The perception of a virtual environment depends on the user and the task the user is currently performing in that environment. Models of the human visual system can thus be exploited to significantly reduce computational time when rendering high fidelity images, without compromising the perceived visual quality. This paper considers how an image can be selectively rendered when a user is performing a visual task in an environment. In particular, we investigate to what level viewers fail to notice degradations in image quality, between nontask related areas and task related areas, when quality parameters such as image resolution, edge antialiasing and reflection and shadows are altered.