Modification of biont sensory inputs, memory, and consciousness at a distance using electromagnetic fields and ultra/infra sound inputs.
Since before the Information Age it was known that biont brains evolved to be instruments of survival of the organisms carrying of them, not perfect recording and storage devices. As neural science progressed in the 20th and 21st centuries CE, a variety of experiments led to the discovery that human brains (and biont brains in general) did not so much directly perceive the world, as recreate an approximation based on available sensory inputs. Furthermore, human memories were not exact recordings of events, but rather re-creations or re-imaginings of what was initially perceived, which could be modified over time as they were re-edited in the recall process or over-written or consolidated with new perceived events. It was only a short step from these discoveries to attempting to induce changes in memory and perception via artificial stimulation.
By the early Information Age, researchers using transcranial magnetic stimulation and later ultrasound, had caused objects to appear and disappear from a subject's visual field, conducted conversations with subjects who did not notice that the person they were speaking with had changed mid-way through the discussion, and induced mood swings, blindness, hallucinations, and involuntary limb movements (which the subject insisted were voluntary against all evidence to the contrary) by proper stimulation of parts of the brain. While early applications outside the lab were initially crude, their use in both entertainment and advertising became somewhat widespread as the Interplanetary Age dawned. However, much of this work was later heavily regulated to the point of virtual extinction after a series of well-publicized accidents that made the public highly distrustful of the technology.
This situation changed drastically with the rise of the transapients. Able to employ superhumanly fine-tuned control of large numbers of effectors simultaneously via angelnetting or (to a lesser degree) under field conditions, even a moderately capable transapient can manipulate baseline and near-baseline biont senses, short term memory, proprioception, and emotions with ease. Using such methods, subjects can be made to experience feelings of spirituality or transcendence, become highly suggestible, believe that something has 'always been' a certain way even if it had just changed in front of their eyes, or simply not perceive an object or activity even if it was in their immediate vicinity. Similar effects can also be induced in various sub-sophont animal species, both Terran and otherwise.
From the First Federation onward the use of Perception Hacking (also sometimes referred to as Ainfluence, AI Mentalism, or Mindgineering) has been heavily regulated, with various laws and restrictions in place about the type of effects that can be used and under what circumstances. In the Current Era, this regulation is backed by archailect edict, but whether or how such rules are enforced can be unclear, particularly in the regions beyond the Civilized Galaxy. Various cultures and clades have attempted to use gengineering or augmentics to render themselves immune to the effects of Perception Hacking, but there are always rumors of hidden 'back doors' in the geneweave or programming that will allow at least some measure of control if a transapient desires it and can justify its actions in doing so (or simply thinks it will not be caught).
The use of Perception Hacking by various transapients or transapient-ruled cultures, whether for good or ill, remains a popular subject among both conspiracy theorists and fabulists of all kinds.