When the government began noticing that some XEDRA explorers of alternate dimensions returned with anomalous capabilities, XEDRA-23--internally called "Project PHAVIAN"--was founded to study these in full. Within the year, this led to the discovery of latent psychic powers in a portion of humanity. On Earth these were minor, almost trivial--the ability to always find lost keys or know the next sentence someone is going to say moments before they do are useful powers, but not lifechanging--but exposure to extra-dimensional energy seemed to increase psionic power. A PHAVIAN test subject who on Earth could manipulate a quarter to make sure it always landed heads up could sometimes throw large objects on the other side of a portal, or even lift a person. Soon after, it was discovered that specific crystalline formations found in extra-dimensional locations had the effect of amplifying psionic power even further, and that exposure to these crystals could awaken powers in previously mundane individuals.
Soon after that, the world ended. The weakening of dimensional barriers has made psionic power much stronger on Earth, but there's no longer anyone around to conduct any experiments on it. It's just one more method that survivors use in the wake of the Cataclysm.
Project PHAVIAN was adequately funded by XEDRA but never more than that, because unlike the various mutagen projects or portal research, they were unable to demonstrate that their areas of expertise produced satisfactory results on Earth. A Project ONYX LIGHTNING test candidate using a matrix crystal could lift and throw a person hard enough to seriously injure or kill them while on some portal immersion dives, but back on Earth they could lift maybe a couple kilograms and move it at an average person's walking pace, and without a matrix crystal they might be able to only lift a dozen grams or only affect the momentum of objects already in motion. Project PHAVIAN never discovered exactly what it was that limited psionic potential, but the current state of psionics on post-Cataclysm Earth is entirely a result of the dimensional weakening brought about by the portal storms.
Project PHAVIAN found more success using matrix crystals in technological research, and at the end of the year before the cataclysm occurred that's where most of their R&D time and money was going toward. The discovery of treatments for XE037 overexposure early the next year pushed Project PHAVIAN into prominence since they could finally directly connect their research with that of with other XEDRA teams, but the lockouts and the cataclysm soon afterward came before any real progress could be made. Given more time, it's possible that matrix technology could have reduced or even eliminated the downsides of the various advanced mutagen lines, or provided a way for safe portal travel without risk of XE037 contamination, but just like the mutagen research teams they did not have that time.
While more non-psions died in the Cataclysm than psions, thanks to the latter receiving accurate hunches or a tree branch suddenly falling on a pursuing zombie or a more dramatic awakening of their powers thanks to the massive portal storm that blanketed the globe, the proportion of humanity with psionic potential is small. Phavian's testing led to estimates of 3%, though they later revised that to "indeterminate" thanks to the ability of matrix crystals to awaken powers in individuals who had failed all psionic aptitude tests. At the time of game start, the majority of psions are feral.