Fenwick seems to be driving at two different points here. First, he seems to be arguing that is unlikely that different physiological mechanisms would produce the same illusion of perceiving outside of the body, but that it would not be surprising for there to be different physiological triggers of an experience that actually occurs outside of the brain. But as Harvey Irwin has pointed out, the crucial physiological state common to most kinds of OBEs may be of cortical arousal, from the very low arousal accompanying meditation or induced OBEs, to the very high arousal accompanying a near-death crisis, coupled with psychological traits such as a high capacity for absorption and a strong need for absorbing experiences (Irwin, "Flight" 303; Irwin, "Domain" 6).
The cases cited in this essay show that many near-death experiences are hallucinations. NDE cases which include false descriptions of the physical environment have been found not only by different near-death researchers, but by researchers searching for evidence that NDEs are hallucinatory. This motivation among researchers makes it impossible to estimate the prevalence of NDEs with clearly hallucinatory features. As Bruce Greyson points out, the file-drawer problem is a likely factor here: NDE accounts with clearly hallucinatory features may end up filed away indefinitely, while only more dramatic accounts are deemed fit for publication by NDE researchers (Greyson, "Near-Death" 344). Similarly, NDEs with obviously hallucinatory traits seem particularly likely to be underreported by NDErs themselves, given the disparity between how real one's NDE felt at the time and the realization that it could not possibly reflect reality if, for instance, the NDEr communicated with his still-living mother in an ostensibly transcendental realm. Nevertheless, given that many NDEs are already known to be hallucinations, it is likely that other NDEs are hallucinations as well.
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The rhetoric pervading Tart's account implies that scientism or dogmatic materialism is the only obstacle to accepting a survivalist interpretation of NDEs. But this is simply not the case. First, it is crucially important to note that one could have good reasons for disbelieving that NDEs are visions of an afterlife . For instance, this essay has actually presented data which suggests that NDEs are glimpses of another world after death. One need not have any commitment to materialism—dogmatic or otherwise—to doubt that genuine glimpses of an afterlife would involve train rides, false out-of-body perceptions, or encounters with living persons, fictional characters, and mythological creatures. It is entirely possible that an afterlife exists but that NDEs are not glimpses of it—a view similar to the Buddhist belief that the dying pass through several illusory bardo states generated by their own minds before entering the 'real' afterlife (Fox 94-96).