Modality-, feature-, and strategy-dependent organization of low-level working memory.

Previous research has shown that, when multiple similar items are maintained in working memory, recall precision declines. Less is known about how heterogeneous sets of items across different features within and between modalities impact recall precision. In two experiments, we investigated modality (Experiment 1, n = 79) and feature-specific (Experiment 2, n = 154) load effects on working memory performance. First, we found a cross-modal advantage in continuous recall: Orientations that are memorized together with a pitch are recalled more precisely than orientations that are memorized together with another orientation. The results of our second experiment, however, suggest that this is not a pure effect of sensory modality but rather a feature-dependent effect. We combined orientations, pitches, and colors in pairs. We found that memorizing orientations together with a color benefits orientation recall to a similar extent as the cross-modal benefit. To investigate this absence of interference between orientations and colors held in working memory, we analyzed subjective reports of strategies used for the different features. We found that, although orientations and pitches rely almost exclusively on sensory strategies, colors are memorized not only visually but also with abstract and verbal strategies. Thus, although color stimuli are also visually presented, they might be represented by independent neural circuits. Our results suggest that working memory storage is organized in a modality-, feature-, and strategy-dependent way.