In studies of 2D visual attention, eye-tracking data show a so-called "center-bias", which means that fixationsare biased towards the center of 2D still images. However, in stereoscopic visual attention, depth is anotherfeature having great influence on guiding eye movements. Relatively little is known about the impact of depth.Several studies mentioned that people tend to look at the objects at certain depth planes. Therefore, it isreasonable to suppose the existence of a "depth-bias". But studies proving or quantifying this depth-bias arestill limited. We conducted a binocular eye-tracking experiment by showing synthetic stimuli on a stereoscopicdisplay. Observers were required to do a free-viewing task through active shutter glasses. Gaze positions ofboth eyes were recorded for obtaining the depth of fixation. Stimuli were well designed in order to let thecenter-bias and depth-bias affect eye movements individually. Results showed that the number of fixationsvaried as a function of depth planes. There was also a relationship between the duration of fixation and thedepth plane where the objects were located.