Sensory threshold

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In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probability curve. [1] Methods have been developed to measure thresholds in any of the senses.

Contents

Several different sensory thresholds have been defined; [2]

History

The first systematic studies to determine sensory thresholds were conducted by Ernst Heinrich Weber, a physiologist and pioneer of experimental psychology at the Leipzig University. [3] His experiments were intended to determine the absolute and difference, or differential, thresholds. Weber was able to define absolute and difference threshold statistically, which led to the establishment of Weber's Law and the concept of just noticeable difference to describe threshold perception of stimuli.

Following Weber's work, Gustav Fechner, a pioneer of psychophysics, studied the relationship between the physical intensity of a stimulus and the psychologically perceived intensity of the stimulus. [4] Comparing the measured intensity of sound waves with the perceived loudness, Fechner concluded that the intensity of a stimulus changes in proportion to the logarithm of the stimulus intensity. His findings would lead to the creation of the decibel scale. [3]

Measuring and testing sensory thresholds

Defining and measuring sensory thresholds requires setting the sensitivity limit such that the perception observations lead to the absolute threshold. The level of sensitivity is usually assumed to be constant in determining the threshold limit. There are three common methods used to determine sensory thresholds: [2]

  1. Method of Limits:
    In the first step, the subject is stimulated by strong, easily detectable stimuli that are decreased stepwise (descending sequence) until they cannot detect the stimulus. Then another stimulation sequence is applied called ascending sequence. In this sequence, stimulus intensity increases from subthreshold to easily detectable. Both sequences are repeated several times. This yields several momentary threshold values. In the following step, mean values are calculated for ascending and descending sequences separately. The mean value will be lower for descending sequences. In case of audiometry, the difference of the means in case of ascending vs. descending sequences has a diagnostic importance. In the final step, the average of the previously calculated means will result in the absolute threshold.
  2. Method of constant stimuli:
    Stimuli of varying intensities are presented in random order to a subject. Intensities involve stimuli which are surely subthreshold and stimuli which are surely supra-threshold. For the creation of the series, the approximate threshold judged by a simpler method (i.e.: by the method of limits). The random sequences are presented to the subject several times. The strength of the stimulus, perceived in more than half of the presentations, will be taken as the threshold.
  3. Adaptive method:
    Stimulation starts with a surely supra-threshold stimulus; then further stimuli are given with an intensity decreased in previously-defined steps. The series is stopped when the stimulus strength become subthreshold (this is called the turn phenomena). Then the step is halved, and the stimulation is repeated, but now with increasing intensities, until the subject perceives the sound again. This process is repeated several times, until the step size reaches the preset minimal value. With this method, the threshold value can be delineated very accurately. The initial size of the step can be selected depending on the expected accuracy.

In measuring sensory threshold, noise must be accounted for. Signal noise is defined as the presence of extra, unwanted energy in the observational system which obscures the information of interest. As the measurements come closer to the absolute threshold, the variability of the noise increases, causing the threshold to be obscured. [5] Different types of internal and external noise include excess stimuli, nervous system over- or under-stimulation, [6] and conditions that falsely stimulate nerves in the absence of external stimuli.

A universal absolute threshold is difficult to define a standard because of the variability of the measurements. [7] While sensation occurs at the physical nerves, there can be reasons why it is not consistent. Age [8] or nerve damage can affect sensation. Similarly, psychological factors can affect perception of physical sensation. Mental state, memory, [9] mental illness, [10] fatigue, and other factors can alter perception.

Aviation use

When related to motion in any of the possible six degrees of freedom (6-DoF), the fact that sensory thresholds exist is why it is essential that aircraft have blind-flying instruments. Sustained flight in cloud is not possible by `seat-of-the-pants' cues alone, since errors build up due to aircraft movements below the pilot's sensory threshold, ultimately leading to loss of control.

See also

Related Research Articles

<span class="mw-page-title-main">Perception</span> Interpretation of sensory information

Perception is reality. All perception involves signals that go through the nervous system, which in turn result from physical or chemical stimulation of the sensory system. Vision involves light striking the retina of the eye; smell is mediated by odor molecules; and hearing involves pressure waves.

<span class="mw-page-title-main">Weber–Fechner law</span> Related laws in the field of psychophysics

The Weber–Fechner laws are two related hypotheses in the field of psychophysics, known as Weber's law and Fechner's law. Both laws relate to human perception, more specifically the relation between the actual change in a physical stimulus and the perceived change. This includes stimuli to all senses: vision, hearing, taste, touch, and smell.

<span class="mw-page-title-main">Absolute threshold of hearing</span> Minimum sound level that an average human can hear

The absolute threshold of hearing (ATH), also known as the absolute hearing threshold or auditory threshold, is the minimum sound level of a pure tone that an average human ear with normal hearing can hear with no other sound present. The absolute threshold relates to the sound that can just be heard by the organism. The absolute threshold is not a discrete point and is therefore classed as the point at which a sound elicits a response a specified percentage of the time.

<span class="mw-page-title-main">Sensory nervous system</span> Part of the nervous system responsible for processing sensory information

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons, neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they produce. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual processes by studying the effect on a subject's experience or behaviour of systematically varying the properties of a stimulus along one or more physical dimensions".

<span class="mw-page-title-main">Stimulation</span> Providing something that rouses the recipient to activity

Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." An interesting or fun activity can be described as "stimulating", regardless of its physical effects on senses. Stimulate means to act as a stimulus to; stimulus means something that rouses the recipient to activity; stimuli is the plural of stimulus.

<span class="mw-page-title-main">Stimulus (physiology)</span> Detectable change in the internal or external surroundings

In physiology, a stimulus is a detectable change in the physical or chemical structure of an organism's internal or external environment. The ability of an organism or organ to detect external stimuli, so that an appropriate reaction can be made, is called sensitivity (excitability). Sensory receptors can receive information from outside the body, as in touch receptors found in the skin or light receptors in the eye, as well as from inside the body, as in chemoreceptors and mechanoreceptors. When a stimulus is detected by a sensory receptor, it can elicit a reflex via stimulus transduction. An internal stimulus is often the first component of a homeostatic control system. External stimuli are capable of producing systemic responses throughout the body, as in the fight-or-flight response. In order for a stimulus to be detected with high probability, its level of strength must exceed the absolute threshold; if a signal does reach threshold, the information is transmitted to the central nervous system (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.

Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.

<span class="mw-page-title-main">Nociceptor</span> Sensory neuron that detects pain

A nociceptor is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, so the threat can be mitigated; this process is called nociception.

The threshold of pain or pain threshold is the point along a curve of increasing perception of a stimulus at which pain begins to be felt. It is an entirely subjective phenomenon. A distinction must be maintained between the stimulus and the person's or animal's resulting pain perception. Although an IASP document defines "pain threshold" as "the minimum intensity of a stimulus that is perceived as painful", it then goes on to say that:

Traditionally the threshold has often been defined, as we defined it formerly, as the least stimulus intensity at which a subject perceives pain. Properly defined, the threshold is really the experience of the patient, whereas the intensity measured is an external event. It has been common usage for most pain research workers to define the threshold in terms of the stimulus, and that should be avoided ... The stimulus is not pain (q.v.) and cannot be a measure of pain.

In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time. This limen is also known as the difference limen, difference threshold, or least perceptible difference.

<span class="mw-page-title-main">Ernst Heinrich Weber</span> German psychologist

Ernst Heinrich Weber was a German physician who is considered one of the founders of experimental psychology. He was an influential and important figure in the areas of physiology and psychology during his lifetime and beyond. His studies on sensation and touch, along with his emphasis on good experimental techniques led to new directions and areas of study for future psychologists, physiologists, and anatomists.

<span class="mw-page-title-main">Sensory neuron</span> Nerve cell that converts environmental stimuli into corresponding internal stimuli

Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduction. The cell bodies of the sensory neurons are located in the dorsal ganglia of the spinal cord.

Stevens' power law is an empirical relationship in psychophysics between an increased intensity or strength in a physical stimulus and the perceived magnitude increase in the sensation created by the stimulus. It is often considered to supersede the Weber–Fechner law, which is based on a logarithmic relationship between stimulus and sensation, because the power law describes a wider range of sensory comparisons, down to zero intensity.

In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus – light, sound, touch, etc. – that an organism could detect. Under the influence of signal detection theory, absolute threshold has been redefined as the level at which a stimulus will be detected a specified percentage of the time. The absolute threshold can be influenced by several different factors, such as the subject's motivations and expectations, cognitive processes, and whether the subject is adapted to the stimulus.
The absolute threshold can be compared to the difference threshold, which is the measure of how different two stimuli must be for the subject to notice that they are not the same.

<span class="mw-page-title-main">Motion simulator</span> Type of mechanism

A motion simulator or motion platform is a mechanism that creates the feelings of being in a real motion environment. In a simulator, the movement is synchronised with a visual display of the outside world (OTW) scene. Motion platforms can provide movement in all of the six degrees of freedom (DOF) that can be experienced by an object that is free to move, such as an aircraft or spacecraft:. These are the three rotational degrees of freedom and three translational or linear degrees of freedom.

In physiology, psychology, or psychophysics, a limen or a liminal point is a sensory threshold of a physiological or psychological response. Such points delineate boundaries of perception; that is, a limen defines a sensory threshold beyond which a particular stimulus becomes perceivable, and below which it remains unperceivable.

A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. Although in some cultures five human senses were traditionally identified as such, many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.

Stochastic resonance is a phenomenon that occurs in a threshold measurement system when an appropriate measure of information transfer is maximized in the presence of a non-zero level of stochastic input noise thereby lowering the response threshold; the system resonates at a particular noise level.

As long as humans have experienced pain, they have given explanations for its existence and sought soothing agents to dull or cease painful sensations. Archaeologists have uncovered clay tablets dating back as far as 5,000 BC which reference the cultivation and use of the opium poppy to bring joy and cease pain. The Greek writer Homer's The Odyssey, written in 800 BC, features the character of Telemachus using opium to soothe his pain and forget his worries. While some cultures researched analgesics and allowed or encouraged their use, others perceived pain to be a necessary, integral sensation. Physicians of the 19th century used pain as a diagnostic tool, theorizing that a greater amount of personally perceived pain was correlated to a greater internal vitality, and as a treatment in and of itself, inflicting pain on their patients to rid the patient of evil and unbalanced humors.

References

  1. ↑ Smith, Christopher U. M. (20 November 2008). Biology of Sensory Systems. John Wiley & Sons. pp. 34–5. ISBN   978-0-470-69438-1 . Retrieved 11 October 2014.
  2. 1 2 "Determination of sensory thresholds". ttktamop.elte.hu. Retrieved 2016-12-02.
  3. 1 2 "Sensation: Thresholds and Psychophysics". users.ipfw.edu. Retrieved 2016-12-02.
  4. ↑ Swets, John A. (1961-07-21). "Is There a Sensory Threshold?". Science. 134 (3473): 168–177. Bibcode:1961Sci...134..168S. doi:10.1126/science.134.3473.168. ISSN   0036-8075. PMID   13774294.
  5. ↑ Cohn, Theodore E; Lasley, D J (1986). "Visual sensitivity". Annual Review of Psychology. 37: 495–521. doi:10.1146/annurev.ps.37.020186.002431. ISSN   0066-4308. PMID   3963783.
  6. ↑ "Sensory Processing - Introduction to Concepts". classes.kumc.edu. Retrieved 2016-12-02.
  7. ↑ Meddis, Ray; Lecluyse, Wendy (2011). "The psychophysics of absolute threshold and signal duration: A probabilistic approach" (PDF). Journal of the Acoustical Society of America. 129 (5): 3153–3165. Bibcode:2011ASAJ..129.3153M. doi:10.1121/1.3569712. ISSN   0001-4966. PMID   21568418.
  8. ↑ Humes, Larry E; Busey, Thomas A; Craig; Kewley-Port (1009). "The effects of age on sensory thresholds and temporal gap detection in hearing, vision, and touch". Attention, Perception, & Psychophysics. 71 (4): 860–871. doi:10.3758/APP.71.4.860. ISSN   1943-3921. PMC   2826883 . PMID   19429964.
  9. ↑ Thurgood, Clementine; Whitfield, T W A; Patterson (2011). "Towards a visual recognition threshold: New instrument shows humans identify animals with only 1 ms of visual exposure". Vision Research. 51 (17): 1966–1971. doi: 10.1016/j.visres.2011.07.008 . ISSN   0042-6989. PMID   21787801.
  10. ↑ Adler, Georg; Gattaz, Wagner F (1993). "Pain perception threshold in major depression". Biological Psychiatry. 34 (10): 687–689. doi:10.1016/0006-3223(93)90041-B. PMID   8292672. S2CID   10091855.
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