AGING AND INTRAINDIVIDUAL VARIABILITY IN PERFORMANCE: ANALYSES OF RESPONSE TIME DISTRIBUTIONS
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Summary
This study investigates whether older adults exhibit greater intraindividual variability in performance due to fundamental cognitive deficits, such as lapses in attention or intention, or simply because they are slower responders. While previous research established that older adults are more variable and slower than younger adults, it remained unclear if this variability persisted after accounting for speed differences. The authors hypothesized that if age-related cognitive lapses were the cause, older adults’ response time (RT) distributions would show greater positive skew than those of younger adults, independent of overall slowing. To test this, nine young adults (mean age 20.9) and nine older adults (mean age 73.9) performed nearly 2,000 trials of a same–different judgment task. The task required participants to determine if two characters belonged to the same category (letters or non-letters). Data were analyzed by comparing semi-interquartile (SIQ) ranges, fitting ex-Gaussian and Weibull functions, and constructing quantile–quantile (Q–Q) plots. The analysis focused on asymptotic performance (sessions 2 and 3) to control for practice effects, as older adults showed greater improvement in speed during the initial session. The results confirmed that older adults were slower and had larger SIQ ranges than younger adults. However, a strong, linear relationship existed between median RT and SIQ range across all participants, conditions, and sessions. When this relationship was accounted for, older adults were no more variable than younger adults; in fact, within the range of overlapping RTs, older adults were slightly less variable. Furthermore, Q–Q plots and distribution fitting revealed no evidence that older adults’ RT distributions were more skewed. Instead, the distributions appeared to be simple magnifications of the younger adults’ distributions, with slopes greater than 1.0 but no positive acceleration indicative of increased skew. The findings suggest that the greater performance variability observed in older adults is primarily a by-product of their slower average response times, rather than evidence of increased attentional lapses or frontal lobe dysfunction. The study supports the existence of a general law governing the relation between average RT and variability, which holds true both between subjects (regardless of age) and within subjects (as practice increases speed and reduces variability). This implies that age-related increases in variability do not necessarily reflect distinct cognitive mechanisms but are consistent with general principles of behavioral performance.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | OpenAlex-citations | — | — | 1 | 2026-06-25 |
| archive | success | semantic_scholar | — | — | 6 | 2026-06-26 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-25 |
| chunk | success | chunk | — | — | 1 | 2026-06-25 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-25 |
| promote | success | — | — | — | 1 | 2026-06-25 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-25 |
| verify | success | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified.
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