Effects of increased memory load on short-term facilitation of repetition in persons with aphasia

The ability to repeat a word involves activation of phonological and semantic representations of words that must be maintained until the utterance is produced. In aphasia, the language and verbal STM impairment frequently co-occur and studies indicate that the severity of these impairments are highly correlated (Martin & Ayala, 2004). One account of this co-occurrence is that the word processing impairment in aphasia is due to an inability to maintain activation of semantic and phonological representations of words over the time course of comprehending, repeating, or producing a word. When severe, this impairment affects single and multiple word processing as well as verbal STM capacity, as measured by verbal span. When milder, the impairment affects multiple word processing and verbal STM capacity. This intimate relationship of lexical access/retrieval and the ability to maintain activation of a word’s representations suggests a need to consider the role of verbal memory load on language performance. For example, it has been shown recently that performance on semantic judgment tasks is significantly reduced when memory load on the task is increased (Martin, Kohen, Kalinyak-Fliszar, Soveri & Laine, 2012). This study also identified two factors contributing to this effect, semantic STM capacity and an executive function, inhibition (performance on the Simon Task). Additionally, it has been shown that performance on phonological and lexical-semantic tasks is compromised by imposing an interval between stimulus and response (Martin, Kohen & Kalinayk-Fliszar, 2010; Martin, 2012). Evidence that increased memory load impairs language performance has prompted some researchers to target the ability to tolerate increased memory load in language tasks as a means of improving language function as well as increasing verbal STM capacity. For example, Majerus, Van der Kaa, Renard, Van der Linden, & Poncelet (2005) treated a phonological STM deficit using delayed repetition of word pairs. There were improvements in digit and nonword span, nonword repetition, rhyme judgments, and by the client’s self-report, comprehension in conversational contexts. Fridriksson, Holland, Beeson, & Morrow (2005) treated three cases of anomia using spaced-retrieval treatment, which varied interval time between presentations of a picture to be named (more time when named correctly and less time when named incorrectly). Compared to a cueing hierarchy treatment, the spaced retrieval approach showed more lasting improvements in follow-up testing. Kalinyak-Fliszar, Kohen & Martin (2011) used nonword and multisyllabic word repetition tasks combined with a delayed response (5 seconds) to improve phonological abilities of a person with conduction aphasia. Improvements were noted in repetition of treated stimuli and other language and verbal STM measures: rhyming and synonymy judgments, word pair repetition and seven verbal span tasks (of eleven administered). These studies indicate that incorporation of variations in verbal memory load into language treatments can improve language function. However, it has not been demonstrated that the addition of STM load provides any greater benefit over and above the language treatment task. In this study, we use a short-term repetition facilitation paradigm to determine if increased memory load added to a repetition task improves performance more than repetition alone