I've been thinking something similar specifically regarding the black triangles for a while. People are convinced they saw them (they "know what they saw"), but it's never corroborated by photos or independent testimony.
I've been wondering if the triangle shape has a specific neurological cause, like suddenly being able to see your blind spot, or something like is theorised with DMT geometric visions reflecting the actual shape or physical connections in the brain.
I think that's an interesting idea, but it must be unlikely that the majority of "black triangle witness" reports are due to a neuropharmacological or neurophysiological cause that the witnesses have in common.
Problems with a neurological factor as cause for "triangle" sightings are:
(1) Neuromedical conditions that affect low- or intermediate-level processing (e.g. a hypothetical "surplus" of a specific neurotransmitter, or simple [neuroanatomically limited] focal seizures) also tend to affect higher-level processing, with effects on behaviour, broader cognition and sometimes level of consciousness.
An observer might notice unusual symptoms, affect and/or behaviour in someone experiencing altered perception due to neuropharmacological/ neurophysiological causes.
(2) The black triangle "flap" in Belgium, around 1989-1992, and some reports of seemingly-similar craft in the USA, are largely geographically and historically isolated. It's unlikely that there is a neurological propensity for seeing black triangles that exists largely e.g. in the Belgian population (and distributed amongst Belgians who are not closely related AFAIK) and in a couple of pockets in the USA, that first emerged in 1989 but abated in two or three years.
(Wikipedia article, "Belgian UFO wave",
https://en.wikipedia.org/wiki/Belgian_UFO_wave).
The rapid emergence of black triangle reports in Belgium, November 1989, and their eventual reduction/ cessation in two or three years, is not compatible with any known neuropathology.
It is unlikely that a disparate group, largely in one nation, would experience the onset of a highly specific symptom- seeing a flying black triangle- without any other symptoms or deficits, effectively at the same time, and that this condition would spontaneously disappear within three years.
It must also be unlikely that all the witnesses consumed a recreational drug, or were exposed to a toxin or environmental stressor, that produced this one highly specific result (although illicit drug labs
have inadvertently manufactured compounds with unexpected 'targeted' effects, think of the instant Parkinson's disease caused by MPTP- which selectively killed dopaminergic cells in the substantia nigra- in some Californian drug users in the '80s,
Wikipedia article
https://en.wikipedia.org/wiki/MPTP).
(3) The black triangle witnesses saw their "UFOs" in the sky. They were not troubled by seeing black triangles on the pavement, bedroom ceiling or in shopping malls.
People using (e.g.) DMT can experience hallucinations wherever they look (AFAIK).
I guess we could invoke the vestibular system and theorise that some neurological effect was triggered when the head was tilted upward or something like that, but this seems an inelegant "patch" to the theory (and again, doesn't explain why "witnesses" didn't see triangles indoors, or did see triangles in the sky at apparently low elevations).
(4) The Kanizsa triangle is a figure used to demonstrate how we "see" illusory contours; it shows how our visual system helps us by "filling in the blanks" at a pre-conscious level .
But Kanizsa was not saying that we have a sub-system that preferentially sees triangles, although area V2 of the visual cortex plays a role in processing illusory contours, and V4 "recognises" simple shapes:
External Quote:
Unlike V2, V4 is tuned for object features of intermediate complexity, like simple geometric shapes, although no one has developed a full parametric description of the tuning space for V4.
From Wikipedia,
https://en.wikipedia.org/wiki/Visual_cortex
We can see illusory contours in Kanizsa-style figures for many shapes, including complex forms.
Our ancestors could see a leopard partly "eclipsed" by tall grass, they didn't have to think about what the separate vertical "strips" of visible leopard represented.
There was some discussion on another thread here about how reports of UFOs have changed over time;
https://www.metabunk.org/threads/how-have-descriptions-of-uaps-changed-over-the-years.12619/
I strongly suspect that most UFO reports (excluding those which are deliberate deceptions) are misidentifications, mistaken recall, or less often, brief perceptual artefacts from sleep disturbance or originating from stress or even expectations.
Just as black triangles were "in vogue" in the late 80's, early 90's, "classic" flying saucers of the late 40's and 50's all looked a bit like how they were
supposed to look-
exactly like a gas lamp's top cover in some cases, like a hubcap in others.
The reported flying saucers were preceded by their illustrations on the bright SF pulp-magazine covers of the 1920's, 30's and 40's. The term "flying saucer", a journalist's misquote of Kenneth Arnold's 1947 description, seemed to tap into the imagination of (a section of) the public. Lots of flying saucer reports followed, first in the USA, later Canada, Europe and elsewhere.
Metabunker Duke raised the question- if Arnold's journalist had used a different description, would the subsequent UFO reports reflect that?
Black triangles came about not long after the F-117 Nighthawk was revealed, and there had been much speculation about even higher-tech US programs, "Aurora", and "TR-3B" (as mentioned by this thread's OP)
It often has a "TR-3B" description of a black triangle with lights
I'm not suggesting that "black triangle" reports were the result of sighting these aircraft (though maybe some were), more that there was a cultural impression of secret, hi-tech aircraft being black deltas. This might, at some level, have influenced witnesses
(and there's the Star Wars Imperial Star Destroyer- admittedly not black).
I think- as Edward Current suggested, IIRC- that there is a very strong cultural/ social influence on UFO reports.