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Q: Frequency of the human eye ( Answered,   6 Comments )
Subject: Frequency of the human eye
Category: Science > Physics
Asked by: eagleeye-ga
List Price: $5.00
Posted: 27 Sep 2002 16:16 PDT
Expires: 27 Oct 2002 15:16 PST
Question ID: 69880
When a wheel spins at a certain rate, it appears stationary to the
human eye. I assume this has something to do with the frequency of the
human eye relative to the frequency of rotation of the spinning wheel.
What is this frequency? Similarly, on certain spinning items, which
appear meaningless when stationary, you can suddenly read words and
images once the item is spinning at a certain rate. How are these
images created and who designs these images?

Request for Question Clarification by alienintelligence-ga on 29 Sep 2002 00:26 PDT
Hi eagleeye,

From your question I have gotten the 2 main
1) What is the human eye's field frequency 
2) How do you exploit this CFF (Critical Flicker Frequency)
   to simulate apparent images.
3) Who designs these images.

1 and 2... are easy to answer. 3, might require a
clarification from you. Are you wanting manufacturers
of these visual toys and gadgets? Or do you want to 
know the artists of the optical illusions?

Subject: Re: Frequency of the human eye
Answered By: drdavid-ga on 02 Oct 2002 15:16 PDT
You raise a number of important issues with your questions and
comments, some of which have generated a lot of controversy over the
course of far more than the 25 years you have been teaching
speed-reading. However, most of the key experimental work is also at
least that old, and those results still stand. You may wish to
question some of the results and even do new experiments, but you
would do well to start by reviewing the work that has already been

First, to answer your specific question about spinning tops, wheels
and similar devices:

To the extent that any such device appears to freeze motion blur
present in moving images, it does so by stroboscopic freezing of the
image. The eye has no "natural frequency" which can do so on its own.
There are different ways of implementing the strobe effect: strobe
illumination, vibrating shutters, moving slits, but they all have the
effect of giving you a short snapshot of the moving image, short
enough in time to freeze the motion blur. The persistence of human
vision may then prevent the image from appearing to flicker as long as
the image repetition rate is fast enough (let’s say, greater than
about 20 frames per second if you are willing to tolerate some
flicker--modern computer displays generally use at least 60-80 frames
per second to avoid any appearance of intensity flicker). Fluorescent
illumination with common inexpensive ballasts generates a strobe
effect at the line frequency (50 or 60 Hz) that can cause an
unintended strobe illumination. Computer monitors, TVs and movie
projectors also generate well-known unintended strobe effects for
things like rotating wheels on vehicles.

That said, your real question has to do with training aids for
speed-reading. First, how does fluent adult reading work? Much of the
research was done by K Rayner et al:

EW McConkie & K Rayner, "Identifying the Span of the Effective
Stimulus in Reading: Literature and Theories of Reading," in H Singer
& RB Ruddle, ed., "Theoretical Models & Processes of Reading,"
International Reading Association, Newark, DE, 1976

K Rayner, "Eye Movements in Reading and Information Processing,"
Psychological Bulletin, 85:618-60, 1978.

SE Taylor, "Fluency in Silent Reading," Taylor Associates (Reading

Fluent reading is about 10% saccadic motion (jumps between fixations)
and 90% fixation. Average saccade length is 8-9 characters (range
2-18). About 10-20% of these are retrograde (backwards). Average
fixation length is 200-250 ms (range 100-500). Within a fixation, you
can perceive and recognize 2-3 characters to the left and 5-8
characters to the right (for a left-to-right language such as
English). Word shape and other visual queues that can aid in planning
saccades can be perceived over larger distances (up to about 12
character spaces to either side of fixation).

There is thus some possible room for training improved speed by trying
to reduce fixation time toward 100 ms. This, I think, is what you
hoped to achieve by your “spinning top.” To answer your question as to
how to generate such training images, the easiest way is with a
computer monitor. A monitor is inherently much faster than the 100-500
ms range you would be presenting. Whether artificial training aids
which force a word presentation rate can decrease fixation time during
normal reading is not clear or proven to my knowledge. However, it is
probably only a small part of the skills that are trained in rapid
fluent reading. Ten fixations per second at about one word per
fixation would only get you to about 600 words per minute. To achieve
the typical "speed-reading" claim of at least 1000 words per minute
with high comprehension probably involves a number of speed
strategies: skimming (skipping some words), knowing how to rapidly
extract key words and concepts, looking for topic sentences and
factual data, developing good test-taking skills. Whether it is even
desirable to read 1000 words per minute for any material (such as
textbooks) that must be studied in any depth is, of course, debatable
as well, though an emphasis on reading efficiently with good
comprehension is clearly worthwhile.

Additional material on speed reading can be found with a Google search

"speed reading"
Subject: Re: Frequency of the human eye
From: digsalot-ga on 27 Sep 2002 17:31 PDT
Hi eagle

I may very well be wrong but it sounds like you are doing some kind of
class/homework report or perhaps a science project.

Each of these may need a different direction of research to find the
answer you need.  Let us know which it is.
Subject: Re: Frequency of the human eye
From: asterisk_man-ga on 27 Sep 2002 18:15 PDT
First, I have a feeling that you may be confused. If you look directly
at a spinning wheel it will simply look more blury the faster it
spins. Under normal lightning conditions (not a stobe) it will not
look like it is stopping or reversing or any other phenomonon you were
expecting. The things you are describing are seen when there is some
sampling of the position of the wheel such as with a strobe or with a
video camera. I believe that you will find that all the spinning items
that display something when spinning do so because various parts of
the image become smeared together. If you can point to some specific
examples of the spinning items you're thinking of I will try to
explain them more specifically.
Again, the human eye does not have a sampling frequency that would
cause the undersampling effect you described.
Subject: Re: Frequency of the human eye
From: thenextguy-ga on 27 Sep 2002 21:25 PDT
Are you talking about indoors, under fluorescent lights?  Or in front
of a TV in a darkened room?  Those things will function as strobe
Subject: Re: Frequency of the human eye
From: eagleeye-ga on 27 Sep 2002 22:48 PDT
I am trying to investigate whether the human eye can be trained to
increase its response to movement. I need to imprint words onto a
disk. When stationary, the words are concealed in the clutter on the
disk. When the disk is rotated at a particular speed, the words will
become visible. Then if the disk is rotated even faster, can the eye
be trained to adapt to the higher speed and still get to see the
words. Firstly, I need to know how to create the digital image in such
a way that the words only become visible at a certain speed of
rotation. I once saw this effect achieved on a promotional spinning
top. I have investigated this with collectors of unusual spinning tops
- no success. I assume that it must be some sort of mathematical /
digital effect. Some record players use this concept - a series of
black and white lines on the side of the platter and a strobe light -
when the white lines appear stationary, then you know that the
turntable is spinning at the right speed. I want to apply the same
concept to the human eye and then train the eye to respond to faster
Subject: Re: Frequency of the human eye
From: eagleeye-ga on 27 Sep 2002 22:56 PDT
I once saw a spinning top. When the top was stationary, the artwork
appears to be a clutter of dots. When the top was spun, and reached a
certain speed, the clutter resolved to a picture and words. I am
trying to find such a top or someone to design such artwork. Then a
want to measure the speeds of rotation for various people - the speed
at which they can read the image/words. Then my gradually increasing
the speed, ascertain whether they can adapt to higher speeds versus
the untrained eye. This would not be under any artificial lighting
conditions. I am doing this as part of my research into speed reading.
Why can some people read and comprehend at many thousands of words a
minute while others cannot? I have been teaching speed reading for 25
years and now want to start a scientific evaluation of these people.
Subject: Re: Frequency of the human eye
From: alan0-ga on 28 Sep 2002 00:02 PDT
An entirely different effect is the appearance of colour when spinning
a top which only has black and white on it. I don't think that these
effects have anything to do with the light source or strobing - but I
could not find the theory. See the link below for examples of optical
illusions with spinning tops.

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