Material taken from the "Specific Aims" section of recent grant proposals

NIH "Language Comprehension"

The ability to comprehend sentences is among the most remarkable and distinctive human skills, and its impairment or loss following (e.g.) brain damage is among the most devastating of human illnesses. Our research program has, for many years, endeavored to understand the basic mechanisms of the human ability to turn a stream of words into a message, focusing on how readers and listeners impose structure on the incoming stream. This process is termed "parsing," and we assume that it is a precondition for comprehension. Readers and listeners obtain meaning from a structured stream of words, not an unstructured collection of words and phrases. We further assume that the ability to impose structure on a stream of words is at the heart of the human ability to understand language, and that its loss is at the heart of certain aphasias.

Through the 1980s, the psychological study of parsing was dominated by the "garden-path model," proposed by Frazier (Frazier, 1979; Frazier, 1987a; cf. Frazier & Clifton, 1996, Chapter 1) as a refinement of Kimball's (1973) proposals. This model contrasted with the "detective-style" models that existed previously (Fodor, Bever & Garrett, 1974), which were little more than lists of "strategies" or "cues" that were claimed to be relevant to parsing. It made strong and testable claims about the process of parsing, and made clear predictions about what sentence structures would be easy and difficult. The garden-path model was challenged in many ways (cf. Altmann, 1989), but arguably remained the "default parsing model" until very recent years.

Currently, however, parsing theory is becoming far more interesting and exciting. Attractive alternatives to garden-path theory have been proposed. Some retain the basic approach of garden-path theory (in its emphasis on the use of grammar in a symbolic parsing model), but emphasize different aspects of the grammar (Pritchett, 1988; Pritchett, 1992), or add some parallelism or underspecification to parsing representations (Crocker, 1994; Crocker, in press; Gibson, 1991; Gorrell, 1995). Other alternatives challenge the basic assumptions of the garden-path model, proposing more modern and explicit versions of the old "detective models" in the modern guise of constraint satisfaction models (MacDonald, Pearlmutter & Seidenberg, 1994a; MacDonald, Pearlmutter & Seidenberg, 1994b; McClelland, St. John & Taraban, 1989; Tanenhaus & Trueswell, 1995; Trueswell & Tanenhaus, 1994).

These developments have prompted us to re-examine experimentally some of the fundamental assumptions of our garden-path approach. One line of experiments we propose tests our basic assumption that the parser is serial and depth-first (Frazier, 1990; Frazier, 1995; Frazier & Clifton, 1996 submitted), initially creating a single analysis at a time to interpret. Competing constraint-satisfaction models assume that the parser activates a range of different analyses, in parallel, which compete to result in a preferred analysis. We propose experiments to test for the existence of activated analyses other than our presumed primary analysis, and to test other predictions that distinguish between garden-path and parallel constraint-satisfaction theories.

We have also been extending garden-path theory in fundamental ways, to permit it (unlike nearly all existing theories) to deal with what we call "non-primary phrases" (roughly, adjunct phrases and other phrases that cannot be a main predicate or its complement or argument; see below for a precise statement). We term our proposals "construal theory" (Frazier & Clifton, 1996). We have already conducted several tests of these new proposals, and describe several additional tests and extensions in the current grant proposal.

Finally, we continue to examine empirically a topic that has been at the heart of our research program since its inception, the processing of long-distance dependencies. The existence of long-distance dependencies (grammatical dependencies between "moved" phrases such as wh-question phrases and their "underlying" location) poses a difficult problem for any theory of human sentence parsing. At the same time, it gives human language its expressive power (permitting, e.g., quantification and variable binding). We propose experiments that examine the processing of sentences with long-distance dependencies in the context of the questions we have already raised (garden-path theory and its competitors, and its extension, construal theory), as well as experiments that introduce new concepts (such as roles in event structures) into claims about sentence processing.

NIH Language Comprehension (2001)

The ability to comprehend sentences is among the most remarkable and distinctive human skills, and its impairment or loss following (e.g.) brain damage is among the most devastating of human illnesses. Our research program has, for many years, endeavored to understand the basic mechanisms of the human ability to turn a stream of words into a message, focusing on how readers and listeners impose structure on the incoming stream. We have to date focused on this process of "parsing," and we assume that it is a precondition for interpretation and comprehension of language. Readers and listeners obtain meaning from a structured stream of words, not an unstructured collection of words and phrases, and our previous research has contributed substantially to the understanding of, and debate about, how people parse sentences (Frazier, 1978; Frazier, 1987; Frazier & Clifton, 1996).

Substantial disagreements remain about the nature of the parsing process, and we will continue gathering data designed to resolve these disagreements. However, we believe that enough is known about parsing to justify a shift in emphasis to studying the process of interpreting a parsed sentence (cf. Frazier, 1999a). There are many aspects to interpretation, including (1) evaluating the Logical Form of sentences, (2) determining reference and co-reference of referring phrases, (3) determining the relation of sentences to prior discourse and to context including identifying presuppositions, inferences, and discourse structure, and (4) assessing the speaker/author's intention in producing the sentence in its particular context. We propose to conduct experiments on a subset of topics in interpretation, concentrating primarily on the interpretation of elliptical constructions but extending this concentration to include the processing of focus and presupposition, the interpretation of bound pronouns, and the identification of sentence regions or domains that are taken as primarily relevant to the interpretation of new linguistic input.

We propose some principles described below (primarily the Conjunction Principle and a principle of cost-free structure-copying we call "copy ") that impose conceptual coherence on this range of topics. Our experiments are designed to test these principles using both off-line and on-line techniques. The initial experiments focus on how readers and listeners comprehend sentences and short discourses where they must "fill in" material to be able to interpret them. These include, among other forms, VP ellipsis (Keith gave a talk and Sandy did too) and question-answer pairs. Later experiments broaden the range of constructions that we examine and explore interactions between grammatical form and semantic factors such as focus, presupposition, and causality.

We believe that our understanding of the parsing process, while incomplete in major aspects, is adequate to support productive research on how the products of parsing are interpreted. The experiments we describe below, in addition to testing specific proposals about the nature of interpretation, should help support a better understanding of a variety of issues in language comprehension. These issues include the role of focus and presupposition in integrating sentences with discourse, the nature of the syntactic domains within which different forms of processing take place, and the nature of the processes that are distinct and that are shared between sentence comprehension and discourse comprehension (see Frazier, 1999b, for some speculations on this last point). We also we believe that basic work on the relation between sentence comprehension and discourse comprehension will support deeper insights into the nature of aphasia and other language disorders, and note the existence of recent work, described briefly below, discussing whether some of the phenomena that agrammatic aphasics exhibit are essentially syntactic (Friedman & Grodzinsky, 1997) or discourse-based (specifically, reflective of the overuse of ellipsis; de Roo, 2000).

NSF Prosody in Language Comprehension

In order to understand a sentence or discourse, readers and listeners must use their implicit knowledge of the grammar of their language to put the meanings of its words together. A great deal has been learned about how this process takes place during reading. Less is known about the aspects of the process that are specific to listening. The proposed research will explore how a listener uses the prosody of a sentence (informally speaking, its rhythmic and melodic structure) to determine its message. The specific goals of the research are to work toward identifying precisely what aspects of the prosody of a sentence affect a listener's comprehension and to examine the cognitive processes that enable a listener to use prosody. Broader goals include working toward the development of a theory of spoken language comprehension that specifies how prosodic descriptions are arrived at and how they interact with other sources of information about language and potentially enabling technological improvements in communication, for instance in human-computer spoken interaction.

The proposed research will explore just which aspects of a sentence's prosody listeners use in identifying its structure and meaning. It will evaluate the thesis that a listener constructs a global prosodic representation of a sentence rather than simply relying on local prosodic cues. This thesis makes it crucial to address the question of what in the global prosodic representation is actually effective in guiding sentence comprehension.

Some of the proposed experiments examine how ambiguous phrases can be attached to different points in the phrases that precede them. For instance, in a sentence like Sammy learned that Bill telephoned after John visited, the adjunct phrase after John visited could modify either learn or telephone. Such a phrase should be more likely to attach high, modifying the main clause verb learn, if it is preceded by an intonational boundary, which is signalled by pitch movement and temporal changes. The proposed experiments investigate whether different types of intonational boundaries have different effects and evaluate the claim that only an "informative" boundary will affect interpretation. They evaluate a definition of "informative" that claims a boundary is informative if it is phonologically larger than certain structurally-defined earlier boundaries. The experiments provide several different tests, using several different grammatical constructions, of whether prosodic boundaries that are informative under this definition encourage high attachment of ambiguous phrases

Other experiments addresses the hypothesis that listeners take unusual ("marked") prosody to indicate an unusual interpretation of a sentence. This "markedness strategy" has been proposed a number of times, and several pieces of experimental evidence seem to be consistent with it. However, the markedness strategy may be only a crude approximation to reality. The proposed experiments, which study the interpretation of pronouns, reflexives, and quantified NPs, attempt to determine whether the phenomena described by the markedness hypothesis actually reflect simpler, more general prosodic principles of focus and accent.