School of Psychology, University of Leeds, Leeds LS2 9JT, UNITED KINGDOM.
Falls and gait impairment in older populations present a major challenge to healthcare systems and reduce quality of later life. There is evidence that cognitive decline contributes to falls and gait impairment in older adults and may, therefore, serve as a marker for persons at risk. Intraindividual variability (IIV; trial-to-trial fluctuations in response time across a neurocognitive task) may have screening potential in this respect as this measure is thought to capture unique information about cognitive function not captured by other neuropsychological metrics. The present research, therefore, examined relationships between IIV, gait and falls in cognitively intact older adults. The extent to which relationships varied according to age and the demands placed on the individual when assessing IIV and gait, was also investigated. Finally, a mediational approach identified potential mechanisms underpinning these relationships. Systematic reviews of published research were followed by cross- sectional experimental studies and a longitudinal investigation. The findings provided mixed evidence of a link between IIV and falls. There was strong cross-sectional evidence that greater IIV was associated with poorer gait performance, and that this relationship strengthened with increasing age. Variability better predicted gait outcomes when gait was assessed under more demanding dual-task conditions, and when IIV measures were derived from tasks with higher executive demands. Tests of mediation suggested that processing speed underpinned relationships between IIV and less demanding single-task gait, whereas executive function played a greater role in more demanding gait conditions. Together, the outcomes suggest that IIV measures have potential as an early screening tool for gait impairment, and also falls. Importantly, general slowing accounts of cognitive ageing explained findings when IIV and gait were assessed under lower demand conditions, whereas frontal lobe/executive control perspectives provided a better account when demands were greater.