Searching for the trace: Examining phonological processing during articulatory suppression in healthy adults

Research Conducted as part of MSc Psychology Conversion at Middlesex University.

Background
Conduction Aphasia (CA) is a relatively rare form of aphasia characterized by repetition problems but relatively unimpaired comprehension (Baldo et al., 2008; Bartha & Benke, 2003). The hallmarks of acute CA are phonemic paraphasias, conduit d’approche and difficulty finding words during spontaneous speech production; the single word repetition deficit also increases with word length (Bartha & Benke, 2003). In deep dysphasia, a rare form of CA, the repetition of single concrete words is less impaired than that of non-words and low imageability words (Majerus et al. 2001; Majerus, 2013).

Although originally thought to be an output problem, CA is now considered an auditory-verbal short-term memory deficit. The most robust model for working memory was first formulated in 1975 by Baddeley. His model comprises of a central executive and two storage systems; the phonological loop and the visuospatial sketchpad (Baddeley, 2006). According to Baddeley’s working memory model, the phonological store maintains auditory information very briefly, allowing time for a phonological trace to be rehearsed through sub-vocalisation. This rehearsal stage is called the phonological loop. Once consolidated, the phonological trace is stored in our short-term memory (Baddeley, 2003). Articulatory suppression (the process of repeatedly articulating unrelated words) is thought to block the process of sub-vocalisation and therefore the phonological trace is degraded (Repovs & Baddeley, 2006). During articulatory suppression, the ability to remember the auditorily presented items is impaired (Repovs & Baddeley, 2006).

Research with CA patients has shown that whilst they cannot not repeat verbatim what is said to them, they do retain the gist of what has been said (Baldo et al., 2008). In Baldo et al.’s study, during repetition recognition tasks CA patients were required to listen to sentences and then asked to point to the sentence they had just heard. On each trial three sentences were presented. On some trials two distractor sentences contained semantically-distinct words (eg. ‘The pigeons entered the stadium.’ and ‘The players entered the stadium’), whilst on other trials the distractor sentences contained semantically-similar words (eg. ‘The mug was broken.’ and ‘The cup was broken’). CA patients performed well on the semantically-distinct tasks, but made significantly more errors when the distractors contained semantically-similar words compared to matched controls with left-hemisphere brain injuries. Baldo et al. suggest that CA patients cannot rely on the phonological trace and rely upon a lexical-semantic pathway for repetition instead. There is now evidence to support two distinct neuronal pathways for lexical-semantics and phonological processing in short term memory (Majerus, 2013).

Aims & Objectives
The proposed research aims to simulate the repetition deficits of CA in normal healthy adults by overloading the phonological loop via articulatory suppression. The timing of the articulatory suppression (concurrent to presentation or delayed) will show whether the phonological deficit in CA occurs at the point of encoding or during sub-vocal rehearsal. We will also examine if the deficit occurs at the same locus for non-words and real words.

The experiments will involve a series of repetition recognition tasks with real words and non-words. Participants will listen to information whilst undertaking articulatory suppression. They will then be asked to indicate which sentence they heard from a selection of three sentences. The target sentence will be presented with two distractor sentences containing semantically similar and semantically distinct words.

Methodology
Data will be collected from participants with the use of Superlab software and will be analysed with SPSS. Students will be recruited from the first year pool of Psychology Undergraduates at Middlesex University. Participants will be screened for their language skills; English must be their mother tongue or they must have 10 years’ experience speaking English.

References
Baddeley, A. (2003). Working memory: Looking back and looking forward. Nature Reviews Neuroscience, 4(10), 829-839.
Baldo, J. V., Klostermann, E. C., &Dronkers, N. F. (2008). It’s either a cook or a baker: Patients with conduction aphasia get the gist but lose the trace. Brain and language, 105(2), 134-140.
Bartha, L., &Benke, T. (2003). Acute conduction aphasia: an analysis of 20 cases. Brain and language, 85(1), 93-108.
Majerus, S., Lekeu, F., de Linden, M. V., & Salmon, E. (2001). Deep dysphasia: Further evidence on the relationship between phonological short-term memory and language processing impairments. Cognitive Neuropsychology, 18(5), 385-410.
Majerus, S. (2013) Language repetition and short-term memory: an integrative framework. Frontiers in Human Neuroscience, 1, 0.
Repovš, G., &Baddeley, A. (2006). The multi-component model of working memory: explorations in experimental cognitive psychology. Neuroscience, 139(1), 5-21.