Psychology
Sensory Threshold
Sensory threshold refers to the point at which a stimulus is detectable by an individual's sensory system. It represents the minimum level of stimulation required for a person to perceive a sensory experience, such as sight, sound, taste, touch, or smell. Understanding sensory thresholds is important in psychology as it helps to study perception and how individuals respond to various stimuli.
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12 Key excerpts on "Sensory Threshold"
eBook - ePub- Nancy Fenton, Jessica Flitter, Jessica Flitter(Authors)
- 2015(Publication Date)
- Research & Education Association(Publisher)
Chapter 6 Sensation and PerceptionWhat does one know about his or her world? Since the beginning of scientific psychology, psychologists have been interested in understanding sensation and perception and how these two interconnected processes relate to cognition and behavior. Psychophysics , a branch of psychology strongly influenced by German scientist Gustav Fechner , studies how physical stimuli (sensations) translate to psychological experiences (perceptions). Sensation involves how an organism receives stimuli and information from the surrounding world via the sensory organs. Psychophysicists investigate the human senses, including vision, audition (hearing), gustation (taste), olfaction (smell), somatic (touch, temperature, pain), vestibular, and kinesthetic. Each sense has specific receptor cells located in the sense organs, which transform physical stimuli into neural impulses in a process known as transduction . The complementary process to sensation is perception , which involves the interpretation of sensations. Perception includes the cognitive processes of receiving, encoding, storing, and organizing sensations.STUDY TIPBe able to distinguish between the processes of sensation and perception .ThresholdsHow intense does a stimulus have to be to produce a sensation? Psychophysicists have answered this question with absolute thresholds , or the minimum intensity of stimulation needed for detection 50 percent of the time. For example, an experimenter attempting to find an individual’s absolute threshold for sound may walk away from the individual with a ticking watch. As soon as the individual cannot reliably hear the watch 50 percent of the time, the experimenter has determined that individual’s approximate absolute threshold for sound.A subliminal stimulus is a weak stimulus presented below threshold that cannot be consciously registered. Research has questioned if very weak or quick stimuli below one’s level of consciousness can be interpreted; this is known as subliminal perception . Although subliminal commands to change behaviors have not been confirmed, there is some evidence that subliminal stimuli may have a subtle influence on behavior, but the influence is neither strong nor long-lasting. Any claims by advertisers that subliminal messages can change complex behaviors, such as ending addictions or learning a new language, are not
eBook - PDF- Ronald Comer, Elizabeth Gould, Adrian Furnham(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
A stimulus must, however, reach a certain level of intensity before we can detect it. The process of sensory transduction occurs only when the stimuli reach this level, or threshold. If a stimulus were too weak, we would not even know it was there. The minimum stimulation necessary for detection is called the absolute threshold (Table 7.2). Although the absolute threshold is dif- ferent for every person, in most cases it is surprisingly small. For instance, many people are capable of detecting a candle flame many kilometres away on a clear night (Galanter, 1962). Researchers have also worked to determine the smallest difference that we are able to notice between two stimuli of the same type, such as the smells wafting from two different meals. This measure is called the difference threshold or just noticeable difference . When sensory systems are working well, the difference threshold is also remarkably small. Thresholds may limit our abilities in some ways, but they are also very useful to us. Imagine if you noticed every lit- tle change in wind pattern or each individual fibre in your clothing. You probably would not be very comfortable if you noticed all of these small details. Many individuals with autism appear to do this, however.
eBook - PDF- Nancy Ogden, Michael Boyes, Evelyn Field, Ronald Comer, Elizabeth Gould(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
threshold the point at which the magnitude or intensity of a stimu- lus initiates a neural impulse. absolute threshold the minimal stimulus necessary for detection by an individual 50 percent of the time. difference threshold or just noticeable difference the minimal difference between two stimuli necessary for detection of a difference between the two. Sight Hearing Touch Taste Smell FIGURE 5.1 Sensory receptor cells Each sensory system contains specialized cells that are activated by particular physical stimuli. TABLE 5.1 How Sensory Transduction Converts Environmental Stimuli into Neural Activity Sensory System Physical Stimuli Olfactory (smell) Odorants (airborne chemicals) Somatosensory (touch, heat, pain) Pressure or damage to the skin Gustatory (taste) Chemicals (typically in food) Auditory (hearing) Sound waves Visual (sight) Light (photons) 170 CHAPTER 5 Sensation and Perception criteria, are necessary because detection of signals usually occurs in noisy environments. Here “noise” refers to extraneous information that interferes with a signal. For example, if you are trying to smell the milk to determine whether it is sour, the task of smelling the milk is less “noisy” if you are standing alone in the kitchen than if you are standing in the kitchen with your roommate who is wearing cologne and making a tuna sandwich while fresh coffee is brewing. As well, people use response criteria to determine how certain they need to be before they acknowledge the detection of a stimulus (Szalma & Hancock, 2011). For example, if you make a mistake and assume that the milk is safe and you are wrong, you end up drinking a bit of the sour milk. However, the consequence of drinking sour milk is not dangerous. Compare that situation with how careful you would need to be if instead you had to detect whether the week- old chicken in the refrigerator was still safe to eat.
- Lorelle J. Burton, Drew Westen, Robin M. Kowalski(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
It does this so quickly and automatically that we are unaware of anything but the end product. INTERIM SUMMARY Sensation begins with an environmental stimulus; all sensory systems have specialised cells called sensory receptors that respond to environmental stimuli and typ- ically generate action potentials in adjacent sensory neu- rons. The process of converting stimulus information into neural impulses is called transduction. Within each sen- sory modality, the brain codes sensory stimulation for inten- sity and quality. Absolute thresholds Even if a sensory system has the capacity to respond to a stimulus, the individual may not experience the stimulus if it is too weak. The minimum amount of physical energy needed for an observer to notice a stimulus is called an absolute threshold. One way that psychologists measure absolute thresholds is by presenting a particular stimulus (light, sound, taste, odour, pressure) at varying intensities and determining the level of stimulation necessary for the person to detect it about 50 percent of the time. Pdf_Folio:291 CHAPTER 7 Sensation and perception 291 A psychologist trying to identify the absolute threshold for sound of a particular pitch would present participants with sounds at that pitch, some so soft they would never hear them and others so loud they would never miss them. In between would be sounds they would hear some or most of the time. The volume at which most participants hear the sound half the time but miss it half the time is defined as the absolute threshold; above this point, people sense stimulation most of the time.
- Stephen F. Davis, William Buskist, Stephen F. Davis, William F. Buskist(Authors)
- 2007(Publication Date)
- SAGE Publications, Inc(Publisher)
Thresholds A threshold, in common parlance, is a boundary. There is a threshold at a door that defines the boundary between being in the room and being outside the room. There is a direct analogy between the threshold of a room and a Sensory Threshold. In sensory terms, the threshold defines a boundary between perception and nonperception. Just as there is an ambiguous point as you enter a room where it is not clear whether you are in or out of the room, there is usually a small range of intensities where people will sometimes report that they perceive and at other times report that they do not perceive the same stimulus. Absolute Threshold The absolute threshold is the minimal level of energy that the sensory system reliably detects—for example, the dimmest light or least intense sound that can be detected. Thus, studies measuring absolute thresholds are detection experiments. Difference Threshold A difference threshold is the minimal difference between two stimuli that an observer can reliably discriminate. The ability to tell that one sound is just louder than another is a difference threshold or just noticeable difference (JND). Whereas absolute thresholds measure detection, difference thresholds measure discrimination . Point of Subjective Equality The point of subjective equality (PSE) is reached when two stimuli appear identical in some manner to the observer. For example, there is the classic illusion of length in the Müller-Lyer illusion (Figure 20.1). In this illustration, both lines are the same length, but most people say that the figure on the right with the arrowheads pointed in toward the line looks longer. To measure the PSE, the length of the line on the right could be adjusted until it appeared to the observer to be the same length as the line on the left. BASIC PSYCHOPHYSICAL METHODS In this section we discuss several of the most basic psycho-physical methods.
eBook - PDF- John P. Houston, Helen Bee, David C. Rimm(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
Some of the specialized nerve endings, or sensory receptors, have been studied more closely than others. When we discuss the various sensory systems we will note some of the differences between receptors that perform different functions. Absolute threshold Clearly, not all levels of stimulus energy will cause our receptors to re-spond. Therefore, we will want to learn how much of a particular energy is required to trigger one of these specialized receptors. There are levels of light that are so low we cannot detect them. There are sounds we can't hear, and pressures so slight that our touch receptors cannot detect them. Before we can begin to understand the sensory systems, we need to know the minimum amount of stimulus energy to which the receptors will respond. The minimal size of the stimulus that is required for the individual to respond is referred to as the absolute threshold. The absolute threshold for any sensory system is established by presenting increasing amounts of stimulus until the subject is able to detect the presence of the stimulus 50% of the time. Thus if we wish to establish an absolute visual threshold, we might expose subjects to a series of dots of light at varying levels of brightness. The level of brightness at which the subjects could detect the stimulus 50% of the time would be called the absolute threshold. Some approximate absolute threshold levels are given in Table 1. They are only approximations, because the absolute threshold is absolute in name only. In any actual situation, there is a range of stimulation in which a subject can detect a given input some of the time but not all of the time.
eBook - ePub- George Mather(Author)
- 2014(Publication Date)
- Routledge(Publisher)
et al., 1951). The anatomical uniformity of the cerebral cortex led people to believe that neural function was also uniform. Theorists believed that perception was mediated by large-scale patterns of activity across the entire cortex, rather than responses in small groups of cells. When single-unit recordings revealed that individual cells were highly specialized in terms of their stimulus preferences, new psychophysical theories emerged in which perception was said to depend on the relative activity of comparatively small populations of detectors tuned to different stimuli (as in the explanation for the MAE). An extreme version of this theoretical perspective posited individual cells that were able to encode the identity of a complex entity such as your grandmother, or a Volkswagen car (Gross, 2002). These early theories were limited because they lacked a broad theoretical perspective that took into account the tasks performed by the sensory systems, and the problems they faced in completing those tasks. The conceptual framework described in the next chapter supplies the necessary theoretical sophistication.SummaryPsychophysics supplies scientific tools for studying the relation between physical stimuli and perceptual experience. They were first developed by Weber and Fechner in the 1800s.Absolute thresholds measure the minimum amount of stimulation required for a perceptual response, and provide useful information about the state of sensory receptors.Differential thresholds measure the minimum change in stimulation required for a noticeable perceptual change. They identify which stimuli produce the sharpest perceptual discrimination.
eBook - PDF- Catherine A. Sanderson, Karen R. Huffman(Authors)
- 2019(Publication Date)
- Wiley(Publisher)
One of the most intriguing insights from psychophysics is that what is out there is not directly reproduced inside our bodies. At this moment, there are light waves, sound waves, odors, tastes, and microscopic particles touching us that we cannot see, hear, smell, taste, or feel. We are consciously aware of only a narrow range of stimuli in our environment. Difference and Absolute Thresholds German scientist Ernst Weber (1795–1878) was one of the first to study the smallest difference between two weights that could be detected (Foley & Bates, 2019; Schwartz & Krantz, 2016). This difference threshold, also known as Weber’s law of just noticeable differences (JND), is the minimum difference that is consciously detectable 50 percent of the time (Figure 4.4). Transduction The process of converting sensory stimuli into neural impulses that are sent along to the brain (e.g., transforming light waves into neural impulses). Coding The process in which neural impulses travel by different routes to different parts of the brain; it allows the brain to detect various physical stimuli as distinct sensations. Psychophysics The study of the link between the physical charac- teristics of stimuli and the psycho- logical experience of them. Difference threshold The small- est physical difference between two stimuli that is consciously detectable 50 percent of the time; also called the just noticeable difference (JND). (Motor cortex) Primary vision area Primary olfaction (smell) area Primary audition (hearing) area Primary gustation (taste) area (Somatosensory cortex) Primary somatosensation (touch, pain, and temperature) area Temporal Lobe Frontal Lobe Parietal Lobe Occipital Lobe FIGURE 4.3 Sensory processing within the brain Neural mes- sages from the various sense organs must travel to specific areas of the brain in order for us to see, hear, smell, and so on.
eBook - PDFSensory Systems
Anatomy, Physiology and Pathophysiology
- Aage R. Moller(Author)
- 2002(Publication Date)
- Academic Press(Publisher)
Detecting the presence of a stimulus was probably the primary advantage of the evolution of such senses as vision and hearing when vertebrate species began to adapt to terrestrial life. Detecting odors was also important for many species. Early in the development of species, discrimination between different kinds of stimuli was of less importance. Much later in the evolution of terrestrial vertebrates it was still important to be able to detect the faintest sound or the weakest light, but the ability to discriminate between different stimuli became increasingly important as vertebrate species developed sensory systems adapted to these needs. In this chapter, we will discuss such basic properties as the threshold of detection and the perception of strength and their relation to the physical properties of stimulation. The purpose is to provide the reader with a general overview of basic psychophysics in order to support the perspective on the main theme of this book, namely that of the anatomy and physiology of sensory systems. For more details on psychophysics, the readers are referred to standard texts on the subject. II. Threshold of Detection 10' 1 0 ' 10' o 10' •o B 10 Q. E < 10' 10'^ 10 Wave length of light N Diameter of hydrogen molecule —' 1— 50 100 1 1 500010000 500 1000 Frequency (Hz) FIGURE 1.1 Threshold of hearing in a human subject. Circles indicate the ampUtude of the dis-placement of the tympanic membrane at threshold (in cm);'^^ the soUd line is a curve fit to the data points. II. THRESHOLD OF DETECTION In psychophysics the threshold of detection of a physical stimulus refers to the minimum amount of the stimulus that is needed for the sensory system to elicit a behavioral response. The threshold varies between sensory systems, between animal species, and as a function of the properties of the stimulus. The sensitivity of sensory systems is enormous and it surpasses most of our technical systems.
eBook - PDF- Siri Carpenter, Karen Huffman(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
a. To measure your senses, an examiner presents a series of signals that vary in intensity, and asks you to report which signals you can detect. In a hearing test, the softest level at which you can consistently hear a tone is your absolute threshold. The examiner then compares your threshold with those of people with normal hearing to determine whether you have hearing loss. How do we know this? How can scientists measure the exact amount of stimulus energy it takes to trigger a con-scious experience? The answers come from the field of psy-chophysics , which studies and measures the link between the physical characteristics of stimuli and the sensory ex-perience of them (see Figure 4.2 ). There is an interesting and ongoing controversy about whether we can be affected by subliminal stimuli, sensations © Carmen Martínez Banús/iStockphoto Karen KasmauskiI/NG Image Collection b. Researchers have established absolute thresholds for various senses. Sense Absolute threshold Vision A candle flame seen from 30 miles away on a clear, dark night Audition (hearing) The tick of an old-fashioned watch at 20 feet Olfaction (smell) One drop of perfume spread throughout a six-room apartment Gustation (taste) One teaspoon of sugar in two gallons of water Body senses A bee’s wing falling on your cheek from a height of about half an inch ▲ c. A dog’s absolute and difference thresholds for smell are far more sensitive than those of a human. For this reason, specially trained dogs provide invaluable help in sniffing out dangerous plants, animals, drugs, and ex-plosives, tracking criminals, and assisting in search-and-rescue operations. Some researchers believe dogs can even detect chemical signs of certain illnesses, such as diabetes or cancer (Akers & Denbow, 2008). ▲ © ZoneCreative/iStockphoto below our absolute threshold, even when we’re not aware of them.
eBook - PDF- Karen R. Huffman, Katherine Dowdell, Catherine A. Sanderson(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
Shown here in the red-colored labels are the primary locations in the cerebral cortex for vision, hearing, taste, smell, and somatosen- sation (which includes touch, pain, and temperature sensitivity). Understanding Sensation 119 we analyze and then filter incoming sensations before sending neural impulses on for further processing in other parts of our brains. Without this natural filtering of stimuli, we would con- stantly hear blood rushing through our veins and feel our clothes brushing against our skin. Some level of filtering is needed to prevent our brains from being overwhelmed with unneces- sary information. All species have evolved selective recep- tors that suppress or amplify information for survival. Humans, for example, cannot sense ultraviolet light, electric or magnetic fields, the ultrasonic sound of a dog whistle, or infrared heat patterns from warm-blooded animals, as some other animals can. Psychophysics How can scientists measure the exact amount of stimulus energy it takes to trigger a conscious experience? The answer comes from the field of psychophysics, which studies and measures the link between the physical characteristics of stimuli and the psychological experience of them. One of the most intriguing insights from psychophysics is that what is out there is not directly reproduced inside our bodies. At this moment, there are light waves, sound waves, odors, tastes, and microscopic particles touching us that we cannot see, hear, smell, taste, or feel. We are consciously aware of only a narrow range of stimuli in our environment. German scientist Ernst Weber (1795–1878) was one of the first to study the smallest differ- ence between two weights that could be detected (Goldstein, 2014; Schwartz & Krantz, 2016). This difference threshold, also known as Weber’s law of just noticeable differences (JND), is the minimum difference that is consciously detectable 50% of the time (Figure 4.3).
eBook - ePubQuantitative Sensory Analysis
Psychophysics, Models and Intelligent Design
- Harry T. Lawless(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
This idea is often attributed to the philosopher Herbart, who wrote in 1824 that mental events had to be stronger than some critical amount in order to be consciously experienced (Gescheider, 1997). Thus, at any given moment, for a single observer, a stimulus with energy below the threshold is not detected, and a stimulus above the threshold is. This is an all-or-nothing concept of threshold, as shown in Figure 1.2. As appealing as this concept seemed, it was almost impossible to demonstrate. Attempts to measure the threshold soon encountered a major problem: the sensitivity of the observer seemed to change from moment to moment. Although one might still like the idea that at any moment there was a fixed threshold, and that crossing it caused a sensation, attempts to bring the concept into the laboratory rendered the idea questionable, and of limited utility. Let us assume you are doing a study with changing sound pressure levels and that you ask your observer to respond “yes” when they hear something and “no” when they do not. We present all the stimulus tones of different levels many times in random order. When we plot the percentage of “yes” responses against the sound pressure levels, we do not see the all-or-nothing function of Figure 1.2, but rather a curve resembling an ogive or sigmoid shape, as shown in Figure 1.3a. This was the first psychometric function, a term used to describe the probability of response as a function of the stimulus, such as its energy or sound pressure level. From this time forward, most people conceived of a threshold in practical terms, as a statistical entity rather than a fixed point. As a practical matter then, it became useful to call this empirical or experimental threshold the level at which detection occurs 50% of the time
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