When measuring a particular phenomenon or cognitive state, it is interesting to use multiple measures. This allows you to inspect the similarity and differences of these measures, and serves as an indication of the validity of the measures. This is also referred to as triangulation.
In my study, I will measure workload with two systems that measure galvanic skin response (GRS) and two systems that measure heart rate variability (HRV). Not all systems allow for reliable time-stamping, however, making it difficult to synchronize the different systems' recordings. In order to triangulate the data, I must know how the time-lines overlap. Currently, the best approach is to start the System1, and then, with a stopwatch, measure the time it takes to start System2. Then, you can ignore/remove the data of System1 for that period of time and the data is lined up.
As an alternative I though to elicit a clear physiological response that would show in each system (by for example scaring the people or, less favorable, giving people electrical shocks). The goal is to have a physiological response that is distinguishable form any normal HRV or GSR response. Is there a reliable way to elicit and identify such a response in HRV or GSR?
I want thus that the HRV/GSR-response can be used as a "start of the experiment" marker or trigger that is recorded in each system. This way, I do not have to worry about synchronization until the analysis of the data.