A multimedia decoder unit having error concealment and fast muting capabilities. The method includes the steps of making available to a user an electronic evaluation form, inputting a first set of data into the electronic form corresponding to the user, submitting the form including the first set of data for review to a second user and inputting a second set of data into the electronic form corresponding to the second user. Electric pulses are applied to the cell and resultant signals are measured. Similarly, when the user is a software developer, the user is directed to a version of an application program that is being developed; otherwise, the user is directed to a production version of the application program. By introducing such display mask 114, the region visible upon the display surface differs depending on the viewpoint position of the user.