<p>The <a href="http://www.georgemather.com/MotionDemos/MAEQT.html" rel="nofollow noreferrer">waterfall after-effect</a> is an illusion falling into a broader class of visual illusionary apparent movements caused by watching a constant motion for an extended period of time. The <strong><a href="http://www.michaelbach.de/ot/mot-adapt/index.html" rel="nofollow noreferrer">motion after-effect</a></strong> can be explained by adaptation of visual neurons that respond selectively to movement. Motion-sensitive visual neurons are tuned to a specific direction. Exposure to a continuous motion in one particular direction fatigues specifically those visual neurons that are tuned to that direction as they continuously fire. When the visual stimulus stops, it alters the balance of activity in favor of cells tuned to the opposite direction, as these are the least fatigued by the stimulus and this causes the after-effect <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3087115/" rel="nofollow noreferrer">(Mather <em>et al</em>., 2008)</a>. </p>

<p>The motion-after effect does work well with more discreet stimuli too. </p>

<p>To start with, <a href="https://youtu.be/qLDKcZB8Eaw" rel="nofollow noreferrer">here</a> is an example of a more standard waterfall effect illusion (see Fig. 1 for a related impression still image). </p>

<p><a href="https://i.sstatic.net/JI5Iz.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/JI5Iz.jpg" alt="![waterfall"></a><br>
<sup>Fig. 1. Waterfall. source: <a href="https://www.youtube.com/watch?v=356PMFKY904" rel="nofollow noreferrer">Carlos Vasquez</a></sup> </p>

<p>And in <a href="https://www.youtube.com/watch?v=oNhcpOIQCNs" rel="nofollow noreferrer">this video</a> an example is shown of the waterfall after effect with more discreet stimuli. Not particularly your standard marquee sign but it comes close and there's a definite motion after effect observable (Fig. 2). </p>

<p><a href="https://i.sstatic.net/bHLlt.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/bHLlt.png" alt="movie still"></a><br>
<sup>Fig. 2. Movie still from <a href="https://www.youtube.com/watch?v=oNhcpOIQCNs" rel="nofollow noreferrer">this video</a></sup></p>

<p>However, I think your question is specifically whether a motion after-effect occurs with <a href="https://en.wikipedia.org/wiki/Chase_(lighting)" rel="nofollow noreferrer">chase-lighting</a> as often seen in <a href="https://en.wikipedia.org/wiki/Marquee_(sign)" rel="nofollow noreferrer">Marquees signs</a> (Fig. 3). </p>

<p><a href="https://i.sstatic.net/e4BBH.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/e4BBH.gif" alt="marquees"></a><br>
<sup>Fig. 3. Marquees sign showing illusionary apparent motion. source: <a href="https://www.tewksburyschools.org/site/default.aspx?DomainID=145" rel="nofollow noreferrer">Old Turnpike School</a></sup></p>

<p>The <strong>chasing-light stimulus in itself is a <a href="https://en.wikipedia.org/wiki/Chase_(lighting)" rel="nofollow noreferrer">visual illusion</a></strong>, as there <strong>is no true motion involved</strong>. Instead, it is generated by using electronic circuitry to activate lights serially with a certain time delay in-between activations. Because there is no motion involved as such, I believe the after effect will not occur, or very weakly. At least, I couldn't observe an after effect after watching several chase lightings for a while. For example, the chase lightings in Fig. 1 become ambiguous when I look at it a while, <em>i.e.</em>, the lights actually spontaneously reverse their direction when staring at it for a while. The only thing I see when I look away, personally, is a colorful blob, and no motion after-effect.</p>

<p><sub><strong>Reference</strong><br>
<strong>-</strong> <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3087115/" rel="nofollow noreferrer">Mather <em>et al</em>., <em>Trends Cog Sci</em> (2008); <strong>12</strong>(12): 481-7</a></sub></p>

CC BY-SA 3.0
2017-09-18T10:34:29.217Z
2017-09-18T18:31:37.703Z
2017-09-18T18:31:37.703Z
AliceD
<p>If you watch a waterfall for several seconds and then suddenly change your gaze to a fixed object it appears to briefly move upward.</p>

<p>But if instead you're looking at a scrolling LED marquee sign, does the motion aftereffect still take place? In reality nothing is actually moving on the marquee sign because the LEDs are all fixed in place.</p>

<p>The answer to this question probably has interesting implications as to where in the visual pipeline motion is being processed. The difference between the actual waterfall and the scrolling LED marquee might also be a good way to separate out various aspects of motion processing. I'd be curious in hearing commentary on this.</p>

<perception><vision><neurophysiology><optical-illusion>
Is there a waterfall visual after-effect with discrete inputs?
John Berryman
# Is there a waterfall visual after-effect with discrete inputs?

(Asked by: username_0 on 2017-09-15)

If you watch a waterfall for several seconds and then suddenly change your gaze to a fixed object it appears to briefly move upward.

But if instead you're looking at a scrolling LED marquee sign, does the motion aftereffect still take place? In reality nothing is actually moving on the marquee sign because the LEDs are all fixed in place.

The answer to this question probably has interesting implications as to where in the visual pipeline motion is being processed. The difference between the actual waterfall and the scrolling LED marquee might also be a good way to separate out various aspects of motion processing. I'd be curious in hearing commentary on this.

**Tags:** perception, vision, neurophysiology, optical-illusion


---

## 1 answers

### Answer by username_1 on 2017-09-18. Score: 2

The [waterfall after-effect](http://www.georgemather.com/MotionDemos/MAEQT.html) is an illusion falling into a broader class of visual illusionary apparent movements caused by watching a constant motion for an extended period of time. The **[motion after-effect](http://www.michaelbach.de/ot/mot-adapt/index.html)** can be explained by adaptation of visual neurons that respond selectively to movement. Motion-sensitive visual neurons are tuned to a specific direction. Exposure to a continuous motion in one particular direction fatigues specifically those visual neurons that are tuned to that direction as they continuously fire. When the visual stimulus stops, it alters the balance of activity in favor of cells tuned to the opposite direction, as these are the least fatigued by the stimulus and this causes the after-effect [(Mather *et al*., 2008)](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3087115/).

The motion-after effect does work well with more discreet stimuli too.

To start with, [here](https://youtu.be/qLDKcZB8Eaw) is an example of a more standard waterfall effect illusion (see Fig. 1 for a related impression still image).

[![![waterfall](https://i.sstatic.net/JI5Iz.jpg)](https://i.sstatic.net/JI5Iz.jpg)  
Fig. 1. Waterfall. source: [Carlos Vasquez](https://www.youtube.com/watch?v=356PMFKY904)

And in [this video](https://www.youtube.com/watch?v=oNhcpOIQCNs) an example is shown of the waterfall after effect with more discreet stimuli. Not particularly your standard marquee sign but it comes close and there's a definite motion after effect observable (Fig. 2).

[![movie still](https://i.sstatic.net/bHLlt.png)](https://i.sstatic.net/bHLlt.png)  
Fig. 2. Movie still from [this video](https://www.youtube.com/watch?v=oNhcpOIQCNs)

However, I think your question is specifically whether a motion after-effect occurs with [chase-lighting](https://en.wikipedia.org/wiki/Chase_(lighting)) as often seen in [Marquees signs](https://en.wikipedia.org/wiki/Marquee_(sign)) (Fig. 3).

[![marquees](https://i.sstatic.net/e4BBH.gif)](https://i.sstatic.net/e4BBH.gif)  
Fig. 3. Marquees sign showing illusionary apparent motion. source: [Old Turnpike School](https://www.tewksburyschools.org/site/default.aspx?DomainID=145)

The **chasing-light stimulus in itself is a [visual illusion](https://en.wikipedia.org/wiki/Chase_(lighting))**, as there **is no true motion involved**. Instead, it is generated by using electronic circuitry to activate lights serially with a certain time delay in-between activations. Because there is no motion involved as such, I believe the after effect will not occur, or very weakly. At least, I couldn't observe an after effect after watching several chase lightings for a while. For example, the chase lightings in Fig. 1 become ambiguous when I look at it a while, *i.e.*, the lights actually spontaneously reverse their direction when staring at it for a while. The only thing I see when I look away, personally, is a colorful blob, and no motion after-effect.

**Reference**  
**-** [Mather *et al*., *Trends Cog Sci* (2008); **12**(12): 481-7](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3087115/)


---

