An Experimental Investigation of Syntactic Priming and the Lexical Boost in Language Production

An essential part of producing a sentence involves the construction of its syntax. How this is done is a fundamental question in language production research. People often have choices how to express a message. For example, they can say either (1a) or (1b); both sentences express a similar meaning, but their syntactic structures are different.

1a. The driver showed the overall to the mechanic.
1b. The driver showed the mechanic the overall.

Research has shown that people tend to repeat recently spoken or heard structures: they tend to produce (1a) more often after hearing (2a) than (2b), and (1b) more often after (2b) than (2a), a finding termed "structural priming".

2a. The doctor gave the syringe to the nurse.
2b. The doctor gave the nurse the syringe.

Structural priming can inform us about the structural representations that people access during language production. One critical finding is that structural priming is stronger when the verb in the sentence to be produced is the same as in the previous sentence: the "lexical boost effect". For example, (1a) is more strongly primed by "The doctor showed the syringe to the nurse" than by (2a). There is currently much debate about the origin of the lexical boost and the precise circumstances under which it occurs.
Based on pilot studies, we suggest a hierarchical account, which assumes that hierarchical relations play an important role in the lexical boost: a structural representation (e.g., "the syringe to the nurse/the nurse the syringe") is associated not just with its own head (e.g., "gave"), but with any head of a structure in which the representation is embedded. This account makes novel predictions about the lexical boost. For example, despite the fact that "hesitated" in (3a) is not the head of "the syringe to the nurse/the nurse the syringe", priming should be larger when the prime (3a) and target to be produced (3b) contain the same verb ("hesitated") than when the verbs are different ("decided" and "hesitated"), because these verbs are the head of the larger structure "to show the overall to the mechanic/the mechanic the overall".

3a. The driver hesitated/decided to show the overall to the mechanic/the mechanic the overall. (prime)
3b. The doctor hesitated to give ... (target)

In contrast, repetition of "doctor" in (4) should not result in a lexical boost, because it is not the head of a structure that contains "the syringe to the nurse/the nurse the syringe".

4a. The driver/doctor showed the overall to the mechanic/the mechanic the overall. (prime)
4b. The doctor hesitated to give ... (target)

These predictions are different from existing accounts. The experiments will investigate which account makes the correct assumptions about how syntactic structures are mentally represented. We will ask approximately 40 participants to read aloud primes such as (3a, 4a) and then to provide a completion to targets such as (3b, 4b). Around 40 prime-target pairs will be tested.
A series of experiments will address several major questions. In addition to the question of whether the lexical boost occurs when the repeated word is the head of a structure in which the primed structure is embedded, we will ask whether the distance between the repeated word and the primed structure matters. Other questions will concern the duration of the boost and whether it is due to explicit memory of the repeated word from the prime. This is important for understanding language production and will contribute to language production models. Research so far has not provided clear answers to the question of what structural information is stored and with which words. Our study will lead to a better understanding of how people produce syntax and contribute to a more precise model of structural priming.

Speakers often repeat the syntax of sentences, a phenomenon called "structural priming". When experimentally elicited, structural priming can inform us about the processes underlying sentence production. In the proposed project, we will focus on the "lexical boost effect", the finding that structural priming is stronger when specific words in the sentences are also repeated. This will inform us how syntactic structures are organised around specific words and allow us to test the main theories of structural priming. The ultimate aim of the project is to develop a more precise model of how speakers mentally represent syntax. The results will lead to a refinement of current models of language production. As explained in the "academic beneficiaries" section, this will benefit a wide variety of language research, including language production research, computational modelling, linguistic theory and memory research.

Non-academic impact
Although our project will primarily have academic beneficiaries, our understanding of how and when language users repeat sentence structures can be useful for the development of automatic language generation and comprehension systems such as in car navigation systems, automatized text summarising, automatic translation and augmentative alternative communication systems for people who cannot speak. First, if these systems repeat structure in a similar way as humans do, they will produce more naturalistic language. Second, repeating structures from a previous utterance could facilitate natural language generation, because the system does not need to generate structure from scratch. Natural language generation systems have the potential to increase both economic competitiveness and the effectiveness of public services by facilitating communication and information transfer. When used for augmentative alternative communication, they enhance people's well-being.

Professional skills
The project will have a direct impact on the skills of the staff involved. The postdoctoral researcher will develop several professional skills that are transferrable to other employment sectors. They include working in an international team (Dundee, Ghent, Umeå), coordinating the collaboration between the universities involved, giving presentations and writing articles, computer and statistical analysis skills, and publicising the work to both the scientific community and the wider public. The division of Psychology in Dundee has a research apprenticeship scheme that allows undergraduate students to assist in a research project. As part of this scheme, we will recruit students to help us on the project. This will give the postdoctoral researcher experience in supervision while the undergraduate students get experience in material construction, running experiments and data analysis.

Outreach
In the past, the PI has had press coverage in newspapers and the local radio. We will liaise with the Press Office at the University of Dundee to attract coverage in the media. In order to publicise our work to the wider public, we also aim to present at "Café Science", which is a series of scientific talks to the public in Dundee, and contribute to exhibitions at the Science Festival organised by the Dundee Science Centre. A website interfacing with Twitter and Facebook will be used to publicise our research to the wider public. The aim of these outreach activities is to inform the public interested in understanding how language is shaped by the mind and how current developments in language science inform us about this.