Age-Related Deficits on the Trail-Making Test Part A: Separating Specific Deficits of Visual Search from Generalized Sensorimotor Slowing

Trail-Making Test part A (TMT-A) is sensitive to the speed of perceptual processing, the speed of motor programming and the proficiency of visual search. Here we explore why, in previous work, performance on TMT-A was found to decay in old age. We (1) distangle the contribution of visual search from that of basic perceptuo-motor processing by implementing a control version of TMT in which visual search is minimized, (2) investigate the role of task experience by embedding TMT in a context that models daily workplace activities of some but not other participants and (3) explore the age deficits on TMT-A at the level of eye movements. Ten young adults (YA), ten older adults without task experience (OA), as well as ten older adults with task experience (OE) participated in a barcode scanning task in which numbered parcels had to be scanned in ascending order. The parcels were placed in a regular, easily predicable order for TMT-C, but in a mixed order for an unspeeded and a speeded version of TMT-A. We found no group differences for completion time and gaze pattern in TMT-C. Completion time increased and the gaze pattern changed accordingly in TMT-A, and changes were more pronounced in OA and OE compared to YA. Specifically, older persons had a longer completion time, their gaze took longer to move from one scanned parcel to the next, but their gaze didn't rest longer on a scanned parcel. The differential effects of old age on TMT-A versus TMT-C, and the effects of age on the gaze pattern in TMT-A, provide converging evidence that age-related slowing on TMT-A was related to specific deficits of visual search, not to generalized deficits of sensorimotor processing. Slowing on TMT-A was not modified by instructions (speeded versus unspeeded), nor by decades of work-related experience on a similar task.