When Real Motion Becomes Too Slow to Trust

Introduction

Experiments on autokinesis reveal a more important problem than the familiar observation that a stationary light can seem to move. They show that real motion itself can become unreliable when it is sufficiently slow and the target is viewed without useful visual references. In a 2024 experiment, observers watched a small dot that genuinely moved through darkness at several controlled speeds. At the slowest speed, their reported direction was strongly influenced by each observer’s own pattern of autokinetic illusion. As the dot moved faster, perception increasingly followed its true direction. The same slow movement was judged much more accurately when the room was illuminated.[ScienceDirect]sciencedirect.comScienceDirect Autokinesis Reveals a Threshold for Perception of Visual MotionAutokinesis Reveals a Threshold for Perception of Visual Motion - ScienceDirectApril 5, 2024…Published: April 5, 2024

That finding matters for UFO and UAP reports involving distant lights. A witness may not simply face a choice between “stationary” and “moving”. At very low apparent speeds, genuine displacement and illusory displacement can compete in perception, making the direction and path of a remote light surprisingly difficult to judge by eye alone.

How researchers compare real and illusory motion

The 2024 study by Yihao Liu and colleagues at Johns Hopkins approached autokinesis in an unusually direct way. Rather than merely asking whether a stationary dot seemed to move, the researchers first measured the apparent motion produced when the target really was stationary. Participants manually reproduced what they perceived using an optically tracked device, allowing the researchers to construct an individual pattern of autokinetic motion for each observer. Repeated measurements showed that these perceived-motion patterns had significant within-person consistency.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

The researchers could then introduce actual target motion and ask a more revealing question: when real movement is weak, does perception follow the physical target or the observer’s autokinetic pattern?

Twelve participants viewed a small target moving horizontally or vertically. The slowest physical speed was 0.16 degrees of visual angle per second, at which the dot took about 30 seconds to cross the display. Other trials increased that speed by factors of two, three, four and six. Participants were dark-adapted before the dark trials, while an additional condition presented the slowest movement with the lights on.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

The crucial comparison was therefore not between movement and complete immobility. It was between three competing situations:

This design allowed the researchers to measure whether perceived direction resembled the target’s actual trajectory or the observer’s previously recorded autokinetic pattern. That makes the experiment especially useful for understanding ambiguous lights in the night sky: the physical target can genuinely be moving while its perceived path is nevertheless substantially distorted by autokinesis.[ScienceDirect]sciencedirect.comScienceDirect Autokinesis Reveals a Threshold for Perception of Visual MotionAutokinesis Reveals a Threshold for Perception of Visual Motion - ScienceDirectApril 5, 2024…Published: April 5, 2024

The approach also has historical roots. Pearce and Matin developed a “nulling” technique in the 1960s in which physical motion was imposed opposite to perceived autokinetic motion until the observer no longer reliably experienced movement in one direction. That work already implied that real and autokinetic motion could oppose one another within the same perceptual judgement. The newer experiment extends the idea by systematically varying the speed of a genuinely moving target and recording its perceived trajectory.[ResearchGate]researchgate.netResearch Gate The measurement of autokinetic speedThe measurement of autokinetic speedJanuary 1, 1966…Published: January 1, 1966

The low-speed threshold problem

The clearest result was that slow physical movement in darkness was poorly represented in perceived direction. At the base speed of 0.16°/s, the researchers’ direction-accuracy measure was low in darkness. When exactly the same slow speed was presented with the lights on, accuracy became high. Increasing the target’s physical speed in darkness also progressively improved the correspondence between perceived and actual direction; the statistical effect of speed was highly significant.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

Another analysis makes the size of the ambiguity particularly clear. At the lowest speed in darkness, 78% ± 2% of the measured perceived-motion vectors did not occupy the same directional bin as the target’s actual movement. The corresponding figure fell as the physical speed increased, while it was only 34% ± 2% when the lowest-speed movement was viewed in the light.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

More importantly, those errors were not simply random. The researchers compared the erroneous directions with the pattern previously produced by autokinesis for each participant. Their measure of alignment with autokinesis was highest at the slowest dark speed, 0.44 ± 0.03, and progressively declined as physical speed increased, reaching 0.26 ± 0.03 at six times the base speed. At the slow speed with the lights on it was lower still, at 0.23 ± 0.02. The difference across conditions was statistically significant.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

In practical terms, the experiment produced a transition rather than a sharp universal cut-off. When the real motion signal was weak, perception tended to inherit more of the observer’s autokinetic pattern. As the physical movement became stronger, its true direction increasingly won out. The authors therefore describe the results as evidence for a threshold for accurate perception of motion signals, rather than proposing one fixed speed below which human beings simply cannot see movement.[ScienceDirect]sciencedirect.comScienceDirect Autokinesis Reveals a Threshold for Perception of Visual MotionAutokinesis Reveals a Threshold for Perception of Visual Motion - ScienceDirectApril 5, 2024…Published: April 5, 2024

That distinction is important. The experiment does not establish that 0.16°/s is a universal human motion threshold. The result came from a particular stimulus, viewing geometry and experimental setting, and autokinesis itself varies between individuals and with factors such as illumination and available visual cues. Instead, the evidence shows that motion accuracy deteriorates as the physical signal becomes weaker relative to perceptual instability.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

Older experiments reinforce the idea that the boundary between “real” and “apparent” movement is not perceptually clean. Walker and Meyer found that even movement too weak to have an obvious conscious perceptual counterpart could alter the course of autokinesis. Earlier work also showed that providing additional information about a target’s position — in one experiment, allowing observers to grasp the target-light mount — delayed autokinesis and reduced its magnitude and duration. Together, these findings indicate that apparently tiny changes in sensory evidence can alter what observers experience as target movement.[BPS Psych Hub]bpspsychub.onlinelibrary.wiley.comBPS Psych HubThe subliminal perception of movement and the course of autokinesis - Walker - 1978 - British Journal of Psychology - Wiley…

Why darkness changes the answer

The illuminated condition in the 2024 experiment is particularly revealing because the target itself did not have to move faster for perception to improve. At the same slow physical speed, adding environmental visual information greatly increased directional accuracy.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

That result fits the broader understanding of autokinesis as a problem of unstable spatial reference. Normally, the visual system can judge a moving object relative to other objects and combine retinal information with signals concerning the observer’s own eye, head and body movements. A tiny isolated light in darkness strips away much of that supporting information. Under those conditions, a weak physical motion signal has to compete with uncertainty about the stability of the visual scene itself.[ScienceDirect]sciencedirect.comScienceDirect Autokinesis Reveals a Threshold for Perception of Visual MotionAutokinesis Reveals a Threshold for Perception of Visual Motion - ScienceDirectApril 5, 2024…Published: April 5, 2024

Experiments also caution against reducing the effect to the simple claim that involuntary eye movements directly make the light appear to move. For example, image-stabilisation experiments have shown that stabilising a target against horizontal eye movements can markedly reduce the horizontal component of autokinesis, demonstrating an important relationship between eye-position signals and the illusion. Other work has found more complicated relationships between fixation and perceived movement. The modern picture is therefore one of interaction between retinal motion, eye-position information and the visual system’s attempt to maintain a stable representation of space.[PubMed]pubmed.ncbi.nlm.nih.govAUTOKINETIC MOVEMENT: SELECTIVE MANIPULATION OF DIRECTIONAL COMPONENTS BY IMAGE STABILIZATION - PubMedJanuary 10, 1964…Published: January 10, 1964

The 2024 results add a particularly useful piece to that picture: instability does not merely create fictitious movement when the world is stationary. It can also contaminate the perceived direction of movement that really exists when that movement is weak enough.

Why distant UFO lights are especially ambiguous

For UFO and UAP investigation, the experimental variable that matters is angular speed — how quickly a light changes position across the observer’s visual field — rather than its speed in kilometres per hour. A physically fast object at great distance can have very little apparent angular movement. Conversely, a nearby object moving much more slowly can sweep rapidly across the sky. This means that the perceptual difficulty demonstrated experimentally is relevant whenever a distant unresolved light moves only gradually against a dark, poorly referenced background.

Consider a witness watching what appears to be a single light low in an otherwise dark sky. If its actual angular motion is strong and sustained, perception should increasingly follow the real trajectory. But if it drifts only slightly, the 2024 results show why visual judgement becomes less trustworthy: the observer can perceive a mixture in which genuine movement is present but its apparent direction is pulled towards the pattern that the same observer experiences during autokinesis.[PubMed Central (PMC)]pmc.ncbi.nlm.nih.govPubMed Central (PMC)Autokinesis reveals a threshold for perception of visual motion - PMC…

That is more subtle than saying that “a star can look as though it moves”. It means reports of small reversals, sideways wandering or uncertain changes of direction deserve particular caution when they involve a point-like light with no visible structure or reference frame. Such testimony may accurately describe the observer’s experience while being an unreliable measurement of the object’s physical trajectory.

Aviation guidance provides a real-world parallel. The US Federal Aviation Administration explicitly warns that a static light stared at in darkness can appear to move and treats autokinesis as a potential source of pilot disorientation. Its current safety material likewise describes stars, planets and aircraft lights against very dark backgrounds as situations in which apparent movement can occur, recommending systematic scanning rather than prolonged fixation.[Federal Aviation Administration]faa.govFederal Aviation Administration Chapter 8. Medical Facts for PilotsFederal Aviation Administration Chapter 8. Medical Facts for Pilots

None of this means that slow-moving nocturnal lights should automatically be classified as autokinetic illusions. The experiment demonstrates almost the opposite of such a simplistic rule: some targets really are moving, yet observers can still misperceive how they are moving. Autokinesis is therefore most useful as a warning about the evidential limits of unaided visual tracking, not as a universal explanation for UFO reports.

The strongest discriminator is independent positional information. A stable horizon, buildings, stars captured in the same image, calibrated video, repeated angular measurements or simultaneous observations from separated locations can provide reference information that naked-eye viewing lacks. Where those references are absent, descriptions such as “it slowly drifted left, stopped, then moved back” should not automatically be treated as precise records of physical manoeuvres.

The experimental lesson is narrower but stronger: below some condition-dependent level of motion strength, the visual system’s estimate of a light’s direction becomes increasingly vulnerable to its own instability. The 2024 Johns Hopkins study shows this quantitatively. Slow real motion in darkness can begin to resemble autokinetic motion; faster motion or better visual references restore much more reliable direction judgements.[ScienceDirect]sciencedirect.comScienceDirect Autokinesis Reveals a Threshold for Perception of Visual MotionAutokinesis Reveals a Threshold for Perception of Visual Motion - ScienceDirectApril 5, 2024…Published: April 5, 2024

For investigations of distant nocturnal UFO or UAP lights, that makes very slow apparent movement one of the situations in which eyewitness trajectory alone carries the least certainty. A light need not be stationary for autokinesis to matter. The harder and more experimentally supported problem is that a genuinely moving light can move too slowly for its true path to dominate what the observer sees.

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