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6.5.2 Physiological Measures
An alternative to self-reports is physiological measures. Physiological changes
during music listening are related to the activation of the autonomic nervous system
(ANS), which is responsible for regulating a variety of peripheral functions. There
is a large amount of studies establishing the relationship between physiological
responses and musical emotion during music listening (see Sect.
6.6
of this chap-
ter). Physiological measures are considered to be unbiased, more objective mea-
sures of emotional responses to music. They can be easily and noninvasively
recorded and analyzed. They are also able to capture changes in emotional
responses that would remain unnoticed in self-reports (Cacioppo et al.
2000
).
The most commonly assessed physiological measures are electrodermal, car-
diovascular, and respiratory responses. Electrodermal activity is quanti
ed in terms
of skin conductance (SC), which is considered to re
ect arousal (Boucsein
1992
). It
has been shown that SC increases linearly with arousal of emotional stimuli,
whereas no differences in valence were found. In general, emotionally powerful
music tends to increase SC more than less emotional music (Rickard
2004
).
The most frequently used cardiovascular measures include heart rate (HR), blood
pressure (BP), and heart rate variability (HRV). Most of the existing studies on the
effect of music on heart rate indicate that music listening can cause changes in heart
rate (Nyklicek et al.
1997
; Bernardi et al.
2006
). These changes can be easily
measured through ECG (Electrocardiogram). It was shown that high arousal music
tends to increase the heart rate, whereas sedative music tends to decrease it. On the
other hand, HRV is associated with valence and has been found to be higher during
high positive valence (Cacioppo et al.
2000
). Krumhansl (
1997
) reported increases
in HRV during sad and happy music.
Respiration is also strongly linked to emotional responses to music. Most of the
existing studies show an increase in respiration or breathing rate during music
listening (Krumhansl
1997
; Gomez and Danuser 2004; Nyklicek et al.
1997
).
Breathing rate is closely related to heart rate changes during music listening since
the two systems are considered as two weakly coupled oscillators and through this
coupling respiration regulates heart rate. Recent experiments provide evidence that
both respiration rate and heart rate entrain musical rhythm.
Muscular tension and particularly facial expressions are among the potential
measures of emotional states. Facial expressions are measured through electro-
myography (EMG) by placing electrodes on zygomaticus (associated with fur-
rowing of the eyebrows) and corrugator (associated with rising of the corners of the
lips) muscles. The results of existing measurements on zygomaticus and corrugator
showed increased zygomatic muscle activity during high arousal and positive
valence music, whereas greater corrugator activity was reported for musical
excerpts of negative valence (Larsen et al.
2003
; Witvliet and Vrana
2007
). Thus,
EMG activity can be considered as a promising measure of valence. An additional
important result is that using facial EMG, discrete emotions can be recognized
(Thayer and Faith
2001
; Khalfa et al.
2008
). Facial expressions have been so far
