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I: Psycholinguistics The field of linguistics focuses on identifying and explaining what components (i.e., types of abstract representations) and constraints are involved in mapping between forms and meanings. The field of psycholinguistics takes linguistic knowledge a step further and applies it in studies that aim to understand (a) the nature and dynamics of processing within and between levels of linguistic representation, and (b) the interface between language and other types of cognitive processing. If this distinction isn't clear to you now, it hopefully will be by the end of this unit! II: Linguistic vs. Psycholinguistic Accounts of Aphasia In this section, we will look at two aspects of aphasia, agrammatism and para-phasia/grammatism, and examine how linguistic and psycholinguistic approaches account for each type of disorder. Agrammatism Linguistic Account A linguistic account of agrammatism describes it as a “language-based” disturbance of grammatical morphology and syntactic representations. For example, Grodzinsky (2000) argues that agrammatic aphasic individuals have lost some of the representations in their syntactic tree—namely, everything above and including the Tense node. Moreover, Grodzinsky links this loss exclusively to Broca’s area. One of the consequences of this presumed loss is that agrammatic individuals can no longer access information in the COMP position. Thus, if a sentence involves a Wh- element in COMP (more specifically, Spec of CP) that was moved from another sentence position, the trace left behind by such movement cannot be co-indexed with the Wh-element in COMP, nor its NP head/referent in the Subject NP position. As a result, the Subject NP that is relativized cannot receive its thematic role via the trace position as in the figure below. Grodzinsky refers to this account as the “trace deletion hypothesis” (TDH). There are a number of fundamental limitations to Grodzinsky’s linguistic TDH account of agrammatism (see also, Grodzinsky, 2010). First, it doesn’t account for all the data. Agrammatic individuals have difficulty processing verbs and certain grammatical morphology which do not entail positions in Tense or COMP. Second, there is considerable variability in aphasic individual’s comprehension of sentences with moved constituents (as well as their use of verbs, grammatical morphology, etc) indicating that there hasn’t been a loss of the COMP node (or any other linguistic knowledge). Third, the TDH doesn’t explain why traces might be affected (rather than AGR or NP), nor why moved constituents, verbs, and grammatical morphology are all vulnerable. Fourth, the same pattern of agrammatic performance can be seen in different populations: children, aphasics, and normal adults under stressful processing conditions. Certainly one cannot argue that normal adults “lose” traces! All of these challenges to TDH point to the need for an alternative explanation of agrammatic performance. Psycholinguistic Accounts In contrast to the linguistic account, psycholinguistic explanations of agrammatism appeal to the cognitive processing demands associated with producing or comprehending linguistic elements and their relations. For example, establishing relations among noun phrases via syntax places demands on working memory capacity, a finite pool of processing resources (or brain energy) that enables concurrent storage/rehearsal and computation of information. Thus, to the extent that such relations are not transparent, performance should decrease. In the sentence “The girl who the boy chased tripped over a cat,” one must establish meaning relations between the Subject NP (The girl) and the embedded Verb (chased), but this relationship, or thematic role assignment, is not transparent due to the movement of the Wh- pronoun “who” from its post-verbal position. Therefore, in order to correctly understand this sentence, a person must not only have intact grammatical knowledge, but he/she must also be able to hold onto the Subject NP until its trace is encountered (i.e., after “chased”) and then assign the role of Theme to “The girl.” These storage and concurrent information processing operations place demands on working memory, which because it is finite in capacity, means that there will be less energy available for other processing. The following figures represent one conceptualization of working memory capacity (phonological loop and central executive) and the brain regions thought to support its various components.