Interference between postural control and mental task performance in patients with vestibular disorder and healthy controls

Objectives-To determine whether interference between postural control and m ental task performance in patients with balance system impairment and healt hy subjects is due to general capacity limitations, motor control interfere nce, competition for spatial processing resources, or a combination of thes e. Method-Postural stability was assessed in 48 patients with vestibular disor der and 24 healthy controls while they were standing with eyes closed on (a ) a stable and (b) a moving platform. Mental task performance was measured by accuracy and reaction time on mental tasks, comprising high and low load , spatial and non-spatial tasks. Interference between balancing and perform ing mental tasks was assessed by comparing baseline (single task) levels of sway and mental task performance with levels while concurrently balancing and carrying out mental tasks. Results-As the balancing task increased in difficulty, reaction times on bo th low load mental tasks grew progressively longer and accuracy on both hig h load tasks declined in patients and controls. Postural sway was essential ly unaffected by mental activity in patients and controls. Conclusions-It is unlikely that dual task interference between balancing an d mental activity is due to competition for spatial processing resources, a s levels of interference were similar in patients with vestibular disorder and healthy controls, and were also similar for spatial and nonspatial task s. Moreover, the finding that accuracy declined on the high load tasks when balancing cannot be attributed to motor control interference, as no motor control processing is involved in maintaining accuracy of responses. Theref ore, interference between mental activity and postural control can be attri buted principally to general capacity limitations, and is hence proportiona l to the attentional demands of both tasks.