sb.conductedanexperimentinwhichtheeffectsof3formsofnonverbalbehavior（……）onperceptionsofpowerbases（……）wereinvestigatedamongstasampleofU.S.students.

　　如果你是想把括号脱掉,那就改成

　　sb.conductedanexperimentamongasampleofU.S.students,tryingtofigureouttheeffectsoffacialexpression,visualbehaviorandbodyposturehaveontheperceptionsofsixformsofpowerbases,whicharereward,coercive,legitimate,referent,expert,andcredibility.

　　Facialexpression,visualbehavior,andbodyposture,these3formsofnonverbalbehaviorwereinvestigatedamong

　　asampleofU.S.studentshowtheyexerteffectsonperceptionsofthesixformsofpowerbases:reward,coercive,legitimate,referent,expert,andcredibility.