Effects of age and age-related differences in auditory information processing on fluid and crystallized intelligence

Speed and fidelity of basic information processing and fluid intelligence deteriorate with age, while crystallized intelligence remains stable. There is also evidence that indices of basic information processing correlate with fluid intelligence in a college population. We hypothesized that age-related changes in simple auditory information processing may explain a significant proportion of age-related decline in fluid, but not crystallized intelligence. To test this hypothesis, we obtained two-tone frequency discrimination thresholds as well as scores on fluid and crystallized intelligence tests in a group of healthy adults spanning ages from 18 to 83. We then compared linear models specifying the relations among those measures. The model postulating age effects on fluid intelligence mediated by differences in frequency discrimination fitted the data better than the model restricted to direct effects of age in fluid intelligence. No effects of information-processing index or age on crystallized intelligence were observed.