Intraindividual variability in latency and accuracy of cognitive performance across both trials and occasions was examined in 3 groups of older adults: healthy adults, adults with arthritis, and adults diagnosed with mild dementia. Participants completed 2 reaction-time and 2 episodic-memory tasks on 4 occasions. Results indicated that intraindividual variability in latency was greater in individuals diagnosed with mild dementia than in adults who were neurologically intact, regardless of their health status. Individual differences in variability were stable over time and across cognitive domains. Intraindividual variability was also related to level of performance and was uniquely predictive of neurological status, independent of level of performance. Results suggest that intraindividual variability may be a behavioral indicator of compromised neurological mechanisms.

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Inconsistency in latency across trials of 2-choice reaction time data was analyzed in 273 participants ranging in age from 6 to 81 years. A U-shaped curve defined the relationship between age and inconsistency, with increases in age associated with lower inconsistency throughout childhood and higher inconsistency throughout adulthood. Differences in inconsistency were independent of practice, fatigue, and age-related differences in mean level of performance. Evidence for general and specific variability-producing processes was found in those aged less than 21 years, whereas only a specific process, such as attentional blocks, was evident for those 21 years and older. The findings highlight the importance of considering moment-to-moment changes in performance in psychological research.

Measures of visual fixation and of focused manipulation of an array of familiar and of novel toys were evaluated for three groups of infants: thirty-two 8-montholds and thirty-two 12-month-olds for whom both arrays contained three toys, and thirty-two 12-month-olds for whom both arrays contained five toys. Prior to testing, half of the infants in each group had been habituated to the familiar array, whereas the other half had been familiarized but interrupted before habituation could be completed. The results showed that habituated infants in each group preferred to look at and manipulate toys in a novel array. In contrast, interrupted infants preferred toys in a familiar array, but only if the array was complex relative to age (three toys for 8-month-olds and five toys for 12-montholds) and only with the focused manipulation measure. If the stimulus was simple and/or the response measured was visual fixation, interrupted infants showed no preference for either array. The results provided evidence of a progression from familiarity preference to novelty preference that is not tied to a particular age but occurs repeatedly as new stimuli are encountered. Age-related changes are present, however, in the effective complexity of the stimuli, the amount of familiarization, and the form of response necessary to elicit the progression.Preparation of this article and the research reported Hunter, Ross, and Ames (1982) found faherein was supported by Social Sciences and Humanities miliarity preferences in 12-month-olds, and Research Council of Canada Doctoral Fellowship 453-" _, 3 * f . , ~ . JT ,-j /,no<>\ 79-4479 and Natural Science and Engineering Research Rose > Gottfried, Carmmar, and Bndger (1982) Council Grant A8291.have reported similar findings for 3Va-to 6'/2-We wish to thank Katherine Covell and Susan Khazaie month-olds, for their help in data collection, and Robert B. McCall An alternative view is that the shift from fo ^™ S SSSttS Mich^A.

A growing body of research suggests that substantial variability exists among cognitive abilities within individuals. This within-person variability across cognitive domains is termed dispersion. The present study investigated the relationship between aging and dispersion of cognitive functions both quantitatively (overall levels of dispersion) and qualitatively (patterns of dispersion) in a sample of 304 nondemented, older adults aged 64 to 92 years (M = 74.02). Quantitatively, higher levels of dispersion were observed in the old-old adults (aged 75-92 years) and those identified as having experienced cognitive decline, suggesting that dispersion level may serve as a marker of cognitive integrity. Qualitatively, three distinct dispersion profiles were identified through clustering methods, and these were found to be related to demographic, health, and performance characteristics of the individuals, suggesting that patterns of dispersion may be meaningful indicators of individual differences.