The Signals

Four types of signals were measured during the driving task: skin conductance, respiration, muscle activity and heart activity. Heart activity was measured using both a blood volume pulse (BVP) sensor and an electrocardiograph (EKG) sensor. These sensors were chosen because they are minimally invasive and can provide a continuous record of the subject's response to driving stressors.

  

Figure: A diagram showing the BVP (left) and EKG placement (right) The BVP uses a backscatter method in which light from the sensor source is reflected by the volume of blood in the capillary and measured by the adjacent photo-detector. The EKG placement on the torso was chosen so as to minimize motion artifacts. Both diagrams are from the Thought Technology User's Manual[Tho94].