single seizure detectors to form a distributed detection
system and apply our previously proposed blind algo-
rithm on multichannel information fusion. First, we
formulate the set of nonlinear equations consisting of
the unknown a priori probabilities of the binary hy-
potheses and the unknown probabilities of false alarm
and missed detection. Then, we estimate these un-
knowns using the corresponding multinominal dis-
tribution, maximum likelihood estimation and actual
count of decisions made by different detectors. Fi-
nally, we present the analytical expression of overall
error probability when the true values of the parame-
ters are given and explore the effect of our blind algo-
rithm to the overall seizure detection. To the evalua-
tion purposes, we use a proposed neonatal EEG model
(Rankine et al., 2007) to generate neonatal EEG sig-
nals.
2 SIGNAL MODEL
2.1 Local Detectors
Several neonatal EEG seizure detection algorithms
exist in the literature. In this paper we implemented
the following three algorithms that have been pro-
posed for the neonatal seizure detection:
Liu’s Algorithm. In(Liu, 1992) the authors fo-
cused on the rhythmic characteristic of neonatal EEG
seizure and proposed a detection algorithm using au-
tocorrelation analysis. Due to the periodicity of EEG
seizure, its autocorrelation function has more peaks
with similar periodicity of the original signal. In con-
trast, normal neonatal EEG does not have clear pe-
riodicity, so its autocorrelation usually has irregular
peaks. A scoring system described in (Liu, 1992) can
be used to determine the degree of periodicity of the
EEG signal quantitatively in order to identify the ex-
istences of the seizure activities.
Gotmans’s Algorithm. In (Gotman, 1997) the au-
thors proposed three different seizure detection meth-
ods to detect three types of seizures: rhythmic dis-
charges, multiple spikes, and very slow rhythmic dis-
charges, respectively. In this paper, we only focus on
the rhythmic discharge detection since it could iden-
tify 90% of the seizures detected by all three detection
algorithms. The rhythmicity of a signal can be repre-
sented in the frequency domain by a high and narrow
peak at the frequency of that signal. Therefore, in the
spectrum of the EEG segment containing seizure ac-
tivities, a large distinct peak is expected to appear at
the main frequency of EEG seizure.
Local
Detector LD
Local
Detector LD
Local
Detector LD
Phenomenon
Fusion
Center
u
u
u
1
2
n
y
1
y
2
y
n
u
0
1
2
n
Figure 1: Parallel Distributed Detection System.
Celka’s Algorithm. The algorithm reviewed in this
section was proposed in (Celka and Colditz, 2002).
They performed the singular spectrum analysis and
the information theoretic-based signal subspace se-
lection to examine the complexity of the EEG signal.
This detection algorithm has three main steps: Pre-
processing, singular spectrum analysis, and minimum
description length.
2.2 Distributed Detection System
Each of the algorithms reviewed in the previous sec-
tion can be considered as a single detector. Since the
statistical properties of neonatal EEG can vary signif-
icantly from patient to patient, it is difficult to evalu-
ate the performance of existing single detectors since
they are all based on mathematical models whose per-
formances change on different data sets. Thus, it mo-
tivates us to combine the existing single detectors and
utilize their strengths by extending previous results
on blind multichannel information fusion (Liu et al.,
2007). Figure 1 shows the structure of a typical paral-
lel distributed detection system with N detectors. The
role of the local detectors LD
n
is to make local deci-
sion u
n
based on their own observations y
n
. All the lo-
cal decisions are then sent to the fusion center, where
the global decision u
0
is made based on a fusion rule
in order to minimize the overall probability of error.
In this work, we only focus on the case of three local
detectors, i.e, N = 3, unless otherwise stated. Addi-
tional detectors can be added into the system when-
ever more information is required to make final deci-
sion. Although increasing the number of detectors has
the potential to reduce the detection error probability,
it also increases the computational cost.
2.3 Local Detectors
The local detectors LD
n
havetheir own decision rules.
We use the three algorithms reviewed in Section 2.1
to formulate the local decision rules.
We perform hypothesis testings (local decisions)
with two hypotheses:
H
0
: The EEG signal does not contain seizure
BIOSIGNALS 2011 - International Conference on Bio-inspired Systems and Signal Processing
366