<s>
The	O
P3a	B-Algorithm
,	O
or	O
novelty	O
P3	O
,	O
is	O
a	O
component	O
of	O
time-locked	O
(	O
EEG	B-Application
)	O
signals	O
known	O
as	O
event-related	B-Algorithm
potentials	I-Algorithm
(	O
ERP	O
)	O
.	O
</s>
<s>
The	O
P3a	B-Algorithm
is	O
a	O
positive-going	O
scalp-recorded	O
brain	O
potential	O
that	O
has	O
a	O
maximum	O
amplitude	B-Application
over	O
frontal/central	O
electrode	O
sites	O
with	O
a	O
peak	O
latency	O
falling	O
in	O
the	O
range	O
of	O
250	O
–	O
280	O
ms.	O
</s>
<s>
The	O
P3a	B-Algorithm
has	O
been	O
associated	O
with	O
brain	B-Application
activity	I-Application
related	O
to	O
the	O
engagement	O
of	O
attention	O
(	O
especially	O
orienting	O
and	O
involuntary	O
shifts	O
to	O
changes	O
in	O
the	O
environment	O
)	O
and	O
the	O
processing	O
of	O
novelty	O
.	O
</s>
<s>
In	O
1975	O
Squires	O
and	O
colleagues	O
conducted	O
a	O
study	O
attempting	O
to	O
resolve	O
some	O
of	O
the	O
questions	O
surrounding	O
what	O
neural	O
process	O
the	O
P300	B-Algorithm
reflects	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
several	O
researchers	O
suggested	O
that	O
there	O
needed	O
to	O
be	O
active	O
attention	O
towards	O
the	O
target	O
stimuli	O
in	O
order	O
to	O
elicit	O
a	O
P300	B-Algorithm
,	O
in	O
part	O
because	O
stimuli	O
that	O
were	O
ignored	O
resulted	O
in	O
a	O
P300	B-Algorithm
with	O
a	O
smaller	O
amplitude	B-Application
or	O
no	O
P300	B-Algorithm
at	O
all	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
some	O
research	O
had	O
shown	O
that	O
subjects	O
exhibit	O
a	O
P300	B-Algorithm
to	O
unpredictable	O
stimuli	O
in	O
an	O
ongoing	O
repetitive	O
series	O
of	O
stimuli	O
,	O
even	O
when	O
the	O
stimuli	O
were	O
classified	O
as	O
irrelevant	O
and	O
subjects	O
were	O
asked	O
to	O
ignore	O
them	O
while	O
completing	O
another	O
task	O
(	O
i.e.	O
</s>
<s>
It	O
was	O
intriguing	O
that	O
you	O
could	O
elicit	O
a	O
P300	B-Algorithm
in	O
conditions	O
with	O
active	O
attention	O
and	O
those	O
of	O
non-attention	O
.	O
</s>
<s>
Upon	O
further	O
investigation	O
it	O
turned	O
out	O
that	O
when	O
comparing	O
the	O
two	O
types	O
of	O
P300	B-Algorithm
potentials	O
,	O
they	O
differed	O
in	O
latency	O
and	O
scalp	O
topography	O
.	O
</s>
<s>
to	O
suggest	O
that	O
there	O
were	O
two	O
distinct	O
psycho-physiological	O
entities	O
that	O
had	O
been	O
referred	O
to	O
collectively	O
as	O
the	O
P300	B-Algorithm
.	O
</s>
<s>
recorded	O
EEG	B-Application
during	O
an	O
auditory	O
odd-ball	B-Algorithm
paradigm	I-Algorithm
with	O
various	O
conditions	O
.	O
</s>
<s>
They	O
termed	O
this	O
potential	O
the	O
P3a	B-Algorithm
in	O
order	O
to	O
distinguish	O
it	O
from	O
its	O
relative	O
,	O
the	O
P3b	B-Algorithm
,	O
which	O
was	O
a	O
positive-going	O
potential	O
that	O
occurred	O
at	O
310	O
–	O
380	O
ms	O
when	O
the	O
infrequent	O
tones	O
were	O
attended	O
to	O
.	O
</s>
<s>
The	O
newly	O
coined	O
"	O
P3a	B-Algorithm
"	O
had	O
a	O
peak	O
amplitude	B-Application
occurring	O
at	O
frontal	O
midline	O
sites	O
while	O
the	O
P3b	B-Algorithm
peak	O
amplitude	B-Application
occurred	O
over	O
parietal	O
midline	O
sites	O
.	O
</s>
<s>
Consistent	O
with	O
this	O
historical	O
separation	O
of	O
the	O
two	O
components	O
,	O
typically	O
if	O
a	O
stimulus	O
is	O
a	O
rare	O
non-target	O
then	O
the	O
recorded	O
EEG	B-Application
waveform	O
has	O
characteristics	O
associated	O
with	O
the	O
P3a	B-Algorithm
,	O
whereas	O
attended	O
targets	O
elicit	O
a	O
P3b	B-Algorithm
.	O
</s>
<s>
P3a	B-Algorithm
amplitudes	B-Application
tend	O
to	O
be	O
maximal	O
over	O
frontal/central	O
sites	O
on	O
the	O
scalp	O
,	O
such	O
as	O
FCz/Cz	O
in	O
the	O
international	O
10-20	B-Algorithm
system	I-Algorithm
,	O
which	O
is	O
the	O
standard	O
electrode	O
placement	O
system	O
of	O
many	O
ERP	O
labs	O
around	O
the	O
world	O
.	O
</s>
<s>
P3b	B-Algorithm
amplitudes	B-Application
are	O
generally	O
greater	O
at	O
sites	O
like	O
Pz	O
.	O
</s>
<s>
While	O
many	O
things	O
can	O
affect	O
the	O
latency	O
of	O
the	O
P3b	B-Algorithm
,	O
P3a	B-Algorithm
latencies	O
often	O
occur	O
75-100	O
ms	O
earlier	O
than	O
P3b	B-Algorithm
peak	O
latencies	O
,	O
and	O
around	O
250-280	O
ms.	O
</s>
<s>
The	O
3-stimulus	O
oddball	B-Algorithm
paradigm	I-Algorithm
is	O
one	O
of	O
the	O
primary	O
paradigms	O
used	O
to	O
elicit	O
a	O
prominent	O
P3a	B-Algorithm
.	O
</s>
<s>
This	O
paradigm	O
is	O
a	O
modification	O
of	O
the	O
oddball	B-Algorithm
task	I-Algorithm
that	O
is	O
used	O
to	O
elicit	O
a	O
P3b	B-Algorithm
.	O
</s>
<s>
When	O
these	O
infrequent	O
,	O
novel	O
stimuli	O
(	O
for	O
example	O
,	O
the	O
sound	O
of	O
dog	O
barks	O
or	O
color	O
forms	O
)	O
are	O
presented	O
in	O
the	O
series	O
of	O
more	O
typical	O
target	O
and	O
standard	O
stimuli	O
(	O
for	O
example	O
,	O
tones	O
or	O
letters	O
of	O
the	O
alphabet	O
)	O
,	O
a	O
P3a	B-Algorithm
that	O
is	O
larger	O
over	O
the	O
frontal	O
and	O
central	O
areas	O
of	O
the	O
brain	O
is	O
produced	O
in	O
response	O
to	O
auditory	O
,	O
visual	O
,	O
and	O
somatosensory	O
stimuli	O
.	O
</s>
<s>
Deviant	O
stimuli	O
from	O
auditory	O
,	O
visual	O
,	O
and	O
somatosensory	O
modalities	O
are	O
all	O
sufficient	O
for	O
eliciting	O
a	O
P3a	B-Algorithm
.	O
</s>
<s>
For	O
example	O
,	O
Grillon	O
and	O
colleagues	O
used	O
this	O
design	O
when	O
they	O
tested	O
for	O
the	O
effects	O
of	O
rare	O
non-target	O
(	O
deviant	O
)	O
auditory	O
stimuli	O
on	O
subjects	O
 '	O
EEG	B-Application
activity	O
.	O
</s>
<s>
In	O
their	O
results	O
it	O
was	O
apparent	O
that	O
the	O
P300	B-Algorithm
they	O
recorded	O
to	O
the	O
rare	O
non-target	O
tones	O
was	O
in	O
fact	O
a	O
P3a	B-Algorithm
.	O
</s>
<s>
The	O
rare	O
non-target	O
tones	O
resulted	O
in	O
a	O
P300	B-Algorithm
(	O
P3a	B-Algorithm
)	O
with	O
a	O
shorter	O
latency	O
that	O
was	O
distributed	O
more	O
towards	O
the	O
front	O
of	O
the	O
scalp	O
when	O
compared	O
to	O
the	O
P300	B-Algorithm
(	O
P3b	B-Algorithm
)	O
elicited	O
by	O
rare	O
target	O
stimuli	O
.	O
</s>
<s>
The	O
3	O
stimulus	O
oddball	B-Algorithm
paradigm	I-Algorithm
provides	O
a	O
flexible	O
way	O
to	O
examine	O
the	O
P3a	B-Algorithm
across	O
stimulus	O
modality	O
and	O
tasks	O
.	O
</s>
<s>
Yamaguchi	O
and	O
Knight	O
conducted	O
a	O
study	O
using	O
mechanical	O
tactile	O
stimuli	O
(	O
finger	O
taps	O
)	O
and	O
electric	O
shocks	O
to	O
the	O
wrist	O
within	O
a	O
3-stimulus	O
oddball	B-Algorithm
paradigm	I-Algorithm
.	O
</s>
<s>
They	O
were	O
interested	O
in	O
seeing	O
if	O
subjects	O
would	O
elicit	O
a	O
P3a	B-Algorithm
to	O
novel	O
somatosensory	O
stimuli	O
.	O
</s>
<s>
They	O
found	O
that	O
both	O
types	O
of	O
the	O
novel	O
somatosensory	O
stimuli	O
did	O
in	O
fact	O
produce	O
P3a	B-Algorithm
’s	O
that	O
had	O
a	O
more	O
frontal	O
distribution	O
than	O
responses	O
to	O
target	O
stimuli	O
.	O
</s>
<s>
Shock	O
novels	O
also	O
resulted	O
in	O
a	O
significantly	O
shorter	O
P3a	B-Algorithm
latency	O
.	O
</s>
<s>
Two	O
important	O
factors	O
for	O
determining	O
the	O
amplitude	B-Application
of	O
the	O
P3a	B-Algorithm
include	O
habituation	O
and	O
target	O
discrimination	O
.	O
</s>
<s>
One	O
major	O
difference	O
between	O
the	O
P3b	B-Algorithm
and	O
the	O
P3a	B-Algorithm
is	O
that	O
only	O
the	O
P3a	B-Algorithm
habituates	O
with	O
repeated	O
presentation	O
.	O
</s>
<s>
The	O
P3a	B-Algorithm
's	O
rapid	O
amplitude	B-Application
reduction	O
with	O
exposure	O
to	O
repeated	O
trials	O
of	O
novel	O
stimuli	O
supports	O
the	O
idea	O
that	O
the	O
P3a	B-Algorithm
is	O
the	O
electrophysiological	O
representation	O
of	O
the	O
orienting	O
response	O
(	O
which	O
also	O
habituates	O
in	O
behavior	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
Grillon	O
and	O
colleagues	O
used	O
a	O
3	O
stimulus	O
odd-ball	B-Algorithm
paradigm	I-Algorithm
wherein	O
they	O
presented	O
subjects	O
with	O
a	O
condition	O
in	O
which	O
the	O
deviant	O
stimuli	O
were	O
constant	O
and	O
a	O
condition	O
in	O
which	O
the	O
deviant	O
stimuli	O
were	O
always	O
novel	O
.	O
</s>
<s>
Their	O
results	O
showed	O
the	O
largest	O
P3a	B-Algorithm
amplitude	B-Application
in	O
response	O
to	O
deviant	O
stimuli	O
that	O
were	O
novel	O
.	O
</s>
<s>
Another	O
factor	O
that	O
affects	O
P3a	B-Algorithm
amplitude	B-Application
is	O
target	O
discrimination	O
.	O
</s>
<s>
It	O
is	O
interesting	O
that	O
although	O
the	O
P3a	B-Algorithm
is	O
elicited	O
by	O
non-target	O
deviant	O
stimuli	O
,	O
the	O
nature	O
of	O
the	O
target	O
stimuli	O
affect	O
the	O
P3a	B-Algorithm
response	O
.	O
</s>
<s>
It	O
seems	O
that	O
the	O
amplitude	B-Application
of	O
the	O
P3a	B-Algorithm
may	O
be	O
affected	O
by	O
an	O
individual	O
’s	O
ability	O
to	O
distinguish	O
target	O
stimuli	O
from	O
standard	O
stimuli	O
.	O
</s>
<s>
When	O
this	O
discrimination	O
is	O
easy	O
,	O
non-target	O
deviant	O
stimuli	O
produce	O
a	O
P300	B-Algorithm
that	O
is	O
smaller	O
than	O
the	O
target	O
P3b	B-Algorithm
and	O
is	O
largest	O
over	O
parietal	O
sites	O
.	O
</s>
<s>
Although	O
the	O
P3a	B-Algorithm
has	O
been	O
dissociated	O
from	O
the	O
P3b	B-Algorithm
,	O
its	O
amplitude	B-Application
and	O
latency	O
may	O
be	O
affected	O
by	O
factors	O
that	O
also	O
modulate	O
the	O
P3b	B-Algorithm
.	O
</s>
<s>
The	O
P3a	B-Algorithm
has	O
been	O
linked	O
with	O
novelty	O
or	O
orienting	O
and	O
involuntary	O
shifts	O
to	O
changes	O
in	O
the	O
environment	O
.	O
</s>
<s>
Some	O
have	O
suggested	O
that	O
the	O
P3a	B-Algorithm
and	O
P3b	B-Algorithm
are	O
variants	O
of	O
the	O
same	O
ERP	O
response	O
that	O
varies	O
in	O
scalp	O
topography	O
as	O
a	O
function	O
of	O
attention	O
and	O
task	O
demands	O
.	O
</s>
<s>
In	O
other	O
cases	O
,	O
however	O
,	O
the	O
two	O
can	O
be	O
dissociated	O
:	O
for	O
example	O
,	O
patients	O
with	O
temporal-parietal	O
lesions	O
and	O
an	O
absent	O
visual	O
P3a	B-Algorithm
response	O
have	O
partial	O
preservation	O
of	O
their	O
visual	O
target	O
P3b	B-Algorithm
.	O
</s>
<s>
These	O
results	O
indicate	O
that	O
at	O
least	O
partially	O
non-overlapping	O
neural	O
circuits	O
may	O
be	O
engaged	O
during	O
P3a	B-Algorithm
and	O
P3b	B-Algorithm
generation	O
.	O
</s>
<s>
Neural	O
sources	O
of	O
the	O
P3a	B-Algorithm
have	O
been	O
hypothesized	O
to	O
arise	O
from	O
frontal	O
lobe	O
functioning	O
and	O
to	O
involve	O
frontal	O
lobe	O
attention	O
mechanisms	O
.	O
</s>
<s>
Magnetic	O
resonance	O
imaging	O
(	O
MRI	O
)	O
studies	O
looking	O
at	O
gray	O
matter	O
volume	O
and	O
P3a	B-Algorithm
amplitude	B-Application
show	O
stronger	O
correlations	O
when	O
non-target	O
,	O
startling	O
stimuli	O
are	O
viewed	O
.	O
</s>
<s>
Lesion	O
studies	O
indicate	O
that	O
prefrontal	O
and	O
temporal-parietal	O
cortex	O
contribute	O
to	O
auditory	O
P3a	B-Algorithm
generation	O
.	O
</s>
<s>
The	O
P3a	B-Algorithm
is	O
suspected	O
to	O
also	O
reflect	O
interactions	O
between	O
the	O
frontal	O
lobe	O
and	O
the	O
hippocampus	O
,	O
as	O
patients	O
with	O
focal	O
hippocampal	O
lesions	O
have	O
reduced	O
P3a	B-Algorithm
amplitude	B-Application
from	O
novel	O
distracters	O
.	O
</s>
