Optical Illusions or Visual Phenomena? ( II )

The Notorious Frankfurter Illusion

What to do & see

If you have two roughly equivalent eyes you will see a "sausage" floating in front of you in mid air, by following these steps:

1. Hold your hands in front of you, at 20–30 cm distance from you, at eye level.
2. Point your index fingers against each other, leaving about 2 cm distance between them.
3. Now look “through” your fingers, into the distance behind them.
4. The sausage should appear now, and you can change its length by varying the distance between the finger tips.
5. For most observers, the sausage will look blurred, at least initially.
6. If you try to look at the sausage, it will disappear, it is only present if you look at something more distant than your fingers.
7. It helps if the background is rather homogenous and has a color very different from your fingers.

Basically, this "sausage" is caused by two mechanisms,
1. physiological double images, and
2. interocular rivalry and suppression.

When you look at your fingers, the gaze direction of your two eyes is angled towards each other, so that their lines of sight meet at the target. When you then look into the distance, your eyes shift slightly outward, making their lines of sight nearly parallel. For close objects the image in the two eyes is consequently no longer at the right position, the images are no longer merged and can appear double for your “inner eye”. This is quite normal and occurs all the time, usually these double images are suppressed. So, if the two images overlap, why then doesn't the compound image look like the neighbouring figure on the right?

At the end of the image of each finger, there is a rivalry between the image from the two eyes when the brain tries to combine them. In one eye the finger ends, in the other it continues. So what does your brain do in such rivalry situations? If the two images are rather similar, the percept can oscillate between the alternatives. Here, however, we have a high contrast step in one eye, namely the end of the finger, where it is replaced by the background. In rivalry the eye with the higher contrast wins, at least locally; this is here meant by the term "suppression". In the figure on the left this high contrast step is symbolised by the yellow halo.


Hermann Grid

The widely known Hermann-grid illusion (Hermann 1870).

Dark patches appear in the street crossings, except the ones which you are directly looking at.

Rather weak, but in every textbook…

See below for the classical explanation. HOWEVER: see the next page for a convincing rejection of this explanation.

The classical explanation

1. Why do we see the dark patches?

Look at the left part of the left diagram and assume an on-center retinal ganglion cell. Its receptive field is indicated by the reddish disk. When the ganglion cell is, by chance, looking at the grating so that its centre ('+') is positioned at a crossing (left-top), there are 4 bright patches in the inhibitory surround. A ganglion cell looking at a street (left-bottom) however only gets 2 inhibitory patches, so it will have a higher spike rate then the one at the crossings. This was measured by Baumgartner (1960) in Freiburg, see picture on the right.

2. Why don't we see the patches when we look right at them?

Because then we direct the fovea at the crossings, and in the fovea the receptive fields are much smaller (see the small reddish disks on the right of the left figure). With such small receptive fields it obviously does not matter whether they are at the crossings or not.

3. Why is this explanation, so plausible it sounds –and it is in every textbook– not the full story?

See the next page for a simple refutation.


Scintillating Grid

If you look around in the neighbouring figure you will notice the appearance and disappearance of black dots at the crossings.

Even though this figure looks similar to the Hermann-Grid, it is markedly more vivid. Furthermore, the effect is probably caused by different mechanisms than those causing the Hermann-Grid effect.

Question: Do the streets or the squares influence the colour of the apparent disks?

As you notice in the neighbouring figure, red streets leave the disks black. But if the squares are red (move mouse over figure), the disks acquire a reddish tint...


Impossible Objets

What to observe –

The neighbouring contraption consists of the so-called “devil’s fork” (top right, also known as “blivet”), the “Penrose Frame” (centre) and the “hexnut” (3 of them bottom left, an enlarged specimen bottom right). Boggle your mind when trying to envisage to build such an object.

Comment –

Our brain reconstructs an internal 3-dimensional world model from the flat retinal image.

The oldest –known to me– example of an impossible scene: “Madonna and Child ~ Adoration of the Magi” from the Pericope of Henry II around 1025. The impossible architecture in that painting, however, seems not done purposefully to me, in contrast to Hogarth’s ‘Frontispiece’. Often the first impossible object is attributed to Reutersvard (a design for a Swedish stamp), however Albers and Hogarth were clearly earlier. After the Penroses formally described the phenomenon, examples abound, beautifully drawn for instance by Escher.

A draw-it-yourself impossible object

On the left you see an animation where you can draw along.

Start with 6 vertical equidistant lines, give them hats. You get a rendition of “3 towers” or a “three-pronged fork”. Obviously, a sensible 3-dimensional interpretation.

Cover the top, and draw connecting circle segments at the bottom. You see the bottom of a square bar, bent into an U-shape. Again, a sensible 3-dimensional interpretation.

However, uncovering the top also reveals the fact that the two interpretations are not compatible with each other.

to be continued....

HTML Comment Box is loading comments...

Optical Illusions or Visual Phenomena?

What do you think about this post?
Is it optical illusions or visual phenomena?


Anamorphosis

What to see

The neighboring picture by Hans Holbein is called “The Ambassadors”. Every thing is painted very realistic, in trompe-l'oeil style. But what is the strange shape in the bottom foreground?

What to do

You could try a slanting look on the image from top right. Easier: further down I have cut out this shape; with the slider at the right you can change its angle, with the slider at the bottom its horizontal scale. This allows you to make the shape recognisable. Two tips: (1) set both sliders to rather low values, (2) memento mori.

The shape is rendered with a strong perspective distortion, an example of an anamorphotic display. Now in the National Gallery in London, the painting originally hung at the bottom of a staircase, so when descending the angle was just so.

Anamorphotic images can also involve mirroring on curved surfaces, cylinders or cones.

Blotted Letters

These look like random shapes... until you move the mouse over them.

The effect presumably is related to the fact that the borders of letters vs. background are indistinguishable from the borders of letters vs. ink blot.

Blur and Picture Content

Painting “All is Vanity” by Charles Allen Gillbert (1873-1929). Place mouse over image and observe the change.

This is not an “optical illusion” proper, it’s more a physical effect. With the strong spatial low-pass filtering, the blurred version simply lacks the fine details. However, one could also argue that the low-spatial frequency information is masked by high spatial frequencies like in the “Lincoln effect” by Harmon & Julesz (1973).








Def Leppard album "RetroActive"

Wotherspoon "Gossip, and Satan came also"

Wotherspoon "Society, a portrait"

Dali "Voluptate Mors"

Dali "Ballerina"

Cher, album "Heart of stone"

"L" Amour de Pierrot

Au revoir!

"La famille Impériale de Russie"

Cat or Couple?

French postcard (on Planet Perplex)

Judge Magazine cover, 1894 “Death to our industries!”

Enigma

Stare at the centre of the figure for a while. Some "scintillating" activity will build up in the violet and blue annuli. Some observers also report a circular rotation within these regions, things will begin to “run around in circles”.

This image “The Enigma” is by Isia Leviant (1981), Palais de la Decouverte, Paris.


Face on Mars

In 1976 the Viking Orbiter radioed back many images from Mars. Among those form the Cydonia region, one depicted a rock formation that strongly resembled a human or humanoid face staring straight up into the heavens.

You can probably guess what was made of this… "Pareidolia" is the term for neurological or psychological phenomena where vague images are interpreted by the brain as specific images. Statistically speaking, it is a type I error, a “false positive”.

A nice article “Paranormal Phenomena: The Face on Mars, Once and for All” contains some background material on the ensuing kerfuffle, including links to large NASA images of the entire regions photographed.

In 1998, the Mars Global Surveyor (MGS) reached the Red Planet with far better, more high-resolution equipment than Viking had carried. Initially, NASA had not planned to re-map the Cydonia region, but public outcry was so great that in April 1998, the MGS was programmed to re-photograph segments of the Cydonia region, including at least one of the face. If you move the mouse over the adjacent figure, the newer photo appears, roughly shifted and rotated to match the one taken 22 years earlier. You can judge for yourself whether you interpret this as a face about 2.5 km tall, 2 km wide and about 0.5 km of height.

Of course, none of the inevitable conspiracy theories was quenched by the new image.


Face in Beans

Find the face among the beans.

The picture is accompanied by all sorts of inferences on your mental development depending on delay until you find the face in there, which are even though they begin with “According to recent medical evidence”.

Can you see a face in beans?





Face in Blocks

What to do & observe

Observe the figure on the top right. It’s just a number of brownish blocks. Click once on the button "finer" ( if you have a editing application). Recognisable now? Perhaps if you deliberately blur the image, by screwing up your eyes or squinting? Yes, still too difficult. Go finer, and try after every step if it becomes recognisable via blurring.

This demonstration is based on the “Lincoln illusion” first reported by Harmon & Jules 1973. More generically it’s referred to as “block masking”. Since you have some training now, try blurring the black and white figure on the left. Another well-known face? Well, that was easy, since you were (or your visual system) was primed.

It seems plausible that the high spatial frequencies of the block edges reduce the signal-to-noise ratio for the "real" content. Blurring acts as a low-pass filter, reducing the high masking frequencies. In this respect the present phenomenon differs from “Blur and picture content”, because there the high spatial frequencies don't just mask, they also contain content.

This is the result of editing the picture :

It is simple, right?
Are you think this post above about optical illusions? or visual phenomena?
To be able to differentiate optical illusions and visual phenomena, follow my post next week.. okay?

God Bless us.. ^^

HTML Comment Box is loading comments...

Optical Illusions (II)

Spine Drift

What to see ^^

In the image to the right you see an array of spindly thingies (“spines”), with a gap demarkating a square in the middle. Does the central square appear to float, to move relative to the background?

If so, you are perceiving seeming movement, namely Kitaoka’s “Spine Drift” illusion. It is strongly affected by eye movements, thus perceived differently by different people.

What to do ^^b

To enhance the illusion: shake your display a little (easy, of course, with a notebook or iPad). Or scroll a bit, or shake you head, or glance around the display, or use the “shake” button.

If you press the “rotate 90°” button you will find: Whenever the central and peripheral spines are parallel or at 180°, there is no illusion of differential movement; when they're at 90° –whichever way– the illusion occurs. Whith the wheel you can try out any angle.

Eye movements cause motion blur on the retina. When applying motion blur to the original spine object (below, left), the resultant retinal image differs strongly in contrast between blur directions.

Thus when the retinal motion is at 45° (or –45°), the retinal image is very poor in contrast. It is well known that reduced contrast reduces perceived speed , so when the movement is in the 45°-direction the image seems to lag. When the central square and the surround differ in their spine directions by 45°, eye-movement induced retinal motion blur (in one of the two), causing differential contrast reduction, and thus a seeming shift between central square and surround.


Contrast Gain Control

What to do

Gaze for a few seconds at the fixation cross in the centre of the neighbouring image pair. The left image is blurred, and the right has high contrast, ok.

Now move the mouse pointer over the image and judge the contrast of the two new halves.

What to observe

After the change, on the left part you will (initially) perceive high contrast, on the right markedly less contrast. This persists only for a few seconds, then it becomes apparent that the 2 halves are, as indeed the case, identical.

Contrast adaptation (slow, seconds) and contrast gain control (fast, ≈100 ms) are at work all over the place, and be it ‘just’ to make up for the inhomogeneity of retinal sampling. The basic idea is to have the contrast transfer characteristic adapt optimally to the mean contrast, and blur reduces the contrast specifically for high spatial frequencies.

Corrugated Plaid

Compare the top and bottom gray squares for their brightness. They appear (and, indeed, physically are) equal. Moving the mouse over the image removes the red bars. Now the squares appear in a different context, and lo and behold, they do not look equal anymore.

When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material.


These are some optical illusions. There are still some that I will show in the post next week. So, follow my post every week, and you will find something that very admirable.
Keep On Spirit!!
God Bless You All.. d^^b

Eye Jitter ( An Optical Illusions)

  The phe­nom­ena on this page rely on your eye move­ments. You will be mov­ing them any­way (you can never keep your eyes re­ally still), but the demon­stra­tions are aided by mov­ing your dis­play (if pos­si­ble), or by scrolling the page in small steps.

The first sam­ple on the right called “Ouchi Il­lu­sion”. When you shake your head rapidly, or bet­ter shake the dis­play, a cen­tral disk will seg­re­gate as a dis­tinct ob­ject, which in ad­di­tion seems to be float­ing top the back­ground.

This image on the left is called “Out of Focus”. It also leads to a seem­ing shift of the cen­tral disk with re­spect to the sur­round. It is very ef­fec­tively pro­voked by the eye move­ments oc­cur­ring dur­ing read­ing. So, while you are read­ing this cast your “inner eye” to the left and watch for a seem­ing de­cou­pling of disk and back­ground. You may also ob­serve that the disk floats above the back­ground. (Image re­pro­duced with kind per­mis­sion.)

This sam­ple called “Float­ing Mo­tion”.  We needn't to shake the screen, or the sac­cades from read­ing, just by ex­ploratory eye move­ments over the image the cen­tre square “de­cou­ples”. Here the back­ground seems to move, while the cen­tral square re­mains in place, and seems to float on top. 

It's easy to practise optical illusion, right? 

You can find them and make a different thing to every picture.. 

This needn't a tool or aplication.. Even you can make it by yourselves.. 

This is a simple thing when you think it's not difficult..

In other post, I want to discussed about optic illusions and the figure of illusionist.

So, check it out.. =D

God Bless You.. ^^

Real Or Illusion? o_O

An out of body experience is an experience that is owned by a few people. Some of them claimed to have seen his soul out of his body and floated to a place that they do not even know. But actually it is something that can be explained by logic and rationality.Experience they can get from different things. For example, because of the influence of drugs, physical trauma, pressure from a variety of things, and others. For a more detailed explanation of this phenomenon, see the explanation below:
In simple terms this phenomenon is caused by a disturbance in one part of the brain that processes the sensing chamber and its relationship to our bodies. in normal conditions, these brain regions provide feedback about our body position, so that in the absence of any visual information that we receive, we can know exactly where your feet are and we can move our hands feel it, even at the time of darkness. In certain circumstances, part of the disorder so as to provide a false picture of the position of the body, coupled with the inability of the person to move the body, it is the perceived loss of control of the body which is then projected outside the body.
From the results of scientific research, we find that the experience of the soul that comes out of the body is the result of processes in the human brain. And if it is the result of the human brain, then how about an illusion? is also the same illusions with hallucinations?
If in a previous post we talked about the illusion, so now we will discuss about the hallucinations. Because of illusions and hallucinations linked to each other and are inseparable.
According to the Wikipedia dictionary Hallucinations are perceptions in a conscious state without any real stimulus to the senses. Quality of perception is perceived by people with very clear, substantial and in fact came from outer space. This definition can distinguish hallucinations to dreams, fantasy, illusion and pseudohalusinasi (not the same as the real perception, but not under controlled conditions). Examples of this phenomenon is when someone is having vision problems, which he thought he saw an object, but the sense of vision that others can not capture the same object.
Hallucinations also be distinguished from delusions on perception, where sensory stimuli capture the real, but real perception that the receipt was given different meanings and (bizzare). So that more people are delusional to believe in things that are or are not into logic.
Hallucinations can be divided based on the senses that react when these perceptions are formed, namely :

^^ Visual hallucinations

Visual hallucinations is a hallucination involving the sense of sight. Vision is the ability to recognize and interpret light, one of the senses. Organs that used to look at is the eyes. Many animals are not too keen senses of vision and use other senses to recognize its environment, such hearing to bat. Decreased the power of human vision can use a tool or lasik surgery to correct vision.

^^ Auditory hallucinations

Auditory hallucinations is a hallucination involving the sense of hearing. Hearing is the ability to recognize the voice. In humans and vertebrate animals, this is done mainly by the auditory system that consists of the ear, nerves, and brain.
Not all sounds can be recognized by all animals. Some species can recognize certainamplitude and frequency. Humans can hear from 20 Hz to 20,000 Hz. When forced tohear very high frequencies continuously, the auditory system may be damaged.

^^ Olfactory hallucinations

Olfactory hallucinations is a hallucination involving the sense penciuman.Penciuman or olfaksi, is the feeling ofcatching or smell. This feeling is mediated by sensory cells in the nasal cavitytespesialisasi vertebrates, and by analogy, sensory cells in the antennae of invertebrates.Air inhaler for animals, the olfactory system detects chemicals asiri or, in the case ofaccessory olfactory system, the liquid phase. In the organisms that live in water, such asfish or crustaceans, the chemicals contained in water in the surrounding medium. Smell, like taste, is a form of kemosensor. Chemicals that activate the olfactory system, usuallyin very small concentrations, are called odors.

^^ Hallucinations gustatory

Hallucinations gustatory is a hallucination involving the sense of taste. Taste or gustasi is a form of directchemoreceptors and is one of the five traditional senses. This sense refers to the ability to detect the flavor of a substance such as food or poison. In humans and many othervertebrates, the senses of taste associated with the sense of smell in the brain's perception of taste. Classical taste sensations include sweet, salty, sour, and bitter.Later, experts psychophysical and neuroscience proposes to add another category,especially savory (umami) and fatty acids.
Taste is a sensory function of the central nervous system. Taste receptor cells in humansare found on the surface of the tongue, soft palate, and pharynx and epiglottis epithelium.

^^  Tactile hallucinations

Tactile hallucinations is a hallucination involving the sense of palpability in the skin. Because there is a layer onthe skin that can stimulate and respond to stimuli that exist outside the body. So that the stimulus or stimuli that can be channeled by the receptors to the brain for processing.

To be able to distinguish between illusion and hallucination, try to answer the questionbelow:
The question below is the question of illusion. Try to think, then you will get the answer.Good luck .. ^ ^

How many faces are depicted in this tree?

This is the answer :

There are 10 faces. Can you find all of the faces?

Are you able to distinguish it now?
It's easy and simple right?
Follow the next post about illusion, then you will be able to better understand this topic.Wait for the post next week with an episode that is not less interesting with this post.
God bless you all .. ^ ^
Keep on the spirit!