Hemifield asymmetries differentiate VSTM for single- and multiple-feature objects

Abstract

Visual short-term memory (VSTM) is a capacity-limited system for maintaining visual information across brief durations. Limits in the amount of information held in memory reflect processing constraints in the intraparietal sulcus (IPS), a region of the fronto-parietal network also involved in visual attention. During VSTM and visual attention, areas of IPS demonstrate hemispheric asymmetries. While the left hemisphere represents information in only the right-hemifield, the right hemisphere represents information across the visual field. In visual attention, hemispheric asymmetries are associated with differences in behavioral performance across the visual field. In order to assess the degree of hemifield asymmetries in VSTM, we measured memory performance across the visual field for both single- and two- feature objects. Consistent with theories of right hemisphere dominance, there was a memory benefit for single-feature items in the left visual hemifield. However, when the number of features increased, the behavioral bias reversed, demonstrating a benefit for remembering two-feature objects in the right-hemifield. On an individual basis, the cost of remembering an additional feature in the hemifields was correlated, suggesting that the shift in hemifield biases reflected a redistribution of resources across the visual field. Furthermore, we demonstrate that these results cannot be explained by differences in perceptual or decision making load. Our results are consistent with a flexible resource model of VSTM in which attention and/or working memory demands result in representation of items in the right hemifield by both the left and right hemispheres.

Task set induces dynamic reallocation of resources in visual short-term memory

“…Therefore, when task demands require greater resources in the right visual field than are available from the left hemisphere, the right hemisphere dynamically reallocates resources to the right visual field. This is supported by findings that increasing attentional (Poynter & Roberts, 2012) and memory (Sheremata & Shomstein, 2014) demands results in a benefit for right visual field representations.…”

“…Consistent with these studies, VSTM performance was impaired when participants were required to maintain two features in memory. Furthermore, in this condition visual field asymmetries reverse, demonstrating a right visual field benefit (Sheremata & Shomstein, 2014). This reversal is again predicted by brain imaging in healthy individuals that demonstrate whole field representations emerge with increased attention (Sheremata & Silver, 2015;Szczepanski et al, 2010) and memory demands (Sheremata et al, 2010).…”

“…Sample size was determined using power analyses from a previous report (Sheremata & Shomstein, 2014) that employed similar stimuli and task demands. Participants ranged in age from 18 years to 23 years, had normal or corrected-to-normal vision, and gave informed consent approved by the George Washington Institutional Review Board.…”

“…For example, it has been demonstrated that hemispheric asymmetries seen in VSTM result in behavioral asymmetries across the visual field that are dependent on the number of features to be remembered (Sheremata & Shomstein, 2014). Namely, it was demonstrated that there is an advantage for items held in VSTM in the left visual field when encoding and storing a single feature.…”

“…In particular, task set should modulate VSTM performance for single-feature trials that, under normal circumstances, do not demonstrate measurable asymmetries across the visual field (Sheremata & Shomstein, 2014). To modulate VSTM task set, performance was measured for single-feature trials under two difference context scenarios: (i) embedded among other single-feature trials; and (ii) embedded among mostly two-feature trials.…”