The topics ofsensation and perception are among the oldest and most crucial in all ofpsychology. People are equipped through senses such as sight, hearing and tastethat help us to take in the world about us. Amazingly, our senses have thecapacity to transform real-people information into electrical information that canbe processed by the brain. The way we translate this information-- ourperceptions-- is what leads to our experiences of the human being. In this module,you will learn about the biological processes of sensation and exactly how these deserve to beunified to create perceptions.

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Learning Objectives

Differentiate the processes of sensation and perception.Explain the basic principles of sensation and also perception.Describe the attribute of each of our senses.Summary the anatomy of the sense organs and their projections to the nervous device. Apply expertise of sensation and perception to genuine civilization examples.Exsimple the after-effects of multimodal perception.Introduction

"Once I was hiking at Cape Lookout State Park in Tillamook, Oregon. After passing through a vibrantly colored, pleasantly scented, temperate rainforest, I came down on a cliff overlooking the Pacific Ocean. I got hold of the cold steel railing close to the edge and looked out at the sea. Below me, I could view a pod of sea lions swimming in the deep blue water. All roughly me I could smell the salt from the sea and also the scent of wet, fallen leaves." 

This description of a single memory highlights the method a person’s senses are so crucial to our endure of the people around us.

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Our senses combine to create our perceptions of the human being.

Before pointing out each of our extrasimple senses individually, it is crucial to cover some basic ideas that apply to every one of them. It is more than likely finest to start with one very vital difference that can often be confusing: the difference in between sensation and perception. The physical procedure in the time of which our sensory organs—those connected via hearing and also taste, for example—respond to external stimuli is dubbed sensation. Sensation happens as soon as you eat noodles or feel the wind on your confront or hear a vehicle horn honking in the distance. Throughout sensation, our sense organs are engaging in transduction, the conversion of one develop of energy into another. Physical energy such as light or a sound wave is converted right into a type of energy the brain deserve to understand: electrical stimulation. After our brain receives the electric signals, we make sense of all this stimulation and begin to appreciate the complex world around us. This psychological process—making feeling of the stimuli—is dubbed perception. It is during this procedure that you are able to identify a gas leak in your house or a song that reminds you of a details afternoon invested via friends.

Regardless of whether we are talking about sight or taste or any type of of the individual senses, tright here are a variety of standard principles that influence the method our sense organs work-related. The first of these influences is our ability to detect an external stimulus. Each sense organ—our eyes or tongue, for instance—calls for a minimal amount of stimulation in order to detect a stimulus. This absolute threshost explains why you don’t smell the perfume someone is wearing in a classroom unless they are somewhat close to you. Since absolute thresorganize transforms throughout the day and also based on what various other stimuli you have actually freshly competent, researchers specify absolute thresorganize as the minimum about of stimulation essential to detect a stimulus 50% of the moment.

The means we meacertain absolute thresholds is by using an approach dubbed signal detection. This process involves presenting stimuli of varying intensities to a research participant in order to determine the level at which he or she can reliably detect stimulation in a offered sense. During one kind of hearing test, for example, a perchild lis10s to progressively louder tones (founding from silence). This form of test is called the technique of limits, and it is an effort to determine the point, or thresorganize, at which a perboy begins to hear a stimulus (watch Further Resources for a video demonstration). In the example of louder tones, the approach of borders test is making use of ascending trials. Some method of boundaries tests use descending trials, such as making a light thrive dimmer until a perkid have the right to no much longer see it. Correctly indicating that a sound was heard is dubbed a hit; failing to perform so is dubbed a miss. Additionally, indicating that a sound was heard as soon as one wasn’t played is called a false alarm, and appropriately identifying when a sound wasn’t played is a correct rejection.

Thstormy these and various other researches, we have actually been able to gain an knowledge of just how exceptional our senses are. For instance, the huguy eye is qualified of detecting candlelight from 30 miles amethod in the dark. We are also capable of hearing the ticking of a watch in a quiet environment from 20 feet amethod. If you think that’s impressive, I encourage you to review more about the too much sensory capabilities of nonhumale animals; many type of pets possess what we would consider super-huguy abilities.

A similar principle to the absolute thresorganize questioned above underlies our capability to detect the distinction in between two stimuli of various intensities. The differential threshold (or difference threshold) or just noticeable difference (JND), for each sense has actually been studied making use of equivalent methods to signal detection. To highlight, uncover a friend and also a few objects of recognized weight (you’ll need objects that weigh 1, 2, 10 and 11 lbs.—or in metric terms: 1, 2, 5 and also 5.5 kg). Have your frifinish hold the lightest object (1 lb. or 1 kg). Then, relocation this object via the next heaviest and also ask him or her to tell you which one weighs more. Reliably, your frifinish will certainly say the second object every single time. It’s incredibly straightforward to tell the distinction once something weighs double what an additional weighs! However, it is not so straightforward once the difference is a smaller portion of the as a whole weight. It will be much harder for your frifinish to reliably tell the difference in between 10 and also 11 lbs. (or 5 versus 5.5 kg) than it is for 1 and 2 lbs. This is phenomenon is referred to as Weber’s Law, and it is the principle that bigger stimuli call for larger differences to be noticed. Similar to the absolute threshost, your ability to alert distinctions varies throughout the day and also based upon what various other stimuli you have newly skilled so the distinction threshost is identified as the smallest difference detectable 50% of the moment.

Crossing into the human being of perception, it is clear that our experience influences just how our brain procedures things. You have tasted food that you like and also food that you don’t favor. Tright here are some bands you enjoy and also others you can’t stand also. However, in the time of the time you first eat somepoint or hear a band also, you procedure those stimuli making use of bottom-up processing. This is once we construct approximately perception from the individual pieces. Sometimes, though, stimuli we’ve knowledgeable in our past will influence exactly how we process new ones. This is referred to as top-dvery own processing. The ideal means to illustrate these 2 principles is with our ability to review. Read the adhering to quote out loud:

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Figure 1. An example of stimuli handling.

Notice anypoint odd while you were analysis the message in the triangle? Did you notification the second “the”? If not, it’s most likely because you were reading this from a top-dvery own method. Having a second “the” doesn’t make feeling. We know this. Our brain knows this and also doesn’t expect there to be a 2nd one, so we have a propensity to skip best over it. In various other words, your past suffer has adjusted the way you perceive the creating in the triangle! A beginning reader—one who is utilizing a bottom-up approach by closely attfinishing to each piece—would certainly be less likely to make this error.

Finally, it should be provided that when we endure a sensory stimulus that doesn’t readjust, we stop paying attention to it. This is why we don’t feel the weight of our clothes, hear the hum of a projector in a lecture hall, or check out all the tiny scratches on the lenses of our glasses. When a stimulus is consistent and unaltering, we endure sensory adaptation. This occurs because if a stimulus does not change, our receptors quit responding to it. A excellent instance of this occurs when we leave the radio on in our car after we park it at house for the night. When we listen to the radio on the means residence from work the volume appears reasonable. However before, the next morning as soon as we start the vehicle, we can be startled by just how loud the radio is. We don’t remember it being that loud last night. What happened? We adapted to the consistent stimulus (the radio volume) over the course of the previous day and also enhanced the volume at assorted times. 

Now that we have actually introduced some basic sensory principles, let us take on each one of our fascinating senses individually.

Vision

How vision works

Vision is a tricky issue. When we check out a pizza, a feather, or a hammer, we are actually seeing light bounce off that object and right into our eye. Light enters the eye via the pupil, a tiny opening behind the cornea. The pupil regulates the amount of light entering the eye by contracting (acquiring smaller) in bright light and dilating (obtaining larger) in dimmer light. Once past the pupil, light passes through the lens, which concentrates an image on a thin layer of cells in the back of the eye, referred to as the retina.

Since we have 2 eyes in different locations, the image focused on each retina is from a slightly different angle (binocular disparity), offering us via our perception of 3D area (binocular vision). You have the right to appreciate this by holding a pen in your hand, extending your arm in front of your challenge, and also looking at the pen while closing each eye consequently. Pay attention to the apparent place of the pen family member to objects in the background. Depfinishing on which eye is open, the pen shows up to jump back and forth! This is just how video game manufacturers produce the perception of 3D without special glasses; 2 slightly various images are presented on peak of one an additional.

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Figure 2. Diagram of the human eye. Notice the Retina, labeled here: this is the location of the Cones and Rods in the eye.

It is in the retina that light is transduced, or converted into electric signals, by specialized cells dubbed photoreceptors. The retina has 2 major kinds of photoreceptors: rods and also cones. Rods are mainly responsible for our ability to check out in dim light conditions, such as throughout the night. Cones, on the various other hand also, administer us through the capability to see shade and also fine information as soon as the light is brighter. Rods and also cones differ in their circulation throughout the retina, through the highest possible concentration of cones uncovered in the fovea (the main area of focus), and rods overcoming the periphery (see Figure 2). The difference in circulation have the right to define why looking straight at a dim star in the sky renders it seem to disappear; there aren’t enough rods to process the dim light!

Next off, the electrical signal is sent out with a layer of cells in the retina, eventually traveling down the optic nerve. After passing with the thalamus, this signal renders it to the main visual cortex, where indevelopment about light orientation and also activity start to come together (Hubel & Wiesel, 1962). Indevelopment is then sent out to a selection of different areas of the cortex for more complex handling. A few of these cortical regions are sensibly specialized—for example, for handling deals with (fusidevelop confront area) and body components (extrastriate body area). Damage to these locations of the cortex have the right to perhaps cause a details type of agnosia, through which a person loses the ability to perceive visual stimuli. A good instance of this is illustrated in the creating of famous neurologist Dr. Oliver Sacks; he knowledgeable prosopagnosia, the inability to recognize deals with. These specialized regions for visual acknowledgment comprise the ventral pathway (also called the “what” pathway). Other locations connected in handling location and activity consist of the dorsal pathway (likewise referred to as the “where” pathway). Together, these pathways process a large amount of information about visual stimuli (Goodale & Milner, 1992). Phenomena we regularly describe as optical illusions provide misleading indevelopment to these “higher” areas of visual processing (see Additional Resources for websites containing exceptional optical illusions).

Dark and light adaptation

Humans have the capacity to adapt to alters in light problems. As mentioned before, rods are primarily associated in our ability to watch in dim light. They are the photoreceptors responsible for allowing us to check out in a dark room. You can notification that this night vision capability takes about 10 minutes to revolve on, a procedure called dark adaptation. This is bereason our rods come to be bleached in normal light conditions and call for time to recover. We endure the oppowebsite result once we leave a dark movie theatre and also head out into the afternoon sun. Throughout light adaptation, a large variety of rods and cones are bleached at as soon as, leading to us to be blinded for a couple of seconds. Light adaptation happens almost instantly compared through dark adaptation. Interestingly, some civilization think piprices wore a patch over one eye in order to keep it adapted to the dark while the other was adapted to the light. If you desire to turn on a light without shedding your night vision, don’t issue around wearing an eye patch, simply use a red light; this wavelength doesn’t bleach your rods.

Color vision

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Figure 3. Stare at the facility of the Canadian flag for fifteen secs. Then, shift your eyes amethod to a white wall or blank piece of paper. You need to check out an "after image" in a various color system.

Our cones permit us to watch details in normal light problems, and also shade. We have cones that respond preferentially, not solely, for red, green and also blue (Svaetichin, 1955). This trichromatic concept is not new; it dates back to the early on 1ninth century (Young, 1802; Von Helmholtz, 1867). This theory, yet, does not define the odd impact that occurs once we look at a white wall after staring at a picture for about 30 seconds. Try this: stare at the image of the flag in Figure 3 for 30 secs and also then automatically look at a sheet of white paper or a wall. According to the trichromatic theory of color vision, you should check out white when you perform that. Is that what you experienced? As you can watch, the trichromatic concept doesn’t explain the afterimage you simply experienced. This is where the opponent-process concept comes in (Hering, 1920). This theory states that our cones sfinish information to retinal ganglion cells that respond to pairs of colors (red-green, blue-yellow, black-white). These specialized cells take information from the cones and also compute the difference in between the 2 colors—a process that defines why we cannot see reddish-green or bluish-yellow, as well as why we see afterimages. Color deficient vision have the right to result from problems via the cones or retinal ganglion cells affiliated in shade vision.

Hearing (Audition)

Several of the many renowned celebrities and also peak earners in the people are musicians. Our worship of musicians may seem silly as soon as you take into consideration that all they are doing is vibrating the air a details way to create sound waves, the physical stimulus for audition.

People are qualified of acquiring a huge amount of indevelopment from the basic qualities of sound waves. The amplitude (or intensity) of a sound wave codes for the loudness of a stimulus; higher amplitude sound waves result in louder sounds. The pitch of a stimulus is coded in the frequency of a sound wave; higher frequency sounds are greater pitched. We can likewise gauge the quality, or timbre, of a sound by the complexity of the sound wave. This enables us to tell the difference between bbest and dull sounds and herbal and synthesized instruments (Välimäki & Takala, 1996).

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Figure 4. Diagram of the human ear. Notice the Cochlea labeled here: it is the location of the auditory Hair Cells that are tonotopically arranged.

In order for us to feeling sound waves from our setting they need to reach our inner ear. Lucky for us, we have advanced tools that permit those waves to be funneled and enhanced during this journey. Initially, sound waves are funneled by your pinna (the external part of your ear that you deserve to actually see) right into your auditory canal (the hole you stick Q-tips right into despite package advising against it). Throughout their journey, sound waves ultimately reach a thin, stretched membrane dubbed the tympanic membrane (eardrum), which vibrates against the 3 smallest bones in the body—the malleus (hammer), the incus (anvil), and also the stapes (stirrup)—jointly referred to as the ossicles. Both the tympanic membrane and the ossicles amplify the sound waves prior to they enter the fluid-filled cochlea, a snail-shell-favor bone framework containing auditory hair cells arranged on the basilar membrane (check out Figure 4) according to the frequency they respond to (dubbed tonotopic organization). Depending on age, humans deserve to commonly detect sounds in between 20 Hz and also 20 kHz. It is inside the cochlea that sound waves are converted into an electric message.

Due to the fact that we have actually an ear on each side of our head, we are qualified of localizing sound in 3D space pretty well (in the exact same way that having 2 eyes produces 3D vision). Have you ever before dropped something on the floor without seeing wright here it went? Did you alert that you were rather qualified of locating this object based upon the sound it made when it hit the ground? We deserve to reliably locate something based on which ear receives the sound initially. What around the height of a sound? If both ears receive a sound at the same time, how are we qualified of localizing sound vertically? Research in cats (Populin & Yin, 1998) and also humans (Middlebrooks & Environment-friendly, 1991) has actually pointed to differences in the quality of sound waves relying on vertical positioning.

After being processed by auditory hair cells, electric signals are sent with the cochlear nerve (a department of the vestibulocochlear nerve) to the thalamus, and also then the primary auditory cortex of the tempdental lobe. Interestingly, the tonotopic company of the cochlea is maintained in this location of the cortex (Merzenich, Knight, & Roth, 1975; Romani, Williamkid, & Kaufguy, 1982). However before, the function of the major auditory cortex in processing the wide variety of attributes of sound is still being explored (Walker, Bizley, & Schnupp, 2011).

Balance and the vestibular system

The inner ear isn’t just associated in hearing; it’s additionally connected with our capability to balance and also detect wright here we are in space. The vestibular device is consisted of of three semicircular canals—fluid-filled bone frameworks containing cells that respond to transforms in the head’s orientation in space. Information from the vestibular system is sent out through the vestibular nerve (the various other division of the vestibulocochlear nerve) to muscles involved in the movement of our eyes, neck, and various other parts of our body. This indevelopment enables us to preserve our gaze on a things while we are in motion. Disturbances in the vestibular mechanism can result in concerns via balance, consisting of vertigo.

Touch

Who doesn’t love the softness of an old t-shirt or the smoothness of a clean shave? Who actually enjoys having sand also in their swimsuit? Our skin, the body’s biggest organ, gives us through all sorts of information, such as whether somepoint is smooth or bumpy, hot or cold, or even if it’s painful. Somatosensation—which contains our capability to sense touch, temperature and pain—transduces physical stimuli, such as fuzzy velvet or scalding water, into electrical potentials that deserve to be processed by the brain.

Tactile sensation

Tactile stimuli—those that are connected through texture—are transduced by unique receptors in the skin referred to as mechanoreceptors. Just like photoreceptors in the eye and also auditory hair cells in the ear, these allow for the conversion of one sort of power right into a form the brain have the right to understand.

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Figure 5. A illustration of the somatosensory cortex in the brain and also the areas in the huguy body that correspond to it - they are drawn in propercent to the most sensitive or the many innervated parts of the body.

After tactile stimuli are converted by mechanoreceptors, information is sent out with the thalamus to the primary somatosensory cortex for additionally handling. This region of the cortex is organized in a somatotopic map wright here different regions are sized based on the sensitivity of particular components on the opposite side of the body (Penfield & Rasmussen, 1950). Put ssuggest, miscellaneous locations of the skin, such as lips and fingertips, are more sensitive than others, such as shoulders or ankles. This sensitivity can be represented via the distorted prosections of the human body presented in Figure 5.

Pain

Many people, if asked, would love to get rid of pain (nociception), because the sensation is incredibly unpleasant and doesn’t show up to have apparent worth. But the perception of pain is our body’s means of sending us a signal that somepoint is wrong and also needs our attention. Without pain, just how would certainly we recognize once we are accidentally touching a warm cooktop, or that we must remainder a strained arm after a tough workout?

Phantom limbs

Records of civilization experiencing phantom limbs after amputations have actually been approximately for centuries (Mitchell, 1871). As the name argues, civilization via a phantom limb have actually the sensations such as itching seemingly coming from their absent limb. A phantom limb can likewise involve phantom limb pain, sometimes explained as the muscles of the lacking limb uncomfortably clenching. While the mechanisms underlying these sensations are not completely construed, there is proof to support that the damaged nerves from the amputation site are still sending information to the brain (Weinstein, 1998) and also that the brain is reacting to this indevelopment (Ramachandran & Rogers-Ramachandran, 2000). Tbelow is an exciting therapy for the alleviation of phantom limb pain that works by tricking the brain, making use of a unique mirror box to produce a visual depiction of the missing limb. The approach allows the patient to manipulate this depiction right into a much more comfortable place (Ramachandran & Rogers-Ramachandran, 1996).

Smell and also Taste: The Chemical Senses

The 2 a lot of underappreciated senses have the right to be lumped right into the broad category of chemical senses. Both olfactivity (smell) and guterminal (taste) call for the transduction of chemical stimuli into electric potentials. I say these senses are underappreciated bereason the majority of human being would provide up either among these if they were forced to provide up a sense. While this might not shock a lot of readers, take into consideration just how a lot money civilization spend on the perfume sector every year ($29 billion US Dollars). Many type of of us pay a lot more for a favorite brand also of food bereason we prefer the taste. Clat an early stage, we people care around our chemical senses.

Olfaction (smell)

Unfavor any kind of of the various other senses debated so much, the receptors associated in our perception of both smell and also taste bind directly through the stimuli they transduce. Odorants in our environment, very regularly mixtures of them, bind with olfactory receptors found in the olfactory epithelium. The binding of odorants to receptors is thshould be similar to just how a lock and key opeprices, with different odorants binding to various specialized receptors based upon their shape. However, the form theory of olfactivity isn’t universally welcomed and also different theories exist, consisting of one that argues that the vibrations of odorant molecules correspond to their subjective smells (Turin, 1996). Regardmuch less of how odorants bind through receptors, the result is a pattern of neural task. It is believed that our memories of these trends of activity underlie our subjective experience of smell (Shepherd, 2005). Interestingly, bereason olfactory receptors sfinish projections to the brain through the cribriform plate of the skull, head trauma has the potential to reason anosmia, due to the severing of these relationships. If you are in a line of occupational where you constantly endure head trauma (e.g. experienced boxer) and you develop anosmia, don’t worry—your sense of smell will more than likely come earlier (Sumner, 1964).

Guterminal (taste)

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Ghold Pepper, additionally known as Bhut Jolokia is just one of the hottest peppers in the world, it’s 10 times hotter than a habanero, and also 400 times hotter than tabasco sauce. What carry out you think would certainly take place to your taste receptor cells if you took a bite out of this little guy?

Taste functions in a similar fashion to smell, only with receptors uncovered in the taste buds of the tongue, dubbed taste receptor cells. To clarify a prevalent misconception, taste buds are not the bumps on your tongue (papillae), but are situated in small divots roughly these bumps. These receptors also respond to chemicals from the external setting, except these chemicals, referred to as tastants, are consisted of in the foods items we eat. The binding of these chemicals through taste receptor cells results in our perception of the five basic tastes: sweet, sour, bitter, salty and umami (savory)—although some researchers argue that there are more (Stewart et al., 2010). Researchers offered to think these tastes developed the basis for a map-choose organization of the tongue; tbelow was also a clever rationale for the idea, about how the back of the tongue sensed bitter so we would certainly recognize to spit out poisons, and the front of the tongue sensed sweet so we might identify high-power foodstuffs. However before, we currently know that all areas of the tongue with taste receptor cells are qualified of responding to eextremely taste (Chandrashekar, Hoon, Ryba, & Zuker, 2006).

Throughout the procedure of eating we are not restricted to our sense of taste alone. While we are chewing, food odorants are forced ago approximately locations that contain olfactory receptors. This combination of taste and also smell gives us the perception of flavor. If you have doubts about the interaction in between these two senses, I encourage you to think back to think about exactly how the spices of your favorite foods are influenced when you have actually a cold; everything is pretty bland and boring, right?

Putting it all Together: Multimodal Perception

Though we have invested the majority of this module extending the senses individually, our real-world endure is many frequently multimodal, entailing combinations of our senses into one perceptual endure. This should be clear after reading the description of walking via the forest at the start of the module; it was the combicountry of senses that enabled for that endure. It shouldn’t shock you to find out that at some suggest indevelopment from each of our senses becomes incorporated. Indevelopment from one sense has actually the potential to affect how we perceive indevelopment from an additional, a process dubbed multimodal perception.

Interestingly, we actually respond more strongly to multimodal stimuli compared to the amount of each single modality together, an result dubbed the superadditive result of multisensory integration. This have the right to describe exactly how you’re still able to understand what friends are saying to you at a loud concert, as lengthy as you are able to get visual cues from watching them speak. If you were having actually a quiet conversation at a café, you most likely wouldn’t require these extra cues. In fact, the principle of inverse efficiency claims that you are less most likely to benefit from added cues from other modalities if the initial unimodal stimulus is solid sufficient (Stein & Meredith, 1993).

Since we are able to procedure multimodal sensory stimuli, and the results of those procedures are qualitatively various from those of unimodal stimuli, it’s a fair presumption that the brain is doing something qualitatively various as soon as they’re being processed. There has actually been a prospering body of evidence because the mid-90’s on the neural correlates of multimodal perception. For example, neurons that respond to both visual and also auditory stimuli have actually been determined in the superior tempdental sulcus (Calvert, Hansen, Iversen, & Brammer, 2001). In addition, multimodal “what” and “where” pathways have actually been proposed for auditory and tactile stimuli (Renier et al., 2009). We aren’t restricted to analysis around these areas of the brain and what they do; we have the right to endure them via a couple of exciting examples (see Further Resources for the “McGurk Effect,” the “Double Flash Illusion,” and the “Rubber Hand also Illusion”).

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Conclusion

Our superior sensory abilities permit us to suffer the the majority of enjoyable and also many miserable experiences, as well as everything in between. Our eyes, ears, nose, tongue and also skin carry out an interchallenge for the brain to connect through the human being around us. While tbelow is simplicity in extending each sensory modality individually, we are organisms that have actually developed the ability to process multiple modalities as a linked endure.

Outside Resources

Audio: Auditory Demonstrations from Richard Warren’s lab at the University of Wisconsin, Milwaukeehttp://www4.uwm.edu/APL/demonstrations.htmlAudio: Auditory Demonstrations. CD publiburned by the Acoustical Society of America (ASA). You have the right to listen to the demonstrations herehttp://www.feilding.net/sfuad/musi3012-01/demos/audio/Book: Ackermale, 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 that mistook his wife for a hat: And various other clinical tales. Simon and Schuster.http://www.oliversacks.com/books-by-oliver-sacks/man-mistook-wife-hat/Video: Acquired expertise and also its influence on our three-dimensional interpretation of the world - 3D Street Art