Trail Making Tests in Extended Reality: A Critical Review with Implications for Cognitive Ageing

Extended reality (XR) versions of the Trail Making Test and Color Trails Test are promising for assessing and training cognition in older adults. However, each XR adaptation is a new instrument, whose display, interaction technique, timing rules and layouts may change what it measures. This critical narrative review maps these implementations by software lineage and appraises their evidence for assessment and training against common criteria. The Trail Making Test in Virtual Reality (TMT-VR), whose source code was inspected, serves as a measurement case. XR trail-making tests showed convergence with paper and computerised versions, varying by test part and sample, and clinical group differences (e.g., Parkinson's disease, mild cognitive impairment). However, gaps in reliability (e.g., randomised forms), validation (e.g., norms, prospective samples) and reporting (e.g., error handling, build identity) emerged, and no training benefit attributable to the trail-making component was identified. The TMT-VR case shows how interaction technique, timing rule, error handling and unlogged layouts shape a score's meaning. Future tests should log layouts and events, estimate alternate-form reliability and undergo prospective validation, and training trials should isolate the trail-making component. Several XR trail-making tests have moved beyond feasibility, and reported tolerability during supervised sessions supports further evaluation in older adults.