Explaining individual differences in linguistic proficiency

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Garden-Path Effects and Recovery in Aphasia

How people resolve and recover from syntactic ambiguity has been a central research topic in the psycholinguistic literature on sentence comprehension. It has attracted less attention in the literature on communicative impairments. However, there is increasing evidence that brain damage can affect how adults understand syntactically ambiguous sentences, both for right-hemisphere brain damage (e.g., Schneiderman & Saddy, 1988) and left-hemisphere damage (e.g., Novick, Trueswell & Thompson-Schill, 2005). Understanding how persons with aphasia (PWA) comprehend syntactically ambiguous sentences is therefore important to evaluating their communicative function, specifically their sentence comprehension ability. Syntactically ambiguous sentences are often referred to as garden-path sentences (Bever, 1970). These sentences lead comprehenders “down the garden path”: they cause readers or listeners to briefly misinterpret an ambiguous word or phrase, initially misanalyzing its syntactic role in the sentence. Subsequent information then indicates that this initial interpretation was incorrect, forcing comprehenders to reinterpret the sentence. This garden-path effect has been consistently found in healthy young and older adults (Christianson, et al., 2001, 2006; Ferreira & Henderson, 1991; Frazier & Rayner, 1982). Syntactic ambiguity resolution may be particularly strongly affected by reduced cognitive function such as reduced working memory (WM), common in healthy aging (e.g., Christianson, et al., 2006; Kemper et al., 2004). Kemper and colleagues (2004) found that older adults showed larger garden-path effects than younger adults, spending longer reading and re-reading garden-path sentences, and that these age-related differences were mediated by WM. This finding provides evidence of the importance of WM in resolving syntactic ambiguities. Christianson, et al. (2006) found that older adults’ comprehension question accuracy for garden-path sentences was correlated with their WM span. This finding provides evidence of the role of WM in successful recovery from a garden path. However, there has been little research on whether PWA also exhibit garden-path effects in their real-time comprehension of syntactically ambiguous sentences, or how successfully they recover from such garden paths. PWA have also been argued to have reduced WM capacity which contributes to their sentence comprehension deficits (e.g., Miyake, Carpenter & Just, 1994). WM is likely involved in the reanalysis of garden-path sentences (Kemper, et al., 2004), since reanalysis requires performing operations on structures held in memory. This study therefore examined the comprehension of garden-path sentences in PWA, and tested how their on-line garden-path effects and their off-line garden-path recovery were predicted by WM and short-term memory (STM)

Resolving Semantic Ambiguities in Sentences: Cognitive Processes and Brain Mechanisms

fMRI studies of how the brain processes sentences containing semantically ambiguous words have consistently implicated (i) the left inferior frontal gyrus (LIFG) and (ii) posterior regions of the left temporal lobe in processing high-ambiguity sentences. This article reviews recent findings on this topic and relates them to (i) psycholinguistic theories about the underlying cognitive processes and (ii) general neuro-cognitive accounts of the relevant brain regions. We suggest that the LIFG plays a general role in the cognitive control process that are necessary to select contextually relevant meanings and to reinterpret sentences that were initially misunderstood, but it is currently unclear whether these control processes should best be characterised in terms of specific processes such as conflict resolution and controlled retrieval that are required for high-ambiguity sentences, or whether its function is better characterised in terms of a more general set of ‘unification’ processes. In contrast to the relatively rapid progress that has been made in understanding the function of the LIFG, we suggest that the contribution of the posterior temporal lobe is less well understood and future work is needed to clarify its role in sentence comprehension

Ageing makes us dyslexic

Background: The effects of typical ageing on spoken language are well known: word production is disproportionately affected while syntactic processing is relatively well preserved. Little is known, however, about how ageing affects reading.Aims: What effect does ageing have on written language processing? In particular, how does it affect our ability to read words? How does it affect phonological awareness (our ability to manipulate the sounds of our language)?Methods & Procedures: We tested 14 people with Parkinson's disease (PD), 14 typically ageing adults (TAA), and 14 healthy younger adults on a range of background neuropsychological tests and tests of phonological awareness. We then carried out an oral naming experiment where we manipulated consistency, and a nonword repetition task where we manipulated the word-likeness of the nonwords.Outcomes & Results: We find that normal ageing causes individuals to become mildly phonologically dyslexic in that people have difficulty pronouncing nonwords. People with Parkinson's disease perform particularly poorly on language tasks involving oral naming and metalinguistic processing. We also find that ageing causes difficulty in repeating nonwords. We show that these problems are associated with a more general difficulty in processing phonological information, supporting the idea that language difficulties, including poorer reading in older age, can result from a general phonological deficit.Conclusions: We suggest that neurally this age-induced dyslexia is associated with frontal deterioration (and perhaps deterioration in other regions) and cognitively to the loss of executive processes that enable us to manipulate spoken and written language. We discuss implications for therapy and treatment

The kindergarten-path effect revisited: children’s use of context in processing structural ambiguities

Research with adults has shown that ambiguous spoken sentences are resolved efficiently, exploiting multiple cues—including referential context—to select the intended meaning. Paradoxically, children appear to be insensitive to referential cues when resolving ambiguous sentences, relying instead on statistical properties intrinsic to the language such as verb biases. The possibility that children’s insensitivity to referential context may be an artifact of the experimental design used in previous work was explored with 60 4- to 11-year-olds. An act-out task was designed to discourage children from making incorrect pragmatic inferences and to prevent premature and ballistic responses by enforcing delayed actions. Performance on this task was compared directly with the standard act-out task used in previous studies. The results suggest that young children (5 years) do not use contextual information, even under conditions designed to maximize their use of such cues, but that adult-like processing is evident by approximately 8 years of age. These results support and extend previous findings by Trueswell and colleagues (Cognition (1999), Vol. 73, pp. 89–134) and are consistent with a constraint-based learning account of children’s linguistic development.</p

Cascading Activation Across Levels of Representation in Children's Lexical Processing

Recent work in adult psycholinguistics has demonstrated that activation of semantic representations begins long before phonological processing is complete. This incremental propagation of information across multiple levels of analysis is a hallmark of adult language processing but how does this ability develop? In two experiments, we elicit measures of incremental activation of semantic representations during word recognition in children. Five-year-olds were instructed to select a target (logs) while their eye-movements were measured to a competitor (key) that was semantically related to an absent phonological associate (lock). We found that like adults, children made increased looks to competitors relative to unrelated control items. However unlike adults, children continued to look at the competitor even after the target word was uniquely identified and were more likely to incorrectly select this item. Altogether, these results suggest that early lexical processing involves cascading activation but less efficient resolution of competing entries.Psycholog

Concept Typicality Responses in the Semantic Memory Network

For decades concept typicality has been recognized as critical to structuring conceptual knowledge, but only recently has typicality been applied in better understanding the processes engaged by the neurological network underlying semantic memory. This previous work has focused on one region within the network – the Anterior Temporal Lobe (ATL). The ATL responds negatively to concept typicality (i.e., the more atypical the item, the greater the activation in the ATL). To better understand the role of typicality in the entire network, we ran an fMRI study using a category verification task in which concept typicality was manipulated parametrically. We argue that typicality is relevant to both amodal feature integration centers as well as category-specific regions. Both the Inferior Frontal Gyrus (IFG) and ATL demonstrated a negative correlation with typicality, whereas inferior parietal regions showed positive effects. We interpret this in light of functional theories of these regions. Interactions between category and typicality were not observed in regions classically recognized as category-specific, thus, providing an argument against category specific regions, at least with fMRI

The role of executive control in resolving grammatical number conflict in sentence comprehension

In sentences with a complex subject noun phrase, like “The key to the cabinets is lost”, the grammatical number of the head noun (key) may be the same or different from the modifier noun phrase (cabinets). When the number is the same, comprehension is usually easier than when it is different. Grammatical number computation may occur while processing the modifier noun (integration phase) or while processing the verb (checking phase). We investigated at which phase number conflict and plausibility of the modifier noun as subject for the verb affect processing, and we imposed a gaze-contingent tone discrimination task in either phase to test whether number computation involves executive control. At both phases, gaze durations were longer when a concurrent tone task was present. Additionally, at the integration phase, gaze durations were longer under number conflict, and this effect was enhanced by the presence of a tone task, whereas no effects of plausibility of the modifier were observed. The finding that the effect of number match was larger under load shows that computation of the grammatical number of the complex noun phrase requires executive control in the integration phase, but not in the checking phase