Abstract
Space and time structure our visual experience, yet little is known about the role of temporal aspects for visual working memory (VWM). We have recently shown that both spatial and temporal properties are incidentally encoded along with to-be-remembered information, providing reference frames for storage and retrieval. In our prior work, we used rich spatiotemporal contexts, as they might be encountered in natural environments: Memory contents could be differentiated based on (a) absolute spatial/temporal coordinates, (b) relative spatial/temporal coordinates, or (c) their position in a categorical spatial/temporal order. The drawback of this approach is that it leaves open the question of specifically which spatiotemporal properties are critical. In a series of experiments, we used a colour change-detection task to test each of these possibilities by transforming spatial and/or temporal structures of item presentation at retrieval relative to encoding. More specifically, spatial and/or temporal coordinates were (a) multiplied by a constant factor, expanding or shrinking the entire configuration (global change), (b) multiplied by different factors, changing relative inter-item distances (relational change), or (c) switched, changing the order of items in a spatial or temporal sequence (ordinal change). Such transformations of the external reference frame at retrieval should only affect performance if the metric of the internal reference frame in VWM is not invariant to this type of transformation. We found that ordinal and relational changes of either the spatial or temporal structure impaired performance, whereas global changes had no effect. Thus, reference frames appear to be established by inter-item relations – including relative distances between items as well as their order – rather than absolute positions in space or time. These results corroborate and extend previous findings for the spatial domain, and highlight functional similarities between the spatial and temporal dimensions by revealing the same metrical properties for temporal reference frames.