Ageing and attentional control

Abstract

The research examines the structural bottleneck account and the resource account of the substantial dual-task deficits among older adults. Procedures from two common dual-task methodologies—the psychological refractory period and the relative-priority manipulation—were used to encourage maximization of the joint performance. Performance and time-sharing strategies from subjects between the ages of 20 and 70 years were examined. Age-related declines in time-sharing efficiency and in the precision of the executive control process were observed. The age-related effect was larger when two manual responses were required than when one manual and one vocal response were required, but no evidence for obligatory sequential processing was found. Except for the most demanding conditions, comparable practice effects were observed between the younger and older subjects, suggesting considerable cognitive plasticity in the older subjects. Implications for the two attentional accounts were discussed.

Keywords:

• Attentional control
• Cognitive ageing
• Divided attention
• Time-sharing strategy
• Dual-task performance

Acknowledgments

The research was supported by National Science Foundation Grant BCS-9910750 and the National Institute of Aging Grant AG08589. The author is especially grateful to Michael Vidulich for the theoretical discussions throughout the research process. The author thanks Bryan Stork, George Reis, Andrew Schieltz, Jeff Flinn, Andrew Krum, and Caleb Hildenbrandt for their assistance at various stages of the project. The data from young adults under the age of 30 have been published in Tsang (2006). Aspects of these data have been presented at the Annual Meeting of Psychonomics, November 2003. The earlier paper focused on the theoretical implications of some of the methodological issues in examining the nature of time-sharing performance. The current paper included subjects from 20 to 70 years of age and focuses on understanding the attentional mechanisms that underlie the age-related difficulty in dual-task performance. The current paper is based on completely new analyses that included all subjects (three age groups) whereas the earlier paper included only the young subjects (one age group).

Notes

¹ Time sharing has been used both in the switching (e.g., Hirst & Kalmar, 1987) and in the simultaneous sharing (e.g., Gopher, 1993) sense in the literature. The present paper examines two theoretical frameworks that have opposing views on whether attention is switched or shared when more than one task is being processed. The paper therefore does not a priori specify an exclusive use of the term.

² Response grouping whereby Task 1 response was deliberately delayed to coincide with Task 2 response was discouraged because it is a response tactic that is not mandated by either of the two hypothesized attentional mechanisms. Intentional response grouping, however, can obscure the true process that underlies the dual-task performance (e.g., Ulrich & Miller, 2007). Results obtained with the explicit instructions to group the responses (e.g., Hartley & Maquestiaux, 2007) are therefore difficult to interpret.

³ To determine the best reaction time of a single-task condition, the trials with the highest accuracy for that task were first identified. The fastest trial reaction time among these high accuracy trials would be recorded as the best reaction time for that task condition. For dual tasks, to determine the best performance of Task A in the A–B pair, the trials with the best Task B performance were first identified (using the same procedure for the single-task condition), then the best Task A performance among these trials would be recorded.

⁴ Subjects could earn the most points by being within 3% of their optimized accuracy standard and fewer points by being within 6%. If points were earned for accuracy, additional points could be earned for RT being within 100 ms and 75 ms of the optimized Planikin and Sternberg standards, respectively. Fewer points would be earned if the RT was within 200 ms and 150 ms of the optimized Planikin and Sternberg standards, respectively. The accuracy and RT ranges used were based on preliminary testing.

⁵ Standardizing the RT was especially helpful in the differential-priority condition because RT reflected not only the demand of the individual task but also its priority. For example, if the raw optimized Sternberg RT was faster than the maximized Planikin RT, it could reflect a true priority effect or simply that the Sternberg task naturally required less processing time. Similarly, if the raw optimized Planikin RT was slower than the maximized Sternberg RT, it could reflect a violation of task priority or simply that the Planikin task required more processing time. Analysis of the raw performance was reported in Tsang et al. (2003) and produced essentially the same statistical results.

⁶ Although the 200-ms cut-off was somewhat arbitrary, no dual-task standard deviation for any age group was smaller than 200 ms late in practice for any task in any priority condition. The 200-ms cut-off was also one that had been used in the literature (e.g., Tombu & Jolicœur, 2005; Ulrich & Miller, 2007).

⁷ Each sample histogram was based on two trials of responses from a single subject. Additional samples can be found in Tsang et al. (2003).

⁸ The RT decrement averaged over the manual and speech responses when the Sternberg task was completed first in the equal-priority condition late in practice were 407 ms, 572 ms, and 608 ms for the young, middle-aged, and older group, respectively.