Are embedding decisions independent?

Evidence from preposition(al) phrases

Abstract Full Paper (PDF)

One of the more difficult challenges in linguistics research concerns detecting how constraints might apply to the process of constructing phrases and clauses in natural language production. In previous work (Wallis 2019) we considered a number of operations modifying noun phrases, including sequential and embedded modification with postmodifying clauses. Notably, we found a pattern of a declining additive probability for each decision to embed postmodifying clauses, albeit a pattern that differed in speech and writing.

In this paper we use the same research paradigm to investigate the embedding of an altogether simpler structure: postmodifying nouns with prepositional phrases. These are approximately twice as frequent and structures exhibit as many as five levels of embedding in ICE-GB (two more than are found for clauses). Finally the embedding model is simplified because only one noun phrase can be found within each prepositional phrase. We discover different initial rates and patterns for common and proper nouns, and certain subsets of pronouns and numerals. Common nouns (80% of nouns in the corpus) do appear to generate a secular decline in the additive probability of embedded prepositional phrases, whereas the equivalent rate for proper nouns rises from a low initial probability, a fact that appears to be strongly affected by the presence of titles.

It may be generally assumed that like clauses, prepositional phrases are essentially independent units. However, we find evidence from a number of sources that indicate that some double-layered constructions may be being added as single units. In addition to titles, these constructions include schematic or idiomatic expressions whose head is an ‘indefinite’ pronoun or numeral.

Detecting direction in interaction evidence

IntroductionPaper (PDF)

I have previously argued (Wallis 2014) that interaction evidence is the most fruitful type of corpus linguistics evidence for grammatical research (and doubtless for many other areas of linguistics).

Frequency evidence, which we can write as p(x), the probability of x occurring, concerns itself simply with the overall distribution of a linguistic phenomenon x – such as whether informal written English has a higher proportion of interrogative clauses than formal written English. In order to calculate frequency evidence we must define x, i.e. decide how to identify interrogative clauses. We must also pick an appropriate baseline n for this evaluation, i.e. we need to decide whether to use words, clauses, or any other structure to identify locations where an interrogative clause may occur.

Interaction evidence is different. It is a statistical correlation between a decision that a writer or speaker makes at one part of a text, which we will label point A, and a decision at another part, point B. The idea is shown schematically in Figure 1. A and B are separate ‘decision points’ in a given relationship (e.g. lexical adjacency), which can be also considered as ‘variables’.

Figure 1: Associative inference from lexico-grammatical choice variable A to variable B (sketch).

This class of evidence is used in a wide range of computational algorithms. These include collocation methods, part-of-speech taggers, and probabilistic parsers. Despite the promise of interaction evidence, the majority of corpus studies tend to consist of discussions of frequency differences and distributions.

In this paper I want to look at applications of interaction evidence which are made more-or-less at the same time by the same speaker/writer. In such circumstances we cannot be sure that just because B follows A in the text, the decision relating to B was made after the decision at A.

Capturing patterns of linguistic interaction

This paper is an earlier, and longer, version of the study published in IJCL 24:4. A couple of results have been superseded by a reanalysis. It is presented in its 2012 form in this blog post for historical interest and because it may have been cited. There is nothing fundamentally wrong with the paper, but a discrepancy in the results of Experiment 4 was identified (highlighted in the PDF).

Abstract Full Paper (PDF)

Numerous competing grammatical frameworks exist on paper, as algorithms and embodied in parsed corpora. However, not only is there little agreement about grammars among linguists, but there is no agreed methodology for demonstrating the benefits of one grammar over another. Consequently the status of parsed corpora or ‘treebanks’ is suspect.

The most common approach to empirically comparing frameworks is based on the reliable retrieval of individual linguistic events from an annotated corpus. However this method risks circularity, permits redundant terms to be added as a ‘solution’ and fails to reflect the broader structural decisions embodied in the grammar. In this paper we introduce a new methodology based on the ability of a grammar to reliably capture patterns of linguistic interaction along grammatical axes. Retrieving such patterns of interaction does not rely on atomic retrieval alone, does not risk redundancy and is no more circular than a conventional scientific reliance on auxiliary assumptions. It is also a valid experimental perspective in its own right.

We demonstrate our approach with a series of natural experiments. We find an interaction captured by a phrase structure analysis between attributive adjective phrases under a noun phrase with a noun head, such that the probability of adding successive adjective phrases falls. We note that a similar interaction (between adjectives preceding a noun) can also be found with a simple part-of-speech analysis alone. On the other hand, preverbal adverb phrases do not exhibit this interaction, a result anticipated in the literature, confirming our method.

Turning to cases of embedded postmodifying clauses, we find a similar fall in the additive probability of both successive clauses modifying the same NP and embedding clauses where the NP head is the most recent one. Sequential postmodification of the same head reveals a fall and then a rise in this additive probability. Reviewing cases, we argue that this result can only be explained as a natural phenomenon acting on language production which is expressed by the distribution of cases on an embedding axis, and that this is in fact empirical evidence for a grammatical structure embodying a series of speaker choices.

We conclude with a discussion of the implications of this methodology for a series of applications, including optimising and evaluating grammars, modelling case interaction, contrasting the grammar of multiple languages and language periods, and investigating the impact of psycholinguistic constraints on language production.