title: 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.
authors.affiliation: a Psychology Department , University of Windsor , Windsor , ON , Canada.
authors.forename: Sam
authors.initials: S
authors.lastname: Iskandar
authors.affiliation: b Psychology Department , Baycrest , Toronto , ON , Canada.|c Psychology Department , University of Toronto , Toronto , ON , Canada.
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Murphy
authors.affiliation: a Psychology Department , University of Windsor , Windsor , ON , Canada.
authors.forename: Anne D
authors.initials: AD
authors.lastname: Baird
authors.affiliation: d Psychology Department , Iowa State University , Ames , IA , USA.
authors.forename: Robert
authors.initials: R
authors.lastname: West
authors.affiliation: e Credit Valley Neuropsychology Group , Toronto , ON , Canada.
authors.forename: Maria
authors.initials: M
authors.lastname: Armilio
authors.affiliation: c Psychology Department , University of Toronto , Toronto , ON , Canada.|f Rotman Research Institute , Baycrest & University of Toronto , Toronto , ON , Canada.
authors.forename: Fergus I M
authors.initials: FI
authors.lastname: Craik
authors.affiliation: c Psychology Department , University of Toronto , Toronto , ON , Canada.|f Rotman Research Institute , Baycrest & University of Toronto , Toronto , ON , Canada.|g Ontario Brain Institute , Toronto , ON , Canada.
authors.forename: Donald T
authors.initials: DT
authors.lastname: Stuss
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D000704:Analysis of Variance; D001288:Attention; D056344:Executive Function; D005260:Female; D006801:Humans; D007206:Individuality; D007807:Language Tests; D008297:Male; D017440:Photoperiod; D011581:Psychological Tests; D013997:Time Factors; D014705:Verbal Behavior; D055815:Young Adult
keywords: cognitive aging; executive functioning; performance variability; time of day; verbal fluency