Matthew Goldrick

Discreteness and interactivity in spoken word production.

Five theories of spoken word production that differ along the discreteness-interactivity dimension are evaluated. Specifically examined is the role that cascading activation, feedback, seriality, and interaction domains play in accounting for a set of fundamental observations derived from patterns of speech errors produced by normal and brain-damaged individuals. After reviewing the evidence from normal speech errors, case studies of 3 brain-damaged individuals with acquired naming deficits are presented. The patterns these individuals exhibit provide important constraints on theories of spoken naming. With the help of computer simulations of the 5 theories, the authors evaluate the extent to which the error patterns predicted by each theory conform with the empirical facts. The results support a theory of spoken word production that, although interactive, places important restrictions on the extent and locus of interactivity.

Cascading activation from phonological planning to articulatory processes: Evidence from tongue twisters

Research into spoken word production has often focused on the interaction of lexical selection processes and phonological planning. Less attention has been given to the relationship between phonological planning and articulatory processes. The current study considers evidence from the tongue-twister paradigm to investigate such potential interactions. Acoustic analyses of various parameters of obstruents voicing in tongue twister productions show that errors induced in tongue twisters leave acoustic “traces” of the intended target. For example, the voice-onset time of “k”→[g] error tokens had a mean VOT that was longer than correctly produced “g”→[g] tokens, reflecting a trace of the voiceless [k] target. This effect is attributed to the cascade of partially activated phonological representations of the target consonant into articulatory processes. Consistent with this account, a post-hoc analysis revealed an additional influence of cascading activation from word-level processes; traces of the target were reduced in word outcomes relative to nonword outcomes. Finally, extension of these analyses to a set of secondary cues to obstruent voicing showed that non-local cues are not influenced by tongue twister production errors.

Lexical and Post-Lexical Phonological Representations in Spoken Production.

Theories of spoken word production generally assume a distinction between at least two types of phonological processes and representations: lexical phonological processes that recover relatively arbitrary aspects of word forms from long-term memory and post-lexical phonological processes that specify the predictable aspects of phonological representations. In this work we examine the spoken production of two brain-damaged individuals. We use their differential patterns of accuracy across the tasks of spoken naming and repetition to establish that they suffer from distinct deficits originating fairly selectively within lexical or post-lexical processes. Independent and detailed analyses of their spoken productions reveal contrasting patterns that provide clear support for a distinction between two types of phonological representations: those that lack syllabic and featural information and are sensitive to lexical factors such as lexical frequency and neighborhood density, and those that include syllabic and featural information and are sensitive to detailed properties of phonological structure such as phoneme frequency and syllabic constituency.

Mechanisms of interaction in speech production

Many theories predict the presence of interactive effects involving information represented by distinct cognitive processes in speech production. There is considerably less agreement regarding the precise cognitive mechanisms that underlie these interactive effects. For example, are they driven by purely production-internal mechanisms (e.g., Dell, 1986) or do they reflect the influence of perceptual monitoring mechanisms on production processes (e.g., Roelofs, 2004)? Acoustic analyses reveal the phonetic realisation of words is influenced by their word-specific properties – supporting the presence of interaction between lexical-level and phonetic information in speech production. A second experiment examines what mechanisms are responsible for this interactive effect. The results suggest the effect occurs on-line and is not purely driven by listener modelling. These findings are consistent with the presence of an interactive mechanism that is online and internal to the production system.

Limited interaction in speech production: Chronometric, speech error, and neuropsychological evidence

Results from chronometric and speech errors studies provide convergent evidence for both lower and upper bounds on interaction within the speech production system. Some degree of cascading activation is required to account for patterns of speech errors in neurologically intact and impaired speakers as well as the results of recent chronometric studies. However, the strength of this form of interaction must be limited to account for the occurrence of selective deficits in the production system and restrictions on the conditions under which interactive effects influence reaction times. Similarly, some amount of feedback from phonological to word-level representations is necessary to account for patterns of speech errors in neurologically intact and impaired individuals as well as the influence of phonological neighbours on response latency. This interactive mechanism must also be limited to account for restrictions on the types of speech errors produced following selective deficits within the production system. Results from a variety of empirical traditions therefore converge on the same conclusion: interaction is present, but it must be crucially limited.

The interaction of lexical and sublexical information in spelling: What's the point?

Most theories of spelling propose two major processes for translating between orthography and phonology: a lexical process for retrieving the spellings of familiar words and a sublexical process for assembling the spellings of unfamiliar letter strings based on knowledge of the systematic correspondences between phonemes and graphemes. We investigated how the lexical and sublexical processes function and interact in spelling by selectively interfering with the sublexical process in a dysgraphic individual. By comparing spelling performance under normal conditions and under conditions of sublexical disruption we were able to gain insight into the functioning and the unique contributions of the sublexical process. The results support the hypothesis that the sublexical process serves to strengthen a target word and provide it with a competitive advantage over orthographically and phonologically similar word neighbours that are in competition with the target for selection.

Phonological neighborhood effects in spoken word production: An fmri study

The current study examined the neural systems underlying lexically conditioned phonetic variation in spoken word production. Participants were asked to read aloud singly presented words, which either had a voiced minimal pair (MP) neighbor (e.g., cape) or lacked a minimal pair (NMP) neighbor (e.g., cake). The voiced neighbor never appeared in the stimulus set. Behavioral results showed longer voice-onset time for MP target words, replicating earlier behavioral results [Baese-Berk, M., & Goldrick, M. Mechanisms of interaction in speech production. Language and Cognitive Processes, 24, 527–554, 2009]. fMRI results revealed reduced activation for MP words compared to NMP words in a network including left posterior superior temporal gyrus, the supramarginal gyrus, inferior frontal gyrus, and precentral gyrus. These findings support cascade models of spoken word production and show that neural activation at the lexical level modulates activation in those brain regions involved in lexical selection, phonological planning, and, ultimately, motor plans for production. The facilitatory effects for words with MP neighbors suggest that competition effects reflect the overlap inherent in the phonological representation of the target word and its MP neighbor.

A restricted interaction account (RIA) of spoken word production: The best of both worlds

Theories of spoken word production generally assume that mapping from conceptual representations (e.g., [furry, feline, domestic]) to phonemes (e.g., /k/, /æ/, /t/) involves both a meaning-based process and a sound-based process. A central question in this framework is how these two processes interact with one another. Two theories that occupy extreme positions on the continuum of interactivity are reviewed: a highly discrete position (e.g., Levelt, Roelofs, & Meyer, 1999), in which the two processes occur virtually independently; and a highly interactive position (e.g., Dell et al., 1997) in which the two processes exert considerable mutual influence over one another. Critical examination of the empirical data reveals that neither position can account for the full range of findings. An alternative position, the restricted interaction account (RIA), is described. By combining aspects of both highly discrete and highly interactive accounts, RIA can account for the existing empirical data, as well as for more recent challenges to interactive accounts.

Optimization and Quantization in Gradient Symbol Systems: A Framework for Integrating the Continuous and the Discrete in Cognition

Mental representations have continuous as well as discrete, combinatorial properties. For example, while predominantly discrete, phonological representations also vary continuously; this is reflected by gradient effects in instrumental studies of speech production. Can an integrated theoretical framework address both aspects of structure? The framework we introduce here, Gradient Symbol Processing, characterizes the emergence of grammatical macrostructure from the Parallel Distributed Processing microstructure (McClelland, Rumelhart, & The PDP Research Group, 1986) of language processing. The mental representations that emerge, Distributed Symbol Systems, have both combinatorial and gradient structure. They are processed through Subsymbolic Optimization-Quantization, in which an optimization process favoring representations that satisfy well-formedness constraints operates in parallel with a distributed quantization process favoring discrete symbolic structures. We apply a particular instantiation of this framework, λ-Diffusion Theory, to phonological production. Simulations of the resulting model suggest that Gradient Symbol Processing offers a way to unify accounts of grammatical competence with both discrete and continuous patterns in language performance.

SPEAKING WORDS: CONTRIBUTIONS OF COGNITIVE NEUROPSYCHOLOGICAL RESEARCH

We review the significant cognitive neuropsychological contributions to our understanding of spoken word production that were made during the period of 1984 to 2004–since the founding of the journal Cognitive Neuropsychology. We then go on to identify and discuss a set of outstanding questions and challenges that face future cognitive neuropsychological researchers in this domain. We conclude that the last 20 years have been a testament to the vitality and productiveness of this approach in the domain of spoken word production and that it is essential that we continue to strive for the broader integration of cognitive neuropsychological evidence into cognitive science, psychology, linguistics, and neuroscience.