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Sensation And Perception



Sensation is our ability to detect senses like touch, pain, vision, or the movement and positioning of our body. Perception is the way in which the brain processes and communicates these senses to the rest of the body. Some may have difficulty detecting sensation at all due to skin integrity or anatomical factors. Others can detect sensation, however, the way their brain processes sensory input may not be perceived accurately. For example, some people are more sensitive to vestibular input, such as spinning or motion, than others. Two people may be spinning the same amount of time and at the same speed, but only one of the two gets sick.




Sensation and Perception


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This principle can be applied to things like perception of pain, or perception of touch in general. Someone who is hyperresponsive to touch may be annoyed by certain fabrics or textures of objects, while someone who is under responsive to touch may not realize their skin is becoming irritated from brushing up against the edge of their keyboard. The ability to sense stimuli is different than the way the body interprets it.


Because we have two eyes in different locations, the image focused on each retina is from a slightly different angle (binocular disparity), providing us with our perception of 3D space (binocular vision). You can appreciate this by holding a pen in your hand, extending your arm in front of your face, and looking at the pen while closing each eye in turn. Pay attention to the apparent position of the pen relative to objects in the background. Depending on which eye is open, the pen appears to jump back and forth! This is how video game manufacturers create the perception of 3D without special glasses; two slightly different images are presented on top of one another.


Records of people experiencing phantom limbs after amputations have been around for centuries (Mitchell, 1871). As the name suggests, people with a phantom limb have the sensations such as itching seemingly coming from their missing limb. A phantom limb can also involve phantom limb pain, sometimes described as the muscles of the missing limb uncomfortably clenching. While the mechanisms underlying these phenomena are not fully understood, there is evidence to support that the damaged nerves from the amputation site are still sending information to the brain (Weinstein, 1998) and that the brain is reacting to this information (Ramachandran & Rogers-Ramachandran, 2000). There is an interesting treatment for the alleviation of phantom limb pain that works by tricking the brain, using a special mirror box to create a visual representation of the missing limb. The technique allows the patient to manipulate this representation into a more comfortable position (Ramachandran & Rogers-Ramachandran, 1996).


During the process of eating we are not limited to our sense of taste alone. While we are chewing, food odorants are forced back up to areas that contain olfactory receptors. This combination of taste and smell gives us the perception of flavor. If you have doubts about the interaction between these two senses, I encourage you to think back to consider how the flavors of your favorite foods are impacted when you have a cold; everything is pretty bland and boring, right?


What does it mean to sense something? Sensory receptors are specialized neurons that respond to specific types of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. For example, light that enters the eye causes chemical changes in cells that line the back of the eye. These cells relay messages, in the form of action potentials (as you learned when studying biopsychology), to the central nervous system. The conversion from sensory stimulus energy to action potential is known as transduction.


You have probably known since elementary school that we have five senses: vision, hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation). It turns out that this notion of five senses is oversimplified. We also have sensory systems that provide information about balance (the vestibular sense), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature (thermoception).


While our sensory receptors are constantly collecting information from the environment, it is ultimately how we interpret that information that affects how we interact with the world. Perception refers to the way sensory information is organized, interpreted, and consciously experienced. Perception involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts. This is called top-down processing.


There is another factor that affects sensation and perception: attention. Attention plays a significant role in determining what is sensed versus what is perceived. Imagine you are at a party full of music, chatter, and laughter. You get involved in an interesting conversation with a friend, and you tune out all the background noise. If someone interrupted you to ask what song had just finished playing, you would probably be unable to answer that question.


Motivation can also affect perception. Have you ever been expecting a really important phone call and, while taking a shower, you think you hear the phone ringing, only to discover that it is not? If so, then you have experienced how motivation to detect a meaningful stimulus can shift our ability to discriminate between a true sensory stimulus and background noise. The ability to identify a stimulus when it is embedded in a distracting background is called signal detection theory. This might also explain why a mother is awakened by a quiet murmur from her baby but not by other sounds that occur while she is asleep. Signal detection theory has practical applications, such as increasing air traffic controller accuracy. Controllers need to be able to detect planes among many signals (blips) that appear on the radar screen and follow those planes as they move through the sky. In fact, the original work of the researcher who developed signal detection theory was focused on improving the sensitivity of air traffic controllers to plane blips (Swets, 1964).


Our perceptions can also be affected by our beliefs, values, prejudices, expectations, and life experiences. As you will see later in this module, individuals who are deprived of the experience of binocular vision during critical periods of development have trouble perceiving depth (Fawcett, Wang, & Birch, 2005). The shared experiences of people within a given cultural context can have pronounced effects on perception. For example, Marshall Segall, Donald Campbell, and Melville Herskovits (1963) published the results of a multinational study in which they demonstrated that individuals from Western cultures were more prone to experience certain types of visual illusions than individuals from non-Western cultures, and vice versa. One such illusion that Westerners were more likely to experience was the Müller-Lyer illusion: the lines appear to be different lengths, but they are actually the same length.


Children described as thrill-seekers are more likely to show taste preferences for intense sour flavors (Liem, Westerbeek, Wolterink, Kok, & de Graaf, 2004), which suggests that basic aspects of personality might affect perception. Furthermore, individuals who hold positive attitudes toward reduced-fat foods are more likely to rate foods labeled as reduced-fat as tasting better than people who have less positive attitudes about these products (Aaron, Mela, & Evans, 1994).


The concept of sensation and perception explains how humans interact with the outside world. But what is sensation and perception? Sensation and perception are two separate processes, but they are two sides of the same coin. In sensation and perception, sensory stimuli are taken from the environment and sent to the brain.


Sensation is the first step to creating perceptions about the outside world. Through sensation, humans can turn sensory inputs from the environment into signals understood by the brain. Once the signals are in the brain, then perception can occur.


How is sensation and perception related? Perception takes sensations and adds another step: noticing the sensations. Perception involves the organization, interpretation, and conscious experience of sensations. The brain creates meaning from the electrical impulse sent via nervous system.


Without the nervous system, sensation and perception would be impossible. Through a process called transduction, sensory inputs are turned into electrical signals and transmitted to the brain.


The optic nerve has no photoreceptors that capture light, so the eye cannot process images to send to the brain. With no available picture, the brain creates an image. This image is based on the brain's perception of what should be there.


Humans draw on both sensation (input from sensory organs) and learned knowledge about the world. Schemas help organize information through grouping, like gestalt grouping. Schemas inform perceptions and choices about the people and objects in life.


Psychologists maintain two main thresholds for sensation and perception. The absolute threshold and the difference threshold are two different ways to measure how humans perceive stimuli.


All humans get the same sensory information input. However, every human has a unique brain. Therefore, different humans perceive the same sensations in different ways. Sensations are the same, but perceptions differ.


What is sensation and perception? Sensation is input about the physical world obtained by our sensory receptors and sent to the brain through the nervous system. Perception is the process by which the brain selects, organizes, and interprets these sensations. 041b061a72


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