I believe there is a difference between eye-fatigue (and thus the eye-focus shifting, brighten-dimming, parts of vision fading out, as a result of tiredness of the gaze) < whether more tense in focus, or more relaxed > and the TGS.
Also the affect upon the neural-pathways (discharges and amplitudes) wouldn't seem to be directly observable- anymore than how a Video-Tvshow may change scenes from a happy scene to a dramatic-fight without the "signal" changing.. and likewise if you observe the frequency of the file-signal and it jumps, that may not have any relation to the content.
I believe the best way to determine/recognize the change is not by the content, nor the quality of the experience so much (how it feels, or how it looks) but more in terms of one’s sense of self (as shift in to TGS “where/how” one is perceiving changes to a whole different pt of view)…
and the best way for this, beyond setting up the best conditions, is to get a Contact with an Entity and 'get in the vibe' with them... on the same wave-length- I find one's Conscious state shifts (if you are relating to an Entity and in the same mind-space think about and relate to "normal-concerns" at the same time.. that jumps back and forth... rather only have "in your mind" the Entity and the Work you are doing... and you can Drift.
Thus its like being in a boat, if you just focus inside the boat, you can look outside and recognize that you have moved (thus inner-psychologically allow that movement to happen- as if you notice it as it if occurring, we automatically/autonomically subcon resist it, in the same way that our body reacts to balance itself/adjusts body-temperature, etc.)- but if you find an Entity (that "is" in a different frequency, so to speak, and get in synch with "their" presence... which allows a Recognition of a way to change that isn't obvious; then one can "follow the breadcrumbs" back to what was found/dis-covered)
-sort of like recognizing an AHA! where you get an understanding all coming-together, that can seem to be "not so obvious" and yet it is dramatically-extreme in another sense (ie the AHA metaphor- in the moment that one has an extreme understanding, that is quite dramatic and can change your entire life.. ie "once you've seen XYZ, nothing is ever the same"..
[ just after posting above I saw a quote from TaoTe Ching that specifically relates to this task (from Ch 10) ]
" In llluminating clarity to penetrate the Four Directions, Can you be effortless?"
-not just with little effort, vs intending it strongly, but effortless/without any sense of doing… nor of blocking it… it shines, what does that reveal to your Sight? -softening (not “making it happen”)