Titolo della tesi: Behavioral and electrophysiological investigation of the interplay between selective spatial attention and visual short-term memory in visual consciousness
Visual experience appears instantaneous, but a lot is going on behind the scenes. Visual information processing extensively draws on, and interacts with, various resources including visual short-term memory and selective attention, involving several brain regions. Research in visual experience, information processing, attention, working memory and their neural counterparts has increasingly become specialized, and therefore fragmented.
Special emphasis has been placed on examining the interplay between selective attention and visual short-term memory (VSTM) processes, encompassing iconic memory, fragile-VSTM, and working memory. However, the question of what exactly is the role of attention at the stages of iconic, fragile, and working memory, is beset with controversies, which are closely intertwined with the role of selective attention in visual consciousness. In consciousness studies, it is common to distinguish between phenomenal and access consciousness. The first refers to the way we experience the world through the visual information given to us by the visual system and represents the subjective, first-person experience of sensory contents. The second involves our ability to use visual information for complex processing such as reasoning, planning and decision making. This distinction features in two prominent theories of consciousness: Global Neuronal Workspace Theory and Recurrent Processing Theory. The present thesis examines the contribution of selective spatial attention, to the formation and maintenance of visual information within VSTM, with a particular focus on sensory memory stages, associated with phenomenal consciousness. The first chapter introduces iconic memory, fragile-VSTM, and working memory, along with the two research paradigms that have dominated research in this field: partial report and change detection. Additionally, an overview of key models and theories of visual consciousness, along with insights into the neural correlates of consciousness, will establish the framework for the subsequent studies. The first study (Chapter 2) presents a systematic review of behavioral, electroencephalographic, and neuroimaging studies conducted with partial report and change detection paradigms. This review highlights that while the role of selective attention in working memory is well-supported, its role within sensory memory stages (iconic memory and fragile-VSTM) remains a topic of considerable debate. Notably, different attentional manipulations show distinct effects on sensory memory, with spatial attention particularly influencing sensory memory representations. The second study (Chapters 3 and 4) consists of a behavioral and electrophysiological investigation into the role of spatial attention in sensory memory stages. Using a change detection paradigm, attention was manipulated through a spatial pre-cue, predicting (i.e., valid condition) or not predicting (i.e., invalid condition) the location of the probe. EEG data were collected to monitor spatial attentional resource allocation and to explore interactions between attention, memory, and conscious perception by tracking N2pc, VAN, and P3b components during maintenance. Findings revealed that sensory memory is affected by the modulation of spatial attention during the encoding phase, showing both attentional diversion costs and facilitation benefits. The interaction between spatial attention and sensory memory was further confirmed by electrophysiological results. VAN—but not P3b— resulted implicated in conscious perception, showing interactions with the pre-cue manipulation, which suggests that attentional mechanisms during encoding influenced VAN expression. The third study (Chapter 5) focuses on a more in-depth exploration of the role of spatial attention in memory trace formation and maintenance. A change-detection double retro-cueing paradigm was employed to assess the maintenance and retrieval of both attended and unattended items. Results confirmed the critical role of spatial attention in forming and maintaining sensory memory traces, showing that spatially attended items were more easily retrieved and better maintained, whereas unattended items either failed to enter sensory memory or were too fragile to be retained. The results of this thesis reveal a complex interplay between sensory memory and spatial attention, suggesting that conscious perception is strongly facilitated by, but not entirely dependent on, spatial attention.