Provided are methods, data processing systems and computer program product for monitoring user activity and monitoring the effectiveness of objects within a virtual environment such as an immersive, computer-simulated 3D environment. An embodiment of the invention monitors the attention given to a virtual object by one or more avatars, by associating a viewing region with each object that requires attention monitoring, and detecting when an avatar is within the viewing region of the object simultaneously with the object being within an attention region (typically a clipped field of view) of the avatar. The viewing region is a 3D volume within which a surface of the virtual object is deemed to be effectively viewable.