Nothing

Sense data are supposed representation of real objects in the world outside the mind, about whose existence and properties we often can be mistaken.

According to the theory, sense data objects appear to us exactly as they are. For example, when we turn a coin it appears to us as elliptical. This appearance is not identical with the coin, since the coin is perfectly round. Therefore it is sense data, which somehow represents the round coin to us.

Another example is the reflection which appears to us in a mirror. There is nothing corresponding to the reflection in the world external to the mind, for our reflection appears to us as the image of a human being apparently located inside a wall or a wardrobe. The appearance is therefore a mental object, a sense data object.

From a subjective experience of perceiving something, it is theoretically impossible to distinguish something which exists independently of oneself from an hallucination or mirage. Thus, we do not have any direct access to the outside world that allows us to distinguish it from an illusion based on identical sense data.

Distortion

Phantom rings are the sensation and the false belief that one can hear his or her mobile phone ringing or feel it vibrating, when in fact the telephone is not doing so. Other terms for this concept include ringxiety and fauxcellarm. Some sound experts believe that because cellphones have become a fifth limb for many, people now live in a constant state of phone vigilance, and hearing sounds that seem like a telephone’s ring can send an expectant brain into action.

They may be experienced while taking a shower, watching television, or using a noisy device. Humans are particularly sensitive to auditory tones between 1,000 and 6,000 hertz, and basic mobile phone ringers often fall within this range. This frequency range can generally be more difficult to locate spatially, thus allowing for potential confusion when heard from a distance. False vibrations are less understood, however, and could have psychological or neurological sources.

In addition to cellular phones, other attention grabbing devices such as sirens, trucks backing up, horns or crying babies in a commercial message have been generically labeled as phantom ringing. Some doorbells or telephone ring sounds are modeled after pleasant sounds from nature. This backfires when such devices are used in rural areas containing the original sounds. The owner is faced with the constant task of determining if it is the device or the actual sound.

Separation

Rubin’s vase is a famous set of cognitive optical illusions developed around 1915 by the Danish psychologist Edgar Rubin. The illusion generally presents the viewer with a mental choice of two interpretations, each of which is valid. Often, the viewer sees only one of them, and only realizes the second valid interpretation after some time or prompting. When the viewer attempts to simultaneously see the interpretations together, they suddenly cannot see the first interpretation anymore, and no matter how they try they simply cannot encompass both interpretations simultaneously; one occludes the other.

The illusions are useful because they are an intuitive demonstration of the figure-ground distinction the brain makes during visual perception. Rubin’s figure-ground distinction influenced the Gestalt psychologists, who discovered many similar illusions themselves. It involves higher-level cognitive pattern matching in which the overall picture determines its mental interpretation, rather than the net effect of the individual pieces.

Normally the brain classifies images by what surrounds what, establishing depth and relationships. If something surrounds another thing, the surrounded object is seen as figure, and the presumably further away (and hence background) object is the ground, and vice versa. This makes sense, since if a piece of fruit is lying on the ground, one would want to pay attention to the “figure” and not the “ground”.

However, when the contours are not so unequal, ambiguity starts to creep into the previously simple inequality and the brain must begin “shaping” what it sees. It can be shown that this shaping overrides and is at a higher level than feature recognition processes that pull together the face and the vase images. One can think of the lower levels putting together distinct regions of the picture (each region of which makes sense in isolation), but when the brain tries to make sense of it as a whole, contradictions ensue, and patterns must be discarded.

Comparison

Illusory superiority is a cognitive bias that causes people to overestimate their positive qualities and abilities and to underestimate their negative qualities, relative to others. This is evident in a variety of areas including intelligence, performance on tasks or tests and the possession of desirable characteristics or personality traits. It is one of many positive illusions relating to the self, and is a phenomenon studied in social psychology.

It is often referred to as the above average effect. Other terms include superiority bias, leniency error, sense of relative superiority, and the Lake Wobegon effect (named after Garrison Keillor’s fictional town where “all the children are above average”).

Illusory superiority has been found in individuals’ comparisons of themselves with others in a wide variety of different aspects of life, including performance in academic circumstances (such as class performance, exams and overall intelligence), in working environments (for example in job performance), and in social settings (for example in estimating one’s popularity, or the extent to which one posesses desirable personality traits, such as honesty or confidence), as well as everyday abilities requiring particular skill.

For illusory superiority to be demonstrated by social comparison, two logical hurdles have to be overcome. Some psychological experiments require subjects to compare themselves to an average peer. If we interpret the average as the mean, then it is logically possible for nearly all of the set to be above average if the distribution of abilities is highly skewed. Hence experiments usually compare subjects to the median of the peer group, since by definition it is impossible for most of the set to do better than the median.

A further problem in inferring inconsistency is that subjects might interpret the question in different ways, so it is logically possible that a majority of them are, for example, more generous than the rest of the group each on their own understanding of generosity.

Simulation

A false awakening is an event in which someone dreams they have awoken from sleep. This illusion of having awakened is very convincing to the person. After a false awakening, people will often dream of performing daily morning rituals, believing they have truly awakened. A dream in which a false awakening takes place is sometimes colloquially referred to as a double dream, or a dream within a dream.

It may occur either following an ordinary dream or following a lucid dream in which the dreamer has been aware of dreaming. Particularly if the false awakening follows a lucid dream, the false awakening may turn into a pre-lucid dream, or one in which the dreamer may start to wonder if they are really awake and may or may not come to the correct conclusion.

A false awakening has significance to the simulation hypothesis which states that what we perceive as reality is in truth an illusion as evidenced by our minds’ inability to distinguish between reality and dreams. Therefore, advocates of the simulation hypothesis argue that the probability of our true reality being a simulated reality is affected by the prevalence of false awakenings.

Certain aspects of life may be dramatized or out of place in false awakenings. Things may seem wrong. Details, like viewing a painting on a wall, not being able to talk or difficulty reading are often difficult or impossible. In some experiences, the subject’s senses are heightened, or changed.

Another more realistic type of false awakening, is a continuum. In a continuum, the subject will fall asleep in real life, but in the dream following, the brain will simulate the subject still awake.

Being

The “dream argument” is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine if it is in fact “reality.”

While people dream, they usually do not realize they are dreaming. This has led philosophers to wonder whether one could actually be dreaming constantly, instead of being in waking reality, or at least that one can’t be 100% certain that he or she is not dreaming. In the West, the philosophical puzzle is referred to in writings as early as Plato and Aristotle. Having received serious attention in René Descartes’ Meditations on First Philosophy, the dream argument has become one of the most popular skeptical hypotheses.

In the East, this type of argument is well known as “Zhuangzi dreamed he was a butterfly”. It relates that one night Zhuangzi dreamed that he was a carefree butterfly flying happily. After he woke up, he wondered how he could determine whether he was Zhuangzi who had just finished dreaming he was a butterfly, or a butterfly who had just started dreaming he was Zhuangzi. This was a metaphor for what he referred to as a “great dream.”

He who dreams of drinking wine may weep when morning comes; he who dreams of weeping may in the morning go off to hunt. While he is dreaming he does not know it is a dream, and in his dream he may even try to interpret a dream. Only after he wakes does he know it was a dream. And someday there will be a great awakening when we know that this is all a great dream. Yet the stupid believe they are awake, busily and brightly assuming they understand things, calling this man ruler, that one herdsman ‑ how dense! Confucius and you are both dreaming! And when I say you are dreaming, I am dreaming, too. Words like these will be labeled the Supreme Swindle. Yet, after ten thousand generations, a great sage may appear who will know their meaning, and it will still be as though he appeared with astonishing speed.

Chance

Automatic drawing was developed by the surrealists as a means of expressing the subconscious. In automatic drawing, the hand is allowed to move randomly across the paper. In applying chance and accident to mark making, drawing is to a large extent freed of rational control. Hence the drawing produced may be attributed in part to the subconscious and may reveal something of the psyche, which would otherwise be repressed.

Artists who practised automatic drawing include Joan Miró, Salvador Dalí, Jean Arp and André Breton. The technique was transferred to painting, as seen in Miró’s paintings which often started out as automatic drawings, and has been adapted to other media. Most of the surrealists’ automatic drawings were illusionistic, or more precisely, they developed into such drawings when representational forms seemed to suggest themselves.

In the 1940s and 1950s the French-Canadian group called Les Automatistes pursued creative work based on surrealist principles. They abandoned any trace of representation in their use of automatic drawing. This is perhaps a more pure form of automatic drawing since it can be almost entirely involuntary. To develop a representational form requires the conscious mind to take over the process of drawing, unless it is entirely accidental and thus incidental.

The computer, like the typewriter, can be used to produce automatic writing and automatic poetry. The practice of automatic drawing, originally performed with pencil or pen and paper, has also been adapted to mouse and monitor, and other automatic methods have also been either adapted from non-digital media, or invented specifically for the computer. For instance, filters have been automatically run in some bitmap editor programs such as Photoshop. One of the newest applications of this approach is Dynamic Painting by San Base.

Return

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.

The acoustical illusion can be constructed by creating a series of overlapping ascending or descending scales. Similar to the Penrose stairs optical illusion, as in M. C. Escher’s lithograph Ascending and Descending, or a barber’s pole.

As an example, consider a brass trio consisting of a trumpet, a horn, and a tuba. They all start to play a repeating C scale in their respective ranges, i.e. they all start playing Cs, but their notes are all in different octaves. When they reach the G of the scale, the trumpet drops down an octave, but the horn and tuba continue climbing. They’re all still playing the same pitch class, but at different octaves. When they reach the B, the horn similarly drops down an octave, but the trumpet and tuba continue to climb, and when they get to what would be the second D of the scale, the tuba drops down to repeat the last seven notes of the scale. So no instrument ever exceeds an octave range, and essentially keeps playing the exact same seven notes over and over again. But because two of the instruments are always “covering” the one that drops down an octave, it seems that the scale never stops rising.

Jean-Claude Risset subsequently created a version of the scale where the steps between each tone are continuous, and it is appropriately called the continuous Risset scale or Shepard–Risset glissando. When done correctly, the tone appears to rise continuously in pitch, yet return to its starting note. Risset has also created a similar effect with rhythm in which tempo seems to increase or decrease endlessly.

Although it is difficult to recreate the illusion with acoustic instruments, James Tenney, who worked with Roger Shepard at Bell Labs in the early 1960s, created a piece utilizing this effect, For Ann. The piece, in which up to twelve closely but not quite consistently spaced computer-generated sine waves rise steadily from an A pitched below audibility to an A above, fading in, and back out, of audible volume, was then scored for twelve string players. The effect of the electronic work consists both of the Shepard scale, seamless endlessly rising glissandos, and of a shimmering caused by the highest perceivable frequency and the inability to focus on the multitude of rising tones. Tenney has also proposed that the piece be revised and realized so that all entrances are timed in such a way that the ratio between successive pitches is the golden ratio, which would make each lower first-order combination tone of each successive pair coincide with subsequently spaced, lower, tones.

An independently discovered version of the Shepard tone appears at the beginning and end of the 1976 album A Day At The Races by the band Queen. The piece consists of a number of electric-guitar parts following each other up a scale in harmony, with the notes at the top of the scale fading out as new ones fade in at the bottom. Echoes, a 23-minute song by Pink Floyd, concludes with a rising Shepard tone. The Shepard tone is also featured in the fading piano outro to A Last Straw, from Robert Wyatt’s 1974 opus Rock Bottom.

Repetition

A false awakening is an event in which someone dreams they have awoken from sleep. This illusion of having awakened is very convincing to the person. After a false awakening, people will often dream of performing daily morning rituals, believing they have truly awakened. A dream in which a false awakening takes place is sometimes colloquially referred to as a double dream, or a dream within a dream.

It may occur either following an ordinary dream or following a lucid dream, one in which the dreamer has been aware of dreaming. Particularly if the false awakening follows a lucid dream, the false awakening may turn into a pre-lucid dream, in which the dreamer may start to wonder if they are really awake and may or may not come to the correct conclusion.

A false awakening has significance to the simulation hypothesis which states that what we perceive as true reality is in fact an illusion as evidenced by our minds’ inability to distinguish between reality and dreams. Therefore, advocates of the simulation hypothesis argue that the probability of our true reality being a simulated reality is affected by the prevalence of false awakenings.

Certain aspects of life may be dramatized or out of place in false awakenings. Details like being able to see a painting on a wall, not being able to talk or difficulty reading are common. In some experiences, the human senses are heightened or changed. For instance, one may be able to see things in greater detail, or lesser detail, or one may feel an intense burst of fear and anxiety, or possibly pleasure.

Because the dreamer is still dreaming after a false awakening, it is possible for there to be more than one false awakening in a single dream. Often, dreamers will seem to have awakened, begin eating breakfast, brushing teeth, and so on and then find themselves back in bed, begin daily morning rituals, believe that they have awakened again, and so forth. The French psychologist Yves Delage reported an experience of his own of this kind, in which he experienced four successive false awakenings. The philosopher Bertrand Russell claimed to have experienced about a hundred false awakenings in succession while coming round from a general anaesthetic.

Postulation

The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine if it is in fact reality.

While people dream, they usually do not realize they are dreaming. This has led philosophers to wonder whether one could actually be dreaming constantly, instead of being in waking reality (or at least that one can’t be certain that he or she is not dreaming). Having received serious attention in René Descartes’ Meditations on First Philosophy, the dream argument has become one of the most popular skeptical hypotheses.

Dreaming provides a springboard for those who question whether our own reality may be an illusion. The ability of the brain to trick itself into believing a neuronally generated world is the real world means at least one variety of simulated reality is a common, even nightly event.

Those who argue that the world is not simulated must concede that the mind, at least the sleeping mind, is not itself an entirely reliable mechanism for attempting to differentiate reality from illusion.

This could be seen as a challenge to those who claim a simulated reality requires highly advanced scientific technology, since, if dreaming really is a form of virtual reality, the only apparatus needed to construct a simulated reality capable of fooling the unconscious mind is a human brain.

In Lewis Carroll’s Through the Looking-Glass, Alice finds the Red King asleep in the grass. Tweedledum and Tweedledee tell her that the Red King is dreaming about her, and that if he were to wake up she would “go out—bang!—just like a candle.”