Examining the bottleneck: The influence of stimuli specific expertise on short-term memory capacity

Humans have a limited visual short-term memory capacity (K), which is further reduced when processing certain stimuli (e.g., unfamiliar, visually complex, or low discriminability). To examine how these factors influence the bottleneck in attentional and short-term memory, we conducted a series of studies. Experiment 1 (Dall, Watanabe, Sørensen, 2016) examined how expertise modulate K in Japanese hiragana. Experiment 2 (Dall, Wang, Cai, Chan, Sørensen, 2021) divided Chinese characters into four groups based on frequency of use (high vs. low) and stroke count (high vs. low) and how attention is influenced by number of features and stimuli specific expertise. Experiment 3 (Dall, Chan, Sørensen, in review) used colours to examine how stimuli specific expertise influence contentious categories. We extracted attentional components by varying the exposure duration and modelling the data with the Theory of Visual Attention in all three experiments, measuring K and processing speed (C).
All three papers showed that stimuli specific expertise improved the K. This increase was unrelated to both stimulus complexity (Experiment 2) and precision of the memory (Experiment 3). Nor did visually complexity influence C of even complex and infrequently Chinese characters (e.g., 鹿), whereas C was modulated by familiarity (Experiment 2).
This seems to suggest that the bottleneck in VSTM is influenced by stimuli specific expertise and that this increase cannot be explained as increasing the precision of the stored items.