VFX Atlas
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Pulfrich Effect

1922, Carl Pulfrich's description

Typeface · Rationale

Pulfrich Effect Sight Lines and Apparent Ellipse. Two eyes view colored positions along a horizontal motion path, with sight lines and a dashed ellipse marking the apparent trajectory.
Pulfrich Effect Sight Lines and Apparent Ellipse. Two eyes view colored positions along a horizontal motion path, with sight lines and a dashed ellipse marking the apparent trajectory.Cmglee · CC BY-SA 4.0 · via Wikimedia CommonsView source ↗

Prompt

Apply a Pulfrich Effect visualization as a static motion study, suggesting lateral movement through closely spaced translucent positions that follow a shallow elliptical depth path. Use asymmetric brightness between motion echoes, subtle overlap, and a clear central subject; avoid red-cyan anaglyph coloring. Keep the original subject and composition.

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Identify

With one eye darkened, sideways motion appears to curve through depth. A swinging pendulum seems to follow an elliptical path1 instead of moving within one plane.

Principle

Reduced brightness creates a processing delay2 in the darkened eye's visual pathway. During lateral motion, this timing difference produces binocular disparity3, which the brain interprets as depth.

Example

BBC: Doctor Who — Dimensions in Time, 1993.

Try it out

Watch a pendulum swing sideways with both eyes open, holding one sunglass lens over one eye; then switch eyes.

Background

Carl Pulfrich described this effect in 1922, linking unequal brightness between the eyes to an illusion of depth during motion. A dark filter reduces the light reaching one eye and delays its visual response. The brain therefore combines signals corresponding to slightly different positions of a moving object. It interprets this mismatch as depth, much as it interprets differences between ordinary binocular views. Later television productions used the effect with specially arranged movement and glasses containing one dark lens. A stationary photograph alone cannot demonstrate the defining motion-dependent illusion.

Distinction

Unlike anaglyph 3D, this technique does not separate two encoded views using different colored filters. Its depth illusion depends on motion and unequal visual timing.

Aftermath

The effect shows that perceived depth depends on the timing of visual signals, not just their spatial arrangement.

Further examples · 7 images

AI illustration: Observation of elliptical distortion via monocular darkening
02 AI illustration: Observation of elliptical distortion via monocular darkeningA researcher observes a brass pendulum bob through a single dark filter held over one eye. The visualization on the screen illustrates how the brain misinterprets delayed signals as an elliptical path in depth.Illustration generated for the Atlas (AI)
AI illustration: Perceived depth displacement in lateral pendulum motion
03 AI illustration: Perceived depth displacement in lateral pendulum motionA student wearing a single darkened lens views a pendulum swinging in a simple linear plane. Superimposed graphics demonstrate the perceived circular motion resulting from the signal lag in the shaded eye.Illustration generated for the Atlas (AI)
AI illustration: Subjective depth curvature of a moving linear object
04 AI illustration: Subjective depth curvature of a moving linear objectA laboratory technician uses a sliding red block on a mechanical rail to test depth perception with a monocular filter. The blue orbital path represents the subjective 3D curve generated by the lateral velocity of the object.Illustration generated for the Atlas (AI)
AI illustration: Projected light source exhibiting stereo-anomaly depth
05 AI illustration: Projected light source exhibiting stereo-anomaly depthA man looks through a handheld filter at a bright dot projected onto a flat laboratory screen. The trail of ghostly images shows the apparent shifting of the object forward and backward in space.Illustration generated for the Atlas (AI)
AI illustration: Metronome oscillation transformed into elliptical depth
06 AI illustration: Metronome oscillation transformed into elliptical depthAn observer watches a metronome's weighted arm through a modified pair of spectacles with one opaque lens. The resulting visual overlay shows the flat oscillation appearing to move in a continuous three-dimensional loop.Illustration generated for the Atlas (AI)
AI illustration: Comparison of filtered and unfiltered motion perception
07 AI illustration: Comparison of filtered and unfiltered motion perceptionA side-by-side comparison shows a subject viewing a pendulum with and without the necessary filter applied to one eye. The elliptical graphic serves to illustrate the binocular disparity triggered by the luminosity difference.Illustration generated for the Atlas (AI)

Question

Why does a stationary object not gain depth from the classic Pulfrich effect?

Show possible answer +

Without motion, the processing delay does not create a difference in the object's apparent position between the eyes.

Sources