The Sleeator 2 offers the option to select auditory as well as visual stimuli. As described in the SCF, the stimuli do not necessarily have to be produced immediately when REM sleep is detected. In Sleeator 2 such waiting time thresholds can be entered freely. Moreover, in case of multiple simultaneously selected stimulus types, different thresholds for each stimulus type can be selected, such that it is possible to first start the visual stimuli, and some time later start with the auditory ones. Doing so, one can start the incorporation trials with a stimulus type that has a low risk of waking up the sleeper but a low incorporation rate, too, and later on add more “risky” stimuli. Combining this with the stimulus control described below, the sleeper could stop starting the “risky” stimulus in case of an early stimulus incorporation and lucidity.
In order to not wake up the sleeper directly, stimulus intensity should either be set to a value below waking threshold, or, if this threshold is not known, be started with a very low intensity and then be increased over time. Using this auto-increase method, stimuli might get incorporated at some specific intensity level and the sleeper has the possibility to stop the increase of stimulus intensity by making use of stimulus control with his eyes, as described below. Both auto-increasing stimuli and static stimulus intensity are built-in features of the Sleeator 2.