Short-term memory, working memory, and syntactic comprehension in aphasia

Abstract

Sixty one people with aphasia were tested on ten tests of short term memory (STM) and for the ability to use syntactic structure to determine the meanings of eleven types of sentences in three tasks – object manipulation, picture matching and picture matching with self-paced listening. Multilevel models showed relationships between measures of the ability to retain and manipulate item and order information in STM and accuracy and RT, and a greater relationship between these STM measures and accuracy and RT for several more complex sentence types in individual tasks. There were no effects of measures of STM that reflect the use of phonological codes or rehearsal on comprehension. There was only one effect of STM measures on self-paced listening times. There were double dissociations between performance on STM and individual comprehension tasks, indicating that normal STM is not necessary to perform normally on these tasks. The results are most easily related to the view that STM plays a facilitatory role in supporting the use of the products of the comprehension process to accomplish operations related to tasks.

Profiling text comprehension impairments in aphasia

“…Working memory is not just about storage capacity, indeed, research with healthy adult readers suggests that for text comprehension, the important factor is the ability to allocate attention and control relevant information at any one moment (McVay & Kane, 2012). Impairments in working memory may therefore interact with linguistic deficits (Caplan, Michaud, & Hufford, 2013). For example, difficulty in retrieving relevant information via lexical or syntactic processes will be further compounded by difficulties in deploying that information to build a rich representation of the text (i.e., the situation model).…”

Neurophysiological Markers of Language Recovery in Subacute Stroke

“…In aphasia, the processing of sentences is considered to be heavily dependent on other cognitive functions such as verbal working memory (Caplan et al, 2013) and associated with left IFG (Binder et al, 2009;Binder et al, 2005). In contrast, activity in the left AG associated with semantic processing has been widely reported (Price, 2010) and indeed, a meta-analysis on semantics by Binder et al (2009) identified this region as being the most routinely activated in response to semantic-based tasks.…”

“…Sentence level processing is considered to rely heavily on other cognitive functions, in particular verbal working memory (Caplan, Michaud, & Hufford, 2013). Therefore, the task-related prefrontal activity may actually reflect an increased requirement for attention and cognitive control mechanisms (Geranmayeh, Brownsett, & Wise, 2014) which are reduced in the acute phase, increased in the subacute phase and then return to normal activation patterns in the left hemisphere language areas in the chronic phase once support from the right hemisphere is no longer required (Saur et al, 2006) (this is covered in more depth in the discussion in Chapter 5).…”

“…This poses problems when interpreting task-related brain activity, as it cannot be ascertained whether the brain activity elicited reflects an impaired performance or whether the impaired performance is caused by the underlying neural deficits . A further limitation of the Saur et al (2006) study relates to the use of a sentence level task as sentence comprehension in aphasia is significantly reliant on other cognitive functions, particularly verbal working memory (Caplan et al, 2013). Since task-related activity observed in aphasia often reflects increased cognitive control and attention (Geranmayeh et al, 2014), there is a need to consider less cognitively demanding language tasks that can provide unique insights into aphasia recovery.…”

“…This presents a problem in the interpretation of brain activation as it is unclear whether the activity is indicative of an impaired performance or whether it is attributable to the neural deficit itself which underlies the impairment . In addition, the type of task employed required sentence comprehension which is known to rely significantly on other cognitive functions and in particular on verbal working memory (Caplan et al, 2013). Geranmayeh et al (2014 have suggested that much language-related brain activity observed in aphasia studies can be explained by the upregulation of regions more associated with attention and cognitive control and as such, they suggest that language tasks employed for aphasic patients need to be less cognitively demanding in order that mechanisms associated specifically with language processes can be clearly determined.…”