Different features are stored independently in visual working memory but mediated by object-based representations

The question of whether visual working memory (VWM) stores individual features or bound objects as basic units is actively debated. Evidence exists for both feature-based and object-based storages, as well as hierarchically organized representations maintaining both types of information at different levels. One argument for feature-based storage is that features belonging to different dimensions (e.g., color and orientations) can be stored without interference suggesting independent capacities for every dimension. Here, we studied whether the lack of cross-dimensional interference reflects genuinely independent feature storages or mediated by common objects. In three experiments, participants remembered and recalled the colors and orientations of sets of objects. We independently manipulated set sizes within each feature dimension (making colors and orientations either identical or differing across objects). Critically, we assigned to-be-remembered colors and orientations either to same spatially integrated or to different spatially separated objects. We found that the precision and recall probability within each dimension was not affected by set size manipulations in a different dimension when the features belonged to integrated objects. However, manipulations with color set sizes did affect orientation memory when the features were separated. We conclude therefore that different feature dimensions can be encoded and stored independently but the advantage of the independent storages are mediated at the object-based level. This conclusion is consistent with the idea of hierarchically organized VWM.

关于视觉工作记忆（VWM）是存储单个特征还是绑定对象作为基本单元的问题，目前正激烈争论。既有基于特征存储的证据，也有基于对象存储的证据，以及在不同层级上组织表示，以维持两种类型信息的层次结构。对于基于特征存储的一种论点是，属于不同维度（例如，颜色和方向）的特征可以存储而不相互干扰，这表明每个维度都有独立的存储能力。在本研究中，我们探讨了缺乏跨维度干扰是否真正反映了独立特征存储，还是由共同对象所介导。在三个实验中，参与者记住了并回忆了物体集合的颜色和方向。我们独立操纵了每个特征维度内的集合大小（使颜色和方向在物体间要么相同要么不同）。关键的是，我们将要记住的颜色和方向分配给了同一空间整合的物体或不同空间分离的物体。我们发现，当特征属于整合的物体时，不同维度内精度和回忆概率不受不同维度集合大小操作的干扰。然而，当特征被分离时，颜色集合大小的操作确实影响了方向记忆。因此，我们得出结论，不同的特征维度可以独立编码和存储，但独立存储的优势在基于对象的层面上得到介导。这一结论与层次组织化视觉工作记忆的理念相一致。