Which of the following methods can be employed to determine the appropriate time to wake participants up during the night in a study on the deprivation of certain sleep stages and its effects on cognition, using EOG, EMG, GSR, and EEG recordings? Select all that apply.

A. Watch for lots of activity on the EOG, and high-frequency low-amplitude brain waves on the EEG.
B. Observe changes on the EMG that occur at the same time as changes on the EEG.
C. You can only use EOG, as it's the only recording you can watch in real-time.
D. Look for when skin conductivity increases, as measured by the GSR.