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.