The Cooperative virtual environments, where users simultaneously manipulate objects, are one of the subfields of Collaborative virtual environments (CVEs). In this paper we simulate the use of two string based parallel robots in cooperative teleoperation task. Two users setting on separate machines connected through local network operate each robot. In this context, we investigate the effects of visual aids and oral communication on cooperation, co-presence and users performance. Ten volunteers had to cooperatively perform a peg-in-hole task. A second group of ten subjects perform the same task in a single user setup. The objective of the two experiments is twofold, firstly to compare the task's complexity of single user setup with that of the cooperative environment. Secondly we examine the influence of visual aids and oral communication on user's performance in the two different setups. Results revealed that shadow has a significant effect on task execution while arrows and oral communication not only increase users' performance but also enhance the sense of co-presence and awareness. We also observed that cooperative manipulation was more difficult as compared to single user manipulation.