PURPOSE: The manipulation of visual working memory (VWM) has received increasing interest, by focusing on the underlying mechanisms of manipulation for objects presented at distinct locations. However, no study has explored the manipulation mechanisms for the content of a stored multi-featured object (e.g., retaining color while discarding polygon for a colored-polygon). The current study examined whether participants can selectively retain task-relevant information of a dual-featured object after a retro-cue was presented at the maintenance interval. We hypothesized that the processing nature of a feature at the perceptual stage affected its manipulation in VWM, and tested this hypothesis by adopting two types of dual-featured objects. One is objects composed of highly-discriminable features (colored-oriented-bars) which can be processed via spread attention; the other type is objects containing fine-grained information (colored-polygons) which is processed via focal attention. We predicted that selective maintenance could not occur for the former type but occurred for the latter.
METHODS: Contralateral delay activity (CDA) was adopted as a neural marker during a change detection task, in which two features of an object was initnally memorized. During the maintenance phase, we presented a retro-cue to inform participants to selectively retain color, polygon/orientation, or both.
RESULTS: In line with our prediction, CDA amplitude was significantly lower for retain-color and retain-polygon conditions than for retain-both when colored-polygons were presented as stimuli; however, there was no significant difference between retain-color, retain-orientation, and retain-both conditions when colored-oriented-bars were used as stimuli (Experiment 1). Moreover, the findings cannot be explained by operations over independent objects (Experiment 2).
CONCLUSIONS:we found that the selective maintenance manipulation was modulated by the nature of the constituent elements. In particular, for dual-featured representations containing fine-grained information which needs to be processed via focal attention, the constituent single features can be selectively retained according to the task requirement (e.g., colored polygon). In contrast, for dual-featured representations composed of highly-discriminable information which is processed via spread attention, the stable unit could not be broken to selectively maintain the individual elements (e.g., colored bar).