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sporadic riff. Sporadic riffs are always a repetition of the last played riff; in other
words, it does not change until the system detects active listening behaviour.
In practice, I found it dif
cult to reliably detect active listening behaviour when a
user is consciously trying to change the riffs online. Either more ef
cient EEG
signal processing algorithms need to be employed or the paradigm is
awed, or
both. More work is required to address this problem.
1.8
Neural Processing of Tonality Experiment
In Miranda et al. (
2008
) and Durrant et al. (
2009
), I introduced a functional magnetic
resonance imaging (fMRI) study of tonality, which I developed with Simon Durrant,
a former ICCMR research fellow, and Andre Brechmann, of the Leibniz Institute for
Neurobiology, Germany. The objective of this experiment was to gain a better
understanding of the neural substrates underlying the perception of tonality, with a
view on developing a method to harness their behaviour to control a BCMI. We
looked for differences in neural processing of tonal and atonal stimuli and also for
neural correlates of distance around the circle of
fifths, which describes how close
one key is to another.
Tonality is concerned with the establishment of a sense of key, which in turn
de
nes a series of expectations of musical notes. Within Western music, the octave
is divided into twelve equal semitones, seven of which are said to belong to the
scale of any given key. Within these seven tones, the
first (or lowest) is normally
referred to as the fundamental note of the chord and the one that the key is named
after. A sense of key can be established by a single melodic line, with harmony
implied, but can also have that harmony explicitly created in the form of chord
progressions. Tonality de
nes clear expectations, with the chord built on the
rst
tone (or degree) taking priority. The chords based on the fourth and
fifth degrees
also are important because their constituent members are the only ones whose
constituent tones are entirely taken from the seven tones of the original scale and
occurring with greater frequency than other chords. The chord based on the
fth
degree is followed the majority of the time by the chord based on the
rst degree. In
musical jargon, this is referred to as a dominant-tonic progression. This special
relationship also extends to different keys, with the keys based on the fourth and
fifth degrees of a scale being closest to an existing key by virtue of sharing all but
one scale tone with that key. This gives rise to what is known as the circle of
fifths,
where a change
from one key to another is typically to one of
these other closer keys (Shepard
1982
). Hence, we can de
—
or modulation
—
ne the closeness of keys
based on their proximity in the circle of
fifths, with keys whose
first degree scale
tones are a
fifth apart sharing most of their scale tones, and being perceived as
closest to each other (Durrant et al.
2009
).
Sixteen volunteers, 9 females and 7 males, with age ranging between 19 and
31 years and non-musicians, participated in the experiment. Five experimental
conditions were de
ned:
distant
,
close
,
same
,
initial
and
atonal
(that is, no key)
