AAWSAP DIRD, Technological Approaches to Controlling External Devices, March 2010

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based on skin movement using technology similar to the operation of GPS. This system
would have the same inherent problem of signal conduction through tissue from all
directions. The key indicator of a future advance in EEG technology would be a study
showing noninvasive spiking or ERP signal detection from a coherent group of less than
10,000 neurons. Until progress in localization on this order is demonstrated, EEG-only
devices will remain low bit rate application technologies.
EEG-only sensor control of devices has been pursued with the supposition that signal
transmission directly from the motor cortex will outperform conventional mechanical
operation because the signal transmission delay between the neocortex and muscles in
the extremities will be augmented via a physical circuit. While this is true, the inherent
assumption that complex mechanical interface operation can be replaced with a 1
bit/second low-delay control pathway is incorrect for naturalistic environments. The
millions of channels of two-way communication between the extremities and the brain
naturally present will control naturalistic mechanical devices far better, and provides
the ability to react to an ever-changing environment. Adding significant computer
control and relegating the motor cortex to a supervisory role of low data bandwidth
could have benefits and is a possible path to real-world improved reaction time
application. Also beneficial to reaction time is the combined EMG EEG devices
mentioned above since the pathways between the brain and facial muscles are far
shorter than those to the extremities.
NONINVASIVE BOLD- BASED DEVICES
The detection resolution of hemodynamic responses using fMRI and NIRS type
technologies is expected to improve in the near, medium, and far terms. NIRS has been
deployed in naturalistic experiments, specifically, automobile driving, and it is
reasonable to envision such systems becoming small enough to wear in the medium to
far term. The limiting issue with BOLD technologies is that the detectable response is
delayed several seconds from neuronal firing, greatly limiting the cognitive control
applications available to these technologies. Progress in localization to below 0.5 mm 3
in a mobile device could indicate the possibility of high bit transfer rates with the use of
state vector machines, albeit with the inherent delay of the physiology. Until the
localization and portability issues are addressed in tandem, BOLD-only devices are
unlikely to be used for commercial cognitive control interfaces.
The vast majority of experiments in fMRI utilize the General Linear Model (GLM) and
something akin to a canonical hemodynamic response. There exists significant
physiological noise in these data analyses that are traditionally filtered out. The
differential results from Independent Component Analysis (ICA) and GLM analysis of the
same data sets indicate that there may be additional circulatory response mechanisms
with faster onsets than typical BOLD. Future studies indicating that filtering or analysis
methods may be ignoring important detectable signals that have inherently faster
response times would provide a breakthrough path for hemodynamic response
technologies. The current research to monitor on this matter is the technology known
as Inverse MRI which can capture high temporal resolution (100 frames a second for
single slices) T2* variations.
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