It is as if they were now the surface of that sphere itself that is able to expand and contain the “external” environment. Judging by the reports, and especially those studied by Jean-Pierre, the subjects who experienced anomalous but veridical visual perceptions (for example: being able to reach distant or previously unknown places and see events happen that were later reported to have truly happened, or being able to see “through” walls or various obstacles hidden or forlorn objects the existence and aspect of which was later confirmed by people belonging to the hospital medical staff, etc) during an NDE cannot be described as static observers within a dynamically expanding/retracting spherical envelope: it would be more apt to say that it was as if they were that envelope/surface itself, because they did not have any more to revolve around an object to be able to get an overview of all its profiles at various angles, but this visual overview was presented as a unified and simultaneous view of all these profiles (I readily admit that I cannot imagine what it looks like, but maybe we can reach some understanding of that and an approximated representation of it by imagining that it would be the (higher-dimensional?) equivalent of the passage from a succession of 2D visual profiles of an object to a 3D visual presentation of that object.
The people who were able to sufficiently focus their attention on their visual experience and who later thought about the best verbal means to convey the essence of that peculiar perceptual experience, reported that, during their NDE, they were able to see the objects “entirely” as a synchronistical “multi-angle” perspective (and not as our classic/usual diachronically constructed succession of isolated visual profiles of the object with a final amodal completion of its successively hidden profiles).
We must be cautious. I think that, in a way, some of them spoke about a “spherical” or “bubble” impression mainly because of three inter-individually recurring aspects of the experience : 1/ they were able to have a 160° visual field and in some cases there are reports of a 360° visual panorama (I cannot spontaneously remember of any specific observation about the curvature, but I will check in the literature); 2/ they had a peculiar new ability of “projection” or “zooming” (both competing –motor and visual- interpretations of this ability exist) at multi-angle perspectives (as if they were the surface itself of a volume containing a lower space) to see distant places or microscopic details of their spatial environment; 3/they sometimes had peculiar “weightless” (bodily?) sensations (that’s why there are sometimes expressions in their reports like –these are not quotes, only typical samples- “I felt like a floating soap bubble” or “it was as if I was hovering above the room and I was a round cloud”: sometimes, when they think they have an “aerial body” (one of Jean-Pierre’s subjects used that expression), then they become suddenly able to locate their limbs in a kind of new reconstructed body image, but when they stop thinking that they have a body (to be more accurate: when they stop being convinced that since they are not “nothing” and they still exist as “observers” they must logically have a kind of embodiment similar to what we are used to), then they begin to feel either like a medium-sized “spherical” cloud or (less frequently reported) like a mere shrunken “point”. I am not sure to know if it tells us something about the structure of their visual “zooming” and “spreading” ability or rather about their possible new kind of embodiment…
Maybe Bill Rosar's suggestion (stated in "On Looking vs. Being Curved") about the curvature being due to the structure of the eyeballs is interesting and relevant: couldn’t it be compatible with John’s model in which (in the camera comparison) the eyes are described as being only the lenses of our optical system (so maybe: if you change the detecting device, the lenses in our analogical comparison, without modifying the screen itself, then the latter will not appear any more as a curved surface). Maybe that is what happens in NDEs: the eyes are now out of order (or never were functional, like in the cases of congenitally blind people!) and there is a whole new structure doing their job of detection and transmission…and that’s why the new “medium” induces drastic modifications of the visual field (the “screen” part of our device)?