Emotion representation and physiology assignments in digital systems

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C. Peter, A. Herbon / Interacting with Computers 18 (2006) 139–170
2.1. Discrete emotion theories and the concept of basic emotions
Discrete emotion theories claim the existence of historically evolved basic emotions,
which are universal and can therefore be found in all cultures. Several psychologists have
suggested a different number of these, ranging from 2 to 18 categories, but there has been
considerable agreement on the following six: anger, disgust, fear, happiness, sadness and
surprise. Several arguments for the existence of these categories have been provided, like
distinct universal facial signals, distinct universals in antecedent events, presence in other
primates etc. Ekman (and also other researchers) based his assumptions mainly on the
facial expression of emotions. In his studies, facial expressions of emotions were
recognised by people from very different cultures.
Russell (1994), however, found that there are differences in the recognition ability for
subjects of different origins. While western literate groups widely agree about emotions
presented by photographs, people from isolated groups often do not agree with them. These
differences challenge the universality view. Carroll and Russell (1996) conducted an
experiment focussing on emotion recognition from pictures in a semantic context and found
first, that they could not replicate the high recognition rates for the POFA (Pictures of Facial
Affect; Ekman and Friesen, 1976) that had been reported and second, that there exists
situational dominance when pictures are presented in an emotionally different context.
2.1.1. Empirical evidence
Over the last decades, many experiments have been performed in search of universal
physiological patterns specific to basic emotions. Those studies concentrated mainly on
activities of the autonomous nervous system (ANS) and characteristic speech signal
changes. ANS related studies (e.g. Ax, 1953; Ekman et al., 1983; Palomba et al., 1993,
1999; Prkachin et al., 1999; and many others) showed very interesting results each on its
own, but until now no distinct patterns for the six basic emotions mentioned above could
be found that all agree on. The results of the studies are controversial and the variables
measured do not seem to allow distinguishing clearly between different emotions. Some
stable results could be found for variables that seem to characterise certain basic emotions,
especially fear and anger, which are the two that previous studies have focussed on mostly.
Appendix A summarizes 13 of these ANS-studies that resulted in the following
commonalities. For fear: increase of heart rate, skin conductance level and systolic blood
pressure; for anger: increase of heart rate, systolic and diastolic blood pressure. Measuring
sadness seems to be more difficult, which results in the circumstance that only eight out of
the 13 studies assessed that emotion. Because of this, the results are not as clear as for fear
and anger. Christie (2002); Fredrickson et al. (2000) found a decrease in heart rate, while
Levenson et al. (1990); Neumann and Waldstein (2001); Prkachin et al. (1999); Schwartz
et al. (1981) reported an increase of heart rate, while Palomba and Stegagno (1993) could
not find any significant difference to the measured baseline. Disgust seems to represent an
even greater problem. It was only assessed by four out of the 13 studies. The results are not
very promising. Also, measuring positive emotions such as happiness seems to be very
troublesome as can be observed especially in diastolic and systolic blood pressure and
heart rate data, which ranged from decreases to even strong increases in the seven reported