Search

Consensus recommendations for three variants of primary progressive aphasia (PPA), the non-fluent/agrammatic, logopenic and semantic variants, were published in 2011 [Gorno-Tempini et al., 2011]. These recommendations describe the most characteristic language impairments for each variant. However, studies using these criteria in larger groups of patients revealed serious limitations concerning their application. Some of these limitations are related to imprecisions in the description of language features, especially for grammatical features. The aim of this review was to examine studies of inflectional morphology in three variants of PPA and in the disease that is the most relevant for differential diagnosis, namely Alzheimer's disease. MedLine, CINAHL and PsycINFO electronic databases were searched to retrieve all relevant peer-reviewed articles published in English language journals. Despite the focus that has been placed on agrammatism by the consensus recommendations, the studies reviewed do not systematically report impairments of inflectional morphology in the non-fluent/agrammatic variant. Studies also show that some individuals with the logopenic variant present with substantial inflection impairments. Contrary to expectations, some studies reveal the presence of morphological difficulties in the semantic variant. These difficulties concern mostly the production of irregular, low-frequency verbs while regular verbs are spared. Similar difficulties are also reported in studies of people with Alzheimer's disease. Overall, the results show the need to more clearly define the criteria related to grammar and morphology and to better characterise impairment severity. Future research on primary progressive aphasia and other degenerative diseases with language impairments will help refine our expectations regarding language features that characterise each profile. [ABSTRACT FROM AUTHOR]

Abstract: This study uses event-related brain potentials (ERPs) to investigate the temporal sequencing of structural (grammatical) and lexical (semantic) properties of complex words during language comprehension. Morphologically complex words do not only consist of stems and affixes (e.g., ‘feel’+‘-s’), but affixes also contain grammatical structure, viz. feature bundles specifying their morpho-syntactic functions (e.g., -s= [3rd person, singular, present tense]). We examined inflected adjectives of German, which consist of an unaltered stem plus a portmanteau affix encoding case, number and gender. The same group of 24 adult native speakers was tested in two cross-modal ERP priming experiments separately studying effects of lexical–semantic relatedness and related affixes. The results of these experiments revealed clearly distinct brain potentials. Prime-target overlap with respect to morpho-syntactic features was associated with a reduced positivity, whereas lexical-level priming led to a reduced negativity. The former was most pronounced between 200 and 300ms and the latter in a later time window, between 300 and 400ms. We interpret the reduced early positivity as reflecting ease of grammatical processing effort in case of primed (relative to unprimed) morpho-syntactic features and the reduced negativity as signaling facilitation in lexical retrieval for primed (compared to unprimed) words. Our ERP results indicate that grammatical information becomes available earlier than semantic information providing support for structure-first models of language processing. [Copyright &y& Elsevier]

Abstract: The standard task used to study inflectional processing of verbs involves presentation of the stem form from which the participant is asked to generate the past tense. This task reveals a processing disadvantage for irregular relative to regular English verbs, more pronounced for lower-frequency items. Dual- and single-mechanism theories of inflectional morphology are both able to account for this pattern; but the models diverge in their predictions concerning the magnitude of the regularity effect expected when the task involves past-tense generation from meaning. In this study, we asked normal speakers to generate the past tense from either form (verb stem) or meaning (action picture). The robust regularity effect observed in the standard form condition was no longer reliable when participants were required to generate the past tense from meaning. This outcome would appear problematic for dual-mechanism theories to the extent that they assume the process of inflection requires stem retrieval. By contrast, it supports single-mechanism models that consider stem retrieval to be task-dependent. We present a single-mechanism model of verb inflection incorporating distributed phonological and semantic representations that reproduces this task-dependent pattern. [Copyright &y& Elsevier]

Abstract: The aim of the study was to investigate how the input modality affects the processing of a morphologically complex word. The processing of Finnish inflected vs. monomorphemic words and pseudowords was examined during a lexical decision task, using behavioral responses and event-related potentials. The stimuli were presented in two modalities, visually and auditorily, to two groups of participants. Half of the words and pseudowords carried a case-inflection. At the behavioral level, the inflected words elicited a processing cost with longer decision latencies and higher error rates. At the neural level, pseudowords elicited an N400 effect, which was more pronounced in the visual modality. Inflected words elicited an N400 effect in both modalities, which, however, differed in topography and latency. The N400 effect for inflected words most probably reflects access and possible integration of the stem and suffix. The results suggest that the inflectional processing cost stems from the later, lexical-semantic stage of processing in both modalities. The ERP responses to inflected pseudowords did not differ from the ERP responses to monomorphemic pseudowords in either modality, suggesting that combinatorial case-inflection processing requires a real word stem in order to proceed. [Copyright &y& Elsevier]

Abstract: Lexical compounds in English are constrained in that the non-head noun can be an irregular but not a regular plural (e.g. mice eater vs. *rats eater), a contrast that has been argued to derive from a morphological constraint on modifiers inside compounds. In addition, bare nouns are preferred over plural forms inside compounds (e.g. mouse eater vs. mice eater), a contrast that has been ascribed to the semantics of compounds. Measuring eye-movements during reading, this study examined how morphological and semantic information become available over time during the processing of a compound. We found that the morphological constraint affected both early and late eye-movement measures, whereas the semantic constraint for singular non-heads only affected late measures of processing. These results indicate that morphological information becomes available earlier than semantic information during the processing of compounds. [Copyright &y& Elsevier]