title: Neural Mechanisms Underlying Visual Short-Term Memory Gain for Temporally Distinct Objects.
abstract: Recent research has shown that visual short-term memory (VSTM) can substantially be improved when the to-be-remembered objects are split in 2 half-arrays (i.e., sequenced) or the entire array is shown twice (i.e., repeated), rather than presented simultaneously. Here we investigate the hypothesis that sequencing and repeating displays overcomes attentional "bottlenecks" during simultaneous encoding. Using functional magnetic resonance imaging, we show that sequencing and repeating displays increased brain activation in extrastriate and primary visual areas, relative to simultaneous displays (Study 1). Passively viewing identical stimuli did not increase visual activation (Study 2), ruling out a physical confound. Importantly, areas of the frontoparietal attention network showed increased activation in repetition but not in sequential trials. This dissociation suggests that repeating a display increases attentional control by allowing attention to be reallocated in a second encoding episode. In contrast, sequencing the array poses fewer demands on control, with competition from nonattended objects being reduced by the half-arrays. This idea was corroborated by a third study in which we found optimal VSTM for sequential displays minimizing attentional demands. Importantly these results provide support within the same experimental paradigm for the role of stimulus-driven and top-down attentional control aspects of biased competition theory in setting constraints on VSTM.
authors.affiliation: School of Psychology.
authors.forename: Niklas
authors.initials: N
authors.lastname: Ihssen
authors.affiliation: School of Psychology,  MRC Centre for Neuropsychiatric Genetics and Genomics, Institute of Psychological Medicine and Clinical Neurosciences, Cardiff University, UK.
authors.forename: David E J
authors.initials: DE
authors.lastname: Linden
authors.affiliation: School of Psychology, Bangor University, UK.
authors.forename: Claire E
authors.initials: CE
authors.lastname: Miller
authors.affiliation: School of Psychology, University of Birmingham, UK.
authors.forename: Kimron L
authors.initials: KL
authors.lastname: Shapiro
mesh_terms: D001288:Attention / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009483:Neuropsychological Tests; D010775:Photic Stimulation; D011601:Psychophysics; D017603:Signal Detection, Psychological / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: attention; biased competition; fMRI; visual short-term memory; working memory