Word-Frequency Distributions in Chinese- and English- Speaking Older Adults: An Analysis across Languages and Cognitive Statuses

This study investigates how the word-frequency distributions in spoken language reflect cross-linguistic and cognitive differences in older adults. We analyzed Cookie Theft picture descriptions from 96 older adults: 48 Mandarin speakers (24 cognitively impaired and 24 cognitively normal) and 48 English speakers (24 cognitively impaired and 24 cognitively normal) and modeled their word frequency distributions using three functions: Zipf, Zipf-Mandelbrot, and Exponential model. All three models showed excellent goodness of fit at both group and individual levels, indicating that the basic Zipfian structure of lexical distributions is preserved in late life and is not disrupted by mild cognitive impairment. As for the fitting parameters, however, the decay parameter a in the Exponential and Zipf models consistently distinguished Mandarin from English, suggesting that language-specific lexical patterns are robustly encoded in the slope of the distribution but that adding a shift parameter can dampen how clearly a reflects them. By contrast, differences between cognitive groups were weak and inconsistent, implying that parameter a provides only a coarse and context-dependent reflection of cognitive status in short, constrained picture-description tasks.