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Irene M Pepperberg, Melissa Libertus, Lisa Feigenson, Justin Halberda, Hrag Pailian; Evolution and Development of Signature Limits in Mental Manipulation. Journal of Vision 2019;19(10):135. doi: https://doi.org/10.1167/19.10.135.
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The abilities to store and manipulate representations in visual working memory (VWM) allow us to build mental models of the world and reason beyond our perceptual experiences. However, human adults can store only up to 4 items simultaneously (Luck & Vogel, 1997) and manipulate up to 2 items with little-to-no cost (Pailian & Halberda, 2015). Here, we probe the developmental and evolutionary origins of storage and manipulation limits, by testing adults, 6-to-8-year-old-children, and an African Grey Parrot on a live version of the “Shell-Game”. In this task, participants were presented with 2–4 colors that were subsequently occluded by opaque cups. All cups either remained stationary (storage) or swapped positions up to 4 times (manipulation). Memory for a cued item was tested. Consistent with previous findings, adults were able to store up 4 items perfectly and manipulate 2 items with relatively no cost - though manipulating larger set sizes led to errors that increased as a function of the number of swaps performed. In contrast, developmental differences were observed such that children experienced greater difficulty in storing more than 2 items, as well as increased errors across swaps for all set sizes. However, no significant correlation existed between the magnitude of manipulation costs and children’s age. Taken together, these results may suggest that storage and manipulation develop independently across the lifespan. Lastly, the parrot demonstrated above-chance level performance across all conditions, providing evidence that storage and mental manipulation are not uniquely human capacities. Namely, the parrot not only outperformed children’s performance, it demonstrated storage and manipulation abilities that were equal (if not better) than adults’ for all conditions. These results suggest that storage and manipulation may be limited by an evolutionary determined upper-bound, and that investigating mechanisms/substrates shared across these species may prove instrumental towards identifying the loci of VWM constraints.
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