Advances in Neurolinguistics: Semantics of Word Production in Aphasia

Arpita Bose, Ph.D., & Lori Buchanan, Ph.D.
Department of Psychology
University of Windsor, Canada

Gary Libben, Ph.D.
Department of Linguistics
University of Alberta, Canada

Introduction:

Neurolinguistics is focused on understanding neural mechanisms underlying comprehension, production and abstract knowledge of language, be it spoken, signed or written. Historically, neurolinguistics has been most closely associated with aphasiology, the study of linguistic deficits resulting from brain damage. However, in recent years, the field of neurolinguistics has broadened. Researchers are investigating various types of speech-language disorders (e.g., stuttering, dyslexia) as well as normal language processing to better understand the neurological and cognitive bases of language processing.

Neurolinguistics is an interdisciplinary endeavor involving linguistics, psychology, neurobiology, speech-language pathology and computer science, to name a few. Researchers are drawn from a variety of backgrounds and bring a wide range of experimental techniques and differing theoretical perspectives. Researchers in neurolinguistics employ traditional and advanced neurophysiological and brain imaging techniques. Traditional methodologies may include; behavioral data, reaction time and error rate measures to tasks such as picture naming or word comprehension. Advanced technologies may include brain imaging techniques (e.g., Positron Emission Tomography [PET], functional Magnetic Resonance Imaging [fMRI]) and gross electrophysiological techniques (e.g., Electroencephalography [EEG], Event Related Potentials [ERP]).

This article will focus on word processing and lexical access with respect to aphasia, with an emphasis on semantics of word processing. We chose to focus on word processing and/or lexical access because difficulty in naming (e.g., anomia) is virtually universal in aphasia. Errors in naming are generically referred to as paraphasia. Collectively, this term is applied to any unintended error of word or sound choice. Paraphasias include phonemic paraphasia (production of unintended sounds or syllables in the utterance of partially recognizable word, e.g., 'paker' for 'paper'), semantic paraphasia (production of word similar in concept or meaning to the correct production, e.g., 'butter' for 'bread') and neologism (the production of nonsense word or words, usually without recognition of errors, e.g., 'table' becomes 'tilto').

The most studied paraphasia is the semantic error. Semantic errors have long been of interest to aphasiologists for what they reveal about the organization of semantic knowledge and how this explains speech planning (Dell, Schwartz, Martin, Saffran, & Gagnon, 1997). The origin and locus of semantic errors in aphasia have been explained from different perspectives depending on the theoretical background of the researcher (Dell et al., 1997; Levelt, Roelofs, & Meyer, 1999).