Research Paper Assignment on Sensory Illusions

Sensory Illusions

Sensory illusions are distortions of the brain that make it to perceive an object as different from the real external stimulus. Illusions represent essential tools in perceptual research, as they depict areas in the visual cortex that are vital in perception and awareness. The most common sensory illusions include auditory illusions (hearing), visual illusions (seeing), gustatory illusions (taste), tactile illusions (touch), and olfactory illusions (smell). Much of psychological and philosophical studies on perception focus on vision, as visual senses are quite strong in interpreting objects. Some illusions can occur due to illnesses or mental disorders. According to the Gestalt theory, people tend to perceive things in terms of meaningful blueprints or groups, instead of seeing separate parts. Although it is rare for the brain to get something wrong, some studies have suggested that having illusions is a sign of proper functioning of the brain, as it senses confusing situations. Sensory anchors usually vary within an individual under different situations, and in some cases, an individual can be misled by properties of consequent stimuli.

  • Auditory Illusions

Every individual with a working auditory system understands the aspect of hearing, thus experiencing auditory consciousness. In our day-to-day’s activities, the sounds that we may wish to hear may be altered by background noise, making some of the information to disappear. However, our brains have a tendency of filling in the gaps with what they perceive as the right information. The auditory illusion involves inaccurate perception of hearing when an acoustic stimulus is being conveyed through the auditory pathways (Perry 228). The listener usually hears sounds that are not there in the stimulus as he/she fills the gaps. Such illusions underscore areas where the person’s ear and brain diverge from the perfect audio receptors. The spontaneous modulations that occur in sluggish evoked auditory cortical alternations can determine the perceived continuity of disjointed sounds in noise. This occurrence depicts that the suppressive effect has always been available even before an illusion to fill the gaps.

In addition, an “impossible sound” may be an auditory illusion, where the listener hears a missing frequency in a series of harmonic sounds. Auditory illusions are usually common when listening to music or a speech, as the brain has a tendency to load the unexpected gaps of incoming events with rational predictions of what ought to be there (Scharine and Letowski 580). An example of auditory illusion is the increasing beat, where the mind takes hold of any pattern of sound, which is then repeated and perceived as a rhythm. The illusion occurs when the beat is made as if it is increasing in speed, but actually, it is not. 

Seeing lips moving in a noisy environment even when no speech is present could lead to auditory illusion. Such illusions can trigger people to invent devices that could assist people with hearing problems in the future. In addition, when individuals listen to other people talking in foreign language, they perceive it as music. The component of the brain responsible for processing sounds into speech usually gives up, and only pitches are allowed to go through the brain. When an individual is singing along with the music being played through the media player, he/or she fills the gaps with his/her own words to make the song seem sensible. Nonetheless, individuals do not hear all the speech sounding like music, but the general acoustic theory purports that they should hear such speeches as music. 

  • Visual illusions

The humans’ visual experience enables them to analyze various interactions between observable electromagnetic waves and other objects found in the environment. Individuals’ experience on vision is quite strong, as it can create a mosaic of two-dimensional object into a three-dimensional figure through perception. Visual illusions, or optical illusions, involve having visual images that are quite different from the reality. This can happen when the eyes see something, but transfer a different image to the brain. The information that the eyes record and transfer to the brains may diverge from the physical measurement found in individuals’ stimulus source. The image in the brain may fail to conform to the physical description of the source. Visual illusions can operate in numerous ways. The most perplexing visual illusion involves systematic distortions of shapes. Their explanation can be quite challenging, but acceptable, since a practical theory of perception can justify the shapes and offer a basic perceptual process. According to The simplest distortion illusion by Poggendorf in 1860, depicted a visual illusion where a straight line cutting through a rectangle tended to be displaced (Gregory 2). This is shown in Figure 1 below.

Fig 1: Poggendorf Illusion

Visual illusion offers the basis to study how individuals perceive the world, and conditions that compel them to fill gaps on visual images to create what they want to register in their minds. Emphasis on visual illusions is on the attractiveness of the perceptual phenomena, as well as the justification of the visual mechanisms involved. The most troubling visual illusion usually combines numerous activities, all working in one direction to stress the error of interpretation, which the visual system is trying to make. As children, the study of railroad tracks showed a horizon as the end of the track, but that was just a point where our eyes could manage to see, and not the end of the railroad track. An artistic illusion has the capacity to manipulate elements to generate something that did not exist in the physical realm of reality. However, pilots are advised to exercise their mental imagination as they approach runways to avoid aerial perspective illusions, where the brain can increase or decrease the inclination of the runway.

Visual illusions have been critical in the study of conscious awareness.  In the study of motion illusions, perceptual errors could be described by assuming that the brain is pursuing a perfect set of computational rules. Other examples of a visual illusion include a situation when one is watching a ventriloquist, where the audience thinks that the puppet is actually speaking, rather than the puppeteer. The visual system is utilized in interpreting shadows and contrast in geometric illusions. By exploiting the two properties through visual perception, an individual can create an optical illusion by making two squares that are placed on a checkerboard seem to have different hues, whereas in reality, they have the same shade of color. Everything created through Photoshop is essentially visual illusion, as it involves adding elements to a digitized image, which were not there initially (Palermo 6).

Visual illusion can also occur when the neutral circuitry in individual’s visual system evolves to a system that creates an efficient explanation of the usual three-dimensional outlook. The cognitive illusions emerge when individuals interact with the world, resulting to unconscious inferences. Some of the cognitive illusions include paradox illusions, where objects appear to be paradoxical or impracticable. A Penrose triangle is the best example of paradox illusion.  Visual illusions generate an aftereffect phenomenon, which occurs when an individual stares an object that move in one direction for a considerable time, making immobile objects seem to move on the opposite direction. This is a physiological illusion, and occurs due to excessive stimulation of the brains through bright lights. Thus, when interpreting complex images the brains have to recognize the main object and consign other parts to the background. An illusion becomes fundamental because it helps an individual to create an impression that fits him/her, regardless of whether it is right or not right.

  • Gustatory illusions

Tastes are usually goes along with tactile stimulation. Gustation is a neural process that is involved in transportation of information to the brain through specific taste while gastrointestinal fibers are incorporated to engage organism in appropriate feeding behavior (Simon et al. 890). Although food flavors are perceived through the tongue, the nose, as well as eyes, the human brains interpret the entire sensation from the mouth. All sensory information is received from the mouth, as the tongue come into contact with the food. This sensation is similar to both touch and vision, as they also use the body as the point of reception. Gustatory illusions usually focus on taste and are usually associated to bad or foul taste. Human beings have a way of distinguishing between safe and harmful foods through their senses. Illusions of taste are normally expressed as sour, bitter, or metallic, or in some instances, as indescribable (Roberts et al. 250). Prior tastes may lead to gustatory illusions. Such tastes are capable of causing gustatory illusion because individuals tend to consume something with a preconceived impression of its taste. Thus, when individuals make claims on taste, it is essential to inquire from them about what they may have eaten or drank earlier. 

Gustatory illusions are at their peak when something has been tasted and a preconceived idea has already been made concerning the taste. Individuals are likely to eat foods that they are familiar with their taste, and they are likely to be misled by tastes while ordering foods in the restaurants. A gustatory experience depicts that some tastes are already in individual’s mouth or lips while at the same time, it is not possible to verify such tastes, thus, creating an illusion of taste. In most cases, the values of wines are determined through taste, thus, there is a possibility that gustatory illusion is quite strong in determining such values. Experience bartenders often consider this while serving their customers.

Sick people usually experience gustatory illusions due to their medications. People suffering from stroke are sometimes reported to experience gustatory misperceptions (Ferro 46). Most patients who experience the illusion of taste will either brush their teeth or drink water to eliminate such taste, but their efforts seem to be fruitless. The presence of ischemic or hemorrhagic lesion with their posterior circulation makes such patients experience bad taste, as they do not have the capacity to detect real tastes.

  • Tactile Illusions

Human beings are capable of experiencing wrong perceptions through touching. They believe that the test of reality of any object is through touching. Tactile illusions occur when human perception of an object through touching fails to concur with the physical stimulus. While visual and auditory illusions are quite common and verifiable, tactile illusions are quite difficult to measure and substantiate. This is because speaking is rare in touching, as touching depends on the sensory modalities (Chalmers 449). The sense of touch can be easily ignored if it is not at its extremes, but this is the sense that confirms the reality to other senses, and is usually subjected to indistinct sources of information that are likely to generate touch-based illusions.

Haptic perception, or the sense of grasping, usually interacts with other human senses to offer judgment and perceptual estimates. The brain areas that are activated when the tactile illusions happen are the same as those activated when the actual tactile stimulation happens (Shergill 131). Tactile illusions may go unnoticed, as they do not occur frequently. One of the examples of tactile illusions is Aristotle’s illusion. In this illusion, an object touching crossed fingertips is viewed as two objects through a blindfolded subject. The same object is correctly viewed as one when placed between two fingers that are parallel to each other. Running the middle fingers along the nose’s bridge while each finger is on each side results to perception of two different noses (130). The illusion sensation usually occurs because the brain has refused to register that you have already closed the fingers.

The phantom limb is another example of tactile illusion, which involves having a sensation that a missing limb could still be attached to individual’s body and still functioning like other limbs. Phantom sensation can also be felt after the removal of the broken limb, and the person affected could just feel like the limb is shorter, or is in a disfigured position. Emerging technologies have provided mechanisms to ensure that patients with artificial limbs are capable of feeling their limbs through touch. Some tactile illusions result from mental illnesses. For instance, delusional parasitosis is a condition where an individual is falsely convinced that small creatures are overrunning his/her skin (Ferro 44). Although the victim may not talk about it, he/she may feel uneasy and will try to find out whether the feeling is real. This type of delusion usually happens when cortical brain region on the right hemisphere is destroyed.  

  • Olfactory Illusions

Every object that individuals smell usually release some molecules, which are drifted by air towards olfactory cells that incorporate sensitive nerve endings in their nostrils. Receptors in the nostrils usually adapt quickly to a certain stimulus. Olfactory illusions are influenced by certain odors that the olfactory structures have already adapted. Sensory nerves in the nose usually adapt fast to odors, and may cease to respond to certain stimulus. An odor that tends to be strong initially will slowly become imperceptible, just as when an individual becomes oblivious of his/her own body smell. A person may also experience a decrease in sensitivity to a particular odor after being exposed to a new type of odor. Many people are unaware of olfactory sensation until they suffer from cold or flu.

It is rarely possible to encounter a health person with olfactory illusions, thus, anyone experiencing such illusion should be handled with utmost care. This type of illusion is common among mentally ill patients, as large number of people with illusion of smell perceive it through imaginations. If a person walks in the kitchen and experiences a sweet aromatic smell, he/she may not be sure what kind of food that is being cooked, until somebody tells him/her that rice was is being cooked. That person will only be capable of associating that smell with rice because somebody has said so.

Olfactory experience is temporary and discontinuous. This is because access to odorant molecules of the sensory neurons are controlled by sniffs, thus, modulating the sniffing behavior alters olfactory experience. Many odors hang in the air and people tend to associate them with whatever they may be imagining at a particular moment. Olfactory experiences do not enable individuals to relate certain smell to a single object, thus, enhancing the possibility of illusions. This is unlike vision experience where individuals can see the object in the vision. An individual may begin to smelling a dead rat in the house if he/she imagines that there might be a rat in the house. It is possible for an individual to generate olfactory illusion by referring to one type of odor in different names.

Since olfactory experiences do not involve objects, some researchers have suggested that olfactory illusions are not applicable to human activities. According to Stevenson, many people are typically unaware of olfactory illusions, and this may prove that olfactory illusions do not exist, but it is only because they do not regard the subjective nature of illusion (Batty 4). The notion that smells are not related to particular objects does not stick to human minds because the concepts of olfactory sensation do not hold up this claim. Some people usually refer to some odors as “sweet” for lack of better term, but this is unusual perception in olfactory experience, as perceptual recognition of sweetness is usually confirmed by a receptor in the tongue (Stevenson 1893). The odor quality may not be uniform, but people maintain the same perception about a certain object of odor. For instance, people relate coffee with a particular odor, despite substantial disparity in the chemical constituents in coffee. 


Illusions are perceptions, which act against the physical arrangements of individuals’ stimulus situations. Each of the five senses in humans has a sensory receptor that detects what to send to the brain. When the sensory stimulus is still active but perceives objects or information incorrectly, an illusion occurs. Auditory illusions occur when an individual experiences inaccurate perception of hearing when an audio stimulus is being transferred through the auditory pathways. The listener usually receives sounds that are not there in the stimulus, but his/her brain is engaged in filling the gaps to make sense of the speech. Visual illusions happen when a person perceives visual images that vary from the reality. This can occur when the eyes see something, but record different images to the brain. Gustatory illusions involve perceiving different tastes that are usually bad or fouled. Tactile illusions happen when human perception of an object through touching differs from the physical stimulus while olfactory illusions occur when an individual fails to differentiate different smells. Sensory illusions disfigure reality, and happen more in the human senses than in their vision. However, it is quite rare for the brain to be misled; that is why we do not make many mistakes, as the brain perceives most of the information right.

Works Cited

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Ferro, José M. Neuropsychiatric Symptoms of Cerebrovascular Diseases. London: Springer, 2013. Internet resource.

Gregory, Richard L. “Perceptual illusions and brain models.” Proceedings of the Royal Society of London. Series B, Biological Sciences (1968): 279-296.

Palermo, Amy. “Don’t be Fooled by the Complexity of Illusions.” Inside Photoshop 04 2006: 6-9. ProQuest. Web. 24 Apr. 2015.

Perry, E K. New Horizons in the Neuroscience of Consciousness. Amsterdam: John Benjamins Pub, 2010. Print.

 Roberts, Richard J, Mary A. Roberts, Jody R. Murph, George Phillips, and William Sheehan. Mild Traumatic Brain Injury: Episodic Symptoms and Treatment. , 2011. Internet resource.

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Simon, Sidney A., et al. “The neural mechanisms of gustation: a distributed processing code.” Nature Reviews Neuroscience Nov. 2006: 890+. Academic Search Premier. Web. 25 Apr. 2015.

Stevenson, Richard J. “Olfactory illusions: Where are they?” Consciousness and cognition 20.4 (2011): 1887-1898.