Aging of attention: does the ability to divide decline?

Previous research has yielded conflicting results regarding the relationship between adult age and the ability to divide attention between two concurrent tasks. At least some of the inconsistency is probably attributable to methodological variations, such as the manner in which divided-attention ability has been assessed, how single-task performance has been considered, and the degree of control over relative emphasis placed on each task. Two experiments employing procedures sensitive to these concerns were conducted in which a speeded decision task was performed during the retention interval of a letter-memory task. The results of both experiments indicated that there were relatively few age-related influences on dual-task performance vis-à-vis those on single-task performance.

Interpretation of differential deficits: the case of aging and mental arithmetic.

A fundamental issue in research on individual differences is the type of evidence sufficient to justify an inference of selective or distinct deficits in relevant theoretical processes. It is proposed that an important consideration is the extent to which the individual differences in 1 variable are independent of those in another variable. Specifically, the suggestion presented here is that a strong conclusion of selective impairment requires evidence that there is significant group-related variance in 1 variable after the variance in the other relevant variable is controlled. Furthermore, an inference that the groups are equivalent on a particular theoretical process requires evidence that the variable presumed to reflect that process has sufficient unique variance to justify the claim that a distinct process is being assessed. The proposed methods are illustrated with two studies comparing adults of different ages in mental arithmetic tasks.

Adult age differences in long-term memory for performed activities.

Participants in two studies conducted by Salthouse (in press) were called 2 to 182 days after participation and asked to describe the activities that they had performed in the previous study. Hierarchical regression analyses were used to examine the prediction of activity recall from age, speed, and retention interval. Overall, age was associated with 20% of the variance in activity recall, and retention interval was associated with 19%, but there was no significant interaction of age and retention interval. When perceptual speed was entered into the regression equation before age, the age-related variance was reduced by 70%. A small, but statistically significant, amount of age-related variance in activity memory remained after controlling for speed and retention interval.

Influence of task-specific processing speed on age differences in memory.

Two studies were conducted to investigate the aspect(s) of processing involved in the hypothesized speed mediation of adult age differences in memory. Both studies involved a serial memory task in which information was to be recalled either in the original order of presentation, or in a reordered sequence. Results from both studies indicated that task-specific processing durations were slower among older adults than among young adults, but that the attenuation of the age-related variance in memory was nearly as great after statistical control of a task-independent speed measure as after control of task-specific speed measures. These findings are consistent with the hypothesis that a substantial proportion of the adult age-related differences in memory is associated with a decrease with increased age in the speed of executing many cognitive processes, and not simply the speed of one or two specific processes.