  The conflict between vergence (eye movement) and accommodation (crystalline
lens deformation) occurs in every stereoscopic display. It could cause
important stress outside the "zone of comfort", when stereoscopic effect is too
strong. This conflict has already been studied using questionnaires, during
viewing sessions of several minutes. The present pilot study describes an
experimental protocol which compares two different comfort conditions using
electroencephalography (EEG) over short viewing sequences. Analyses showed
significant differences both in event-related potentials (ERP) and in frequency
bands power. An uncomfortable stereoscopy correlates with a weaker negative
component and a delayed positive component in ERP. It also induces a power
decrease in the alpha band and increases in theta and beta bands. With fast
responses to stimuli, EEG is likely to enable the conception of adaptive
systems, which could tune the stereoscopic experience according to each viewer.
