Information Technology Reference
In-Depth Information
These principles are adopted in a number of ways in
The Warren
, and the
inclusion of conditional rules and variations allows for an abundance of creative
implementations. For example, in the
first movement, a cello sound can be played
using the derivative measurement of the increment and decrement of one of the four
EEG input channels. Alongside this a second input channel has an integral control
to regulate a modulation index of the cello sound processing, an example of
interpolating two different primary controls to manipulate one sound. To add further
control within these selection-based mappings, mapping rules were applied to the
four incoming EEG data streams and used at various times during the piece
depending on the required function. Here, we look at three of these rules,
threshold
values
,
timing
and
ordering
.
10.9.1 Threshold Values
All four of the brainwave control signals can act as a single selector using mappings
for when the amplitude is high or low. Beyond this, each input signal can be
assigned to elicit a number of commands. In this technique, user control of
brainwave amplitude (of a speci
c channel) was mapped to a series of functions
across a range of evenly spaced threshold values scaled according to the input
range. When the input signal passes a threshold value, a control command is
triggered. For example, an input range of 1-25 could be treated with the following
rules:
if input == 5 play note C2
if input == 10 play note D2
if input == 15 play note E2
if input == 20 play note F2
Without further consideration, an input signal rising and falling through this
range would excite all of the notes on the way up and on the way down. The use of
timing rules (below) provided the performer with the ability to make speci
c
selections whilst avoiding triggering unwanted commands.
10.9.2 Timing
The majority of the mappings within
The Warren
are led by timing rules. Calcu-
lating the time, a user takes to complete cognitive tasks allows for an added
dimension of control. Expanding the simplified threshold example shown above the
speed at which a brainwave increases towards a threshold value would dictate
whether the in between mapping rules are accepted or not. This allows the per-
former to choose how many of the threshold values within one input range to select
during any one command. For example, if the time between initial excitation and
