EEG Evoked Potential (ERP) is measured using EEG8 multiple EEG amplifiers. For stimuli, methods similar to those used in
A CS / UCS measurement example
apply. Great flexibility is thus available for stimulus presentation patterns. Alternatively, visual or sound generation programs may be run on a second computer linked to the PSYLAB measuring system. Please see examples of this type of hook up in:
An externally generated stimulus measurement example.
Circular or continuous buffer measurement methods allow evaluation of pre-stimulus EEG.
Further in this section an example is given of measurement in an oddball paradigm. Analysis is performed off-line by PSYLAB5.
The measurement program below was loaded into PSYLAB to perform the original oddball measurement task. The commands at the top beginning with '$' are used to set up measurement channels, sample rate etc. The lower part of the program is dynamically interpreted during measurement to control stimuli and otherwise organise the procedure, producing randomized Inter Stimulus Interval and randomized stimulus category.
'************************************************
'P300 measurement in oddball discrimination task
'Standard value = 125; target value = 126
'************************************************
$measure EEG address 1 hires digital 1 "CZ"
$measure EEG address 2 hires digital 1 "CZ"
$measure EEG address 3 hires digital 1 "PZ"
$measure EEG address 4 hires digital 1 "PZ"
$measure event STIMOUT$rate 100
$subject
$random 2
locate 28,2: print "Stimuli presented"
nextTime = 3
MAIN
s1 = rareStimNo+freqStimNo
locate 28,20:print s1
if time > nextTime then gosub STIM
goto MAIN
STIM
if random > 204 then goto RARE
FREQUENT
tone 125,40,.1
freqStimNo = freqStimNo + 1
nextTime = Time + 1 + (random / 100)
nextTime = int(nextTime)
return
RARE
tone 126,85,.1
epcue
rareStimNo=rareStimNo + 1
nextTime = time + 1 + (random / 100)
nextTime = int(nextTime)
if rareStimNo > 31 then goto END
return
END
t = time + 5
delay until time > t
store