The McCollough Effect - An On-line Science Exhibit
Introduction
Take a look at the following grid. It should appear as black stripes on a white background.
Click here and gaze at the two colored grids for a few of minutes. There's no need to stare at a single point on a grid.
If you look at the black-and-white grid again, you should notice a green haze around the horizontal lines, and a magenta haze around the vertical lines. The intensity of this effect varies between individuals. If you don't see this, go gaze at the colored grids for a while longer.
I know what you are thinking: this is a simple afterimage effect. If you think so, walk away from your terminal until you think the after image should be gone. Go home and try it in the morning. Then take a look. Or better, simply rotate the image. Well, maybe that isn't so simple with a CRT, but you could rotate your head.
The Effect
It is called the McCollough Effect, and was originally described by Celeste McCollough in a paper in Science in 1965. It has been the focus of on-going investigation ever since.The effect typically lasts for hours, or even overnight. The duration can be changed by the consumption of coffee and other psychoactive drugs. One paper found that it is stronger in extroverts than introverts, and might be a reliable test for extroversion.
The precise cause of the effect is unknown, and currently under investigation. It is not a simple case of fatigued neurons: there are neurotransmitters involved and appear to be responsible for the long-lasting nature of the effect. It probably takes place in the V1 processing stage of visual information. This is the first image processing after the signal leaves the retina in the eye. The edge detection circuits somehow become associated with the color. At this stage the processing is monocular: the images from the two eyes have not been combined.
The Lab
You can perform experiments on the McCollough effect right here at your terminal. Here are a few questions you might try to answer. I've supplied some images that might help.
- Does it work with other colors? Green and magenta are complimentary colors. What about others? Does color saturation change the result?
- Does the size of the grid matter? Here is a fat color grid and a thin black-and-white grid.
- How long does the effect last? Is it stronger in some people than others? Does age or sex change the strength of the effect?
- Can you cancel the original grid with opposite grids?
- If you cover one eye while inducing the effect, will the other eye see the effect?
- Does room lighting affect the experiment?
Lab Tools
Here are some lab tools. You can probably think of others: even the brightness knob on your screen may have an effect.
- Horizontal green and vertical magenta.
- Vertical medium green, vertical dark green, horizontal medium magenta, horizontal dark magenta.
- Vertical blue, cyan, yellow, red.
- Horizontal blue, cyan, yellow, red.
Further Reading.
References are available upon request.
Links
Check out http://www.uq.edu.au/nuq/jack/rivalry.html.If you have questions or comments, please feel free to send me email.
