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The Spinning Dancer and the Shepard Tone
Posted: 27 August 2011 11:47 PM   [ Ignore ]
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From the wiki HERE

The Spinning Dancer, also known as the silhouette illusion, is a kinetic, bistable optical illusion resembling a pirouetting female dancer. The illusion, created by web designer Nobuyuki Kayahara, involves the apparent direction of motion of the figure. Some observers initially see the figure as spinning clockwise and some counterclockwise.

220px-Spinning_Dancer.gif

So, is she initially spinning clockwise or anticlockwise? OTOH, if one looks away and do not fully concentrate on the spinning dancer, after a few seconds she shifts from spinning clockwise to anticlockwise and vice versa. Why is it so?

Bistable perception:

Depending on the perception of the observer, the apparent direction of spin may change any number of times, although some observers may have difficulty perceiving a change in motion at all. One way of changing the direction perceived is to use averted vision and mentally look for an arm going behind instead of in front, then carefully move the eyes back.

Now, why do we have this visual ambiguity or flip-flop which influences the mind’s interpretation of the direction of rotation of the dancer, therefore we don’t know exactly in which direction she is actually spinning?

And also, audio ambiguity. From the wiki on Shepard tone

A Shepard tone, named after Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves. When played with the base pitch of the tone moving upwards or downwards, it is referred to as the Shepard scale. This creates the auditory illusion of a tone that continually ascends or descends in pitch, yet which ultimately seems to get no higher or lower. It has been described as a “sonic barber’s pole”.

Do play the sound file in the wiki to hear the auditory illusion.

Have fun. grin

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Posted: 28 August 2011 01:51 AM   [ Ignore ]   [ # 1 ]
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Yeah, that’s a fun one. I do some music composition, so auditory illusions are something that I have to be aware of. The Shepard tone is only possible with a computer, though. It’s not possible to create that effect with acoustic instruments.

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Posted: 28 August 2011 03:52 PM   [ Ignore ]   [ # 2 ]
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Geez, maybe I’m too old and need a shot of testosterrone, but I couldn’t see her as spinning at all.  She just remained a stationary image.

Occam

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Posted: 28 August 2011 07:17 PM   [ Ignore ]   [ # 3 ]
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TromboneAndrew - 28 August 2011 01:51 AM

Yeah, that’s a fun one. I do some music composition, so auditory illusions are something that I have to be aware of. The Shepard tone is only possible with a computer, though. It’s not possible to create that effect with acoustic instruments.

Stereophonic sound reproduction relies on illusion. From this article HERE

Stereo or surround audio reproduction relies on illusion to create a believable acoustic image or sound stage, in which instruments, voices and sound effects appear to originate from physical locations other than the actual speakers or headphones.

Top 10 incredible sound illusions HERE

In particular, for me, the phantom melodies, quickening beat and phantom words are remarkable.

The phantom melodies are revealing of how the ear/mind/brain can “create melodies” where none exist.

The quickening beat is utterly convincing.

I hear no brain, nogram and window in phantom words.

Enjoy.  smile

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Posted: 28 August 2011 07:23 PM   [ Ignore ]   [ # 4 ]
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Occam. - 28 August 2011 03:52 PM

Geez, maybe I’m too old and need a shot of testosterrone, but I couldn’t see her as spinning at all.  She just remained a stationary image.

Occam

You must be joking, Occam. What has it got to do with testosterone? LOL

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Posted: 29 August 2011 07:46 AM   [ Ignore ]   [ # 5 ]
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kkwan - 28 August 2011 07:17 PM

Top 10 incredible sound illusions HERE

In particular, for me, the phantom melodies, quickening beat and phantom words are remarkable.

The phantom melodies are revealing of how the ear/mind/brain can “create melodies” where none exist.

The quickening beat is utterly convincing.

I hear no brain, nogram and window in phantom words.

Enjoy.  smile

Ha! I can hear the 18000 Hz. sound. Barely, if I turn my speakers up. And I’m 35 - well over 20 years old.

There are auditory illusions used in music which aren’t listed on that site. A couple of the big ones include:

Complex pitches (i.e., a pitch played by an acoustic instrument) sounding intervals that get low enough start to sound muddy; the closer the interval, the higher the muddiness starts. This has nothing to do with the physics of how the sound propogates through the or even how the instruments sound; our ears develop interference when trying to interpret these intervals. Hence, illusion.

Adjacent pitches on a harmonic series create a phantom pitch that we hear at what would be the fundamental pitch of the harmonic series, at least for most people. This is has been used deliberately for centuries as a way to reinforce the bass sound of an orchestra or pipe organ.

Our ears do not interpret pitch uniformly, although it is the most consistent in the mid-range. We tend to hear low pitches to be slightly higher than they actually are, and high pitches as slightly lower than they actually are. This pitch perception problem becomes noticeable if you listen to tubas and piccolos try to play in tune.

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Posted: 29 August 2011 01:04 PM   [ Ignore ]   [ # 6 ]
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kkwan - 28 August 2011 07:23 PM
Occam. - 28 August 2011 03:52 PM

Geez, maybe I’m too old and need a shot of testosterone, but I couldn’t see her as spinning at all.  She just remained a stationary image.

Occam

You must be joking, Occam. What has it got to do with testosterone? LOL

Really, Kkwan?  The image is obviously of a female with an attractive body and little clothes on.  There were no other facets of the illustration that I saw which could account for anyone (apparently male) seeing her spinnig, so I based my comment on that. 

Occam

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Posted: 29 August 2011 01:22 PM   [ Ignore ]   [ # 7 ]
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Occam, the reason why she is not spinning for you lies in your computer (internet connection?), not you.  grin

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Posted: 29 August 2011 01:55 PM   [ Ignore ]   [ # 8 ]
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George - 29 August 2011 01:22 PM

Occam, the reason why she is not spinning for you lies in your computer (internet connection?), not you.  grin

The picture is a layered .gif file. Would there be some reason why Occam’s software wouldn’t animate the picture?

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Posted: 29 August 2011 06:16 PM   [ Ignore ]   [ # 9 ]
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TromboneAndrew - 29 August 2011 07:46 AM

Ha! I can hear the 18000 Hz. sound. Barely, if I turn my speakers up. And I’m 35 - well over 20 years old.

My computer speakers cannot reproduce 18KHz, so I am not surprised that I could not hear anything at all. Perhaps, through my hi-fi speakers, I would hear something. When I was 35, I could hear 20KHz, but now….......I would rather not know.  grin

Complex pitches (i.e., a pitch played by an acoustic instrument) sounding intervals that get low enough start to sound muddy; the closer the interval, the higher the muddiness starts. This has nothing to do with the physics of how the sound propogates through the or even how the instruments sound; our ears develop interference when trying to interpret these intervals. Hence, illusion.

Adjacent pitches on a harmonic series create a phantom pitch that we hear at what would be the fundamental pitch of the harmonic series, at least for most people. This is has been used deliberately for centuries as a way to reinforce the bass sound of an orchestra or pipe organ.

Our ears do not interpret pitch uniformly, although it is the most consistent in the mid-range. We tend to hear low pitches to be slightly higher than they actually are, and high pitches as slightly lower than they actually are. This pitch perception problem becomes noticeable if you listen to tubas and piccolos try to play in tune.

Fascinating information. Is it possible to provide a link to demonstrate these illusions?

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Posted: 29 August 2011 06:49 PM   [ Ignore ]   [ # 10 ]
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Occam. - 29 August 2011 01:04 PM

Really, Kkwan?  The image is obviously of a female with an attractive body and little clothes on.  There were no other facets of the illustration that I saw which could account for anyone (apparently male) seeing her spinnig, so I based my comment on that. 

Occam

It is a silhouette of a female. Obviously, you must have enough testosterone if you noticed this and that, also she does not spin for males only.  smile

If she did not spin for you, it could be that the gif file was not fully downloaded into your computer.

Are you on a slow or fast internet connection?

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Posted: 29 August 2011 07:16 PM   [ Ignore ]   [ # 11 ]
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George - 29 August 2011 01:22 PM

Occam, the reason why she is not spinning for you lies in your computer (internet connection?), not you.  grin

Possibly so. How about this?

mz_03_10024456721.gif

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Posted: 29 August 2011 07:25 PM   [ Ignore ]   [ # 12 ]
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My Internet connection is dial-up on an old desktop.  My higher speed, more modern laptop is never connected to the Internet.

I really think Mriana and Asanta would recognize the silhouette as female so I don’t think that testosterone is necessary.  And, as I’ve mentioned before, I was administred Aberelix, an experimental anti-testosterone medication, prior to prostate cancer radiation.  It was supposed to be temporary, but it wasn’t so it never made it to the market.

The cartoon girl is also stationary.

Occam

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Posted: 29 August 2011 08:28 PM   [ Ignore ]   [ # 13 ]
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Occam: For the record, I understood your testosterone joke when you mentioned it the first time raspberry

I can see that the girl is spinning on the first picture, and I’ve seen it before in a couple of psych classes here, but I’ve always seen her as spinning clockwise. Usually, with optical illusions, if I stare for a while I “get” the illusion… but for that one, I never did. If I stare at it long enough, I actually get a little bit dizzy and have to look away.

The “sound illusions” are interesting, though. I hadn’t heard of the Shepard Tone.

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Posted: 29 August 2011 09:35 PM   [ Ignore ]   [ # 14 ]
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Occam. - 29 August 2011 07:25 PM

My Internet connection is dial-up on an old desktop.  My higher speed, more modern laptop is never connected to the Internet.

The cartoon girl is also stationary.

The spinning dancer and cartoon girl are 590KB and 227KB respectively. These are quite big gif files. With dial-up speed of only 56kbs and a slow computer, it is possible that the animations will not work.

How about this smaller gif (19KB)?

2_cats.gif

OTOH, my son informs me that internet browsers can be set to stop animations.

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Posted: 30 August 2011 01:21 AM   [ Ignore ]   [ # 15 ]
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Occam, if the file is too big, just open the thread, and go for some coffee. Animated gifs should work in every browser today. Just give it some time to download completely.

About switching the direction: I nearly cannot switch the direction too. But what helps me is to scroll down so much that I only see her feet. Then I can switch. If I then slowly scroll up again, it keeps this direction. Until at some moment, without changing anything the direction has changed. (My preference is to see her turning clockwise (seen from above): how with all of you? Also any preference?)

What do you think changes, kkwan? A qualium? Your attention?

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