Susan Edwards and Christos Salis
Aphasia is an acquired language disorder subsequent to brain damage in the left hemisphere. It is characterized by diminished abilities to produce and understand both spoken and written language compared with the speaker’s presumed ability pre-cerebral damage. The type and severity of the aphasia depends not only on the location and extent of the cerebral damage but also the effect the lesion has on connecting areas of the brain. Type and severity of aphasia is diagnosed in comparison with assumed normal adult language. Language changes associated with normal aging are not classed as aphasia. The diagnosis and assessment of aphasia in children, which is unusual, takes account of age norms.
The most common cause of aphasia is a cerebral vascular accident (CVA) commonly referred to as a stroke, but brain damage following traumatic head injury such as road accidents or gunshot wounds can also cause aphasia. Aphasia following such traumatic events is non-progressive in contrast to aphasia arising from brain tumor, some types of infection, or language disturbances in progressive conditions such as Alzheimer’s disease, where the language disturbance increases as the disease progresses.
The diagnosis of primary progressive aphasia (as opposed to non-progressive aphasia, the main focus of this article) is based on the following inclusion and exclusion criteria by M. Marsel Mesulam, in 2001. Inclusion criteria are as follows: Difficulty with language that interferes with activities of daily living and aphasia is the most prominent symptom. Exclusion criteria are as follows: Other non-degenerative disease or medical disorder, psychiatric diagnosis, episodic memory, visual memory, and visuo-perceptual impairment, and, finally, initial behavioral disturbance.
Aphasia involves one or more of the building blocks of language, phonemes, morphology, lexis, syntax, and semantics; and the deficits occur in various clusters or patterns across the spectrum. The degree of impairment varies across modalities, with written language often, but not always, more affected than spoken language. In some cases, understanding of language is relatively preserved, in others both production and understanding are affected. In addition to varied degrees of impairment in spoken and written language, any or more than one component of language can be affected. At the most severe end of the spectrum, a person with aphasia may be unable to communicate by either speech or writing and may be able to understand virtually nothing or only very limited social greetings. At the least severe end of the spectrum, the aphasic speaker may experience occasional word finding difficulties, often difficulties involving nouns; but unlike difficulties in recalling proper nouns in normal aging, word retrieval problems in mild aphasia includes other word classes.
Descriptions of different clusters of language deficits have led to the notion of syndromes. Despite great variations in the condition, patterns of language deficits associated with different areas of brain damage have been influential in understanding language-brain relationships. Increasing sophistication in language assessment and neurological investigations are contributing to a greater, yet still incomplete understanding of language-brain relationships.
Research in neurolinguistics examines how language is organized and processed in the human brain. The findings from neurolinguistic studies on language can inform our understanding of the basic ingredients of language and the operations they undergo. In the domain of the lexicon, a major debate concerns whether and to what extent the morpheme serves as a basic unit of linguistic representation, and in turn whether and under what circumstances the processing of morphologically complex words involves operations that identify, activate, and combine morpheme-level representations during lexical processing. Alternative models positing some role for morphemes argue that complex words are processed via morphological decomposition and composition in the general case (full-decomposition models), or only under certain circumstances (dual-route models), while other models do not posit a role for morphemes (non-morphological models), instead arguing that complex words are related to their constituents not via morphological identity, but either via associations among whole-word representations or via similarity in formal and/or semantic features. Two main approaches to investigating the role of morphemes from a neurolinguistic perspective are neuropsychology, in which complex word processing is typically investigated in cases of brain insult or neurodegenerative disease, and brain imaging, which makes it possible to examine the temporal dynamics and neuroanatomy of complex word processing as it occurs in the brain. Neurolinguistic studies on morphology have examined whether the processing of complex words involves brain mechanisms that rapidly segment the input into potential morpheme constituents, how and under what circumstances morpheme representations are accessed from the lexicon, and how morphemes are combined to form complex morphosyntactic and morpho-semantic representations. Findings from this literature broadly converge in suggesting a role for morphemes in complex word processing, although questions remain regarding the precise time course by which morphemes are activated, the extent to which morpheme access is constrained by semantic or form properties, as well as regarding the brain mechanisms by which morphemes are ultimately combined into complex representations.
The Japanese psycholinguistics research field is moving rapidly in many different directions as it includes various sub-linguistics fields (e.g., phonetics/phonology, syntax, semantics, pragmatics, discourse studies). Naturally, diverse studies have reported intriguing findings that shed light on our language mechanism. This article presents a brief overview of some of the notable early 21st century studies mainly from the language acquisition and processing perspectives. The topics are divided into various sections: the sound system, the script forms, reading and writing, morpho-syntactic studies, word and sentential meanings, and pragmatics and discourse studies sections. Studies on special populations are also mentioned.
Studies on the Japanese sound system have advanced our understanding of L1 and L2 (first and second language) acquisition and processing. For instance, more evidence is provided that infants form adult-like phonological grammar by 14 months in L1, and disassociation of prosody is reported from one’s comprehension in L2. Various cognitive factors as well as L1 influence the L2 acquisition process. As the Japanese language users employ three script forms (hiragana, katakana, and kanji) in a single sentence, orthographic processing research reveal multiple pathways to process information and the influence of memory. Adult script decoding and lexical processing has been well studied and research data from special populations further helps us to understand our vision-to-language mapping mechanism. Morpho-syntactic and semantic studies include a long debate on the nativist (generative) and statistical learning approaches in L1 acquisition. In particular, inflectional morphology and quantificational scope interaction in L1 acquisition bring pros and cons of both approaches as a single approach. Investigating processing mechanisms means studying cognitive/perceptual devices. Relative clause processing has been well-discussed in Japanese because Japanese has a different word order (SOV) from English (SVO), allows unpronounced pronouns and pre-verbal word permutations, and has no relative clause marking at the verbal ending (i.e., morphologically the same as the matrix ending). Behavioral and neurolinguistic data increasingly support incremental processing like SVO languages and an expectancy-driven processor in our L1 brain. L2 processing, however, requires more study to uncover its mechanism, as the literature is scarce in both L2 English by Japanese speakers and L2 Japanese by non-Japanese speakers. Pragmatic and discourse processing is also an area that needs to be explored further. Despite the typological difference between English and Japanese, the studies cited here indicate that our acquisition and processing devices seem to adjust locally while maintaining the universal mechanism.
Laurie Beth Feldman and Judith F. Kroll
We summarize findings from across a range of methods, including behavioral measures of overall processing speed and accuracy, electrophysiological indices that tap into the early time course of language processing, and neural measures using structural and functional imaging. We argue that traditional claims about rigid constraints on the ability of late bilinguals to exploit the meaning and form of the morphology and morphosyntax in a second language should be revised so as to move away from all or none command of structures motivated from strict dichotomies among linguistic categories of morphology. We describe how the dynamics of morphological processing in neither monolingual or bilingual speakers is easily characterized in terms of the potential to decompose words into their constituent morphemes and that morphosyntactic processing is not easily characterized in terms of categories of structures that are learnable and those that are unlearnable by bilingual and nonnative speakers. Instead, we emphasize the high degree of variability across individuals and plasticity within individuals in their ability to successfully learn and use even subtle aspects of a second language. Further, both of the bilingual’s two languages become active when even one language is engaged, and parallel activation has consequences that shape both languages, thus their influence is not in the unidirectional manner that was traditionally assumed. We briefly discuss the nature of possible constraints and directions for future research.
D. H. Whalen
The Motor Theory of Speech Perception is a proposed explanation of the fundamental relationship between the way speech is produced and the way it is perceived. Associated primarily with the work of Liberman and colleagues, it posited the active participation of the motor system in the perception of speech. Early versions of the theory contained elements that later proved untenable, such as the expectation that the neural commands to the muscles (as seen in electromyography) would be more invariant than the acoustics. Support drawn from categorical perception (in which discrimination is quite poor within linguistic categories but excellent across boundaries) was called into question by studies showing means of improving within-category discrimination and finding similar results for nonspeech sounds and for animals perceiving speech. Evidence for motor involvement in perceptual processes nonetheless continued to accrue, and related motor theories have been proposed. Neurological and neuroimaging results have yielded a great deal of evidence consistent with variants of the theory, but they highlight the issue that there is no single “motor system,” and so different components appear in different contexts. Assigning the appropriate amount of effort to the various systems that interact to result in the perception of speech is an ongoing process, but it is clear that some of the systems will reflect the motor control of speech.
Niels O. Schiller
Neurolinguistic approaches to morphology include the main theories of morphological representation and processing in the human mind, such as full-listing, full-parsing, and hybrid dual-route models, and how the experimental evidence that has been acquired to support these theories uses different neurolinguistic paradigms (visual and auditory priming, violation, long-lag priming, picture-word interference, etc.) and methods (electroencephalography [EEG]/event-related brain potential [ERP], functional magnetic resonance imaging [fMRI], neuropsychology, and so forth).