What is the smallest level of stimulus that can be detected?
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Receptors for each sensory system are limited by the amount of stimulation necessary to elicit a sensation and by the amount of stimulus change that can be detected. In the field of psychology called psychophysics, relationships between physical stimuli and psychological experience are studied. One technique to study such relationships is called the method of constant stimuli, in which stimuli of varying intensities are presented in random order to a subject. The results are used to determine the absolute threshold—the minimum intensity detected by a subject 50% of the time. (Your dog, for instance, has a much lower absolute threshold for sound than you do and hears a car in the driveway before you hear the knock on the door.) Show
The difference threshold—the minimum (physical) distinction between stimulus attributes that can be detected 50% of the time—is also of concern. The difference threshold is also called a just noticeable difference (JND). Ernst Weber, a well‐known early investigator, observed that regardless of their magnitude, two stimuli must differ by a constant proportion for their difference to be detectable. His observations are formulated as Weber's law, which states that the “just noticeable difference” is a constant fraction of the stimulus intensity already present. (If a room is quiet, you can hear a faint knock at the door. But if your CD player is blaring, it takes a loud bang on the door for you to hear it.) If you are exposed to a stimulus that doesn't change over a period of time, sensory adaptation occurs, and you become less sensitive to the stimulus. If you have to study in a room with a constant noise outside, for example, you will usually eventually adapt to the noise, and it will become less offensive. Signal detection. Factors other than the magnitude of the stimulus also affect sensory discriminations. When a discrimination—that is, the detection of a stimulus (a signal)—must be made against a background of noise, the procedure is called signal detection. Signal detection theory takes into account the fact that people are making decisions as they make sensory discriminations. When they attempt to separate a signal change from its background, they may guess, have biases in their judgments, or become less vigilant during the judging process. Knowledge of signal detection theory is useful in many situations—for instance, if one were teaching people to detect accurately small blips on radar screens in an air control tower. Another aspect of sensory perception, subliminal perception (perception without awareness), has been of interest in recent years. However, the data concerning the existence of the phenomenon are still controversial. Basics: neuroscience and psychophysics Nội dung chính Show
Be able to diagnose whether a given experiment measures an absolute threshold, a difference threshold, or is a magnitude estimation experiment Be able to describe a couple of different methods of estimating a threshold Know what a subliminal message is Know Weber’s law (also called Weber-Fechner law) The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. Another way to think about this is by asking how dim can a light be or how soft can a sound be to still be detected half of the time. The sensitivity of our sensory receptors can be quite amazing. It has been estimated that on a clear night, the most sensitive sensory cells in the back of the eye can detect a candle flame 30 miles away (Okawa & Sampath, 2007). Under quiet conditions, the hair cells (the receptor cells of the inner ear) can detect the tick of a clock 20 feet away (Galanter, 1962). It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the brain: This is an absolute threshold. A message below that threshold is said to be subliminal—we receive it, but we are not consciously aware of it. Over the years there has been a great deal of speculation about the use of subliminal messages in advertising, rock music, and self-help audio programs. Research evidence shows that in laboratory settings, people can process and respond to information outside of awareness. But this does not mean that we obey these messages like zombies; in fact, hidden messages have little effect on behavior outside the laboratory (Kunst-Wilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin, Legrain, & Gobancé, 2009; Loersch, Durso, & Petty, 2013). Absolute thresholds are generally measured under incredibly controlled conditions in situations that are optimal for sensitivity. Sometimes, we are more interested in how much difference in stimuli is required to detect a difference between them. This is known as the just noticeable difference (JND) or difference threshold. Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity. As an example, imagine yourself in a very dark movie theater. If an audience member were to receive a text message on her cell phone which caused her screen to light up, chances are that many people would notice the change in illumination in the theater. However, if the same thing happened in a brightly lit arena during a basketball game, very few people would notice. The cell phone brightness does not change, but its ability to be detected as a change in illumination varies dramatically between the two contexts. Ernst Weber proposed this theory of change in difference threshold in the 1830s, and it has become known as Weber’s law: the difference threshold is a constant fraction of the original stimulus, as the example illustrates. Weber’s law is approximately true for many of our senses—for brightness perception, visual contrast perception, loudness perception, and visual distance estimation, our sensitivity to change decreases as the stimulus gets bigger or stronger. However, there are many senses for which the opposite is true: our sensitivity increases as the stimulus increases. With electric shock, for example, a small increase in the size of the shock is much more noticeable when
the shock is large than when it is small. A psychophysical researcher named Stanley Smith Stevens asked people to estimate the magnitude of their sensations for many different kinds of stimuli at different intensities, and then tried to fit lines through the data to predict people’s sensory experiences (Stevens, 1967). What he discovered was that most senses could be described by a power law of the form Both Stevens’ Power Law and Weber’s Law are only approximately true. They are useful for describing, in broad strokes, how our perception of a stimulus depends on its intensity or size. They are rarely accurate for describing perception of stimuli that are near the absolute detection threshold. Still, they are useful for describing how people are going to react to normal everyday stimuli. CC LICENSED CONTENT, SHARED PREVIOUSLY OpenStax, Psychology Chapter 5.1 Sensation and Perception. References: Galanter, E. (1962). Contemporary Psychophysics. In R. Brown, E.Galanter, E. H. Hess, & G. Mandler (Eds.), New directions in psychology. New York, NY: Holt, Rinehart & Winston. Kunst-Wilson, W. R., & Zajonc, R. B. (1980). Affective discrimination of stimuli that cannot be recognized. Science, 207, 557–558. Nelson, M. R. (2008). The hidden persuaders: Then and now. Journal of Advertising, 37(1), 113–126. Okawa, H., & Sampath, A. P. (2007). Optimization of single-photon response transmission at the rod-to-rod bipolar synapse. Physiology, 22, 279–286. Radel, R., Sarrazin, P., Legrain, P., & Gobancé, L. (2009). Subliminal priming of motivational orientation in educational settings: Effect on academic performance moderated by mindfulness. Journal of Research in Personality, 43(4), 1–18. Rensink, R. A. (2004). Visual sensing without seeing. Psychological Science, 15, 27–32. Stevens, S. S. (1957). On the psychophysical law. Psychological Review 64(3):153—181. PMID 13441853 What is the smallest amount of detectable stimuli?An absolute threshold is the smallest level of stimulus that can be detected, usually defined as at least half the time. The term is often used in neuroscience and experimental research and can be applied to any stimulus that can be detected by the human senses including sound, touch, taste, sight, and smell. What is the minimum amount of stimulation that a person can detect?The just noticeable difference (JND), also known as the difference threshold, is the minimum level of stimulation that a person can detect 50% of the time. What is the smallest detectable difference between two stimuli?Just noticeable difference (JND): The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus; also known as difference threshold. What is another name for sensory threshold?It is also known as the differential threshold or difference limen. Differential threshold was first explained by experimental psychologist and physiologist Ernst Weber and the concept was further expanded by Gustav Fechner. JND applies to a variety of senses like hearing, smell, sight, taste and touching. What is the smallest difference in stimuli that can be detected?The difference threshold is the smallest difference in stimulation that can be detected 50 percent of the time. The difference threshold is sometimes called the just noticeable difference (jnd), and it depends on the strength of the stimulus.
What is the minimum amount of stimulation that a person can detect?The just noticeable difference (JND), also known as the difference threshold, is the minimum level of stimulation that a person can detect 50% of the time.
Is the smallest intensity of a stimulus?The smallest detectable stimulus is called the absolute threshold, while the smallest detectable change in the intensity of a stimulus is called the difference threshold.
Is the minimum level of stimulus intensity needed to detect a stimulus?The "absolute threshold of sensation" refers to the minimum intensity of a stimulus that a person can detect half the time. This threshold is not fixed, but varies from person to person and can be influenced by psychological factors, such as expectations, motivation, and alertness.
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