Ask MetaFilter questions tagged with illusion

Why can't I count the Fs?

doublehappy — Sun, 16 Aug 2009 17:52:25 -0800

I have lots of questions about an email FW: I have received many, many times. How many times does the letter F appear in the following sentence?

FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS.

This is ridiculous. There are 6. Even when I know there are 6, I struggle to recount them. The email suggests that only the super-intelligent will count 6, and the rest of us are idiots. I am of, perhaps, slightly above average intelligence, at best, so this may be true.

Being of only slightly above average intelligence, I have lots of questions. Why? Why does our (forgive the simplification, for I don't know how brains work) language brain override our shape recognition brain? (When did language become more important to survival than shape recognition? Are they in fact the same thing?) Wouldn't this also mean that the more intelligent you are, the less Fs you will count, (if we accept language skills are a good measure of intelligence). I take it that this obviously doesn't work in languages where the pronunciation of F and V differs from English, among others (a couple of google searches suggest that the brain perceives'of' as 'ov'). The text is often presented with non-standard line breaks, and I haven't seen this online with different sentences. Is this a phenomenon that can be seen in other texts, or is specific to this particular sentence? Does this phenomenon have a name?

What is the best way to pluralise letters? It seems common to use an apostrophe, and according to a lecturer I had four years ago, this is okay with decades, for example, the 1980's, but it just feels wrong next to a single letter. It's a proper noun, right? So the pluralisation should just be a simple 's'.

Is language even the best tool to talk about language? (See how I accidentally used the word 'talk' in there, presupposing that the only way to have discourse about language is to use language? What's that, post-structuralism?) It seems strange to me that we would, as a species, have reached the best form of communication so early in our existence. Is language the killer app for Humans, alongside thought? (Are they the same thing in some ways?) You can talk about dancing, but you can't dance about it. You can think about talking, and you can talk about thinking.

Sorry - got a bit carried away there... I'll settle for an answer to 'Why can't I identify the Fs in 'OF'?

What caused pitch-shifted echoes of the sound of a fireworks display?

Songdog — Sat, 04 Jul 2009 20:26:14 -0800

What acoustical phenomena explain the apparent pitch-shifted echo I heard while observing tonight's fireworks display? My son and I were sitting in a folding chair on a hillside a little over a mile (<2km) much higher than that of the fireworks. One was higher pitched than the other, but I've already forgotten which was which. I'm sure this was not the sound of the rockets' launch/ascent. We heard the main boom from directly in front of us. From slightly behind our direct left we heard a rolling echo reflected off of a small mountain about a half-mile distant. But the zipping sound seemed to come from between our feet.

The ground in front of us sloped fairly steeply down for a short distance, was level for several hundred feet (~75m) across a neighbor's yard, then descended, slightly and smoothly, to the site from which the fireworks were being launched, no more than 100ft (30m) lower in altitude than the yard where we were seated.

What was I hearing? Some sort of acoustical mirage? A diffraction effect? Interference among echoes? Some expression of sound waves carried through the ground itself? Electrophonic sound rendered audible by the very blades of grass?

Help me tar and feather someone on stage!

minervous — Wed, 03 Sep 2008 14:39:19 -0800

I'm directing a play that calls for an actor to be tarred and feathered on stage. It's a powerful moment, and I'd love to do it. But ... how? Complicating factors:
- the theater we're working in has no on-premesis shower (there is a large mess sink, but no floor drain) and no possibility of altering the building to have one

Things in our favor:
- the actor is game, and largely bald, and willing to be stripped to skivvies
- we have a large metal tub (several, actually) in which to contain the tarring and/or clean-up
- we have a fair budget, so costly-ish solutions need not be ruled out
- this is the climax of the play, and we can make a feathery mess without worrying about later scenes

Any and all ideas welcomed with open arms. Thanks!

Help destroy my childlike innocence...reveal secret.

red cell — Sun, 11 Nov 2007 10:42:31 -0800

How does this card trick/illusion work?

why do colors seem to appear in different planes on my LCD screen?

pmbuko — Wed, 25 Apr 2007 13:08:57 -0800

When I look at an image (on my LCD computer screen) that is composed of a combination of solid colors separated by black borders, I perceive the colors as appearing on different planes of depth, as if the image were three-dimensional. If I close either eye, the illusion collapses. Am I the only one affected by this, or is it a consequence of the way LCDs display color? To attempt to illustrate what I'm talking about, I created a GIF that, to me, strongly produces this effect (no visual trickery involved):

I perceive red, magenta, orange, and cyan to be closer than blue, yellow, and green. Red is always closest, blue is always furthest, and green seems to fall exactly in the middle.

Can anyone explain to me why this is, and if you can even see what I'm seeing?

Hard to gauge speeds at night. Inattention, illusion, or visual deficit?

Anonymous — Mon, 16 Oct 2006 06:12:02 -0800

Is there any sort of recognised optical illusion or visual deficit that can make it hard to realize that a vehicle is stationary? A friend of mine is a lawyer. S/he is looking for a lead that may save someone from going to jail.

My friend's client was driving his truck in the right lane of an elevated road at night. A car had stopped in the lane ahead because the driver's passenger felt sick. There was no stopping lane, nothing was to the right of the car but a guardrail. Three other cars had stopped behind the first car. My friend's client struck the last car, killing the people inside.

I've noticed that it can be hard to gauge speeds at night. In this case the road was lit but there were no visible trees or houses. The driver will have seen the road surface, the guard rail at the side of the road, the poles supporting the street lights, cars travelling in each direction and the stationary cars. Is there any reasonable explanation other than inattention for him not realizing that the cars were stationary? He doesn't recall the moments before the crash.

If it makes any difference, I'm not the lawyer or the client, and I don't know the client.

I need help 'seeing' an optical illusion!

bchaplin — Mon, 16 Oct 2006 02:46:31 -0800

I need help 'seeing' an optical illusion. Picture is inside. I've been staring at this (off and on) for days now, and it's driving me crazy: .
I can see the father, but not the son. Can anyone who does see it point out where his facial features are?

Please explain this illusion

BorgLove — Thu, 10 Aug 2006 22:09:51 -0800

Saw this act on America's Got Talent and have overcome my shame at watching this terrible show to ask, how the hell is it done? http://www.youtube.com/watch?v=RB-wUgnyGv0 Any insights?

What is the name of the flickering light used to create visual illusions?

scodger — Sun, 05 Mar 2006 23:29:42 -0800

What is the name of the flickering light used to create visual illusions? There is a kind of optical illusion caused by watching light flickering at the correct frequencies with eyes closed. IIRC the inventor initially discovered it walking down a tree covered path with eyes closed. Something that appears to be what I am thinking of appears prominantly in the music video for "papercuts" by Broadcast.
Thanks in advance.

How is this magic trick done?

AmbroseChapel — Fri, 04 Nov 2005 14:45:36 -0800

How is this magic trick done? I saw the Chris Angel (or some annoying variant spelling) show on TV the other day.

He did a trick on a moving bus where a girl signed one card from a pack, then he threw the pack at the windshield of the bus. One card stuck, the others fell. Obviously it was her card. But not only that, it was stuck to the OUTSIDE of the glass (they stopped the bus).

Most of his other tricks are Houdini-like things, escaping from a pair of handcuffs inside a barrel and the like, and I either know, or don't care, how they're done. But this one bugs me. Any ideas?

Why the post-sneeze sweet smell?

cortex — Thu, 08 Sep 2005 15:25:58 -0800

What's that sweet post-sneeze smell I smell? Often times after I sneeze, especially after a good nose-clearer, I get a brief smell sensation that I can best describe as being "sweet." (Perhaps a little floral? It's very difficult to put it into words.)

It doesn't last long -- between sneezing just now and endeavoring to post this, it's gone already -- and the odor/sensation is very consistent from sneeze to sneeze over a period of years.

What the heck is this? Is it some olfactory illusion from over-compensation for some anti-this-odor component in my snot? Does this happen to other people?

From the archives: abcde smells something metallic in this thread; no, I don't see sparks when it happens.

Mirror Mirror On the Wall

xo — Fri, 11 Feb 2005 08:13:42 -0800

My bathroom has mirrored walls instead of tiles. When I look at myself in one wall/mirror, I seem slightly shorter and wider than I seem in the other mirror, creating the illusion of a 5 lb difference in my appearance. Is there a way to figure out which mirror (if either) is accurate?

Who is the (French?) man who swallows and regurgitates items at will?

humuhumu — Thu, 02 Dec 2004 14:38:03 -0800

In around 1986/87 (+/- two years), I saw an edition of The Last Resort with Jonathan Ross (failed UK attempt to copy the Letterman chat show format). One of his guests that night was a freakish guy, possibly French, who swallowed things and then extracted them through his stomach. So, he'd swallow some string, then stick a skewer or something through his stomach wall, and hook out the string. Yes, it was that disgusting.
1. Was this real or an illusion? From what I can remember, there were close-ups and it didn't look like it was being faked.
2. Who was this man?