and word order may play at these early stages. Another open question is whether older children (e.g., 4-6 year olds) respond to the same syntactic dimensions as adults during online lexical processing (e.g., in an auditory lexical decision task).