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Figure 8.
Segregation of motion into separate channels of global and local motion. Four small
images, in reading order:
A still image from the input sequence (input), localized eye-nose-
mouth regions (facial regions of interest), optical fl ow calculated between two successive
frames (unmodifi ed fl ow) and estimation of the affi ne fl ow transformation parameters
representing the global fl ow (affi ne fl ow).
Right image:
The residual, or local, fl ow is calculated
by subtracting the affi ne fl ow from the unmodifi ed fl ow, which reduces the overall motion
energy. Residual fl ow caused by facial expressionremains (in theexample caused by eye-,
mouth- and cheek-movement).
(Color image of this fi gure appears in the color plate section at the end of the topic.)
3.2.3 Physiological Features
The physiological signals were acquired using a NEXUS-32 polygraph,
a flexible 32 channel monitoring system. Three physiological channels
were recorded: the electromyogram (EMG) of the corrugator supercilii
and zygomaticus major, and the skin conductance (SCL).
To measure the SCL, two electrodes of the sensor are positioned
on the index finger and the ring finger. Since the sweat glands are
innervated exclusively sympathetically, i.e. without influence of
the parasympathetic nervous system, the electrodermal activity is
considered a good indicator of the “inner” tension of a person. This
aspect can be reproduced particularly impressively by the observation
of a rapid increase in skin conductance within one to three seconds due
to a simple stress stimulus (e.g. deep breathing, emotional excitement
or mental activity).
Electrical muscle activity is also an indicator of general psycho-
physiological arousal, as increased muscle tone is associated with
increasing activity of the sympathetic nervous system, while a
decrease in somatomotor activity is associated with predominantly
parasympathetic arousal. We used two channel EMGs for corrugator
and zygomaticus muscles. EMG responses over facial muscle regions
like corrugator supercilii, which draws the brow downward and
medial ward to form a frown, and zygomaticus major, which elevates
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