Temporal-order information can be maintained in non-conscious working memory

Classical theories hold conscious perception and working memory to be tightly interwoven. Recent work has challenged this assumption, demonstrating that information may be stored for several seconds without any subjective awareness. Does such non-conscious working memory possess the same functional properties as conscious working memory? Here, we probe whether non-conscious working memory can maintain multiple items and their temporal order. In a visual masking task with a delayed response, 38 participants were asked to retain the location and order of presentation of two sequentially flashed spatial positions, and retrieve both after a 2.5 second delay. Even when subjective visibility was nil, subjects' objective forced-choice performance exceeded chance level and, crucially, distinct retrieval of the first and second location was observed on both conscious and non-conscious trials. Non-conscious working memory may therefore store two items in proper temporal order. These findings can be explained by recent models of activity-silent working memory.