Abstract
Visual working memory (VWM) adopts a specific manner of object-based encoding (OBE) to extract perceptual information: Whenever one feature-dimension is selected for entry into VWM, the others are also extracted. Currently most studies revealing OBE probed an ‘irrelevant-change distracting effect’, where changes of irrelevant-features dramatically affected the performance of the target feature. However, the existence of irrelevant-feature change may affect participants’ processing manner, leading to a false-positive result. The current study conducted a strict examination of OBE in VWM, by probing whether irrelevant-features guided the deployment of attention in visual search. The participants memorized an object’s colour yet ignored shape and concurrently performed a visual-search task. They searched for a target line among distractor lines, each embedded within a different object. One object in the search display could match the shape, colour, or both dimensions of the memory item, but this object never contained the target line. Relative to a neutral baseline, where there was no match between the memory and search displays, search time was significantly prolonged in all match conditions, regardless of whether the memory item was displayed for 100 or 1000 ms. These results suggest that task-irrelevant shape was extracted into VWM, supporting OBE in VWM.
Highlights
The establishment of object-based encoding (OBE) in Visual working memory (VWM) is important, because it enables us to understand the encoding mechanisms of VWM, and because it sheds critical light on the intimate interaction between visual perception, VWM, and visual attention[7,8]
The current study conducted a strict examination of the OBE in a new paradigm while keeping the irrelevant dimension stable during the experiment
The authors manipulated the probe type, consisting of a coloured probe, in which the probe colour could change in 50% of the trials, and a black probe, in which the probe colour always changed to the unused colour black. They found that the conjunction-match significantly slowed down the search time relative to the other match conditions, and the irrelevant-match under the black-probe condition considerably slowed down the search time relative to the neutral baseline
Summary
The establishment of OBE in VWM is important, because it enables us to understand the encoding mechanisms of VWM, and because it sheds critical light on the intimate interaction between visual perception, VWM, and visual attention[7,8]. Recent studies provided consistent evidence suggesting that OBE robustly exists in VWM when probing an irrelevant-change distracting effect[4,5,6,7,8,14,15,16,17,18] This distracting effect is revealed in a change-detection task, wherein the participants are required to remember one feature dimension of multi-featured objects and ignore the other one(s). Congruent with the behavioural evidence, ERP studies showed that the irrelevant-feature change elicited a more negative ERP component of the anterior N2 relative to the no-change condition[8,16,17,18] These results suggest that the irrelevant features are automatically selected into VWM in an object-based manner. Even if the memory-matching object was completely unrelated to the location of the search target, search performance (e.g. search time) was significantly impaired when the distractor bars were embedded in the memory-matching items, suggesting that attention was automatically deployed towards items that matched the contents of VWM
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