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Vladislav Khvostov, Igor Utochkin; The time course of retaining the hierarchical representation in visual working memory. Journal of Vision 2017;17(10):122. doi: 10.1167/17.10.122.
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© ARVO (1962-2015); The Authors (2016-present)
It was shown that the features of individual items retrieved from visual working memory (VWM) are systematically biased towards the mean feature of a sample set (Brady & Alvarez, 2011), suggesting hierarchical encoding in VWM. In this work, we investigated how hierarchical representations are stored over time. Observers were shown four white differently oriented triangles for 200 ms and asked to memorize their orientations. After a 1-, 4-, or 7-second delay, they had to report either one individual orientation, or the average orientation of all triangles, rotating a probe circle. We also precued a target (a signal to memorize one particular orientation, all four individual orientations, or the average orientation) or postcued (no signal presented, requiring to remember both the individuals and the average). Using the mixture model (Zhang & Luck, 2008), we estimated the precision and the probability of a tested representation being in VWM, as well as a systematic bias that would indicate hierarchical coding. Participants showed very precise and unbiased memories when only one triangle was precued. However, when they had to remember four orientations their reports were less precise and strongly biased towards the mean, both when the triangles were precued and postcued. However, the bias did not reach the mean, showing that observers had some memory for both the mean and the individual orientations – this is a signature of hierarchical coding. One surprising finding was that the bias towards the mean was slightly stronger after 1 second as compared to 4 or 7 seconds. This suggests that individual representations may be a bit more affected by the mean at early retention stages. However, there were no other substantial changes in the precision, biases, or probability of being in memory with the delay. This suggests that hierarchical representations probably depend more on encoding than retention factors.
Meeting abstract presented at VSS 2017
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