Biomedical Engineering Reference
In-Depth Information
Dry
Water
Gel
800
short thin
sparse hair
medium thin
dense hair
long thick
sparse hair
600
short thin
sparse hair
medium thick
dense hair
long thick
dense hair
400
200
0
Pp 1
Pp 2
Pp 3
Pp 4
Pp 5
Pp 6
Fig. 7.
Time (averaged over two sessions) required for the experimenter to prepare the participant
for the recording
5.3
Convenience and Setup Time
Before and after the usage of the headsets, participants reported their anticipated and
experienced convenience level (see evaluation protocol detailed in Section 3). Although
participants expected that the dry electrode setup will be the least convenient one with
the median score of
3
.
5
on the scale of 1 (unconvenient) to 10 (convenient), compared to
4
.
5
and
6
for water-based and gel ones respectively, this was not reflected in the rating
after the usage of the electrodes. The final median score was
5
for dry,
6
for water-
based, and
5
for gel electrodes. These results also indicate that the water-based solution
would be preferred over the gel one. Note that the users were asked to rate not only the
perceived comfort, but also the practicality of the headsets and the effort required to use
them.
Based on the comments and the discussion with participants we learned that the
participants with shorter hair had the preference for using the dry electrodes, over
water-based and gel ones, while for the participants with the longer hair water-based
electrodes were preferred as the procedure for positioning the dry headset was too long
(see also Figure 7) and/or the headband was too tight. Most participants did not like the
feeling of gel in their hair and the fact that they had to wash the hair after the usage of
gel setup.
Direct comparison of the preparation time, depicted in Figure 7, shows that water-
based electrodes require more preparation time than gel ones, while dry electrodes re-
quire less time than the other two for people with shorter and thiner hair style and more
time for people with longer and/or thick hair style. The former can be partially ex-
plained by the cumbersome 'screwing' procedure required for placing the water-based
electrodes in the EEG headset holes, which had to be redone in case the signal was not
good enough. For the gel setup the procedure required adding more gel between the
scalp and the electrode until the signal was at the acceptable level, which was much
faster. The latter can be explained by the design of the dry electrodes themselves. The
length and the rigidness of the pins was a major problem for obtaining a good signal for
participants with longer hair. The amount of hair under the electrode was in many cases
preventing the pins from getting in contact with the skin on the scalp. Finally, quality of
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