The subjective feeling of being present in a virtual reality (VR) is still a concept without standardised, objective measurement. This objectivity is the key to successful optimization of VR-environments. For example, it could improve the effective modulation of VR-based medical applications. The present study investigates three different VR task demands and their influence on the experienced VR-Presence. In this context, the physiological reactions of electrodermal and cardio-respiratory parameters as well as cognitive correlates of the task-irrelevant auditory novelty-oddball-paradigm were studied. The experiment started with the first condition (rest). The thirteen participants were instructed to ignore the Oddball stimulus. In the second condition (easy) the task was to collect balls in a virtual maze. The participants had to follow a path, which lead to those balls. This path was missing in the third condition (hard). The analysis showed a significant rise of the heart rate, the galvanic skin conductance and the respiratory frequency between the rest and the easy or hard condition, which implies a sympathovagal imbalance with an increased activity of the sympathetic nervous system in the easy and hard condition. This change in activity of the vegetative nervous system is equally indicated by a marginal decrease of the heart rate variability parameters SDNN, RMSSD, HF and SD1 between rest and easy or hard. Furthermore, the amplitude of the p3a component significantly decreased between the conditions rest and easy or hard. These findings suggest an increased attention, as well as an increased emotional and cognitive involvement in the conditions easy and hard in contrast to the rest condition.