Increasing cognitive load with increasing balance challenge: recipe for catastrophe

Abstract

The variety of sometimes contradictory results of studies of the impact of secondary cognitive tasks on postural balance may be attributed to the heterogeneity of balance challenges and tasks deployed and frequent lack of quantitative comparability of tasks. We deployed a wide range of quantitatively graded difficulties of both balance challenge and cognitive tasking to obtain an overview of the spectrum of their interactions in a multi-tasking situation. A differential comparison of the effects of verbally versus spatially loaded tasks, balanced for difficulty, was made and unlike any other study, we contrived to incorporate falls as an experimental variable. In the first study subjects stood in tandem on beams of either 2, 3 and 6 cm or 3, 6 and 8 cm width (according to 'best performance' ability) while performing mental verbal or spatial 'Stroop' tasks. The design was a between groups (sixteen subjects each) comparison (to reduce learning effect) of sway, fall rate and task error, balanced for order. Measurements were taken of centre of pressure, sway velocity at the hip and head displacement. For any beam width there were no within-subject correlations between sway magnitudes and frequency of falls. Spatial task errors increased with balance challenge (hence with magnitude of sway) but verbal performance was maintained independently of balance challenge. The results of the first study provided statistical power estimates for the design of the second focussed experiment which made a within group (twenty four subjects) comparison of the impact of spatial versus verbal tasks on balancing on the hardest beam. The spatial task significantly elevated the incidence of falls whereas the verbal task had no effect on fall rate. The spatial task raised the incidence of falling by 50% (P = 0.0008) in comparison with 'no task'. The verbal task had no effect (P = 0.07). We conclude that sway magnitude is a poor index of multi-task load. Multi-tasking can increase the chance of falling and spatial processing may have a specific impact on balance. The significant elevation of fall frequency during cognitive tasking shows that the 'posture first' principal can be transgressed although the necessary condition for transgression may be that the subject is willing to take risks believing that he can arrest any fall.

Attention modulates adaptive motor learning in the ‘broken escalator’ paradigm

“…Secondly, we did not test whether other cognitive tasks such as verbal or spatial Stroop tests (Barra et al 2006), Brooks Matrix tests (Gresty et al 2003) have similar effects. The advantages of our chosen dual-task are that it allowed Error Percentage scoring (Schmidt 2005) and was increasingly difficult to perform without errors.…”

Continuous cognitive task promotes greater postural stability than an internal or external focus of attention

“…The absence of consistent empirical evidence is postulated to be a result of one of several factors such as the processing demands of the cognitive task [7,13,[15][16][17], the difficulty of the postural task [9,18,19] and the utilization of a stiffening strategy [5,14].…”

Postural control and attentional demand during adolescence

“…Increasing the level of difficulty of the cognitive task involves either increased (Blanchard et al, 2005), decreased (Andersson et al, 2002) or unchanged (Kerr et al, 1985) centre of foot pressure (CoP) excursions. Conversely, the performance of the cognitive task (e.g., backward counting and reaction-time task) can be compromised by a simultaneous control of quiet stance in adults with calf vibration (Andersson et al, 2002), on a beam (Barra et al, 2006) or with suppression or perturbation of sensory information in the elderly . The performance can also remain unchanged (Andersson et al, 2002;Barra et al, 2006).…”

“…Conversely, the performance of the cognitive task (e.g., backward counting and reaction-time task) can be compromised by a simultaneous control of quiet stance in adults with calf vibration (Andersson et al, 2002), on a beam (Barra et al, 2006) or with suppression or perturbation of sensory information in the elderly . The performance can also remain unchanged (Andersson et al, 2002;Barra et al, 2006). Three models are currently used to explain these apparently contradictory results: the cross-domain competition model, the U-shaped non-linear interaction model and the task prioritization model (Lacour et al, 2008).…”