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Vladislav Khvostov, Igor Utochkin, Hee Yeon Im; Interplay between the Ebbinghaus illusion and hierarchical coding in visual working memory. Journal of Vision 2016;16(12):359. doi: 10.1167/16.12.359.
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© 2017 Association for Research in Vision and Ophthalmology.
It was shown that recalled size of an individual item is systematically biased towards the mean size of a set (Brady & Alvarez, 2011), suggesting hierarchical encoding in visual working memory (VWM). Yet, we also observe somewhat opposite trend in perception: perceived size of a circle, surrounded by other circles, is biased away from the mean (e.g., Ebbinghaus illusion). Here we examined the interplay between different biases elicited by perceptual illusion and hierarchical reorganization in VWM. We presented observers with four target circles of different sizes for 2 seconds, followed by a 1-second blank interval, and asked them to recall a size of a probed target circle. In the congruent-bias condition, two smallest target circles were surrounded by even smaller inducers and two largest target circles were surrounded by bigger circles. In this condition, both perceptual illusion and VWM encoding bias would yield the same bias towards the mean size, with two smallest circles overestimated and two largest circles underestimated. In the incongruent-bias condition, however, two smallest circles were surrounded by bigger circles and two largest circles were surrounded by smaller circles, such that perceptual illusion would yield bias away from the mean, unlike the VWM encoding bias towards the mean. For baseline, we also created two control conditions containing randomly intermixed inducers and no inducers at all. Although we observed the strong bias towards the mean in all the conditions, we found the significant difference between the congruent and incongruent bias conditions: the congruent condition amplified the overall bias to the mean, while the incongruent condition attenuated it. This corresponds to a perceptual bias predicted by the direction of the Ebbinghaus illusion in both conditions, indicating the additive interaction between perceptual size illusion and VWM encoding bias on recall, with the stronger effect of VWM encoding bias.
Meeting abstract presented at VSS 2016
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