Editing Affective computing (section)

=====Overview=====

A subject's blood volume pulse (BVP) can be measured by a process called [[photoplethysmography]], which produces a graph indicating blood flow through the extremities.<ref name="Picard, Rosalind 1998">Picard, Rosalind (1998). Affective Computing. MIT.</ref> The peaks of the waves indicate a cardiac cycle where the heart has pumped blood to the extremities. If the subject experiences fear or is startled, their heart usually 'jumps' and beats quickly for some time, causing the amplitude of the cardiac cycle to increase. This can clearly be seen on a photoplethysmograph when the distance between the trough and the peak of the wave has decreased. As the subject calms down, and as the body's inner core expands, allowing more blood to flow back to the extremities, the cycle will return to normal.