{"id":265,"date":"2018-09-03T15:49:55","date_gmt":"2018-09-03T19:49:55","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/thescienceofhumanpotential\/?post_type=chapter&p=265"},"modified":"2021-02-20T13:44:05","modified_gmt":"2021-02-20T18:44:05","slug":"sensation-detecting-stimuli","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/thescienceofhumanpotential\/chapter\/sensation-detecting-stimuli\/","title":{"raw":"Sensation and Human Potential","rendered":"Sensation and Human Potential"},"content":{"raw":"You fill up my senses \/ Like a night in a forest \/ Like the mountains in springtime \/ Like a walk in the rain \/ Like a storm in the desert \/ Like a sleepy blue ocean\/ You fill up my senses\/ Come fill me again<\/em>\r\n\r\nAnnie\u2019s Song<\/em> by John Denver\r\n\r\n \r\n
\r\n

The Importance of Sensation and Perception<\/p>\r\n\r\n<\/header>\r\n

\r\n\r\n \r\n\r\nEat, survive, reproduce. Whether one lives in the rainforest or an urban metropolis, survival requires locating and identifying edible foods and avoiding predators. In Chapter 2, we examined how our nervous system evolved to enable us to address these basic survival needs and how our brain evolved to enable us to consider \u201cwhat\u2019s it all about?\u201d In this chapter, we consider how our nervous system transmits and interprets sensory information, relaying it to parts of the body capable of responding. [pb_glossary id=\"2900\"]Sensation[\/pb_glossary] refers to the initial detection of a stimulus resulting from the physical stimulation of a receptor in a sense organ (e.g., eye, ear, etc.). [pb_glossary id=\"2901\"]Perception[\/pb_glossary] refers to the integration and interpretation of sensory information. Often sensation is described as a bottom-up process, starting with stimulation of a sense organ receptor and moving toward the brain. In contrast, perception is often described as being a top-down process since the initial integration and interpretation takes place in the brain. The importance of sensation and perception to individual and species survival is undeniable.\r\n\r\n \r\n\r\n<\/div>\r\n<\/div>\r\n \r\n

Sensation \u2013 Detecting Stimuli<\/strong><\/h2>\r\nEven very simple organisms possess the ability to sense and respond to environmental stimulation. For example, moths are attracted by light. Aristotle referred to five human senses: [pb_glossary id=\"2902\"]seeing[\/pb_glossary], [pb_glossary id=\"2903\"]hearing[\/pb_glossary], [pb_glossary id=\"2904\"]taste[\/pb_glossary], [pb_glossary id=\"2905\"]smell[\/pb_glossary], and [pb_glossary id=\"2906\"]touch[\/pb_glossary]. Others consider there to be additional senses of temperature ([pb_glossary id=\"3447\"] thermoception [\/pb_glossary]), [pb_glossary id=\"2907\"] pain [\/pb_glossary], muscle tension ([pb_glossary id=\"3448\"] kinesthesia [\/pb_glossary]), and balance ([pb_glossary id=\"3449\"] equilibrium [\/pb_glossary]). Each sense responds to a specific type of physical stimulation and possesses specific receptor cells. Figure 3.1 lists the stimulus, sense organ, and receptor for the different senses.\r\n\r\n \r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Sense<\/strong><\/td>\r\nStimulus<\/strong><\/td>\r\nSense Organ<\/strong><\/td>\r\nReceptor<\/strong><\/td>\r\n<\/tr>\r\n
Vision<\/td>\r\nLight waves<\/td>\r\nEye<\/td>\r\nRods and cones of the retina<\/td>\r\n<\/tr>\r\n
Hearing<\/td>\r\nSound waves<\/td>\r\nEar<\/td>\r\nHair cells of the basilar membrane<\/td>\r\n<\/tr>\r\n
Taste<\/td>\r\nEdible substances<\/td>\r\nTongue<\/td>\r\nTaste buds of the tongue epithelium<\/td>\r\n<\/tr>\r\n
Smell<\/td>\r\nOdorous molecules<\/td>\r\nNose<\/td>\r\nSmell receptor of the nasal epithelium<\/td>\r\n<\/tr>\r\n
Touch<\/td>\r\nTactile stimulus<\/td>\r\nSkin<\/td>\r\nTouch receptors<\/td>\r\n<\/tr>\r\n
Temperature<\/td>\r\nHeat and cold<\/td>\r\nSkin<\/td>\r\nThermoceptor of skin<\/td>\r\n<\/tr>\r\n
Pain<\/td>\r\nIntense mechanical, thermal, or chemical stimulus<\/td>\r\nSkin<\/td>\r\nPain receptor of skin<\/td>\r\n<\/tr>\r\n
Balance and muscle tension<\/td>\r\nPosition of muscles, joints, and tendons<\/td>\r\nEar, skeletal muscles, joints, tendons<\/td>\r\nHair cells of the semicircular canals, nerve endings of the muscles, joints, and tendons<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n

Figure 3.1 The senses<\/em><\/p>\r\n \r\n\r\nEvolution of Sensation<\/strong>\r\n\r\nSensory information, to the extent that it accurately represents the environment, improves adaptation (Gaulin & McBurney, 2003). It should not be surprising that sense organs exist in very simple animals or that more than half the human brain is dedicated to the reception and interpretation of sensory information. Vision enables humans as well as less complex organisms (e.g., insects, sea crabs, birds, etc.) to avoid bumping into objects and to identify food sources. Hearing enables animals to detect the presence and location of dangerous or appetitive objects at a distance. Taste and smell enable us to detect potential foods or poisonous substances. Touch and pain indicate the presence of potentially dangerous objects or conditions (Gaulin & McBurney, 2003).\r\n\r\nIt is possible to study how the human brain evolved to detect, transmit, and interpret sensory information by studying the brains of other animals, especially primates (and particularly monkeys (Kaas, 2008). In comparison to our earlier mammalian ancestors, primate sensory and motor systems are much more complex and divided into a large number of functional units. For example, macaque monkeys possess between 30 and 40 separate cortical areas dedicated to vision and 15 to 20 areas dedicated to hearing. The human brain is approximately 15 times the size of the brain of macaques, possessing approximately 100 billion neurons in comparison to 6.4 billion neurons and over 200 cortical areas. Early primates were small, nocturnal, lived in trees, and ate insects, buds, and fruit. Their eyes were forward-looking and large, implying that vision played an important adaptive role in their survival. The increased number and size of cortical areas dedicated to vision, and increased number of motor areas, enabled coordination of visual information with reaching for and grabbing food while suspended from unsteady tree branches (Kaas, 2008).\r\n\r\n \r\n\r\n\"Image\r\n

Figure 3.2\u00a0 Tree dwelling primate<\/em><\/p>\r\n \r\n\r\nSensory Thresholds<\/strong>\r\n\r\nThe first scientific studies of human sensation and perception were conducted at the University of Leipzig where Wundt later established the first psychology laboratory. This earlier research obviously influenced Wundt\u2019s proposed definition, goals, and methods for the discipline. In 1860, Gustav Fechner published the classic \u201cElements of Psychophysics\u201d, naming the systematic study of the effect of varying the properties of stimuli on sensation and perception. Fechner extended the prior work of Max Weber examining the initial step enabling perception; detecting the presence or change in value of a stimulus. Weber distinguished between these two types of sensory thresholds. An [pb_glossary id=\"2911\"] absolute threshold [\/pb_glossary] is the minimum intensity of a stimulus required for one to detect its presence. For example, how bright does a light have to be or how loud does a tone have to be for a person to notice it. A [pb_glossary id=\"2908\"]difference threshold[\/pb_glossary] (often referred to as the \u201cjust noticeable difference\u201d or jnd) is the minimum amount of change<\/em> in intensity required for a person to notice a difference. Fechner replicated Weber\u2019s findings that the amount of change required is a constant fraction of the comparison stimulus. For example, if the constant jnd for length is one-tenth, you would need to increase a 10-inch line by one inch and a 20-inch line by two inches to notice the difference. This relationship is known as \u201c[pb_glossary id=\"2909\"]Weber\u2019s Law[\/pb_glossary].\u201d\r\n\r\nAdaptation requires detecting changes in one\u2019s environment and behaving in a way which promotes survival. Clearly, one is at a disadvantage if a sense is not functioning optimally. If you ever had your hearing tested, the technician probably used one of the two procedures developed by Weber, the method of limits or the method of constant stimuli. Using the method of limits to determine an absolute threshold, the [pb_glossary id=\"2910\"]amplitude[\/pb_glossary] (i.e., loudness) of a sound would be gradually increased until you report hearing it. Then the amplitude would be decreased until you report no longer hearing it. This would be repeated several times for different frequencies of sounds, from very low bass to very high treble.\r\n\r\nUsually, we think of a single value as determining an absolute or difference threshold. That is, a sound must reach a particular decibel level (loudness) for us to sense its presence. Unfortunately, when testing is conducted, one does not always obtain the same result. This raises the question of how to define what constitutes \u201cthe\u201d (apparently not so absolute) threshold? Is it the value where you first report hearing the sound? Or, is it the value where you always report hearing it? Early on, researchers decided to compromise between these two possibilities. The (not so) absolute threshold is defined as the average of the points at which the sounds appeared and disappeared.\r\n\r\nA similar process would be followed to determine a difference threshold. In this instance, the technician would start with a sound you could hear and gradually increase the amplitude until you reported it being louder. Then the amplitude would gradually be decreased until you reported it being softer, etc. The [pb_glossary id=\"2912\"] jnd[\/pb_glossary] would be defined as the average change required for you to report the tone as being louder or softer.\r\n\r\nA problem with the method of limits is that people sometimes anticipate hearing a stimulus appear or disappear. In order to address this problem, the method of constant stimuli presents sounds at random amplitudes. Unfortunately, the result frequently changes from trial to trial. That is, in testing for an absolute threshold, sometimes the person will report hearing it and sometimes not. So much for absolutes! Weber defined the absolute threshold as that value which the individual reported hearing 50 percent of the time. Similarly, a jnd was defined as the amount of change required for you to report a difference half the time. These procedures and criteria continue to be used for research and diagnostic applications.\r\n\r\nThreshold values change as the result of continual exposure. This phenomenon is called [pb_glossary id=\"2913\"] sensory adaptation [\/pb_glossary]. With the exception of pain and extremely intense stimulation, the nervous system becomes decreasingly sensitive to prolonged events. For example, if someone holds your hand you stop feeling it after a little while. You quickly adapt to hot showers and to the cold when you jump into a pool of water. The same is true after exposure to perfume or after-shave lotion, or to constant background noise (e.g., the sound of a fan). From an adaptive perspective, it is as though once you have detected the presence of a stimulus it is not essential to maintain the same level of sensitivity.\r\n

\r\n

Video<\/h3>\r\nWatch the following video for a demonstration of absolute and difference thresholds\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=wVhiezByMSU\r\n\r\n<\/div>\r\n \r\n\r\nAttributions<\/strong>\r\n\r\nFigure 3.2<\/strong> \"Tree dwelling primate\"<\/a> by Sakurai Midori<\/a> is licensed under CC BY 3.0<\/a><\/span>\r\n\r\n ","rendered":"

You fill up my senses \/ Like a night in a forest \/ Like the mountains in springtime \/ Like a walk in the rain \/ Like a storm in the desert \/ Like a sleepy blue ocean\/ You fill up my senses\/ Come fill me again<\/em><\/p>\n

Annie\u2019s Song<\/em> by John Denver<\/p>\n

 <\/p>\n

\n
\n

The Importance of Sensation and Perception<\/p>\n<\/header>\n

\n

 <\/p>\n

Eat, survive, reproduce. Whether one lives in the rainforest or an urban metropolis, survival requires locating and identifying edible foods and avoiding predators. In Chapter 2, we examined how our nervous system evolved to enable us to address these basic survival needs and how our brain evolved to enable us to consider \u201cwhat\u2019s it all about?\u201d In this chapter, we consider how our nervous system transmits and interprets sensory information, relaying it to parts of the body capable of responding. Sensation<\/a> refers to the initial detection of a stimulus resulting from the physical stimulation of a receptor in a sense organ (e.g., eye, ear, etc.). Perception<\/a> refers to the integration and interpretation of sensory information. Often sensation is described as a bottom-up process, starting with stimulation of a sense organ receptor and moving toward the brain. In contrast, perception is often described as being a top-down process since the initial integration and interpretation takes place in the brain. The importance of sensation and perception to individual and species survival is undeniable.<\/p>\n

 <\/p>\n<\/div>\n<\/div>\n

 <\/p>\n

Sensation \u2013 Detecting Stimuli<\/strong><\/h2>\n

Even very simple organisms possess the ability to sense and respond to environmental stimulation. For example, moths are attracted by light. Aristotle referred to five human senses: seeing<\/a>, hearing<\/a>, taste<\/a>, smell<\/a>, and touch<\/a>. Others consider there to be additional senses of temperature ( thermoception <\/a>), pain <\/a>, muscle tension ( kinesthesia <\/a>), and balance ( equilibrium <\/a>). Each sense responds to a specific type of physical stimulation and possesses specific receptor cells. Figure 3.1 lists the stimulus, sense organ, and receptor for the different senses.<\/p>\n

 <\/p>\n\n\n\n\n\n\n\n\n\n\n\n
Sense<\/strong><\/td>\nStimulus<\/strong><\/td>\nSense Organ<\/strong><\/td>\nReceptor<\/strong><\/td>\n<\/tr>\n
Vision<\/td>\nLight waves<\/td>\nEye<\/td>\nRods and cones of the retina<\/td>\n<\/tr>\n
Hearing<\/td>\nSound waves<\/td>\nEar<\/td>\nHair cells of the basilar membrane<\/td>\n<\/tr>\n
Taste<\/td>\nEdible substances<\/td>\nTongue<\/td>\nTaste buds of the tongue epithelium<\/td>\n<\/tr>\n
Smell<\/td>\nOdorous molecules<\/td>\nNose<\/td>\nSmell receptor of the nasal epithelium<\/td>\n<\/tr>\n
Touch<\/td>\nTactile stimulus<\/td>\nSkin<\/td>\nTouch receptors<\/td>\n<\/tr>\n
Temperature<\/td>\nHeat and cold<\/td>\nSkin<\/td>\nThermoceptor of skin<\/td>\n<\/tr>\n
Pain<\/td>\nIntense mechanical, thermal, or chemical stimulus<\/td>\nSkin<\/td>\nPain receptor of skin<\/td>\n<\/tr>\n
Balance and muscle tension<\/td>\nPosition of muscles, joints, and tendons<\/td>\nEar, skeletal muscles, joints, tendons<\/td>\nHair cells of the semicircular canals, nerve endings of the muscles, joints, and tendons<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Figure 3.1 The senses<\/em><\/p>\n

 <\/p>\n

Evolution of Sensation<\/strong><\/p>\n

Sensory information, to the extent that it accurately represents the environment, improves adaptation (Gaulin & McBurney, 2003). It should not be surprising that sense organs exist in very simple animals or that more than half the human brain is dedicated to the reception and interpretation of sensory information. Vision enables humans as well as less complex organisms (e.g., insects, sea crabs, birds, etc.) to avoid bumping into objects and to identify food sources. Hearing enables animals to detect the presence and location of dangerous or appetitive objects at a distance. Taste and smell enable us to detect potential foods or poisonous substances. Touch and pain indicate the presence of potentially dangerous objects or conditions (Gaulin & McBurney, 2003).<\/p>\n

It is possible to study how the human brain evolved to detect, transmit, and interpret sensory information by studying the brains of other animals, especially primates (and particularly monkeys (Kaas, 2008). In comparison to our earlier mammalian ancestors, primate sensory and motor systems are much more complex and divided into a large number of functional units. For example, macaque monkeys possess between 30 and 40 separate cortical areas dedicated to vision and 15 to 20 areas dedicated to hearing. The human brain is approximately 15 times the size of the brain of macaques, possessing approximately 100 billion neurons in comparison to 6.4 billion neurons and over 200 cortical areas. Early primates were small, nocturnal, lived in trees, and ate insects, buds, and fruit. Their eyes were forward-looking and large, implying that vision played an important adaptive role in their survival. The increased number and size of cortical areas dedicated to vision, and increased number of motor areas, enabled coordination of visual information with reaching for and grabbing food while suspended from unsteady tree branches (Kaas, 2008).<\/p>\n

 <\/p>\n

\"Image<\/p>\n

Figure 3.2\u00a0 Tree dwelling primate<\/em><\/p>\n

 <\/p>\n

Sensory Thresholds<\/strong><\/p>\n

The first scientific studies of human sensation and perception were conducted at the University of Leipzig where Wundt later established the first psychology laboratory. This earlier research obviously influenced Wundt\u2019s proposed definition, goals, and methods for the discipline. In 1860, Gustav Fechner published the classic \u201cElements of Psychophysics\u201d, naming the systematic study of the effect of varying the properties of stimuli on sensation and perception. Fechner extended the prior work of Max Weber examining the initial step enabling perception; detecting the presence or change in value of a stimulus. Weber distinguished between these two types of sensory thresholds. An absolute threshold <\/a> is the minimum intensity of a stimulus required for one to detect its presence. For example, how bright does a light have to be or how loud does a tone have to be for a person to notice it. A difference threshold<\/a> (often referred to as the \u201cjust noticeable difference\u201d or jnd) is the minimum amount of change<\/em> in intensity required for a person to notice a difference. Fechner replicated Weber\u2019s findings that the amount of change required is a constant fraction of the comparison stimulus. For example, if the constant jnd for length is one-tenth, you would need to increase a 10-inch line by one inch and a 20-inch line by two inches to notice the difference. This relationship is known as \u201cWeber\u2019s Law<\/a>.\u201d<\/p>\n

Adaptation requires detecting changes in one\u2019s environment and behaving in a way which promotes survival. Clearly, one is at a disadvantage if a sense is not functioning optimally. If you ever had your hearing tested, the technician probably used one of the two procedures developed by Weber, the method of limits or the method of constant stimuli. Using the method of limits to determine an absolute threshold, the amplitude<\/a> (i.e., loudness) of a sound would be gradually increased until you report hearing it. Then the amplitude would be decreased until you report no longer hearing it. This would be repeated several times for different frequencies of sounds, from very low bass to very high treble.<\/p>\n

Usually, we think of a single value as determining an absolute or difference threshold. That is, a sound must reach a particular decibel level (loudness) for us to sense its presence. Unfortunately, when testing is conducted, one does not always obtain the same result. This raises the question of how to define what constitutes \u201cthe\u201d (apparently not so absolute) threshold? Is it the value where you first report hearing the sound? Or, is it the value where you always report hearing it? Early on, researchers decided to compromise between these two possibilities. The (not so) absolute threshold is defined as the average of the points at which the sounds appeared and disappeared.<\/p>\n

A similar process would be followed to determine a difference threshold. In this instance, the technician would start with a sound you could hear and gradually increase the amplitude until you reported it being louder. Then the amplitude would gradually be decreased until you reported it being softer, etc. The jnd<\/a> would be defined as the average change required for you to report the tone as being louder or softer.<\/p>\n

A problem with the method of limits is that people sometimes anticipate hearing a stimulus appear or disappear. In order to address this problem, the method of constant stimuli presents sounds at random amplitudes. Unfortunately, the result frequently changes from trial to trial. That is, in testing for an absolute threshold, sometimes the person will report hearing it and sometimes not. So much for absolutes! Weber defined the absolute threshold as that value which the individual reported hearing 50 percent of the time. Similarly, a jnd was defined as the amount of change required for you to report a difference half the time. These procedures and criteria continue to be used for research and diagnostic applications.<\/p>\n

Threshold values change as the result of continual exposure. This phenomenon is called sensory adaptation <\/a>. With the exception of pain and extremely intense stimulation, the nervous system becomes decreasingly sensitive to prolonged events. For example, if someone holds your hand you stop feeling it after a little while. You quickly adapt to hot showers and to the cold when you jump into a pool of water. The same is true after exposure to perfume or after-shave lotion, or to constant background noise (e.g., the sound of a fan). From an adaptive perspective, it is as though once you have detected the presence of a stimulus it is not essential to maintain the same level of sensitivity.<\/p>\n

\n

Video<\/h3>\n

Watch the following video for a demonstration of absolute and difference thresholds<\/p>\n