Linking space and ordinal position in working memory: A multi-level meta-analysis of the SPoARC effect

When individuals are asked to keep in mind arbitrary sequences of items such as words, letters, numbers or images, they spatialize them in working memory forming a horizontal mental line. This study is the first meta-analysis of this phenomenon known as SPoARC (Spatial Positional Response Codes) effect or OPE (Ordinal Position Effect). For this purpose, we had access to the raw data of 21 of the 24 behavioral studies ever published on this topic. A multilevel meta-analysis was performed with participants nested within experiments, both used as levels. After confirming the existence of the SPoARC effect, we analyzed it as a function of four features: the size and nature of the memoranda, the pace of presentation of the memoranda and the type of classification of the probes. Results showed that (a) the SPoARC effect varied as a function of the nature of the memoranda, which we suggest highlights the importance of phonological processes in WM spatialization, (b) the SPoARC effect was the largest when the presentation pace was around 3 s per item or above and (c) the SPoARC effect increased when participants were asked to pay attention to the ordinal structure of the memoranda (whenever a temporal classification task is used), confirming the link between order information and WM spatialization.