Abstract

We hypothesized that keeping one’s balance with eyes open in the dark is different and more difficult than eyes closed because the brain continues to process visual inputs in the dark when the eyes are open. On the other hand, when the eyes are closed, the visual system does not signal incongruent information with which the brain must compare the other sensory systems. A variety of cognitive (subtracting backwards by seven as quickly and accurately as possible) and support surface (fixed versus sway-referenced) conditions were used to probe the neural mechanisms underlying the sensory organization processes in healthy young adults. Peak-to-peak anteroposterior sway performance revealed two dissociated components of the treatment effects. The first component came from the visuospatial factor. Balance control during eye closure and eyes open in the dark were found to be similar but poorer than baseline condition (eyes open under typical lighting). The second component was the effect of task difficulty in which balance control in the sway-referenced condition was worse compared to fixed support during eye closure or eyes open in the dark. Analyses of the cognitive performance also revealed different underlying neural mechanisms of the experimental conditions. Subtraction speed under the fixed support surface condition was similar among all the conditions but was faster with eyes closed during the sway-referenced support surface condition. Accuracy was not affected among the visual and surface conditions. We conclude that sensory processing load with eyes closed is lower than eyes open in the dark, thereby allowing cognitive performance to proceed more efficiently. Performing a difficult subtraction task with eyes closed may afford a decrease in dual-task interference since similar brain areas, particularly the parietal region, are involved in both tasks. The results are discussed with reference to clinical application and spatial disorientation in aviation.