Motion Aftereffect (Waterfall)

Interactive motion aftereffect lab: adapt to motion (gratings, rotation, radial), then test; includes presets and top-up adaptation.

⚠️ Warning: Extended high-contrast motion may cause visual fatigue—take breaks.

Motion Aftereffect (Waterfall) — interactive guide

This page explains the motion aftereffect (MAE) and how to use the interactive demo in mae.html. It’s written for all audiences — from a curious reader to a vision researcher — and includes APA‑style references with links.

What you see

If you stare at a moving pattern (a downward waterfall, a drifting grating, rotating dots) for several seconds and then look at a static pattern, the static pattern appears to move in the opposite direction for a short time. That compelling drift is the motion aftereffect. The classic anecdote is by Addams (1834), who noticed the effect after watching the Falls of Foyers and then glancing at nearby rocks.

  • Adapt to downward motion → a stationary test looks like it drifts upwards.
  • Adapt to clockwise rotation → a static test seems to rotate anticlockwise.
  • Adapt to expansion → a static test contracts (and vice versa).

The MAE lasts from a second or two to tens of seconds depending on adaptation time, contrast, motion speed, test type, and whether you keep fixation steady.

Quick start with the demo

  1. Open mae.html and choose the Classic waterfall preset.
  2. Press Start adapting and fixate the + in the centre for ~10–12 s.
  3. When it switches to Test, the static grating should drift upwards.
  4. Use Top‑up 2 s to refresh the effect without re‑setting everything.

Tip: you can also jump straight to No MAE (no adaptation) to verify that without adaptation the static test looks truly stationary.

Controls (what they do)

Adapt stimulus (moving)

  • Type — drifting grating (horizontal/vertical), rotation (dot field), or radial expansion/contraction.
  • Direction — forward vs reverse (e.g., CW vs CCW).
  • Adaptation time — longer adaptation → stronger/longer MAE (with diminishing returns).
  • Speed — faster motion often increases the MAE up to a comfort limit.
  • Spatial frequency — number of cycles across the display (for gratings / rings).
  • Contrast — higher contrast adapts motion detectors more strongly.
  • Dot count — for dot fields (rotation/radial), controls density.
  • Fixation cross — turning it on encourages steady fixation, which strengthens the effect.

Test stimulus (static)

  • Type — choose a stationary grating (horizontal/vertical), radial rings (good for rotation/radial MAE), static noise, or a blank grey field.
  • Test contrast — raises the visibility of the static pattern; a bit of texture helps the MAE grip.
  • Show during adaptation — a faint “ghost” of the test while adapting; some labs use this to keep attention centred.

Run panel

  • Start adapting — begins the timed adaptation period (progress bar shows elapsed proportion).
  • Top‑up 2 s — quick booster without re‑initialising the dots.
  • Go to test — jump to the static test immediately.
  • Stop — return to idle.

Presets

  • Classic waterfall (vertical motion → vertical grating test)
  • Strong rotation (rotating dots → radial rings test)
  • Strong expansion (radial dots → rings)
  • Weak (low contrast)
  • No MAE (no adaptation)

Export

  • Export PNG — saves the current canvas.

Try these experiments

  • Duration curve — fixate and vary Adaptation time (4, 8, 12, 20 s). Estimate the MAE duration each time (when it fully fades). You’ll typically see a quick rise then diminishing returns.
  • Direction & test pairing — adapt with rotation, test with rings; adapt with downward motion, test with vertical grating; adapt with expansion, test with rings. The strongest MAE appears when test structure matches the adapted motion axis.
  • Fixation vs scanning — compare with and without Fixation cross. Scanning the adaptor weakens the MAE for many observers.
  • Interocular transfer (advanced) — adapt with one eye closed, then switch eyes at test. A robust MAE transfers across eyes, implying a cortical locus (beyond monocular retina).
  • Dynamic test — choose Static noise as the test. You will still see a strong MAE, often called the dynamic MAE (a flickering/noisy test can reveal adaptation at later motion stages).

How does it work? (layered explanation)

The intuition

Motion‑sensitive neurons tuned to a direction (e.g., down) adapt or fatigue when they fire strongly for a while. When the motion stops, the adapted population’s response is reduced relative to its opposite‑direction neighbours, so the balance of activity favours the opposite direction — the static test is read as up. This simple opponent‑like account captures the core phenomenon.

Evidence you can feel (and measure)

  • Strength grows with adaptor contrast, speed and duration, saturating with time — classic hallmarks of sensory adaptation (e.g., Wohlgemuth, 1911; Mather, Verstraten, & Anstis, 1998).
  • The MAE transfers between eyes and to different test patterns, pointing to cortical motion areas rather than the retina alone (e.g., Tootell et al., 1995).
  • Microstimulation and single‑unit studies in area MT/V5 show direction‑selective mechanisms that bias motion judgements, consistent with the MAE’s locus (Salzman, Britten, & Newsome, 1990).

A modern picture

  • Multiple stages adapt: early V1 direction‑selective neurons and MT/V5 populations, with normalisation and opponent interactions shaping the percept (reviewed by Anstis, Verstraten, & Mather, 1998; Kohn, 2007).
  • The dynamic MAE (illusory motion on a flickering/noisy test) reflects adaptation beyond strictly low‑level motion energy sensors and reveals higher‑level contributions (Mather, 2008).
  • Form‑motion interactions: matching the test structure (grating vs rings) to the adapted motion axis increases the aftereffect — essentially a tuning effect (summarised in Mather et al., 1998).

What strengthens / weakens the effect

Stronger

  • Longer adaptation time (up to a plateau)
  • Higher adaptor contrast and speed (within comfort)
  • Steady fixation (use the cross)
  • Matching test pattern (e.g., rings after rotation)

Weaker / absent

  • Very short adaptation (<3–4 s)
  • Very low contrast adaptor
  • Mismatched adaptor/test geometry
  • Eye movements or attention away from the adaptor

Notes for teaching & data collection

  • The demo’s Top‑up makes class demonstrations smooth: adapt once, then give brief refreshers before each test.
  • For quick lab exercises, have students record MAE duration vs adaptation time and plot the saturation curve.
  • For a simple interocular demonstration, adapt with one eye occluded and test with the other.
  • Addams, R. (1834). An account of a peculiar optical phenomenon seen after having looked at a moving body. The London and Edinburgh Philosophical Magazine and Journal of Science, 5(29), 373–374. https://en.wikipedia.org/wiki/Motion_aftereffect#History
  • Anstis, S., Verstraten, F. A. J., & Mather, G. (1998). The motion aftereffect. Trends in Cognitive Sciences, 2(3), 111–117. https://www.sciencedirect.com/science/article/pii/S1364661398011926
  • Kohn, A. (2007). Visual adaptation: Physiology, mechanisms, and functional benefits. Vision Research, 47(25), 3125–3131. https://www.sciencedirect.com/science/article/pii/S0042698907002812
  • Mather, G. (2008). Motion aftereffect. Scholarpedia, 3(10), 8295. http://www.scholarpedia.org/article/Motion_aftereffect
  • Mather, G., Verstraten, F. A. J., & Anstis, S. (1998). The motion aftereffect: A modern perspective. MIT Press. https://mitpress.mit.edu/9780262631978/the-motion-aftereffect/
  • Salzman, C. D., Britten, K. H., & Newsome, W. T. (1990). Cortical microstimulation influences perceptual judgements of motion direction. Nature, 346, 174–177. https://www.nature.com/articles/346174a0
  • Tootell, R. B. H., Reppas, J. B., Dale, A. M., Look, R. B., Sereno, M. I., Malach, R., Brady, T. J., & Rosen, B. R. (1995). Visual motion aftereffect in human cortical area MT+ revealed by functional magnetic resonance imaging. Nature, 375, 139–141. https://www.nature.com/articles/375139a0
  • Wohlgemuth, A. (1911). On the after-effect of seen movement (Monograph Supplement 1(3)). British Journal of Psychology. https://psychclassics.yorku.ca/Wohlgemuth/

Accessible summaries:

  • Michael Bach — Motion aftereffect demos and notes: https://michaelbach.de/ot/mot-mae/
  • Wikipedia — overview with history and variants: https://en.wikipedia.org/wiki/Motion_aftereffect

Acknowledgements

The interface is designed for clear demonstrations of classical (static‑test) and dynamic MAE, with rotation and radial variants for teaching complex motion adaptation. If you’d like a version that alternates adapt–test on a fixed schedule and logs key‑press responses, say the word.