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Megan Walsh, Leon Gmeindl, Jonathan Flombaum, Amy Shelton; Spatial working memory is limited by fixed resolution representations of location. Journal of Vision 2010;10(7):751. doi: 10.1167/10.7.751.
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© ARVO (1962-2015); The Authors (2016-present)
Is spatial working memory (SWM) capacity limited by the resolution with which locations are coded in memory? To address this question, we compared the spatial resolution of location representations in two nearly identical tasks typically characterized by different capacity limits. In particular, we first replicated previous work demonstrating that SWM span is reduced when subjects must recall items in a specific serial order (SO) compared to when they may recall in any order (AO). In a follow up experiment we considered whether the different capacity limits in these tasks result from differences in the resolution of position representations. Specifically, standard span trials were intermingled with trials wherein a single target was absent, compared to memory displays, and participants were required to localize the missing target. Resolution was operationally defined as localization precision. Surprisingly, we found no significant resolution differences in SO compared to AO trials. This suggests that SO processing relies on a categorically non-spatial resource, and that it degrades SWM by dual task interference, not by degrading spatial working memory, per se. Importantly, we found no load effect on resolution in the AO condition for target loads within an individual's capacity limit; even a post-hoc comparison for one compared to five targets revealed no significant resolution difference. In other words, there were no per-item costs associated with successfully remembering more targets, revealing that representations are coded at a fixed resolution regardless of load. Perhaps most interestingly, resolution did vary participant-by-participant, and these differences were positively and significantly correlated with individual SWM spans. Participants with greater location resolution could remember more targets. Taken together these results suggest that while, within an individual, objects are always encoded into memory with a fixed spatial resolution, person-by-person, differences in resolution may determine differences in capacity.
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