Nice Message

Poply

Its a message from a worker of Nintendo! Nice message big guy.

Amazing

Just a amazing pic in which a cute cat is trying to eat that bowl,its very funny.

“Rotating Snake” Illusion

First the orig­i­nal “Ro­tat­ing Snake” <http://​www.​ritsumei.​ac.​jp/​~ak­i­taoka/rotsnake.​gif> by Akiyoshi Ki­taoka, mod­i­fied just a lit­tle:

Back­ground – In the image above the strong (and beau­ti­ful) ro­ta­tion of the “wheels” oc­curs in re­la­tion to eye move­ments. On steady fix­a­tion the ef­fect van­ishes. For an ex­plana­tory hy­poth­e­sis, view the an­i­ma­tion on the right. You ma y wish to press the ‘Stop’ but­ton after a while … it gets on one’s nerves ;-). See also Backus & Oruc 2004 for their ex­pla­na­tion. What to ob­serve Even when fix­at­ing steadily, il­lu­sory mo­tion oc­curs on ap­pear­ance/ dis­ap­pear­ance Il­lu­sion does not de­pend on colour Ro­ta­tion di­rec­tion de­pends on the po­lar­ity of the lu­mi­nance steps (I arranged these to evoke a “gear­box ef­fect” here, by mir­ror­ing the im­ages ap­pro­pri­ately) Strength of il­lu­sion de­pends strongly on back­ground lu­mi­nance. The back­ground lu­mi­nance slowly ramps from 0% to 100% au­to­mat­i­cally, or you can use the slider. The il­lu­sion­ary ro­ta­tion is strongest for 50% gray (exact value will de­pend on your mon­i­tor ‘gamma’). Com­ment As Ki­taoka & Ashida (2003) de­scribe, asym­met­ric lu­mi­nance steps are re­quired. Pre­sum­ably ap­pear­ance of these trig­gers mo­tion de­tec­tors (as in the an­i­ma­tion on the right). I as­sume that the ac­tual mech­a­nism is quite sim­i­lar to the “Ro­tat­ing Spokes” il­lu­sion, where asym­met­ric lu­mi­nance steps occur as well. Gre­gory & Heard (1983) were the first to de­scribe that asym­met­ric lu­mi­nance steps cause il­lu­sory move­ment. A “Stress Test”? – No! Re­peat­edly, I was sent such pic­tures with the as­ser­tion that they com­prise a stress test (and some of the peo­ple send­ing me this were deeply wor­ried). And I just found a web page en­ti­tled “test on­line the level of stress” (I will not link to it) which con­tains these state­ments “For a nor­mal per­son, they should all move at a slow pace, barely ro­tat­ing. The slower the pic­tures ro­tate, the bet­ter your abil­ity of han­dling stress: Al­legedly, crim­i­nals see stress test im­ages mov­ing and spin­ning around madly, while se­niors and chil­dren see them still…” This is utter BS!   Don’t get alarmed.   For one, the ef­fect de­pends on eye move­ments, and these are known to dif­fer markedly be­tween sub­jects with­out re­lat­ing clearly to psy­cho­log­i­cal traits. Fur­ther, a few peo­ple do not see it at all (could be around 5%, among them a very renowned vi­sion sci­en­tist), in spite of ap­pro­pri­ate eye move­ments. There are no ac­tual data show­ing re­la­tions to stress (or age), so don't dis­tress your­self when you see it ro­tat­ing strongly or not at all. Sources Gre­gory RL, Heard PF (1983) Vi­sual dis­so­ci­a­tions of move­ment, po­si­tion, and stereo depth: Some phe­nom­e­nal phe­nom­ena. Quar­terly Jour­nal of Ex­per­i­men­tal Psy­chol­ogy 35A:217–237 [PDF] Ki­taoka A, Ashida H (2003) Phe­nom­e­nal char­ac­ter­is­tics of the pe­riph­eral drift il­lu­sion. VI­SION 15:261–262 Backus & Oruc 2004 VSS pre­sen­ta­tion ab­stract + back­ground ma­te­r­ial [seems no longer avail­able] Con­way BR, Ki­taoka A, Yaz­dan­bakhsh A, Pack CC, & Liv­ing­stone MS (2005) Neural basis for a pow­er­ful sta­tic mo­tion il­lu­sion. J Neu­rosci 25:5651–5656 Backus & Oruc (2005) Il­lu­sory mo­tion from change over time in the re­sponse to con­trast and lu­mi­nance. Jour­nal of Vi­sion 5:1055–1069

Silencing by Motion

What to see

On the right, there is a ro­tat­ing ring con­sist­ing of many coloured discs; best fix­ate the cen­tral cross. No­tice any­thing spe­cial? Well, the ring changes ro­ta­tion di­rec­tion, we all can eas­ily agree on that.

What to do

Press the ‘stop’ but­ton. Un­sur­pris­ingly, the ring re­frains from ro­tat­ing. Now it be­comes ob­vi­ous that all the small disks change their colour; going through rain­bow so to speak.

Start­ing the ring ro­ta­tion now and look­ing closely re­veals that the colour change hap­pens all the time, but it is barely not­i­ca­ble dur­ing ro­ta­tion. This can be demon­strated by press­ing the ‘hue–/hue+’ but­ton dur­ing ro­ta­tion; this has nearly no ef­fect dur­ing ring ro­ta­tion.

In­stead of the ring you can also se­lect to ro­tate a pin­wheel in the back­ground with sim­i­lar ef­fect. So it is not rel­e­vant that the small disks them­selves move to im­pare de­tec­tion of the hue change.

Com­ments

This ef­fect was pub­lished early in 2011 by Jor­dan W. Su­chow and George A. Al­varez from Har­vard Uni­ver­sity. It sub­se­quently won, de­servedly, the “Best Il­lu­sion of the Year Con­test”.

In the paper by Su­chow and Al­varaz and their 2011-VSS poster, not only in­ter­est­ing vari­ants but also sev­eral con­crete mech­a­nisms are dis­cussed and tested, which I need not go into here. An in­tu­itive ex­pla­na­tion: pro­cess­ing global mo­tion pre­sents an over­load, which im­pairs cod­ing of the local de­tails. This is a re­ally new ef­fect, and I think it may be re­lated to “mo­tion blind­ness”.

Sources

Su­chow JW, Al­varez GA (2011) Mo­tion Si­lences Aware­ness of Vi­sual Change. Cur­rent Bi­ol­ogy 21:1–5.
That pro­vides links to demon­stra­tion movies with a num­ber of in­ter­est­ing vari­ants.
You can find them also at their demon­stra­tion page.

Burr D (2011) Vi­sual Per­cep­tion: More Than Meets the Eye. Curr Biol 21:R159–R161 (thought­ful ed­i­to­r­ial)

I am thank­ful to Jor­dan for grace­fully al­low­ing me to pre­sent this demon­stra­tion, closely mod­eled after their pub­li­ca­tion.

Motion Induced Blindness

What to see

On the right you see a rotating array of blue crosses and 3 yellow dots. Now fixate on the centre (watch the flashing red/green spot). Note that the yellow spots disappear once in a while: singly, in pairs or all three simultaneously, right?

In reality, the 3 yellow spots are continuously present, honest! This is captively called “motion induced blindness” or MIB.

What to do

You can change the speed (preset to 12 rotations per minute). Disappearance persists down to surprisingly slow speeds.

You can adjust the size (preset to 5 pixels). Disappearance persists up to surprisingly large sizes.

You change the colour of the rotating crosses, the dots and the background. The dots disappear into whatever colour the background has.

The ‘reset’ button at the top restores the standard settings.

Comment

Steady fixation favours disappearance, blinks or gaze shifts induce reappearance. All in all reminiscent of the Troxler effect, but stronger and more resistant to residual eye movements.

In Feb 2008, John from Phoenix posed an intriguing question in the guestbook: If several people observe together, do the yellow dots disappearence disappear at the same time for everyone (synchronised)? I remember I briefly considered this years ago and rejected the hypothesis of synchronised perception as esoteric. I also informally tested this, and it did not occur. I still believe that the disappearence is an individual phenomenon, and thus not synchronised, but this should be formally tested with careful methodology. Should be an interesting experiment! Anyone?

There is no consensus as to the explanation in vision literature yet. I personally think that motion is not necessary, any (temporal) change in the image will suffice. [Note added 2008-03-07: see now Wallis & Arnold, 2008.] A more recent paper from that group (2009) sugggests a link of MIB to “motion blur / motion streak” suppression. If so, MIB would be illusion subserving a useful purpose in everyday vision. This also holds for a different explanatory approach by New & Scholl (2008) who conclude that “rather than being a failure of visual processing, MIB may be a functional product of the visual system’s attempt to separate distal stimuli from artifacts of damage to the visual system itself.”

A simple version of explanation: If you fixate steadily, all structures are imaged on their same retinal location. This leads to local adaptation on the retina (the Troxler effect, often incorrectly addressed as “fatigue”). By adding additional temporal modulation (here the rotation), effectively the background noise is increased. Thus the Troxler disappearence is more pronouned and/or happens faster.

Sources

Bonneh, Cooperman & Sagi (2001) Motion-induced blindness in normal observers. Nature 411:798–801

Wallis TSA & Arnold DH (2008) Motion-induced blindness is not tuned to retinal speed. JOV 8:11, 1–7

Wallis TSA & Arnold DH (2009) Motion-induced blindness and motion streak suppression. Current Biology 19:325–329 [website]

New JJ, Scholl BJ (2008) “Perceptual Scotomas” A functional account of motion-induced blindness. Psychological Science 19(7):653–659

Stepping feet” Motion Illusion

What to observe

Observe the movement of blue and yellow “feet”. The feet seem to step alternately, like tiny feet going tip-tap-tip-tap… This is more pronounced if you do not look directly on the feet, but between them. In reality their movement is always parallel. I find this phenomenon particularly cute.

What to do

With ‘grating±’ you can toggle grating visibility. Without the grating, it is obvious that the feet are not stepping out of phase. ‘contrast±’ dims the grating, helping to appreciate that the feet are always moving completely in parallel. The value stepper at the bottom controls speed.

The stepper above the speed stepper sets the number of bars per foot. This is preset to 4, the effect occurs also at all other even values. For odd values, e.g. 5, the motion also becomes odd: instead of stepping alternately, the feet seem to move like worms, extending and shortening. [This option added 2012.]

The sliders at top and bottom control the luminance of their respective foot. When you make the yellow foot brighter than the light bars of the grating, it does not lag behind any more. When you make it very dark, it moves together with the blue foot. The sliders (added 2010) allow you to experiment with the explanations below, I still prefer the “level 2” explanantion.

There are more buttons with (hopefully) obvious functions.

Comments

Stuart Anstis first demonstrated this illusion in 2003.

Level-1-explanation:

Press the “Color±” button. Now it becomes obvious that the edges of the light ‘foot’ merge with the light bars, and are only visible when they traverse the dark bars. So half of the time there really is no motion cue, and perception goes into default, i.e. no motion. For the dark foot the same holds, only at alternate times.

With reduced contrast of the grating (button “Contrast±”) isoluminance of edges and grating is no longer present, so the effect disappears.

The “worm-like” movement for an odd number of bars per foot is automatically explained as well.

Level-2-explanation:

Level-1-explanation plus: The edge information is only contained in colour, and the (magnocellular) motion system cannot see it.

Level-3-explanation:

The effect still persists when there is a slight contrast between foot and grating (can be achieved with the sliders). Anstis (2004) attributes this to slowing down of motion under conditions of reduced contrast (Thompson 1982), and goes much deeper into the subject.

Level-2007-explanation:

Just when I thought this illusion can be easily understood, there appears this complicated paper Howe et al. (2007), seemingly disproving my above thoughts and suggesting a very intricate explanation. Recently, I included this paper in a seminar and we tried to follow its evidence and reasoning, and couldn't. In consequence, my favoured explanation regresses to levels 1+2 above.

Sources

The demonstration above was inspired by Stuart’s version. Thanks to Wolfgang Wesemann for first drawing my attention to this phenomenon, and Wolfgang Beyer for bright ideas.

Anstis SM (2003) Moving objects appear to slow down at low contrasts. Neural Netw 16:933–938

Anstis SM (2004) Factors affecting footsteps: contrast can change the apparent speed, amplitude and direction of motion. Vision Res 44:2171–2178

Thompson P (1982) Perceived rate of movement depends on contrast. Vision Res 22:377–380

Howe PDL, Thompson PG, Anstis SM, Sagreiya H, Livingstone MJ (2006) Explaining the footsteps, belly dancer, Wenceslas, and kickback illusions. Journal of Vision 6, 1396–1405