The object ofsensation and also perception are amongst the oldest and also most vital in all ofpsychology. World are equipped with senses such as sight, hearing and tastethat help us to take it in the world roughly us. Amazingly, ours senses have actually theability to transform real-world information into electric information the canbe processed by the brain. The means we analyze this information-- ourperceptions-- is what leads to our experience of the world. In this module,you will certainly learn around the organic processes that sensation and how these have the right to becombined to produce perceptions.

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Learning Objectives

Differentiate the procedures of sensation and perception.Explain the simple principles that sensation and also perception.Describe the role of every of ours senses.Outline the anatomy that the sense organs and also their projections come the worried system. Apply understanding of sensation and perception to real world examples.Explain the aftermath of multimodal perception.Introduction

"Once ns was hiking in ~ Cape Lookout State Park in Tillamook, Oregon. After passing through a vibrantly colored, pleasantly scented, warm rainforest, I landed on a cliff overlooking the Pacific Ocean. I ordered the cold steel railing close to the edge and also looked the end at the sea. Below me, I might see a pod that sea lions swim in the deep blue water. All roughly me I can smell the salt native the sea and the scent of wet, collapse leaves." 

This description of a solitary memory highlights the method a who senses room so essential to our suffer of the world around us.

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Our senses incorporate to develop our awareness of the world.

Before stating each of our extraordinary senses individually, that is crucial to cover some simple concepts that apply to every one of them. That is probably best to begin with one very important difference that can regularly be confusing: the difference in between sensation and perception. The physical procedure during which ours sensory organs—those affiliated with hearing and also taste, because that example—respond to external stimuli is dubbed sensation. Emotion happens as soon as you eat noodles or feel the wind ~ above your challenge or hear a automobile horn honking in the distance. Throughout sensation, our feeling organs are engaging in transduction, the switch of one form of power into another. Physical power such together light or a sound tide is converted into a form of power the mind can understand: electric stimulation. ~ our brain receives the electrical signals, we make sense of all this stimulation and also begin to appreciate the facility world approximately us. This psychological process—making feeling of the stimuli—is dubbed perception. That is during this process that you space able come identify a gas leak in your home or a track that reminds you of a certain afternoon spent with friends.

Regardless of even if it is we are talking around sight or taste or any of the individual senses, there are a number of basic values that influence the method our sense organs work. The an initial of these impacts is our capacity to detect an exterior stimulus. Each sense organ—our eye or tongue, for instance—requires a minimal lot of stimulation in order to detect a stimulus. This absolute threshold explains why you don’t smell the perfume who is wearing in a classroom unless they are rather close to you. Because absolute threshold alters throughout the day and also based top top what other stimuli you have recently experienced, researchers define absolute threshold together the minimum around of stimulation necessary to detect a economic stimulation 50% the the time.

The way we measure pure thresholds is by utilizing a method called signal detection. This procedure involves presenting stimuli of varying intensities to a research study participant in stimulate to recognize the level at which that or she have the right to reliably detect stimulation in a given sense. During one form of hear test, because that example, a human being listens to progressively louder tones (starting from silence). This form of check is called the an approach of limits, and it is an initiative to recognize the point, or threshold, in ~ which a person begins to listen a economic stimulation (see additional Resources for a video demonstration). In the example of enlarge tones, the technique of boundaries test is using ascending trials. Some an approach of borders tests use descending trials, such together making a light prosper dimmer till a person can no much longer see it. Appropriately indicating that a sound to be heard is called a hit; failing to do so is dubbed a miss. Additionally, indicating that a sound was heard once one wasn’t played is called a false alarm, and also correctly identifying as soon as a sound wasn’t played is a correct rejection.

Through these and other studies, we have actually been able to get an expertise of just just how remarkable our senses are. Because that example, the person eye is qualified of detecting candlelight indigenous 30 miles away in the dark. Us are also capable of hearing the ticking the a clock in a quiet environment from 20 feet away. If you think that’s amazing, ns encourage you to read an ext about the too much sensory capabilities of nonhuman animals; many pets possess what us would take into consideration super-human abilities.

A comparable principle to the pure threshold discussed above underlies our capability to recognize the difference between two stimuli of different intensities. The differential threshold (or difference threshold) or just noticeable difference (JND), because that each sense has actually been learned using comparable methods to signal detection. To illustrate, find a friend and a couple of objects of known weight (you’ll need objects that sweet 1, 2, 10 and also 11 lbs.—or in metric terms: 1, 2, 5 and 5.5 kg). Have your friend hold the lightest object (1 lb. Or 1 kg). Then, change this object through the next heaviest and ask that or she to tell girlfriend which one weighs more. Reliably, your friend will say the 2nd object every solitary time. It’s very easy to tell the difference when something weighs dual what another weighs! However, it is not so easy once the difference is a smaller percent of the overall weight. It will certainly be much harder for her friend come reliably call the difference between 10 and 11 lbs. (or 5 matches 5.5 kg) 보다 it is for 1 and also 2 lbs. This is phenomenon is dubbed Weber’s Law, and it is the idea the bigger stimuli need larger differences to be noticed. As v the pure threshold, your ability to notification differences varies throughout the day and based ~ above what other stimuli you have recently knowledgeable so the difference threshold is characterized as the smallest distinction detectable 50% of the time.

Crossing into the human being of perception, that is clear the our suffer influences how our mind processes things. You have tasted food the you like and food that you nothing like. There space some bands you enjoy and others you can’t stand. However, throughout the time you an initial eat other or hear a band, you procedure those stimuli utilizing bottom-up processing. This is as soon as we construct up come perception native the separation, personal, instance pieces. Sometimes, though, stimuli we’ve proficient in our previous will influence how we process brand-new ones. This is referred to as top-down processing. The best way to illustrate these two concepts is with our ability to read. Review the adhering to quote out loud:

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Figure 1. An example of stimuli processing.

Notice noþeles odd while you were reading the text in the triangle? go you notification the second “the”? If not, that likely since you were analysis this from a top-down approach. Having actually a second “the” doesn’t do sense. We know this. Our mind knows this and also doesn’t expect there to be a second one, so we have actually a propensity to skip appropriate over it. In other words, your past experience has changed the method you consciousness the creating in the triangle! A start reader—one that is utilizing a bottom-up strategy by carefully attending to every piece—would be much less likely to do this error.

Finally, it must be listed that when we endure a sensory stimulus that doesn’t change, we avoid paying attention to it. This is why us don’t feeling the weight of our clothing, hear the hum the a projector in a lecture hall, or check out all the tiny scratches top top the lenses of ours glasses. As soon as a economic stimulation is consistent and unchanging, we suffer sensory adaptation. This occurs due to the fact that if a stimulus does no change, our receptors quit responding come it. A good example the this occurs as soon as we leave the radio top top in our auto after we park the at house for the night. As soon as we listen to the radio ~ above the method home from work the volume appears reasonable. However, the following morning when we start the car, we could be startled by how loud the radio is. Us don’t remember it being that loud critical night. What happened? We adjusted to the consistent stimulus (the radio volume) over the course of the vault day and increased the volume at various times. 

currently that we have actually introduced some an easy sensory principles, let united state take ~ above each among our fascinating senses individually.

Vision

How vision works

Vision is a tricky matter. When we check out a pizza, a feather, or a hammer, we room actually seeing irradiate bounce off the object and also into our eye. Irradiate enters the eye with the pupil, a tiny opening behind the cornea. The pupil regulates the amount of light entering the eye through contracting (getting smaller) in shining light and dilating (getting larger) in dimmer light. When past the pupil, light passes with the lens, i beg your pardon focuses photo on a slim layer of cell in the back of the eye, referred to as the retina.

Because we have actually two eye in various locations, the image concentrated on each retina is native a slightly different angle (binocular disparity), giving us through our tardy of 3D room (binocular vision). You can appreciate this by stop a pen in your hand, extending your eight in front of your face, and looking at the pen if closing each eye in turn. Pay fist to the obvious position of the pen relative to objects in the background. Depending upon which eye is open, the pen shows up to jump earlier and forth! This is how video game manufacturers develop the perception of 3D without one-of-a-kind glasses; 2 slightly various images room presented on height of one another.

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Figure 2. Chart of the human being eye. An alert the Retina, labeled here: this is the ar of the Cones and also Rods in the eye.

It is in the retina that light is transduced, or convert into electric signals, by specialized cells dubbed photoreceptors. The retina has two main kinds the photoreceptors: rods and also cones. Rods are mainly responsible because that our capacity to check out in dim light conditions, together as during the night. Cones, ~ above the other hand, provide us v the ability to watch color and also fine information when the light is brighter. Rods and also cones different in their distribution across the retina, with the greatest concentration the cones found in the fovea (the main region of focus), and rods dominating the periphery (see figure 2). The distinction in circulation can define why looking directly at a dim star in the sky renders it seem to disappear; there aren’t sufficient rods to procedure the dim light!

Next, the electrical signal is sent through a class of cells in the retina, eventually traveling down the optic nerve. After passing v the thalamus, this signal makes it come the main visual cortex, where information around light orientation and also movement start to come with each other (Hubel & Wiesel, 1962). Info is then sent out to a selection of different areas of the cortex for more complex processing. Few of these cortical regions are reasonably specialized—for example, for processing encounters (fusiform face area) and also body components (extrastriate body area). Damages to these areas of the cortex deserve to potentially result in a specific kind of agnosia, through which a human loses the ability to perceive visual stimuli. A an excellent example of this is illustrated in the composing of well known neurologist Dr. Oliver Sacks; he skilled prosopagnosia, the inability to identify faces. These specialized regions for visual recognition consist of the ventral pathway (also dubbed the “what” pathway). Other locations involved in processing location and also movement comprise the dorsal pathway (also called the “where” pathway). Together, this pathways procedure a big amount that information about visual stimuli (Goodale & Milner, 1992). Phenomena we frequently refer to as optical illusions carry out misleading information to this “higher” locations of visual processing (see added Resources for websites containing remarkable optical illusions).

Dark and also light adaptation

Humans have the capability to adapt to transforms in light conditions. As discussed before, rods space primarily involved in our capacity to see in dim light. They are the photoreceptors responsible for enabling us to check out in a dark room. Girlfriend might an alert that this night vision capacity takes roughly 10 minutes to turn on, a process called dark adaptation. This is since our rods come to be bleached in normal light conditions and require time to recover. We suffer the opposite result when us leave a dark movie theatre and also head out into the afternoon sun. During light adaptation, a huge number of rods and also cones space bleached at once, causing us to it is in blinded because that a couple of seconds. Light adaptation happens nearly instantly compared with dark adaptation. Interestingly, some world think pirates wore a patch over one eye in order to store it adapted to the dark while the various other was adapted to the light. If you desire to rotate on a irradiate without losing your night vision, don’t worry around wearing one eye patch, just use a red light; this wavelength doesn’t bleach her rods.

Color vision

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Figure 3. Rigid at the center of the Canadian flag because that fifteen seconds. Then, transition your eyes far to a white wall or blank piece the paper. You need to see one "after image" in a different shade scheme.

Our cones allow us to check out details in common light conditions, and also color. We have cones that respond preferentially, not exclusively, because that red, green and blue (Svaetichin, 1955). This trichromatic concept is not new; the dates earlier to the beforehand 19th century (Young, 1802; Von Helmholtz, 1867). This theory, however, go not describe the odd impact that occurs when we look at a white wall after staring at a picture for approximately 30 seconds. Try this: rigid at the photo of the flag in figure 3 for 30 seconds and then instantly look at a sheet of white file or a wall. According to the trichromatic concept of shade vision, you must see white once you execute that. Is the what girlfriend experienced? together you have the right to see, the trichromatic concept doesn’t explain the afterimage you just witnessed. This is wherein the opponent-process concept comes in (Hering, 1920). This theory claims that our cones send information to retinal ganglion cells that respond come pairs of color (red-green, blue-yellow, black-white). These committed cells take details from the cones and also compute the difference between the two colors—a process that describes why us cannot view reddish-green or bluish-yellow, and why we watch afterimages. Shade deficient vision can result from issues with the cap or retinal ganglion cells connected in color vision.

Hearing (Audition)

few of the most well-known celebrities and also top earners in the civilization are musicians. Our prayer of musicians might seem silly as soon as you think about that all they are doing is vibrating the wait a certain way to produce sound waves, the physics stimulus because that audition.

human being are qualified of obtaining a huge amount of information from the straightforward qualities that sound waves. The amplitude (or intensity) of a sound wave codes because that the loudness of a stimulus; greater amplitude sound waves an outcome in louder sounds. The pitch the a stimulus is coded in the frequency that a sound wave; greater frequency sound are greater pitched. Us can likewise gauge the quality, or timbre, the a sound through the complexity of the sound wave. This permits us to tell the difference between bright and dull sounds as well as natural and also synthesized instruments (Välimäki & Takala, 1996).

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Figure 4. Chart of the human ear. Notification the Cochlea labeled here: that is the ar of the listening Hair cells that room tonotopically organized.

In bespeak for united state to sense sound waves from our environment they should reach ours inner ear. Lucky for us, us have progressed tools that enable those tide to it is in funneled and enhanced during this journey. Initially, sound waves are funneled by your pinna (the external component of her ear the you can actually see) into your auditory canal (the feet you pole Q-tips into in spite of the crate advising versus it). During their journey, sound waves eventually reach a thin, extended membrane referred to as the tympanic membrane (eardrum), which vibrates versus the 3 smallest bones in the body—the malleus (hammer), the incus (anvil), and the stapes (stirrup)—collectively dubbed the ossicles. Both the tympanic membrane and the ossicles amplify the sound waves before they get in the fluid-filled cochlea, a snail-shell-like bone structure containing auditory hair cell arranged top top the basilar membrane (see figure 4) according to the frequency castle respond to (called tonotopic organization). Relying on age, humans can normally detect sounds in between 20 Hz and 20 kHz. It is within the cochlea the sound waves space converted into an electric message.

Because we have actually an ear on every side of our head, us are capable of localizing sound in 3D room pretty well (in the same method that having actually two eyes produces 3D vision). Have actually you ever before dropped miscellaneous on the floor there is no seeing whereby it went? go you an alert that you were somewhat capable of locating this object based on the sound that made once it struggle the ground? We deserve to reliably locate something based on which ear receive the sound first. What about the height of a sound? If both ears get a sound in ~ the same time, just how are we capable of localizing sound vertically? study in cat (Populin & Yin, 1998) and humans (Middlebrooks & Green, 1991) has pointed to distinctions in the high quality of sound waves relying on vertical positioning.

After gift processed by hear hair cells, electrical signals are sent out through the cochlear nerve (a department of the vestibulocochlear nerve) come the thalamus, and then the primary auditory cortex that the temporal lobe. Interestingly, the tonotopic company of the cochlea is preserved in this area of the cortex (Merzenich, Knight, & Roth, 1975; Romani, Williamson, & Kaufman, 1982). However, the duty of the major auditory cortex in processing the wide range of features of sound is still gift explored (Walker, Bizley, & Schnupp, 2011).

Balance and the vestibular system

The within ear no only connected in hearing; it’s additionally associated v our capacity to balance and also detect where we room in space. The vestibular mechanism is made up of 3 semicircular canals—fluid-filled bone frameworks containing cells that respond to alters in the head’s orientation in space. Information from the vestibular device is sent through the vestibular nerve (the other division of the vestibulocochlear nerve) come muscles affiliated in the activity of ours eyes, neck, and other parts of our body. This information enables us to keep our stare on things while we are in motion. Disturbances in the vestibular device can an outcome in problems with balance, including vertigo.

Touch

Who doesn’t love the soft of an old t-shirt or the smoothness of a clean shave? who actually enjoys having actually sand in their swimsuit? ours skin, the body’s biggest organ, gives us v all species of information, such together whether other is smooth or bumpy, hot or cold, or even if the painful. Somatosensation—which consists of our capability to sense touch, temperature and also pain—transduces physical stimuli, such as fuzzy velvet or scalding water, into electric potentials that can be handle by the brain.

Tactile sensation

Tactile stimuli—those that are associated with texture—are transduced by unique receptors in the skin called mechanoreceptors. Just like photoreceptors in the eye and auditory hair cell in the ear, these allow for the conversion of one type of energy into a kind the mind can understand.

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Figure 5. A illustration of the somatosensory cortex in the mind and the areas in the person body that correspond to it - lock are drawn in proportion to the many sensitive or the many innervated parts of the body.

After tactile stimuli room converted through mechanoreceptors, details is sent through the thalamus to the main somatosensory cortex for additional processing. This region of the cortex is arranged in a somatotopic map where different regions room sized based upon the sensitivity of details parts top top the opposite next of the human body (Penfield & Rasmussen, 1950). Put simply, various locations of the skin, such together lips and fingertips, are an ext sensitive 보다 others, such as shoulders or ankles. This sensitivity have the right to be stood for with the distorted proportions the the human body shown in figure 5.

Pain

Most people, if asked, would love to eliminate pain (nociception), since the sensation is really unpleasant and also doesn’t appear to have noticeable value. However the tardy of pain is ours body’s method of sending out us a signal the something is wrong and also needs ours attention. Without pain, how would we recognize when we are accidentally poignant a hot stove, or the we have to rest a strained arm after a tough workout?

Phantom limbs

Records of human being experiencing phantom four after amputations have been approximately for centuries (Mitchell, 1871). Together the surname suggests, world with a phantom limb have the emotion such as itching seemingly comes from their absent limb. A phantom limb can additionally involve phantom body pain, sometimes defined as the muscle of the absent limb uncomfortably clenching. While the mechanisms underlying this phenomena are not totally understood, there is proof to assistance that the damaged nerves indigenous the amputation website are quiet sending info to the mind (Weinstein, 1998) and also that the brain is reacting to this info (Ramachandran & Rogers-Ramachandran, 2000). There is an exciting treatment because that the alleviation that phantom body pain that functions by tricking the brain, making use of a one-of-a-kind mirror box to develop a visual depiction of the lacking limb. The method allows the patient to manipulate this representation right into a more comfortable position (Ramachandran & Rogers-Ramachandran, 1996).

Smell and also Taste: The chemistry Senses

The two many underappreciated senses have the right to be lumped right into the broad category of chemistry senses. Both olfaction (smell) and also gustation (taste) need the transduction of chemical stimuli into electric potentials. Ns say these senses space underappreciated due to the fact that most human being would offer up either among these if they were required to offer up a sense. If this might not shock a many readers, take it into factor to consider how much money civilization spend top top the perfume industry each year ($29 billion us Dollars). Numerous of united state pay a lot more for a favourite brand the food due to the fact that we prefer the taste. Clearly, we human beings care about our chemical senses.

Olfaction (smell)

Unlike any of the other senses debated so far, the receptors associated in ours perception of both smell and taste bind directly with the stimuli they transduce. Odorants in our environment, an extremely often mixture of them, bind v olfactory receptors uncovered in the olfactory epithelium. The binding the odorants to receptors is assumed to be similar to just how a lock and vital operates, with various odorants binding come different devoted receptors based upon their shape. However, the shape theory that olfaction no universally welcomed and different theories exist, including one that argues that the vibrations the odorant molecule correspond to their spatu smells (Turin, 1996). Regardless of just how odorants bind v receptors, the an outcome is a sample of neural activity. The is believed that our memories that these patterns of task underlie ours subjective endure of smell (Shepherd, 2005). Interestingly, because olfactory receptor send projections to the mind through the cribriform plate that the skull, head trauma has actually the potential to cause anosmia, as result of the severing of these connections. If you are in a heat of work-related where you constantly endure head trauma (e.g. Professional boxer) and also you build anosmia, nothing worry—your feeling of smell will probably come ago (Sumner, 1964).

Gustation (taste)

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Ghost Pepper, additionally known as Bhut Jolokia is just one of the sexty peppers in the world, it’s 10 time hotter 보다 a habanero, and also 400 time hotter 보다 tabasco sauce. What perform you think would happen to her taste receptor cell if you took a bite the end of this small guy?

Taste works in a similar fashion to smell, only with receptors uncovered in the taste sprout of the tongue, dubbed taste receptor cells. To clarify a common misconception, taste buds space not the bump on her tongue (papillae), however are located in tiny divots about these bumps. This receptors likewise respond to chemicals from the external environment, other than these chemicals, dubbed tastants, are contained in the foods items we eat. The binding of this chemicals with taste receptor cells outcomes in our perception the the five simple tastes: sweet, sour, bitter, salty and also umami (savory)—although some scientists argue the there are an ext (Stewart et al., 2010). Researchers used to think these tastes created the basis for a map-like organization of the tongue; over there was even a clever rationale for the concept, around how the earlier of the tongue sensed bitter so we would recognize to spit the end poisons, and the prior of the tongue sensed sweet so we might identify high-energy foods. However, us now understand that all locations of the tongue v taste receptor cells are capable of responding come every taste (Chandrashekar, Hoon, Ryba, & Zuker, 2006).

During the procedure of eat we are not minimal to our feeling of taste alone. While we space chewing, food odorants are forced ago up to areas that save olfactory receptors. This combination of taste and smell provides us the tardy of flavor. If you have doubts around the interaction between these two senses, i encourage you come think earlier to take into consideration how the spices of her favorite foods are impacted when you have a cold; whatever is nice bland and boring, right?

Putting it every Together: Multimodal Perception

Though we have actually spent the bulk of this module covering the senses individually, ours real-world endure is most regularly multimodal, entailing combinations of ours senses right into one perceptual experience. This must be clean after reading the summary of walking with the woodland at the beginning of the module; it to be the combination of senses that permitted for that experience. It do not do it shock friend to discover out that at some allude information from every of our senses i do not care integrated. Info from one sense has actually the potential come influence just how we perceive details from another, a procedure called multimodal perception.

Interestingly, we actually respond an ext strongly come multimodal stimuli compared to the amount of each solitary modality together, one effect called the superadditive effect of multisensory integration. This can describe how you’re quiet able to recognize what friends room saying to you at a loud concert, as lengthy as you are able to acquire visual cues native watching castle speak. If girlfriend were having actually a quiet conversation at a café, you likely wouldn’t require these added cues. In fact, the principle of inverse efficiency states that you space less likely to benefit from additional cues from various other modalities if the initial unimodal economic stimulation is solid enough (Stein & Meredith, 1993).

Because we room able to procedure multimodal sensory stimuli, and also the results of those procedures are qualitatively different from those of unimodal stimuli, the a fair assumption that the brain is doing something qualitatively various when they’re being processed. There has been a farming body the evidence because the mid-90’s ~ above the neural correlates that multimodal perception. Because that example, neurons the respond to both visual and also auditory stimuli have been identified in the superior temporal sulcus (Calvert, Hansen, Iversen, & Brammer, 2001). Additionally, multimodal “what” and also “where” pathways have been proposed for auditory and also tactile stimuli (Renier et al., 2009). We aren’t restricted to reading around these regions of the mind and what castle do; we can experience them through a couple of interesting instances (see extr Resources because that the “McGurk Effect,” the “Double flash Illusion,” and also the “Rubber Hand Illusion”).

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Conclusion

Our superior sensory abilities allow us to experience the most enjoyable and also most miserable experiences, and everything in between. Our eyes, ears, nose, tongue and also skin carry out an user interface for the mind to communicate with the world roughly us. While there is simplicity in spanning each sensory modality independently, we room organisms that have advanced the capability to procedure multiple modalities together a linked experience.

Outside Resources

Audio: listening Demonstrations indigenous Richard Warren’s lab in ~ the university of Wisconsin, Milwaukeehttp://www4.uwm.edu/APL/demonstrations.htmlAudio: auditory Demonstrations. CD released by the Acoustical society of America (ASA). You deserve to listen to the demonstrations herehttp://www.feilding.net/sfuad/musi3012-01/demos/audio/Book: Ackerman, D. (1990). A natural background of the senses. Vintage.http://www.dianeackerman.com/a-natural-history-of-the-senses-by-diane-ackermanBook: Sacks, O. (1998). The guy who mistook his wife for a hat: and also other clinical tales. Simon and Schuster.http://www.oliversacks.com/books-by-oliver-sacks/man-mistook-wife-hat/Video: got knowledge and its affect on our three-dimensional interpretation of the human being - 3D Street Art