The time course of retaining hierarchical representation in visual working memory

Abstract

Hierarchical encoding theory claims that representations of objects in visual working memory (VWM) are not stored independently. Rather, a representation of an item encompasses both individual information about this object as well as the compressed group information about all memorized items (e.g., the average feature value). This study aimed to investigate the time course of maintaining the hierarchical representations in VWM. Participants were presented with four differently oriented triangles for 500 ms. Following a 1-, 4-, or 7-second delay, they reported either an individual orientation or the average orientation of all triangles. Prior to the stimuli presentations, each participant was informed with what needed to be memorized: a specific orientation, all four individual orientations, or an average orientation. Using the mixture model, we estimated a probability of a tested representation being in VWM and its precision, as well as a systematic bias that would indicate hierarchical encoding. We found no difference between the dynamics of maintaining different parts of hierarchical representation (the average and individual objects) which supports the idea that the hierarchical representations are related to encoding, rather than storing information in VWM. Both precision and the probability of an item being in memory were shown to decrease over time. This finding supports "Sudden Death" and "Gradual Decay" accounts for storing hierarchical representations.