Investigating visual short-term memory capacity within and between hemifields

A number of non-mnemonic tasks have revealed the existence of a bilateral field advantage (BFA; i.e. the increase in processing capacity when information is distributed across the two visual fields relative to within a single hemifield) in visual processing. Recent research suggests that the BFA may also extend to visual short-term memory (VSTM). However to date, studies have produced inconsistent findings, demonstrating a BFA in VSTM for spatial locations and orientations but not for colours (Delvenne, 2005; Umemoto, Drew, Ester, & Awh, 2010). Two possible hypotheses may account for those findings. The first suggests that the BFA is a feature of processing spatial information but not identity information (the stimulus domain hypothesis) whilst the second claims that the BFA is a feature of attentional selective processing (the attentional selection hypothesis). With the primary aim to uncover the conditions which promote a BFA in VSTM, the present thesis tested those hypotheses. Since the stimulus domain hypothesis predicts no possibility of a BFA for colour VSTM, Part One investigated whether colour VSTM may exhibit a BFA when the task demands on selective attention are increased. The findings revealed this to be the case, highlighting that the requirement to attentionally filter spatially distinct target stimuli from distracter stimuli promoted the BFA. In Part Two, selective attention was also found to promote a BFA in colour VSTM during maintenance. Specifically, the findings suggest that bilaterally encoded items can better survive decay in VSTM when spatial selective attention is oriented to stimuli locations at the encoding stage. Overall, the findings strongly suggest that the BFA in VSTM is a signature of attentional selective processing during VSTM encoding and VSTM maintenance. Those findings have important implications for our understanding of the capacity limits of VSTM and attention, and interhemispheric communication more generally.