“…For example, it is acknowledged that people respond differentially to stressful stimuli. To detect stress and affect, methods that cater to the individual have been used, such as measuring galvanic skin response (Healey, Picard, & Dabek, 1998), blood volume pressure (Ward & Marsden, 2003), electromyograms (Scheirer, Fernandez, Klein, & Picard, 2002), squeeze pressure on a mouse (van Galen, Liesker, & De Haan, 2004), keystrokes (Vizer, Zhou, & Sears, 2009), and response time (Lemmens, De Haan, van Galen, & Meulenbroek, 2007), among others. These physiological measurements are customized to the user and have even been used to alter computer game difficulty in real time based on the user's current affect (Liu, Agrawal, Sarkar, & Chen, 2009).…”