Human cognitive processing limits can lead to difficulties in performing two tasks simultaneously. This study aimed to evaluate the effect of cognitive load on both simple and complex postural tasks. Postural control was evaluated in 128 noninstitutionalized elderly people (mean age = 73.6 ± 5.6 years) using a force platform on a firm support in control condition (CC) and mental counting condition (MCC) with eyes open (EO) and eyes closed (EC). Then, the same tests were performed on a foam support. Sway path traveled and area covered by the center of foot pressure were recorded, low values indicating efficient balance. On firm support, sway path was higher in MCC than in CC both in EO and EC conditions ( p < 0.001). On foam support, sway path was higher in CC than in MCC in EC condition ( p < 0.001), area being higher in CC than in MCC both in EO ( p < 0.05) and EC (p < 0.001) conditions. The results indicate that cognitive load alters balance control in a simple postural task (i.e. on firm support), which is highlighted by an increase of energetic expenditure (i.e. increase of the sway path covered) to balance. Awareness may not be increased and the attentional demand may be shared between balance and mental task. Conversely, cognitive load does not perturb the realization of a new complex postural task. This result showed that postural control is prioritized (“postural first” principle) when seriously challenged.

Perrin P, Lion A, Bosser G, Gauchard G, Meistelman C. Motion sickness in rally car co-drivers. Aviat Space Environ Med 2013; 84:473–7. Background: Car sickness is a frequent and potentially disabling problem, commonly related to a theory of sensory conflict, in particular visuo-vestibular, and between actual and anticipated sensory signals. This study aimed to evaluate predictors of motion sickness (MS) in rally car co-drivers exposed to various accelerations. Methods: The subjects were 85 rally co-drivers (21 women) who filled in a questionnaire investigating MS symptoms in 4 situations: 1) special stages (competition itself); 2) special stages reconnaissance; 3) reading a book in the car; and 4) rear-seat passenger. The main factors related to MS were also investigated. Results: Women reported more MS than men only in the rear-seat passenger situation. MS is reported with increasing frequency in special stages (2.3%), special stages reconnaissance (15.3%), when reading a book in a car (25.9%), and as a rear-seat passenger (25.9%). Stress (63.0%), on-board smells (46.5%), and on-board temperature (43.0%) were the main risk factors for MS. Discussion: In special stages, the lower MS occurrence could be related to the kind of visual input: central vision focuses mainly on accurate pace notes while peripheral vision is restricted by the crash helmet and the head being bent forward. A cognitive process involved in the interpretation of the dynamic environment may lead to anticipation of upcoming accelerations, optimizing integration of vestibular and proprioceptive signals. During reconnaissance, the constant change of gaze between looking at the specifics of the road and the road book for taking notes requires frequent adjustments of the gain of the vestibulo-ocular reflex and the associated head movements could generate Coriolis accelerations.