Features

The Bliss Master software is mainly intended to display the EEG coherence between two points on the scalp. Since there are four EEG channels available with the Bliss Master EEG machine, there are six different combinations to choose from. The four channels of the EEG machine are O1, F3, F4 and O2 (according to the 10-20 placement system). One can look at the frontal coherence (F3-F4), occipital coherence at the back of the brain (O1-O2), left-side coherence (O1-F3), or right-side coherence (F4-O2). There are also two cross-brain coherences, F3-O2 and O1-F4.

There is a standard coherence chart, which was developed by Dr. Levine in 1976. It is called COSPAR. Coherence is calculated for every 4-second epoch of the EEG data, and displayed as one horizontal line on the chart. Only coherence which is higher than a threshold (i.e. 0.80) is displayed on the chart. For greater clarity there is an additional filter, called Temporal Continuity Filter. Such lines, which represent consecutive epochs, are stacked vertically, which gives the impression of so many islands of high coherence, where the sea has flooded all the peaks of lesser coherence. Here is an example of such a graph:

You can see the mountain range in the middle (around 9-10 Hz), which represents the alpha coherence. On this chart we can also see some beta, theta and delta coherence (this recording is from a meditation session).

The COSPAR chart has its advantages, but some details are more clearly seen on a different kind of a chart, where coherence is colour coded on a two dimensional topological chart. Here is the same recording, as seen with a different, colour coded chart:

Notice that here the highest coherence (more than 0.95) is seen as purple patches. Here you can clearly see such patches in the beginning of the alpha range, as well as appearing in the delta frequency range.

Such charts may look nice, but they need an expert to explain what is going on. So most people want to have something simpler, for example a bar chart. One page in the software is dedicated just to statistics. Here is an example of such a page:

Notice that the bars are coloured differently, depending on the amount of coherence they represent. The colour coding is the same as seen on the previous chart (purple colour means coherence in excess of 0.95). On the right side you can select which of the six possible channel pairs you are interested in (frontal coherence in this case). You can also select which frequency band you are interested in (beta coherence in this case). The average coherence of the selected chart is displayed under the selection section. There is yet another figure displayed on this page, and this is an overall coherence for all the channel pairs.

Another chart has become popular for the sake of public presentations:

Instead of a bar chart the coherence is represented here with a precise, colour-coded chart. The two charts on the top represent the outline of the power of the signal at the selected frequency band for both the channels involved.

There is yet another chart to display the power spectrum for all the four channels:

Here is the power spectrum for the O2 channel, which is on the right side at the back of the brain. You can clearly see the strong alpha power, which is typical for sitting with the eyes closed.