Kennedy, S. (1989) Using video in the BNR usability lab. SIGCHI Bulletin. Vol. 21, No. 2, pp. 92-95.
Sue Kennedy presents in her article a method called Co-Discovery Learning that she and her colleagues had used in evaluating various communication systems. In Co-Discovery Learning two users cooperate and try to discover how to use a new system by trial and error. The experimenters give a list of tasks to the users and leave them performing the tasks. After the users have completed a task, the experimenter immediately asks them to jointly assess the difficulty of the task. Both the discovery and the jointly made assessment give valuable information on the usability problems of the system.
Pair testing has many similarities with this method, but does not necessarily include the joint assessment after each task.