工作记忆容量一般与项目复杂性无关
原文：Working memory span is mostly independent of item complexity (andymatuschak.org)
字母的数量是阿拉伯数字的两倍以上，所以你可能认为，我们能记住的数字串，长度是字母串的两倍。但事实上，典型的工作记忆容量大约是{六}个字母和{七}个数字（例如，Crannell和Parrish，1957）。
参考文献
Crannell, C. W., & Parrish, J. M. (1957). A Comparison of Immediate Memory Span for Digits, Letters, and Words. The Journal of Psychology, 44(2), 319–327. https://doi.org/10.1080/00223980.1957.9713089
Miller, G. A. (1956). The magical number seven, plus or minus two: some limits on our capacity for processing information. Psychological Review, 63(2), 81–97. https://doi.org/10.1037/h0043158 Miller - The magical number seven, plus or minus two