About the interplay between internal and external spatial codes in the mind: implications for serial order.

Previous studies have shown that serial order in verbal working memory is spontaneously coded along the horizontal axis (i.e., the spatial positional association response codes (SPoARC) effect), with the initial items being associated with left and the last items being associated with right. These studies have led to the idea that when the cognitive system is confronted with a sequence of items processed verbally and semantically, it internally generates a spatial coordinate frame onto which memoranda can be bound to maintain their serial information. In this study, the interplay between internal and external spatial codes in the mind was investigated by testing the flexibility of the SPoARC effect. A verbal Sternberg probe detection task was used in which the displayed direction of the items during encoding (centrally, from left-to-right and from right-to-left) and the presentation rate (1- and 5-s/item) were manipulated. SPoARC effects were found in all conditions but were reversed in the right-to-left presentation condition. Follow-up analyses revealed no evidence of any spatial cost for the reversal; moreover, it was not influenced by the presentation rates. These findings suggest that space can be flexibly recruited for the spontaneous coding of serial order. The theoretical implications of these observations are discussed.