In stereoscopic 3D video, it is well-known that humans can perceive high quality 3D video provided that one of the views is in high quality. Hence, in stereo video encoding, the best overall rate vs. perceived-distortion performance may be achieved by reduction of the spatial, temporal and/or quantization resolution of the second view, while keeping the first view in full resolution. Objective stereo video quality metric is a crucial point for the success of unequal rate allocation. Since the perceived 3D video quality does not correlate well with the average PSNR of the two views, we proposed a new quantitative measure using a weighted combination of two PSNR values and a jerkiness measure . In this paper, we investigate whether the PSNR weights should be related with spatial activity in different scaling options and video contents. Spatial activity is examined in terms Of blockiness and blur. The optimal weights for some specific experiments are determined by matching, i.e. searching the best correlation between, subjective quality test results and the objective measure scores on a set of test videos.