Information Technology Reference
In-Depth Information
The BioMuse software provided the ability to manipulate bio-signal to MIDI
mappings. With the large number of MIDI commands available,
this feature
allowed alpha waves to be mapped to note-speci
c MIDI commands, such as Note
On or Note Off, or to affect sounds triggered by other bio-signals, such as Control
Change messages. From 1987, bursts of alpha activity were soni
ed via a MIDI
synthesiser (Lusted and Knapp
1996
), and again the use of opening and closing the
eyes was incorporated into compositions to generate signi
cant differences in alpha
activity.
Earlier we mentioned the piece
Music for Sleeping and Waking Minds
, which is a
more recent work using updated versions of these tools. This is an 8-h-long com-
position intended for night-time listening. Four performers wearing EEG sensors
affect properties of tones using simple direct mappings, in order to project basic
changes in their brainwave activity to an audience. Alongside alpha activity, delta
rhythms and spindles are also measured and mapped to parameters of audio. The
contrast in input parameters is reflected through the resulting sound. Where alpha
rhythms are prominent during modes of light sleep and through closing of the eyes,
delta rhythms, waves between approximately 0
4 Hz, are associated with deepest
levels of sleep. A spindle is recorded as a spike in activity between 11
-
16 Hz with a
-
duration
0.5 s and combines with muscle twitches during periods before deep sleep
(Babadi et al.
2012
). These three classes of brain activity associated with different
stages of sleep are mapped to three musical parameters. Within the composition are
sixteen tones of differing spectra. Each performer controls parameters relating to four
of these tones. An increase in alpha activity applies a tremolo effect to the tones,
prominent delta waves change the timbre of the tones, and spindles trigger envel-
oped tones through a delay effect with feedback (Ouzounian et al.
2011
). Whereas
delta activity and spindles are not wholly controllable, these three elements of brain
activity are effectively communicated through the act of watching the performers
sleep as well as listening to the resulting audio.
≥
10.7
Event-Related Potentials and Auditory Stimuli
Research into using brainwave activity for musical purposes has not been limited to
translating alpha and other rhythms related to meditative states. Studies into ERPs
have led to BCMIs designed to measure brain activity as a direct result of sensory,
cognitive or motor responses. The ability to actively generate brain activity using
ERPs has led to BCMI systems whereby a user has full control over the musical
outcomes.
ERPs are electrophysiological brain responses produced by perception to stimuli
that is presented to a subject. They are locked in time to the event of the stimuli, and
they are sources of controlled and visible variability in brain activity (Donchin et al.
1978
). ERPs highlight the role of anticipation within brain processing as they can
be elicited by deviation from expected events provided by, on the whole repetitive,
stimuli.
