The Modulation of Visual Spatial Memory by Galvanic Vestibular Stimulation

It is now widely accepted that the vestibular system not only affects autonomic motor function but cognitive function too, most notably visuospatial learning and memory. While many studies have explored this association from a biological perspective, few have done so from a psychological one. The aim of this thesis was to identify a possible psychological mechanism by which the vestibular system specifically interacts with spatial memory processes. Artificially stimulating the vestibular system via trans-mastoidal galvanic current (aka GVS) provides a controlled means by which this vestibular-visual spatial interaction can be explored. In a previous study, we showed that search for a location of a 2-D static visual target was facilitated when that target location was initially encoded with in the presence of a brief, subsensory galvanic signal (L. Smith, Gkioka & Wilkinson, 2020). In Chapter 2, I replicated this GVS advantage in new 2-D visual arrays, showing that temporally co-incident vestibular activation can facilitate visual search and spatial memory in subsequent encounters of that same 2-D spatial representation presented during encoding. Chapter 3 explored whether this cross-modal priming would hold in a dynamic 3-D virtual environment, in which external landmarks were manipulated (present/absent) to test whether the GVS priming is dependent on the location of the target relative to other visual stimuli. The GVS prime was more effective in the presence of visual landmarks, whereby participants chose direct routes more frequently and navigated to the target location with higher accuracy. Finally in Chapter 4, I demonstrated that these beneficial priming effects were also evident in people with dementia who showed visuo-spatial short-term memory impairment. Together these studies suggest that the human brain can make use of momentary vestibular signals to help individuate the encoding of visuospatial memories. The results also provide justification for trialling the therapeutic effects of GVS in amnestic populations.