<s>
An	O
event-related	B-Algorithm
potential	I-Algorithm
(	O
ERP	O
)	O
is	O
the	O
measured	O
brain	O
response	O
that	O
is	O
the	O
direct	O
result	O
of	O
a	O
specific	O
sensory	O
,	O
cognitive	O
,	O
or	O
motor	O
event	O
.	O
</s>
<s>
More	O
formally	O
,	O
it	O
is	O
any	O
stereotyped	O
electrophysiological	B-Application
response	O
to	O
a	O
stimulus	O
.	O
</s>
<s>
ERPs	O
are	O
measured	O
by	O
means	O
of	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
.	O
</s>
<s>
The	O
magnetoencephalography	B-Algorithm
(	O
MEG	B-Algorithm
)	O
equivalent	O
of	O
ERP	O
is	O
the	O
ERF	O
,	O
or	O
event-related	B-Algorithm
field	I-Algorithm
.	O
</s>
<s>
Evoked	B-Algorithm
potentials	I-Algorithm
and	O
induced	O
potentials	O
are	O
subtypes	O
of	O
ERPs	O
.	O
</s>
<s>
With	O
the	O
discovery	O
of	O
the	O
electroencephalogram	B-Application
(	O
EEG	B-Application
)	O
in	O
1924	O
,	O
Hans	O
Berger	O
revealed	O
that	O
one	O
could	O
measure	O
the	O
electrical	O
activity	O
of	O
the	O
human	O
brain	O
by	O
placing	O
electrodes	O
on	O
the	O
scalp	O
and	O
amplifying	O
the	O
signal	O
.	O
</s>
<s>
The	O
EEG	B-Application
proved	O
to	O
be	O
a	O
useful	O
source	O
in	O
recording	O
brain	B-Application
activity	I-Application
over	O
the	O
ensuing	O
decades	O
.	O
</s>
<s>
However	O
,	O
it	O
tended	O
to	O
be	O
very	O
difficult	O
to	O
assess	O
the	O
highly	O
specific	O
neural	O
process	O
that	O
are	O
the	O
focus	O
of	O
cognitive	O
neuroscience	O
because	O
using	O
pure	O
EEG	B-Application
data	O
made	O
it	O
difficult	O
to	O
isolate	O
individual	O
neurocognitive	O
processes	O
.	O
</s>
<s>
Event-related	B-Algorithm
potentials	I-Algorithm
(	O
ERPs	O
)	O
offered	O
a	O
more	O
sophisticated	O
method	O
of	O
extracting	O
more	O
specific	O
sensory	O
,	O
cognitive	O
,	O
and	O
motor	O
events	O
by	O
using	O
simple	O
averaging	O
techniques	O
.	O
</s>
<s>
In	O
1964	O
,	O
research	O
by	O
Grey	O
Walter	O
and	O
colleagues	O
began	O
the	O
modern	O
era	O
of	O
ERP	O
component	O
discoveries	O
when	O
they	O
reported	O
the	O
first	O
cognitive	O
ERP	O
component	O
,	O
called	O
the	O
contingent	B-Algorithm
negative	I-Algorithm
variation	I-Algorithm
(	O
CNV	O
)	O
.	O
</s>
<s>
ERPs	O
can	O
be	O
reliably	O
measured	O
using	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
,	O
a	O
procedure	O
that	O
measures	O
electrical	O
activity	O
of	O
the	O
brain	O
over	O
time	O
using	O
electrodes	O
placed	O
on	O
the	O
scalp	O
.	O
</s>
<s>
The	O
EEG	B-Application
reflects	O
thousands	O
of	O
simultaneously	O
ongoing	B-Algorithm
brain	I-Algorithm
processes	I-Algorithm
.	O
</s>
<s>
This	O
means	O
that	O
the	O
brain	O
response	O
to	O
a	O
single	O
stimulus	O
or	O
event	O
of	O
interest	O
is	O
not	O
usually	O
visible	O
in	O
the	O
EEG	B-Application
recording	O
of	O
a	O
single	O
trial	O
.	O
</s>
<s>
To	O
see	O
the	O
brain	O
's	O
response	O
to	O
a	O
stimulus	O
,	O
the	O
experimenter	O
must	O
conduct	O
many	O
trials	O
and	O
average	O
the	O
results	O
together	O
,	O
causing	O
random	O
brain	B-Application
activity	I-Application
to	O
be	O
averaged	O
out	O
and	O
the	O
relevant	O
waveform	O
to	O
remain	O
,	O
called	O
the	O
ERP	O
.	O
</s>
<s>
The	O
random	O
(	O
background	O
)	O
brain	B-Application
activity	I-Application
together	O
with	O
other	O
bio-signals	O
(	O
e.g.	O
,	O
EOG	O
,	O
EMG	O
,	O
EKG	B-Application
)	O
and	O
electromagnetic	O
interference	O
(	O
e.g.	O
,	O
line	O
noise	O
,	O
fluorescent	O
lamps	O
)	O
constitute	O
the	O
noise	O
contribution	O
to	O
the	O
recorded	O
ERP	O
.	O
</s>
<s>
The	O
noise	O
can	O
be	O
approximated	O
by	O
a	O
zero-mean	O
Gaussian	B-General_Concept
random	I-General_Concept
process	I-General_Concept
of	O
variance	O
which	O
is	O
uncorrelated	O
between	O
trials	O
and	O
not	O
time-locked	O
to	O
the	O
event	O
(	O
this	O
assumption	O
can	O
be	O
easily	O
violated	O
,	O
for	O
example	O
in	O
the	O
case	O
of	O
a	O
subject	O
doing	O
little	O
tongue	O
movements	O
while	O
mentally	O
counting	O
the	O
targets	O
in	O
an	O
experiment	O
)	O
.	O
</s>
<s>
Artifact	O
rejection	O
can	O
be	O
performed	O
manually	O
by	O
visual	O
inspection	O
or	O
using	O
an	O
automated	O
procedure	O
based	O
on	O
predefined	O
fixed	O
thresholds	O
(	O
limiting	O
the	O
maximum	O
EEG	B-Application
amplitude	O
or	O
slope	O
)	O
or	O
on	O
time-varying	O
thresholds	O
derived	O
from	O
the	O
statistics	O
of	O
the	O
set	O
of	O
trials	O
.	O
</s>
<s>
Though	O
some	O
ERP	O
components	O
are	O
referred	O
to	O
with	O
acronyms	O
(	O
e.g.	O
,	O
contingent	B-Algorithm
negative	I-Algorithm
variation	I-Algorithm
–	O
CNV	O
,	O
error-related	B-Algorithm
negativity	I-Algorithm
–	O
ERN	O
)	O
,	O
most	O
components	O
are	O
referred	O
to	O
by	O
a	O
letter	O
(	O
N/P	O
)	O
indicating	O
polarity	O
(	O
negative/positive	O
)	O
,	O
followed	O
by	O
a	O
number	O
indicating	O
either	O
the	O
latency	O
in	O
milliseconds	O
or	O
the	O
component	O
's	O
ordinal	B-Language
position	O
in	O
the	O
waveform	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
negative-going	O
peak	O
that	O
is	O
the	O
first	O
substantial	O
peak	O
in	O
the	O
waveform	O
and	O
often	O
occurs	O
about	O
100	O
milliseconds	O
after	O
a	O
stimulus	O
is	O
presented	O
is	O
often	O
called	O
the	O
N100	B-Algorithm
(	O
indicating	O
its	O
latency	O
is	O
100	O
ms	O
after	O
the	O
stimulus	O
and	O
that	O
it	O
is	O
negative	O
)	O
or	O
N1	B-Algorithm
(	O
indicating	O
that	O
it	O
is	O
the	O
first	O
peak	O
and	O
is	O
negative	O
)	O
;	O
it	O
is	O
often	O
followed	O
by	O
a	O
positive	O
peak	O
,	O
usually	O
called	O
the	O
P200	B-Algorithm
or	O
P2	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
P300	B-Algorithm
component	O
may	O
exhibit	O
a	O
peak	O
anywhere	O
between	O
250	O
ms	O
–	O
700	O
ms.	O
</s>
<s>
Unlike	O
microelectrodes	O
,	O
which	O
require	O
an	O
electrode	O
to	O
be	O
inserted	O
into	O
the	O
brain	O
,	O
and	O
PET	B-Application
scans	I-Application
that	O
expose	O
humans	O
to	O
radiation	O
,	O
ERPs	O
use	O
EEG	B-Application
,	O
a	O
non-invasive	O
procedure	O
.	O
</s>
<s>
ERPs	O
provide	O
excellent	O
temporal	B-General_Concept
resolution	I-General_Concept
—	O
as	O
the	O
speed	O
of	O
ERP	O
recording	O
is	O
only	O
constrained	O
by	O
the	O
sampling	O
rate	O
that	O
the	O
recording	O
equipment	O
can	O
feasibly	O
support	O
,	O
whereas	O
hemodynamic	O
measures	O
(	O
such	O
as	O
fMRI	B-Algorithm
,	O
PET	B-Application
,	O
and	O
fNIRS	B-Algorithm
)	O
are	O
inherently	O
limited	O
by	O
the	O
slow	O
speed	O
of	O
the	O
BOLD	B-Algorithm
response	O
.	O
</s>
<s>
ERP	O
research	O
is	O
much	O
cheaper	O
to	O
do	O
than	O
other	O
imaging	O
techniques	O
such	O
as	O
fMRI	B-Algorithm
,	O
PET	B-Application
,	O
and	O
MEG	B-Algorithm
.	O
</s>
<s>
This	O
is	O
because	O
purchasing	O
and	O
maintaining	O
an	O
EEG	B-Application
system	O
is	O
less	O
expensive	O
than	O
the	O
other	O
systems	O
.	O
</s>
<s>
Alternatively	O
,	O
the	O
P300	B-Algorithm
response	O
occurs	O
at	O
around	O
300ms	O
in	O
the	O
oddball	B-Algorithm
paradigm	I-Algorithm
,	O
for	O
example	O
,	O
regardless	O
of	O
the	O
type	O
of	O
stimulus	O
presented	O
:	O
visual	O
,	O
tactile	O
,	O
auditory	O
,	O
olfactory	O
,	O
gustatory	O
,	O
etc	O
.	O
</s>
<s>
Because	O
of	O
this	O
general	O
invariance	O
with	O
regard	O
to	O
stimulus	O
type	O
,	O
the	O
P300	B-Algorithm
component	O
is	O
understood	O
to	O
reflect	O
a	O
higher	O
cognitive	O
response	O
to	O
unexpected	O
and/or	O
cognitively	O
salient	O
stimuli	O
.	O
</s>
<s>
The	O
P300	B-Algorithm
response	O
has	O
also	O
been	O
studied	O
in	O
the	O
context	O
of	O
information	O
and	O
memory	O
detection	O
.	O
</s>
<s>
In	O
addition	O
,	O
there	O
are	O
studies	O
on	O
abnormalities	O
of	O
P300	B-Algorithm
in	O
depression	O
.	O
</s>
<s>
Depressed	O
patients	O
tend	O
to	O
have	O
a	O
reduced	O
P200	B-Algorithm
and	O
P300	B-Algorithm
amplitude	O
and	O
a	O
prolonged	O
P300	B-Algorithm
latency	O
.	O
</s>
<s>
Due	O
to	O
the	O
consistency	O
of	O
the	O
P300	B-Algorithm
response	O
to	O
novel	O
stimuli	O
,	O
a	O
brain	B-Application
–	I-Application
computer	I-Application
interface	I-Application
can	O
be	O
constructed	O
which	O
relies	O
on	O
it	O
.	O
</s>
<s>
By	O
arranging	O
many	O
signals	O
in	O
a	O
grid	O
,	O
randomly	O
flashing	O
the	O
rows	O
of	O
the	O
grid	O
as	O
in	O
the	O
previous	O
paradigm	O
,	O
and	O
observing	O
the	O
P300	B-Algorithm
responses	O
of	O
a	O
subject	O
staring	O
at	O
the	O
grid	O
,	O
the	O
subject	O
may	O
communicate	O
which	O
stimulus	O
he	O
is	O
looking	O
at	O
,	O
and	O
thus	O
slowly	O
"	O
type	O
"	O
words	O
.	O
</s>
<s>
the	O
quiet	O
production	O
of	O
words	O
-	O
which	O
has	O
also	O
been	O
proven	O
by	O
event-related	B-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
Other	O
ERPs	O
used	O
frequently	O
in	O
research	O
,	O
especially	O
neurolinguistics	O
research	O
,	O
include	O
the	O
ELAN	B-Algorithm
,	O
the	O
N400	B-Algorithm
,	O
and	O
the	O
P600/SPS	B-Algorithm
.	O
</s>
