Computer supported collaborative learning (CSCL) has captured many educators and researchers to contribute their efforts on this domain. This study proposed a two-dimension concept to explain learners' collaboration behaviors in a CSCL laboratory setting. A two-dimension process, namely perceptual dimensions and supportive dimensions, is useful to explain why learners' are willing to collaborate online. One hundred undergraduate students were divided into 20 work groups, each group consisting of 5 members. The result showed different group composition of extraverts will influence learners' perceptual dimension of group context variables, which in turn will be associated with supportive dimension of CSCL process. We conclude that educators and CSCL developers should focus not only on the technical factors of system development, but also on learners' psychological factors because of its impacts on the latter process-supportive dimension which especially stands for learners' collective behaviors of collaboration. (Contains 6 tables and 2 figures.)