Independent mechanisms of spatial attention in visual and tactile working memory

摘要

Are attention shifts in visual and tactile working memory (WM) controlled by a unitary supramodal mechanism or by separate modality-specific processes? To track the focus of spatial attention during the concurrent maintenance of visual and tactile information, we measured the visual and tactile contralateral delay activity (CDA/tCDA) components in WM tasks where two sample sets (S1 and S2) were presented sequentially. Participants memorized task-relevant target items in both S1 and S2 and judged whether these targets were presented again at memory test. In Experiments 1 and 2, S1 was bimodal and S2 was only presented in the primary modality (vision in Experiment 1, touch in Experiment 2). The primary-modality S1 and S2 targets were located on the same side or on opposite sides (stay versus shift trials, 50% each); participants performed the primary task alone (unimodal baseline) or additionally memorized stimuli of the secondary modality on the same side as the primary-modality S1 targets (bimodal condition). Shifts of attention in the primary modality were reflected by polarity reversals for the respective (visual or tactile) CDA in the period after S2. Critically, such attention shifts in the primary modality had no effect on the amplitudes and polarity of the tCDA/CDA evoked by the secondary-modality S1 targets in bimodal trials, indicating an independence of spatial selection mechanisms for tactile and visual information. In a third experiment, S1 and S2 were both bimodal and stay/shift trials were independently randomized per modality. Attention shifts in either modality reversed the polarity of the corresponding (visual/tactile) CDA, but did not influence the amplitude or polarity of the tCDA/CDA for the other modality. In conclusion, WM maintenance of visual and tactile information recruits spatially selective processes that operate independently and in parallel in both modalities.