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The Locked-In Syndrome (LIS) is a very rare but devastating condition, characterized by the complete paralysis of the voluntary musculature, except for some eye and eyelid movements. Sometimes, however, the oculomotor control is so compromised, for example in an advanced phase of Amyotrophic Lateral Sclerosis (ALS), that these patients lose the possibility to communicate and interact with the external world. We have developed a prototype of Brain-Computer-Interface (BCI) based on the voluntary shift of attention (gaze) from a far target to a near target, which is associated to a decrease of pupil size, an automatic sympathetic response [1]. In a sample of healthy volunteers, we explored the possibility of exploiting this pupillary response (Pupillary Accommodative Response) in combination with the oscillatory response of the pupil (Pupillary Oscillatory Response) and the visual cortex (Steady-State Visual Evoked Potentials) to flickering stimuli, to establish binary communication (shifting attention to a near target meaning "yes", holding attention on a far target meaning "no"). These three signals (PAR, POR and SSVEP) discriminated when the observer's attention was on the far or the near target, and were decoded by means of a binary classifier (Support Vector Machine) to detect subject's voluntary response. Our results suggest that multiple signal decoding during a simple attention shift in the depth plane can be a robust strategy to communicate with LIS patients when oculomotor control is too poor to use traditional assistive aids based on eye tracking. [ABSTRACT FROM AUTHOR]