Coding of serial order in verbal, visual and spatial working memory.

In the domain of working memory, recent theories postulate that the maintenance of serial order is driven by position marking. According to this idea, serial order is maintained though associations of each item with an independent representation of the position that the item constitutes in the sequence. Recent studies suggest that those position markers are spatial in nature, with the beginning items associated with left side and the end elements with the right side of space (i.e., the ordinal position effect). So far however, it is unclear whether serial order is coded along the same principles in the verbal and the visuospatial domain. The aim of the current study was to investigate whether serial order is coded in a domain general fashion or not. To unravel this question, 6 experiments were conducted. The first 3 experiments revealed that the ordinal position effect is found with verbal but not with spatial information. In the subsequent experiments, the authors isolated the origin of this dissociation and conclude that to obtain spatial coding of serial order, it is not the nature of the encoded information (verbal, visual, or spatial) that is crucial, but whether the memoranda are semantically processed or not. This work supports the idea that serial order is coded in a domain general fashion, but suggests that position markers are only spatially coded when the to-be-remembered information is processed at the semantic level.