Interacting effects of age and time of day on verbal fluency performance and intraindividual variability

Abstract

We explored the effects of age and time of day (TOD) on verbal fluency ability with respect to performance level and intraindividual variability (IIV). Verbal fluency, which involves complex cognitive operations, was examined in 20 older (mean age = 72.8 years) and 20 younger (mean age = 24.2 years) adults with test start time alternating between morning and evening across four days. Older adults generated more words in the morning and younger adults more in the evening, corresponding with self-report peak TOD. Age by TOD interactions were also observed across fluency tasks on the number of switches among subcategory exemplars during word generation and on the IIV observed in switching behavior. Older adults exhibited greater variability in switching in the evening than in the morning, whereas younger adults showed the opposite pattern. These findings demonstrate that processes involving energization (initiating and sustaining) and attentional control may be particularly sensitive to age differences in TOD influences on cognition.

Keywords:

• performance variability
• time of day
• verbal fluency
• cognitive aging
• executive functioning

Acknowledgments

We thank Alexander Minevich for assistance with data collection and the study participants for generously volunteering their time to this project.

Additional information

Funding

Research was supported by Rotman Research Institute postdoctoral fellowships to Kelly J. Murphy and Robert West, McDonnell Research Foundation Grant to Donald T. Stuss and Fergus I. M. Craik, and Canadian Institute of Health Research Master’s Award to Sam Iskandar.