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Ann. psychophysiol. 
ISSN 2412-3188 (Online)|2410-1354 (Print) 

APP| Published By AEIRC| https://doi.org/10.29052/2412-3188.v9.i1.2022.01-05 
 

 
Editorial 

Don't assume that your equipment is doing 
what you think it is 
Richard A. Sherman 

Editor, Annals of Psychophysiology 
 

Abstract 
A perennial problem encountered by both novices and experienced people using 
psychophysiological recording equipment and then using the displays as the basis 
for biofeedback and neurofeedback is that the equipment is frequently not doing 
what the users think it is. Hardware and software are frequently glitchy and 
setting the devices incorrectly makes matters worse. The key question to answer is 
whether the device reliably produces a display clearly related to the physiological 
signal produced by the person being recorded. The editorial emphasizes the need 
to view a raw signal so relationships between the physiology being recorded and 
the display can be accurately assessed. Seven key questions users of 
psychophysiological recording and biofeedback/neurofeedback equipment need 
to answer are delineated. They include: (1) Are the sensors mounted optimally for 
location and orientation, (2) Are the sensors mounted well enough to pick up a 
good signal, (3) Is the device’s bandwidth set appropriately, (4) Is there noise in 
the signal, (5) Does the display accurately reflect changes in the signal, (6) Does the 
display change when the physiological signal does, and (7) Is the display set so 
users can accurately assess the signal? Users are encouraged to get the training 

they need to do a great job when performing recordings. 

 

Keywords 
Recording Errors, Fetal Flaws, Psychophysiological Recording, Biofeedback, 

Neurofeedback. 

 

 

 

 

 

 

 

 

 

Citation: Sherman RA. Don't assume that 
your equipment is doing what you think it 
is. APP. 2022;9(1) :01-05 
 
Corresponding Author Email: 
drrichsherman@gmail.com 
 
DOI: 10.29052/2412-3188.v9.i1.2022.01-05 
 
Received 26/02/2022 
 
Accepted 06/04/2022 
 
Published 01/06/2022 
 
Copyright © The Author(s). 2022. This is 
an open-access article distributed under 
the terms of the Creative Commons 
Attribution 4.0 International License, 
which permits unrestricted use, 
distribution, and reproduction in any 
medium, provided the original author and 
source are credited.  
 

 

Funding: The author(s) received no 
specific funding for this work. 

Conflicts of Interests: The authors have 
declared that no competing interests 
exist. 
 

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ISSN 2412-3188 (Online)| 2410-1354 (Print) 

 

APP| Published By AEIRC| Volume 9 Issue 1 

 

Introduction  
A perennial problem encountered by both 
novices and experienced people using 
psychophysiological recording equipment 
and then using the displays as the basis for 
biofeedback and neurofeedback is that the 
equipment is frequently not doing what the 
users think it is. Hardware and software are 
frequently glitchy and setting the devices 
incorrectly makes matters worse. The 
following are a few of the key areas which 
need to be checked every time a recording is 
made. The key question to answer is whether 
the device reliably produces a display clearly 
related to the physiological signal produced 
by the person being recorded. 
 
Note that the raw signal (or as close to it as 
the device permits) – rather than some 
averaged / integrated version - must be 
viewed when checking the quality of the 
signal and any display based on it as 
integrated signals change too slowly to show 
common artifacts in the signal. 
 
Here are several questions to consider:  
 
1. Are the sensors mounted optimally for 

location and orientation? This is crucial! 
If the sensors are not in the right place to 
pick up the physiologically based signal 
you want, no amount of processing will 
help. This is a common problem for 
people doing EEG recordings using only 
one active and one reference (usually ear 
clip) sensor. If the sensor is not oriented 
properly, it can not pick up the signal 
properly. For example, if the calf muscle 
is being recorded for surface muscle 
tension (SEMG), many people position 
the sensor across the muscle 
(horizontally) rather than along it 
(vertically). As the differential 
amplifiers in SEMG recording systems 
depend on picking up signals as muscles 
depolarize during contraction, they only 

pick-up a relevant signal when the 
active electrodes are placed along the 
length of the muscle. If placed across it, 
all they pick up is noise. 

 
2. Are the sensors mounted well enough to 

pick up a good signal? This is frequently 
a matter of impedance between the skin 
and the sensor for muscle tension and 
EEG. Most high-quality recording 
systems have impedance checks which 
let the user know if the sensor is 
attached well enough to record a good 
signal. Some systems cease recording if 
the impedance becomes too high for a 
good signal. If there is no signal quality 
check screen or system, it is up to the 
user to check the sensor’s impedance. 
Impedance meters tend to cost over 350 
US dollars. The alternative is to have 
considerable expertise in recognizing 
artifacts in the signal and ensuring that 
the display is showing intensities 
proportional to some objective gage 
such as discussed below. 

 

Respiration belts are frequently mounted too 
loosely to pick up changes in breathing or 
are placed incorrectly on the body. This is a 
common problem when recording chest 
breathing among women as the belt needs to 
be mounted either above or below the 
breasts depending on where the most 
change in circumference with inhalation 
occurs. After the optimal location for the belt 
is determined, the user needs to pull the belt 
gently and watch for a proportional change 
in the display. The person being recorded 
should take a deep breath and a shallow 
breath with the display showing a clear 
difference. The raw respiration signal must 
be displayed as a display of respiration rate 
obscures problems with the signal itself. 
 
Photoplethysmographs used to record the 
pulse from a finger frequently don’t work 



 
 

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consistently due to low amounts of blood 
flow to the finger and movement artifacts. It 
is best to record from the largest digit 
available such as the thumb as the change in 
blood flow between pulses is more distinct. 
Subjects have to keep the digit being 
recorded very still throughout the recording. 
If an alternative way of recording the pulse, 
such as wrist to wrist sensors, is available, it 
should be used. Regardless, the display 
needs to be checked by comparing the pulse 
the user feels at the wrist with the reading 
being displayed.  This requires looking at the 
raw pulse signal rather than a heart rate or 
heart rate variability display as these 
calculated displays obscure the fact that the 
actual pulse is not being recorded reliably 
and consistently 

 

3. Is the bandwidth of the device set 
appropriately? Bandwidth refers to the 
frequencies of interest each 
physiological signal generates. For 
example, the bandwidth for alpha EEG 
signals is about four to eight Hertz 
(cycles per second). There will be 
different amounts of power (intensity) 
at each of the frequencies. Each muscle 
produces a typical profile of power at 
various frequencies at each level of 
tension. Typically, the frequencies of 
interest which produce the power 
representative of overall tension in the 
muscle range from about eight to five-
hundred Hertz. Most 
psychophysiological recording systems 
have a default bandwidth which 
permits recording of only a portion of 
the signal reaching the sensors. If the 
system’s bandwidth is set to the wrong 
setting so important parts of the 
muscle’s power is not recorded, then the 
display shows less power than the 
muscle is producing at that level of 
tension. For example, if the device’s 
bandwidth is set to 100 – 200 Hz, but 
most of the muscle’s power is between 

300 and 500 Hz, the display will show 
far less power – which equates to 
“tension” in most people's minds – than 
is actually the case. 

 
4. Is there noise in the signal? This usually 

includes heartbeat artifacts, motion 
artifacts, and electrical noise from poor 
connections. The key is to be able to 
recognize a good quality signal and 
differentiate it from problems such as 
the display breaking up during changes 
in the signal caused by tensing and 
relaxing a muscle (etc.), movement 
artifacts (in which the entire baseline of 
the signal changes) as well as repeated, 
relatively high deflections in the display 
caused by electrical noise and heart beat 
artifacts, etc. Again, the raw (or nearly 
raw signal) has to be viewable on the 
display to determine signal quality. 
Long integration times obscure spasms 
and bad signals. It takes extensive 
training to learn to recognize movement 
artifacts and other sources of noise. Too 
may practitioners spend much of their 
careers feeding back noise because they 
can’t differentiate between noise and a 
good signal. People performing 
psychophysiological recordings need to 
do their homework so they become 
familiar with what noise looks like in the 
various signals being recorded. 

 
5. Does the display of the raw signal 

accurately reflect changes in the 
physiological signal? Most especially, 
does the device produce nearly the same 
numbers when a signal is nearly 
repeated? Users need to know whether 
the device is calibrated so the magnitude 
of the physiological signal is accurately 
reflected by the display. Most devices 
either come with a calibration system or 
need to be calibrated to ascertain 
whether the signal displayed is 
accurately related to the signal being 



 
 

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produced by the person being recorded. 
It is very easy to ignore the technical 
portion of manufacturers’ instructions 
for checking calibration. In cases where 
no calibration system is included with 
the device, it is usually fairly simple to 
check whether a device is producing a 
realistic, repeatable display. For 
example, the number of microvolts 
produced by most muscles in the body 
while at rest (baseline) and near 
maximum tension are well known and 
can be found in the literature. Baselines 
for resting muscles in a normal person 
observed from raw (not 
integrated/averaged) signals should be 
below five microvolts and be very 
consistent without peaks (other than 
heartbeat artifacts) going above five 
microvolts. The readings should be very 
similar between recording sessions 
unless some intervention has been made 
even if the subject has begun 
habituating to the equipment. The 
number of microvolts displayed for 
surface muscle tension signals during 
tensing should be very similar when 
about the same amount of tension is 
generated by the subject. As there is a 
consistent relationship between how 
hard a person squeezes a device such as 
a dynamometer and the number of 
microvolts produced by the major 
muscle used to activate the device, the 
number of microvolts displayed should 
be within a few percentage points when 
the dynamometer is squeezed to the 
same moderate (not maximum) reading. 
The psychophysiological recorder’s 
display cannot vary by more than a few 
microvolts (e.g. show 20 microvolts one 
time and 100 microvolts another) when 
the reading on the dynamometer’s dial 
is the same. The display must show the 
number of microvolts expected of 
moderate tension in that specific muscle 
as defined in the literature. Several 

devices currently on the market show a 
few microvolts at one reading then over 
a thousand in a second reading with the 
same pressure on the dynamometer.  
Dynamometers of sufficient accuracy 
for this purpose cost between ten and 
thirty-five US dollars. 

 
6. Does the display change when the 

physiological signal does? In other 
words, is the device actually recording 
the subject or just producing a realistic 
display? All too often a very realistic 
display of every physiological signal 
being recorded – especially heart rate – 
is actually a copy of signals recorded 
earlier or generated by the system being 
used. This is occasionally caused by 
glitches in the software but more often 
by users themselves who haven’t read 
the manufacturer’s instructions for how 
to start and record the display of the 
physiological signals. The person doing 
the recording must check that the 
display changes when the signal does. 
This requires having the subject change 
each signal such as respiration rate and 
depth, muscle tension, etc. The change 
should be reflected in the display of the 
raw signal immediately. 

 

7. Is the display set so the recording can be 
adequately assessed? Typical visual 
displays of raw signals provided by 
modern psychophysiological recording 
(and biofeedback/neurofeedback) 
equipment consist of sweep speed, 
offset, and amplification of the signal. 
Sweep speed is how quickly the signal 
traverses the monitor from left to right. 
It must be set slow enough so sufficient 
details of the signal can be observed to 
determine whether there are artifacts in 
the signal but fast enough so changes in 
the signal can see seen in detail – as 
when a muscle contracts and relaxes. 
Users may need to change the sweep 



 
 

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APP| Published By AEIRC| Volume 9 Issue 1 

 

speed for each of these purposes. 
Amplification is equivalent to the 
volume. It has to be set high enough to 
see details of the raw signal but not so 
high that the upper and lower portions 
of the signal go off the top and bottom of 
the display when the signal’s power 
changes. Offset is the vertical location of 
signal on the display. If it is set too low 
or too high, part of the signal is cut off 
when the signal’s intensity changes. 

 

Conclusion 
Users of psychophysiological recording 
devices should consider learning enough to 
do a great job when performing recordings. 
If you want to be certain you are doing an 
optimal job recording psychophysiological 
signals of many types, you may want to take 
a course in psychophysiological recording, 

read a book covering many different 
parameters, or read a few articles covering 
recording methodology for the specific 
parameter you want to record. You could 
even (gasp), read the manufacturer’s 
instructions for the system you are using. 
Articles on recording methodology for 
specific signals can be identified through 
searches of the web. The Behavioral 
Medicine R&T Foundation offers excellent 
courses such as “Psychophysiological 
Recording”, “Basic EEG 
Biofeedback/Neurofeedback”, and “Basic 
Biofeedback” which cover recording 
methodology in detail. Books such as “Pain 
assessment and intervention from a 
psychophysiological perspective” also 
discuss recording methodology. 

 

 

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