Individual differences in cognitive processes underlying Trail Making Test-B performance in old age: The Lothian Birth Cohort 1936

The Trail Making Test Part B (TMT-B) is commonly used as a brief and simple neuropsychological assessment of executive dysfunction. The TMT-B is thought to rely on a number of distinct cognitive processes that predict individual differences in performance. The current study examined the unique and shared contributions of latent component variables in a large cohort of older people. Five hundred and eighty-seven healthy, community-dwelling older adults who were all born in 1936 were assessed on the TMT-B and multiple tasks tapping cognitive domains of visuospatial ability, processing speed, memory and reading ability. Firstly, a first-order measurement model examining independent contributions of the four cognitive domains was fitted; a significant relationship between TMT-B completion times and processing speed was found (β = −0.610, p < .001). Secondly, a bifactor model examined the unique influence of each cognitive ability when controlling for a general cognitive factor. Importantly, both a general cognitive factor (g; β = −0.561, p < .001) and additional g-independent variance from processing speed (β = −0.464, p < .001) contributed to successful TMT-B performance. These findings suggest that older adults' TMT-B performance is influenced by both general intelligence and processing speed, which may help understand poor performance on such tasks in clinical populations.