Verbal short-term memory and language processing: what repetition can tell us

This dissertation focuses on two main aspects regarding short-term memory: on the one hand, through a series of behavioral studies on healthy subjects, it is aimed at disentangling the debate on the importance of semantic information during processes involving short-term memory; on the other hand, it suggests the exploitation of differences in short-term memory load during rehabilitation treatments of neurologically impaired patients. Studies 1 and 2 investigated healthy subjects’ performance on serial recall tasks manipulating the familiarity with phonology and semantics of the words used. Results replicated the performance of a patient affected by semantic dementia described by Papagno et al. (2013), and confirmed that short-term memory performance is enhanced by familiarity with the phonological forms of the words, and not by the knowledge of their meanings. Studies 3 and 4 focused on sentence repetition, another task that taps on short-term memory resources. These experiments were aimed at testing the efficacy of a specific sentence repetition treatment protocol for people with aphasia. Using sentences with similar superficial appearance, but with different complexity of the syntactic structure, it is possible to manipulate the memory load required for repetition, and to obtain better performance when using the easier structure to prime the more complex one. This finding could give interesting hints for the development of new treatment approaches at sentence level, accounting for both linguistic theory and memory system. Through Study 5, the efficacy of a non-invasive brain stimulation technique, namely a-tDCS, in improving short-term memory performance was tested: the modulation of cortical excitability of the left inferior parietal lobule, considered to be the neural correlate of a subcomponent of the phonological loop, improves the maintenance of words in their correct order during serial recall. This could be particularly interesting, since tDCS may be used in cognitive rehabilitation of patients with short-term memory impairments.