Proprioception

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The cerebellum is largely responsible for coordinating the unconscious aspects of proprioception.

Proprioception (/ˌproʊprioʊˈsɛpʃən, -priə-/ PROH-pree-o-SEP-shən), from Latin proprius, meaning "one's own", "individual", and capio, capere, to take or grasp, is the sense of the relative position of one's own parts of the body and strength of effort being employed in movement. It is sometimes described as the "sixth sense".

In humans, it is provided by proprioceptors in skeletal striated muscles (muscle spindles) and tendons (Golgi tendon organ) and the fibrous membrane in joint capsules. It is distinguished from exteroception, by which one perceives the outside world, and interoception, by which one perceives pain, hunger, etc., and the movement of internal organs.

The brain integrates information from proprioception and from the vestibular system into its overall sense of body position, movement, and acceleration. The word kinesthesia or kinæsthesia (kinesthetic sense) strictly means movement sense, but has been used inconsistently to refer either to proprioception alone or to the brain's integration of proprioceptive and vestibular inputs.

Proprioception has also been described in other animals such as vertebrates, and in some invertebrates such as arthropods. More recently proprioception has also been described in flowering land plants (angiosperms).

History of study

The position-movement sensation was originally described in 1557 by Julius Caesar Scaliger as a "sense of locomotion". Much later, in 1826, Charles Bell expounded the idea of a "muscle sense", which is credited as one of the first descriptions of physiologic feedback mechanisms. Bell's idea was that commands are carried from the brain to the muscles, and that reports on the muscle's condition would be sent in the reverse direction. In 1847 the London neurologist Robert Todd highlighted important differences in the anterolateral and posterior columns of the spinal cord, and suggested that the latter were involved in the coordination of movement and balance.

At around the same time, Moritz Heinrich Romberg, a Berlin neurologist, was describing unsteadiness made worse by eye closure or darkness, now known as the eponymous Romberg's sign, once synonymous with tabes dorsalis, that became recognised as common to all proprioceptive disorders of the legs. Later, in 1880, Henry Charlton Bastian suggested "kinaesthesia" instead of "muscle sense" on the basis that some of the afferent information (back to the brain) comes from other structures, including tendons, joints, and skin. In 1889, Alfred Goldscheider suggested a classification of kinaesthesia into three types: muscle, tendon, and articular sensitivity.

In 1906, Charles Scott Sherrington published a landmark work that introduced the terms "proprioception", "interoception", and "exteroception". The "exteroceptors" are the organs that provide information originating outside the body, such as the eyes, ears, mouth, and skin. The interoceptors provide information about the internal organs, and the "proprioceptors" provide information about movement derived from muscular, tendon, and articular sources. Using Sherrington's system, physiologists and anatomists search for specialised nerve endings that transmit mechanical data on joint capsule, tendon and muscle tension (such as Golgi tendon organs and muscle spindles), which play a large role in proprioception.

Primary endings of muscle spindles "respond to the size of a muscle length change and its speed" and "contribute both to the sense of limb position and movement". Secondary endings of muscle spindles detect changes in muscle length, and thus supply information regarding only the sense of position. Essentially, muscle spindles are stretch receptors. It has been accepted that cutaneous receptors also contribute directly to proprioception by providing "accurate perceptual information about joint position and movement", and this knowledge is combined with information from the muscle spindles.

Components

A major component of proprioception is joint position sense, which is determined by measuring the accuracy of joint–angle replication. Clinical aspects of joint position sense are measured in joint position matching tests that measure a subject's ability to detect an externally imposed passive movement, or the ability to reposition a joint to a predetermined position. These involve an individual's ability to perceive the position of a joint without the aid of vision. Often it is assumed that the ability of one of these aspects will be related to another; however, experimental evidence suggests there is no strong relation between these two aspects. This suggests that while these components may well be related in a cognitive manner, they may in fact be physiologically separate.

More recent work into the mechanism of ankle sprains suggests that the role of reflexes may be more limited due to their long latencies (even at the spinal cord level), as ankle sprain events occur in perhaps 100 ms or less. In accordance, a model has been proposed to include a 'feedforward' component of proprioception, whereby the subject will also have central information about the body's position before attaining it.

Kinesthesia is a key component in muscle memory and hand-eye coordination, and training can improve this sense (see blind contour drawing). The ability to swing a golf club or to catch a ball requires a finely tuned sense of the position of the joints. This sense needs to become automatic through training to enable a person to concentrate on other aspects of performance, such as maintaining motivation or seeing where other people are.

Basis

The initiation of proprioception is the activation of a proprioreceptor in the periphery. The proprioceptive sense is believed to be composed of information from sensory neurons located in the inner ear (motion and orientation) and in the stretch receptors located in the muscles and the joint-supporting ligaments (stance). There are specific nerve receptors for this form of perception termed "proprioreceptors", just as there are specific receptors for pressure, light, temperature, sound, and other sensory experiences. Proprioreceptors are sometimes known as adequate stimuli receptors. TRPN, a member of the transient receptor potential family of ion channels, has been found to be responsible for proprioception in fruit flies, nematode worms, African clawed frogs, and zebrafish. PIEZO2, a nonselective cation channel, has been shown to underlie the mechanosensitivity of proprioceptors in mice. The channel mediating human proprioceptive mechanosensation has yet to be discovered.

Proprioception of the head stems from the muscles innervated by the trigeminal nerve, where the GSA fibers pass without synapsing in the trigeminal ganglion (first-order sensory neuron), reaching the mesencephalic tract and the mesencephalic nucleus of trigeminal nerve.

Although it was known that finger kinesthesia relies on skin sensation, recent research has found that kinesthesia-based haptic perception relies strongly on the forces experienced during touch. This research allows the creation of "virtual", illusory haptic shapes with different perceived qualities.

Conscious and non-conscious

In humans, a distinction is made between conscious proprioception and non-conscious proprioception:

• Conscious proprioception is communicated by the dorsal column-medial lemniscus pathway to the cerebrum.

• Non-conscious proprioception is communicated primarily via the dorsal spinocerebellar tract and ventral spinocerebellar tract, to the cerebellum.

• A non-conscious reaction is seen in the human proprioceptive reflex, or righting reflex—in the event that the body tilts in any direction, the person will cock their head back to level the eyes against the horizon. This is seen even in infants as soon as they gain control of their neck muscles. This control comes from the cerebellum, the part of the brain affecting balance.

Applications

Field sobriety testing

Proprioception is tested by American police officers using the field sobriety test to check for alcohol intoxication. The subject is required to touch his or her nose with eyes closed; people with normal proprioception may make an error of no more than 20 millimeters, while people suffering from impaired proprioception (a symptom of moderate to severe alcohol intoxication) fail this test due to difficulty locating their limbs in space relative to their noses.

Diagnosis

There are several relatively specific tests of the subject's ability to proprioceive. These tests are used in the diagnosis of neurological disorders. They include the visual and tactile placing reflexes.

Training

Proprioception is what allows someone to learn to walk in complete darkness without losing balance. During the learning of any new skill, sport, or art, it is usually necessary to become familiar with some proprioceptive tasks specific to that activity. Without the appropriate integration of proprioceptive input, an artist would not be able to brush paint onto a canvas without looking at the hand as it moved the brush over the canvas; it would be impossible to drive an automobile because a motorist would not be able to steer or use the pedals while looking at the road ahead; a person could not touch type or perform ballet; and people would not even be able to walk without watching where they put their feet.

Oliver Sacks reported the case of a young woman who lost her proprioception due to a viral infection of her spinal cord. At first she could not move properly at all or even control her tone of voice (as voice modulation is primarily proprioceptive). Later she relearned by using her sight (watching her feet) and inner ear only for movement while using hearing to judge voice modulation. She eventually acquired a stiff and slow movement and nearly normal speech, which is believed to be the best possible in the absence of this sense. She could not judge effort involved in picking up objects and would grip them painfully to be sure she did not drop them.

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Lower limb proprioceptive work

The proprioceptive sense can be sharpened through study of many disciplines. Examples are the Feldenkrais method and the Alexander Technique. Juggling trains reaction time, spatial location, and efficient movement. Standing on a wobble board or balance board is often used to retrain or increase proprioception abilities, particularly as physical therapy for ankle or knee injuries. Slacklining is another method to increase proprioception.

Standing on one leg (stork standing) and various other body-position challenges are also used in such disciplines as Yoga, Wing Chun and T'ai Chi Ch'uan. Also, the vestibular system of the inner ear, vision and proprioception are the main three requirements for balance. Moreover, there are specific devices designed for proprioception training, such as the exercise ball, which works on balancing the abdominal and back muscles.

Joint position matching

"Joint position matching" is an established protocol for measuring proprioception, and joint position sense specifically, without the aid of visual or vestibular information. During such tasks, individuals are blindfolded while a joint is moved to a specific angle for a given period of time, returned to neutral, and the subjects are asked to replicate the specified angle. Measured by constant and absolute errors, ability to accurately identify joint angles over a series of conditions is the most accurate means of determining proprioceptive acuity in isolation to date.

Recent investigations have shown that hand dominance, participant age, active versus passive matching, and presentation time of the angle can all affect performance on joint position matching tasks. Joint position matching has been used in clinical settings in both the upper and lower extremities.

Impairment

Temporary loss or impairment of proprioception may happen periodically during growth, mostly during adolescence. Growth that might also influence this would be large increases or drops in bodyweight/size due to fluctuations of fat (liposuction, rapid fat loss or gain) and/or muscle content (bodybuilding, anabolic steroids, catabolisis/starvation). It can also occur in those that gain new levels of flexibility, stretching, and contortion. A limb's being in a new range of motion never experienced (or at least, not for a long time since youth perhaps) can disrupt one's sense of location of that limb. Possible experiences include suddenly feeling that feet or legs are missing from one's mental self-image; needing to look down at one's limbs to be sure they are still there; and falling down while walking, especially when attention is focused upon something other than the act of walking.

Proprioception is occasionally impaired spontaneously, especially when one is tired. Similar effects can be felt during the hypnagogic state of consciousness, during the onset of sleep. One's body may feel too large or too small, or parts of the body may feel distorted in size. Similar effects can sometimes occur during epilepsy or migraine auras. These effects are presumed to arise from abnormal stimulation of the part of the parietal cortex of the brain involved with integrating information from different parts of the body.

Proprioceptive illusions can also be induced, such as the Pinocchio illusion.

The proprioceptive sense is often unnoticed because humans will adapt to a continuously present stimulus; this is called habituation, desensitization, or adaptation. The effect is that proprioceptive sensory impressions disappear, just as a scent can disappear over time. One practical advantage of this is that unnoticed actions or sensation continue in the background while an individual's attention can move to another concern. The Alexander Technique addresses these unconscious elements by bringing attention to them and practicing a new movement with focus on how it feels to move in the new way.

People who have a limb amputated may still have a confused sense of that limb's existence on their body, known as phantom limb syndrome. Phantom sensations can occur as passive proprioceptive sensations of the limb's presence, or more active sensations such as perceived movement, pressure, pain, itching, or temperature. There are a variety of theories concerning the etiology of phantom limb sensations and experience. One is the concept of "proprioceptive memory", which argues that the brain retains a memory of specific limb positions and that after amputation there is a conflict between the visual system, which actually sees that the limb is missing, and the memory system which remembers the limb as a functioning part of the body. Phantom sensations and phantom pain may also occur after the removal of body parts other than the limbs, such as after amputation of the breast, extraction of a tooth (phantom tooth pain), or removal of an eye (phantom eye syndrome).

Temporary impairment of proprioception has also been known to occur from an overdose of vitamin B6 (pyridoxine and pyridoxamine). Most of the impaired function returns to normal shortly after the amount of the vitamin in the body returns to a level that is closer to that of the physiological norm. Impairment can also be caused by cytotoxic factors such as chemotherapy.

It has been proposed that even common tinnitus and the attendant hearing frequency-gaps masked by the perceived sounds may cause erroneous proprioceptive information to the balance and comprehension centers of the brain, precipitating mild confusion.

Proprioception is permanently impaired in patients that suffer from joint hypermobility or Ehlers-Danlos syndrome (a genetic condition that results in weak connective tissue throughout the body). It can also be permanently impaired from viral infections as reported by Sacks. The catastrophic effect of major proprioceptive loss is reviewed by Robles-De-La-Torre (2006). There is also some evidence that proprioception is impaired in autism spectrum disorders such as Asperger Syndrome.

Proprioception is also permanently impaired in physiological aging (presbypropria).

Plants

Terrestrial plants control the orientation of their primary growth through the sensing of several vectorial stimuli such as the light gradient or the gravitational acceleration. This control has been called tropism. However, a quantitative study of shoot gravitropism demonstrated that, when a plant is tilted, it cannot recover a steady erected posture under the sole driving of the sensing of its angular deflection versus gravity. An additional control through the continuous sensing of its curvature by the organ and the subsequent driving an active straightening process are required. Being a sensing by the plant of the relative configuration of its parts, it has been called proprioception. This dual sensing and control by gravisensing and proprioception has been formalized into a unifying mathematical model simulating the complete driving of the gravitropic movement. This model has been validated on 11 species sampling the phylogeny of land angiosperms, and on organs of very contrasted sizes, ranging from the small germination of wheat (coleoptile) to the trunk of poplar trees. This model also shows that the entire gravitropic dynamics is controlled by a single dimensionless number called the "Balance Number", and defined as the ratio between the sensitivity to the inclination angle versus gravity and the proprioceptive sensitivity. This model has been extended to account for the effects of the passive bending of the organ under its self-weight, suggesting that proprioception is active even in very compliant stems, although they may not be able to efficiently straighten depending on their elastic deformation under the gravitational pull. Further studies have shown that the cellular mechanism of proprioception in plants involves myosin and actin, and seems to occur in specialized cells. Proprioception was then found to be involved in other tropisms and to be central also to the control of nutation.

These results change the view we have on plant sensitivity. They are also providing concepts and tools for the breeding of crops that are resilient to lodging, and of trees with straight trunks and homogeneous wood quality.

The discovery of proprioception in plants has generated an interest in the popular science and generalist media. This is because this discovery questions a long-lasting a priori that we have on plants. In some cases this has led to a shift between proprioception and self-awareness or self-consciousness. There is no scientific ground for such a semantic shift. Indeed, even in animals, proprioception can be unconscious; so it is thought to be in plants.

Time perception

From Wikipedia, the free encyclopedia

A contemporary quartz watch

Time perception is a field of study within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the indefinite and unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Though directly experiencing or understanding another person's perception of time is not possible, such a perception can be objectively studied and inferred through a number of scientific experiments. Time perception is a construction of the sapient brain, but one that is manipulable and distortable under certain circumstances. These temporal illusions help to expose the underlying neural mechanisms of time perception.

Pioneering work, emphasizing species-specific differences, was conducted by Karl Ernst von Baer.

In other words time can be perceived or understood as Subjective Time & Objective Time.

Theories

William J. Friedman (1993) also contrasted two theories for a sense of time:

• The strength model of time memory. This posits a memory trace that persists over time, by which one might judge the age of a memory (and therefore how long ago the event remembered occurred) from the strength of the trace. This conflicts with the fact that memories of recent events may fade more quickly than more distant memories.
• The inference model suggests the time of an event is inferred from information about relations between the event in question and other events whose date or time is known.

Another theory involves the brain's subconscious tallying of "pulses" during a specific interval, forming a biological stopwatch. This theory alleges that the brain can run multiple biological stopwatches at one time depending on the type of task one is involved in. The location of these pulses and what these pulses actually consist of is unclear. This model is only a metaphor and does not stand up in terms of brain physiology or anatomy.

Philosophical perspectives

The specious present is the time duration wherein a state of consciousness is experienced as being in the present. The term was first introduced by the philosopher E. R. Clay in 1882 (E. Robert Kelly), and was further developed by William James. James defined the specious present to be "the prototype of all conceived times... the short duration of which we are immediately and incessantly sensible". In "Scientific Thought" (1930), C. D. Broad further elaborated on the concept of the specious present and considered that the specious present may be considered as the temporal equivalent of a sensory datum. A version of the concept was used by Edmund Husserl in his works and discussed further by Francisco Varela based on the writings of Husserl, Heidegger, and Merleau-Ponty.

Neuroscientific perspectives

Although the perception of time is not associated with a specific sensory system, psychologists and neuroscientists suggest that humans do have a system, or several complementary systems, governing the perception of time. Time perception is handled by a highly distributed system involving the cerebral cortex, cerebellum and basal ganglia. One particular component, the suprachiasmatic nucleus, is responsible for the circadian (or daily) rhythm, while other cell clusters appear to be capable of shorter (ultradian) timekeeping. There is some evidence that very short (millisecond) durations are processed by dedicated neurons in early sensory parts of the brain.

Professor Warren Meck devised a physiological model for measuring the passage of time. He found the representation of time to be generated by the oscillatory activity of cells in the upper cortex. The frequency of these cells' activity is detected by cells in the dorsal striatum at the base of the forebrain. His model separated explicit timing and implicit timing. Explicit timing is used in estimating the duration of a stimulus. Implicit timing is used to gauge the amount of time separating one from an impending event that is expected to occur in the near future. These two estimations of time do not involve the same neuroanatomical areas. For example, implicit timing often occurs to achieve a motor task, involving the cerebellum, left parietal cortex, and left premotor cortex. Explicit timing often involves the supplementary motor area and the right prefrontal cortex.

Two visual stimuli, inside someone's field of view, can be successfully regarded as simultaneous up to five milliseconds.

In the popular essay "Brain Time", David Eagleman explains that different types of sensory information (auditory, tactile, visual, etc.) are processed at different speeds by different neural architectures. The brain must learn how to overcome these speed disparities if it is to create a temporally unified representation of the external world: "if the visual brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, it must wait about a tenth of a second. In the early days of television broadcasting, engineers worried about the problem of keeping audio and video signals synchronized. Then they accidentally discovered that they had around a hundred milliseconds of slop: As long as the signals arrived within this window, viewers' brains would automatically resynchronize the signals". He goes on to say that "This brief waiting period allows the visual system to discount the various delays imposed by the early stages; however, it has the disadvantage of pushing perception into the past. There is a distinct survival advantage to operating as close to the present as possible; an animal does not want to live too far in the past. Therefore, the tenth-of- a-second window may be the smallest delay that allows higher areas of the brain to account for the delays created in the first stages of the system while still operating near the border of the present. This window of delay means that awareness is postdictive, incorporating data from a window of time after an event and delivering a retrospective interpretation of what happened."

Experiments have shown that rats can successfully estimate a time interval of approximately 40 seconds, despite having their cortex entirely removed. This suggests that time estimation may be a low level process.

Types of temporal illusions

A temporal illusion is a distortion in the perception of time. Time perception refers to a variety of time-related tasks. For example:

• estimating time intervals, e.g., "When did you last see your primary care physician?";
• estimating time duration, e.g., "How long were you waiting at the doctor's office?"; and
• judging the simultaneity of events (see below for examples).

Short list of types of temporal illusions:

• Telescoping effect: People tend to recall recent events as occurring further back in time than they actually did (backward telescoping) and distant events as occurring more recently than they actually did (forward telescoping)
• Vierordt's law: Shorter intervals tend to be overestimated while longer intervals tend to be underestimated
• Time intervals associated with more changes may be perceived as longer than intervals with fewer changes
• Perceived temporal length of a given task may shorten with greater motivation
• Perceived temporal length of a given task may stretch when broken up or interrupted
• Auditory stimuli may appear to last longer than visual stimuli
• Time durations may appear longer with greater stimulus intensity (e.g., auditory loudness or pitch)
• Simultaneity judgments can be manipulated by repeated exposure to non-simultaneous stimuli.

Kappa effect

The Kappa effect or perceptual time dilation is a form of temporal illusion verifiable by experiment, wherein the temporal duration between a sequence of consecutive stimuli is thought to be relatively longer or shorter than its actual elapsed time, due to the spatial/auditory/tactile separation between each consecutive stimuli. The kappa effect can be displayed when considering a journey made in two parts that take an equal amount of time. Between these two parts, the journey that covers more distance may appear to take longer than the journey covering less distance, even though they take an equal amount of time.

Eye movements and "Chronostasis"

The perception of space and time undergoes distortions during rapid saccadic eye movements.

Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task demand to the brain appears to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade (e.g., quick eye movement). This elicits an overestimation in the temporal duration for which that target stimulus (i.e., postsaccadic stimulus) was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception. The most well-known version of this illusion is known as the stopped-clock illusion, wherein a subject's first impression of the second-hand movement of an analog clock, subsequent to one's directed attention (i.e., saccade) to the clock, is the perception of a slower-than-normal second-hand movement rate (the seconds hand of the clock may seemingly temporarily freeze in place after initially looking at it).

The occurrence of chronostasis extends beyond the visual domain into the auditory and tactile domains. In the auditory domain, chronostasis and duration overestimation occur when observing auditory stimuli. One common example is a frequent occurrence when making telephone calls. If, while listening to the phone's dial tone, research subjects move the phone from one ear to the other, the length of time between rings appears longer. In the tactile domain, chronostasis has persisted in research subjects as they reach for and grasp objects. After grasping a new object, subjects overestimate the time in which their hand has been in contact with this object. In other experiments, subjects turning a light on with a button were conditioned to experience the light before the button press.

Oddball effect

The perception of the duration of an event seems to be modulated by our recent experiences. Humans typically overestimate the perceived duration of the initial event in a stream of identical events and unexpected “oddball” stimuli seem to be perceived as longer in duration, relative to expected or frequently presented “standard” stimuli.

The oddball effect may serve an evolutionarily adapted “alerting” function and is consistent with reports of time slowing down in threatening situations. The effect seems to be strongest for images that are expanding in size on the retina, in other words, that are "looming" or approaching the viewer, and the effect can be eradicated for oddballs that are contracting or perceived to be receding from the viewer. The effect is also reduced or reversed with a static oddball presented amongst a stream of expanding stimuli.

Initial studies suggested that this oddball-induced “subjective time dilation” expanded the perceived duration of oddball stimuli by 30–50% but subsequent research has reported more modest expansion of around 10% or less. The direction of the effect, whether the viewer perceives an increase or a decrease in duration, also seems to be dependent upon the stimulus used.

Effects of emotional states

Awe

Research has suggested the feeling of awe has the ability to expand one's perceptions of time availability. Awe can be characterized as an experience of immense perceptual vastness that coincides with an increase in focus. Consequently, it is conceivable that one's temporal perception would slow down when experiencing awe.

Fear

Possibly related to the oddball effect, research suggests that time seems to slow down for a person during dangerous events (such as a car accident, a robbery, or when a person perceives a potential predator or mate), or when a person skydives or bungee jumps, where they're capable of complex thoughts in what would normally be the blink of an eye (See Fight-or-flight response). This reported slowing in temporal perception may have been evolutionarily advantageous because it may have enhanced one's ability to intelligibly make quick decisions in moments that were of critical importance to our survival. However, even though observers commonly report that time seems to have moved in slow motion during these events, it is unclear whether this is a function of increased time resolution during the event, or instead an illusion created by the remembering of an emotionally salient event.

A strong time dilation effect has been reported for perception of objects that were looming, but not of those retreating, from the viewer, suggesting that the expanding discs — which mimic an approaching object — elicit self-referential processes which act to signal the presence of a possible danger. Anxious people, or those in great fear, experience greater "time dilation" in response to the same threat stimuli due to higher levels of epinephrine, which increases brain activity (an adrenaline rush). In such circumstances, an illusion of time dilation could assist an efficacious escape. When exposed to a threat, three-year-old children were observed to exhibit a similar tendency to overestimate elapsed time.

Research suggests that the effect appears only at the point of retrospective assessment, rather than occurring simultaneously with events as they happened. Perceptual abilities were tested during a frightening experience — a free fall — by measuring people's sensitivity to flickering stimuli. The results showed that the subjects' temporal resolution was not improved as the frightening event was occurring. Events appear to have taken longer only in retrospect, possibly because memories were being more densely packed during the frightening situation.

People shown extracts from films known to induce fear often overestimated the elapsed time of a subsequently presented visual stimulus, whereas people shown emotionally neutral clips (weather forecasts and stock market updates) or those known to evoke feelings of sadness showed no difference. It is argued that fear prompts a state of arousal in the amygdala, which increases the rate of a hypothesized "internal clock". This could be the result of an evolved defensive mechanism triggered by a threatening situation.

Empathy

The perception of another persons' emotions can also change our sense of time. The theory of embodied mind (or cognition), caused by mirror neurons, helps explain how the perception of other people's emotions has the ability to change one's own sense of time. Embodied cognition hinges on an internal process that mimics or simulates another's emotional state. For example, if person #1 spends time with person #2 who speaks and walks incredibly slowly, person #1's internal clock may slow down.

Depression

Depression may increase one's ability to perceive time accurately. One study assessed this concept by asking subjects to estimate the amount of time that passed during intervals ranging from 3 seconds to 65 seconds. Results indicated that depressed subjects more accurately estimated the amount of time that had passed than non-depressed patients; non-depressed subjects overestimated the passing of time. This difference was hypothesized to be because depressed subjects focused less on external factors that may skew their judgment of time. The authors termed this hypothesized phenomenon "depressive realism."

Changes with age

Psychologists have found that the subjective perception of the passing of time tends to speed up with increasing age in humans. This often causes people to increasingly underestimate a given interval of time as they age. This fact can likely be attributed to a variety of age-related changes in the aging brain, such as the lowering in dopaminergic levels with older age; however, the details are still being debated.^[58][59][60] In an experimental study involving a group of subjects aged between 19 and 24 and a group between 60 and 80, the participants' abilities to estimate 3 minutes of time were compared. The study found that an average of 3 minutes and 3 seconds passed when participants in the younger group estimated that 3 minutes had passed, whereas the older group's estimate for when 3 minutes had passed came after an average of 3 minutes and 40 seconds.

Very young children literally "live in time" before gaining an awareness of its passing. A child will first experience the passing of time when he or she can subjectively perceive and reflect on the unfolding of a collection of events. A child's awareness of time develops during childhood when the child's attention and short-term memory capacities form — this developmental process is thought to be dependent on the slow maturation of the prefrontal cortex and hippocampus.

One day to an 11-year-old would be approximately 1/4,000 of their life, while one day to a 55-year-old would be approximately 1/20,000 of their life. This helps to explain why a random, ordinary day may therefore appear longer for a young child than an adult. The short term appears to go faster in proportion to the square root of the perceiver's age. So a year would be experienced by a 55-year-old as passing approximately 2¼ times more quickly than a year experienced by an 11-year-old. If long-term time perception is based solely on the proportionality of a person's age, then the following four periods in life would appear to be quantitatively equal: ages 5–10 (1x), ages 10–20 (2x), ages 20–40 (4x), age 40–80 (8x).

The common explanation is that most external and internal experiences are new for young children but repetitive for adults. Children have to be extremely engaged (i.e. dedicate many neural resources or significant brain power) in the present moment because they must constantly reconfigure their mental models of the world to assimilate it and manage behaviour properly. Adults however may rarely need to step outside mental habits and external routines. When an adult frequently experiences the same stimuli, they seem "invisible" because already sufficiently and effectively mapped by the brain. This phenomenon is known as neural adaptation. Thus, the brain will record fewer densely rich memories during these frequent periods of disengagement from the present moment. Consequently, the subjective perception is often that time passes by at a faster rate with age.

Effects of drugs

Stimulants produce overestimates of time duration, whereas depressants and anaesthetics produce underestimates of time duration.

Psychoactive drugs can alter the judgment of time. These include traditional psychedelics such as LSD, psilocybin, and mescaline as well as the dissociative class of psychedelics such as PCP, ketamine and dextromethorphan. At higher doses time may appear to slow down, speed up or seem out of sequence. In a 2007 study, psilocybin was found to significantly impair the ability to reproduce interval durations longer than 2.5 seconds, significantly impair synchronizing motor actions (taps on a computer keyboard) with regularly occurring tones, and impair the ability to keep tempo when asked to tap on a key at a self-paced but consistent interval. In 1955, British MP Christopher Mayhew took mescaline hydrochloride in an experiment under the guidance of his friend, Dr Humphry Osmond. On the BBC documentary The Beyond Within, he described that half a dozen times during the experiment, he had "a period of time that didn't end for [him]".

Stimulants can lead both humans and rats to overestimate time intervals, while depressants can have the opposite effect. The level of activity in the brain of neurotransmitters such as dopamine and norepinephrine may be the reason for this. Dopamine has a particularly strong connection with one's perception of time. Drugs that activate dopamine receptors speed up one's perception of time, while dopamine antagonists cause one to feel that time is passing slowly.

The effect of cannabis on time perception has been studied with inconclusive results.

Effects of body temperature

Time perception may speed up as body temperature rises, and slow down as body temperature lowers. This is especially true during stressful events.

Reversal of temporal order judgment

Numerous experimental findings suggest that temporal order judgments of actions preceding effects can be reversed under special circumstances. Experiments have shown that sensory simultaneity judgments can be manipulated by repeated exposure to non-simultaneous stimuli. In an experiment conducted by David Eagleman, a temporal order judgment reversal was induced in subjects by exposing them to delayed motor consequences. In the experiment, subjects played various forms of video games. Unknown to the subjects, the experimenters introduced a fixed delay between the mouse movements and the subsequent sensory feedback. For example, a subject may not see a movement register on the screen until 150 milliseconds after the mouse had moved. Participants playing the game quickly adapted to the delay and felt as though there was less delay between their mouse movement and the sensory feedback. Shortly after the experimenters removed the delay, the subjects commonly felt as though the effect on the screen happened just before they commanded it. This work addresses how the perceived timing of effects is modulated by expectations, and the extent to which such predictions are quickly modifiable. In an experiment conducted by Haggard and colleagues in 2002, participants pressed a button that triggered a flash of light at a distance after a slight delay of 100 milliseconds. By repeatedly engaging in this act, participants had adapted to the delay (i.e., they experienced a gradual shortening in the perceived time interval between pressing the button and seeing the flash of light). The experimenters then showed the flash of light instantly after the button was pressed. In response, subjects often thought that the flash (the effect) had occurred before the button was pressed (the cause). Additionally, when the experimenters slightly reduced the delay, and shortened the spatial distance between the button and the flash of light, participants had often claimed again to have experienced the effect before the cause.

Several experiments also suggest that temporal order judgment of a pair of tactile stimuli delivered in rapid succession, one to each hand, is noticeably impaired (i.e., misreported) by crossing the hands over the midline. However, congenitally blind subjects showed no trace of temporal order judgment reversal after crossing the arms. These results suggest that tactile signals taken in by the congenitally blind are ordered in time without being referred to a visuospatial representation. Unlike the congenitally blind subjects, the temporal order judgments of the late-onset blind subjects were impaired when crossing the arms to a similar extent as non-blind subjects. These results suggest that the associations between tactile signals and visuospatial representation is maintained once it is accomplished during infancy. Some research studies have also found that the subjects showed reduced deficit in tactile temporal order judgments when the arms were crossed behind their back than when they were crossed in front.

Flash-lag effect

In an experiment, participants were told to stare at an "x" symbol on a computer screen whereby a moving blue doughnut-like ring repeatedly circled the fixed "x" point. Occasionally, the ring would display a white flash for a split second that physically overlapped the ring's interior. However, when asked what was perceived, participants responded that they saw the white flash lagging behind the center of the moving ring. In other words, despite the reality that the two retinal images were actually spatially aligned, the flashed object was usually observed to trail a continuously moving object in space — a phenomenon referred to as the flash-lag effect.

The first proposed explanation, called the 'motion extrapolation' hypothesis, is that the visual system extrapolates the position of moving objects but not flashing objects when accounting for neural delays (i.e., the lag time between the retinal image and the observer's perception of the flashing object). The second proposed explanation by David Eagleman and Sejnowski, called the 'latency difference' hypothesis, is that the visual system processes moving objects at a faster rate than flashed objects. In the attempt to disprove the first hypothesis, David Eagleman conducted an experiment in which the moving ring suddenly reverses direction to spin in the other way as the flashed object briefly appears. If the first hypothesis were correct, we would expect that, immediately following reversal, the moving object would be observed as lagging behind the flashed object. However, the experiment revealed the opposite — immediately following reversal, the flashed object was observed as lagging behind the moving object. This experimental result supports of the 'latency difference' hypothesis. A recent study tries to reconcile these different approaches by approaching perception as an inference mechanism aiming at describing what is happening at the present time.

Effects of clinical disorders

Parkinson's disease, schizophrenia, and attention deficit hyperactivity disorder (ADHD) have been linked to abnormalities in dopamine levels in the brain as well as to noticeable impairments in time perception. Neuropharmacological research indicates that the internal clock, used to time durations in the seconds-to-minutes range, is linked to dopamine function in the basal ganglia. Studies in which children with ADHD are given time estimation tasks shows that time passes very slowly for them. Children with Tourette’s Syndrome, in contrast, who need to use the pre-frontal cortex to help them control their tics, are better at estimating intervals of time just over a second than other children.

In his book Awakenings, the neurologist Dr. Oliver Sacks discussed how patients with Parkinson's disease experience deficits in their awareness of time and tempo. For example, Mr E, when asked to clap his hands steadily and regularly, did so for the first few claps before clapping faster and irregularly, culminating in an apparent freezing of motion. When he finished, Mr E asked if his observers were glad he did it correctly, to which they replied "no". Mr E was offended by this because to him, his claps were regular and steady.

Dopamine is also theorized to play a role in the attention deficits present with attention deficit hyperactivity disorder. Specifically, dopaminergic systems are involved in working memory and inhibitory processes, both of which are believed central to ADHD pathology. Children with ADHD have also been found to be significantly impaired on time discrimination tasks (telling the difference between two stimuli of different temporal lengths) and respond earlier on time reproduction tasks (duplicating the duration of a presented stimulus) than controls.

Along with other perceptual abnormalities, it has been noted by psychologists that schizophrenia patients have an altered sense of time. This was first described in psychology by Minkowski in 1927. Many schizophrenic patients stop perceiving time as a flow of causally linked events. It has been suggested that there is usually a delay in time perception in schizophrenic patients compared to normal subjects.

These defects in time perception may play a part in the hallucinations and delusions experienced by schizophrenic patients according to some studies. Some researchers suggest that "abnormal timing judgment leads to a deficit in action attribution and action perception."

Sleep

The perception of time is temporarily suspended during sleep, or more often during REM sleep. This can be attributed to the altered state of consciousness associated with sleep that prevents awareness of the surroundings, which would make it difficult to remain informed of the passing of time — new memories are rarely made during sleep. Therefore, upon waking up in the morning a person subjectively feels no time has passed but reasons that many hours have elapsed simply because it is now light outside. The passing of time must be inferred by observations of objects (e.g., the sun’s location, the moon, a clock's time) relative to the previous evening. So, time may feel as passing "faster" during sleep due to the lack of reference points. Another experience sometimes reported is a long dream seeming to go on for hours when it actually lasted only a few seconds or minutes.

Substance theory

From Wikipedia, the free encyclopedia

Substance theory, or substance–attribute theory, is an ontological theory about objecthood, positing that a substance is distinct from its properties. A thing-in-itself is a property-bearer that must be distinguished from the properties it bears.

Substance is a key concept in ontology and metaphysics, which may be classified into monist, dualist, or pluralist varieties according to how many substances or individuals are said to populate, furnish, or exist in the world. According to monistic views, there is only one substance. Stoicism and Spinoza, for example, hold monistic views, that pneuma or God, respectively, is the one substance in the world. These modes of thinking are sometimes associated with the idea of immanence. Dualism sees the world as being composed of two fundamental substances, for example, the Cartesian substance dualism of mind and matter. Pluralist philosophies include Plato's Theory of Forms and Aristotle's hylomorphic categories.

Ancient Greek philosophy

Aristotle

Aristotle used the term "substance" (Greek: οὐσία ousia) in a secondary sense for genera and species understood as hylomorphic forms. Primarily, however, he used it with regard to his category of substance, the specimen ("this person" or "this horse") or individual, qua individual, who survives accidental change and in whom the essential properties inhere that define those universals.

A substance—that which is called a substance most strictly, primarily, and most of all—is that which is neither said of a subject nor in a subject, e.g. the individual man or the individual horse. The species in which the things primarily called substances are, are called secondary substances, as also are the genera of these species. For example, the individual man belongs in a species, man, and animal is a genus of the species; so these—both man and animal—are called secondary substances.

— Aristotle, Categories 2a13 (trans. J. L. Ackrill)

In chapter 6 of book I the Physics Aristotle argues that any change must be analysed in reference to the property of an invariant subject: as it was before the change and thereafter. Thus, in his hylomorphic account of change, matter serves as a relative substratum of transformation, i.e., of changing (substantial) form. In the Categories, properties are predicated only of substance, but in chapter 7 of book I of the Physics, Aristotle discusses substances coming to be and passing away in the "unqualified sense" wherein primary substances (πρῶται οὐσίαι; Categories 2a35) are generated from (or perish into) a material substratum by having gained (or lost) the essential property that formally defines substances of that kind (in the secondary sense). Examples of such a substantial change include not only conception and dying, but also metabolism, e.g., the bread a man eats becomes the man. On the other hand, in accidental change, because the essential property remains unchanged, by identifying the substance with its formal essence, substance may thereby serve as the relative subject matter or property-bearer of change in a qualified sense (i.e., barring matters of life or death). An example of this sort of accidental change is a change of color or size: a tomato becomes red, or a juvenile horse grows.

Aristotle thinks that in addition to primary substances (which are particulars), there are secondary substances (δεύτεραι οὐσίαι), which are universals (Categories 2a11–a18).

Neither the "bare particulars" nor "property bundles" of modern theory have their antecedent in Aristotle, according to whom, all matter exists in some form. There is no prime matter or pure elements, there is always a mixture: a ratio weighing the four potential combinations of primary and secondary properties and analysed into discrete one-step and two-step abstract transmutations between the elements.

However, according to Aristotle's theology, a form of invariant form exists without matter, beyond the cosmos, powerless and oblivious, in the eternal substance of the unmoved movers.

Stoicism

The Stoics rejected the idea that incorporeal beings inhere in matter, as taught by Plato. They believed that all being is corporeal infused with a creative fire called pneuma. Thus they developed a scheme of categories different from Aristotle's based on the ideas of Anaxagoras and Timaeus.

Neoplatonism

Neoplatonists argue that beneath the surface phenomena that present themselves to our senses are three higher spiritual principles or hypostases, each one more sublime than the preceding. For Plotinus, these are the soul or world-soul, being/intellect or divine mind (nous), and "the one".

Early modern philosophy

means by a substance an entity which exists in such a way that it needs no other entity in order to exist. Therefore, only God is a substance in this strict sense. However, he extends the term to created things, which need only the concurrence of God to exist. He maintained that two of these are mind and body, each being distinct from the other in their attributes and therefore in their essence, and neither needing the other in order to exist. This is Descartes' substance dualism.

Baruch Spinoza denied Descartes' "real distinction" between mind and matter. Substance, according to Spinoza, is one and indivisible, but has multiple "attributes". He regards an attribute, though, as "what we conceive as constituting the [single] essence of substance". The single essence of one substance can be conceived of as material and also, consistently, as mental. What is ordinarily called the natural world, together with all the individuals in it, is immanent in God: hence his famous phrase deus sive natura ("God or Nature").

John Locke views substance through a corpuscularian lens where it exhibits two types of qualities which both stem from a source. He believes that humans are born tabula rasa or “blank slate” – without innate knowledge. In An Essay Concerning Human Understanding Locke writes that “first essence may be taken for the very being of anything, whereby it is, what it is.” If humans are born without any knowledge, the way to receive knowledge is through perception of a certain object. But, according to Locke, an object exists in its primary qualities, no matter whether the human perceives it or not; it just exists. For example, an apple has qualities or properties that determine its existence apart from human perception of it, such as its mass or texture. The apple itself is also “pure substance in which is supposed to provide some sort of ‘unknown support’ to the observable qualities of things”^[vague] that the human mind perceives. The foundational or support qualities are called primary essences which “in the case of physical substances, are the underlying physical causes of the object's observable qualities”. But then what is an object except “the owner or support of other properties”? Locke rejects Aristotle’s category of the forms, and develops mixed ideas about what substance or “first essence” means. Locke’s solution to confusion about first essence is to argue that objects simply are what they are – made up of microscopic particles existing because they exist. According to Locke, the mind cannot completely grasp the idea of a substance as it “always falls beyond knowledge”. There is a gap between what first essence truly means and the mind’s perception of it that Locke believes the mind cannot bridge, objects in their primary qualities must exist apart from human perception.

The molecular combination of atoms in first essence then forms the solid base that humans can perceive and add qualities to describe - the only way humans can possibly begin to perceive an object. The way to perceive the qualities of an apple is from the combination of the primary qualities to form the secondary qualities. These qualities are then used to group the substances into different categories that “depend on the properties [humans] happen to be able to perceive”. The taste of an apple or the feeling of its smoothness are not traits inherent to the fruit but are the power of the primary qualities to produce an idea about that object in the mind. The reason that humans can’t sense the actual primary qualities is the mental distance from the object; thus, Locke argues, objects remain nominal for humans. Therefore, the argument then returns to how “a philosopher has no other idea of those substances than what is framed by a collection of those simple ideas which are found in them.” The mind’s conception of substances “[is] complex rather than simple” and “has no (supposedly innate) clear and distinct idea of matter that can be revealed through intellectual abstraction away from sensory qualities”.

The last quality of substance is the way the perceived qualities seem to begin to change – such as a candle melting; this quality is called the tertiary quality. Tertiary qualities “of a body are those powers in it that, by virtue of its primary qualities, give it the power to produce observable changes in the primary qualities of other bodies”; “the power of the sun to melt wax is a tertiary quality of the sun”. They are “mere powers; qualities such as flexibility, ductility; and the power of sun to melt wax”. This goes along with “passive power: the capacity a thing has for being changed by another thing”. In any object, at the core are the primary qualities (unknowable by the human mind), the secondary quality (how primary qualities are perceived), and tertiary qualities (the power of the combined qualities to make a change to itself and other objects). The corpuscularian hypothesis, by Robert Boyle, states that "all material bodies are composites of ultimately small particles of matter" that "have the same material qualities as the larger composite bodies do". Using this basis, Locke defines his first group, primary qualities, as "the ones that a body doesn't lose, however much it alters". The materials retain their primary qualities even if they are broken down because of the unchanging nature of their atomic particles. If someone is curious about an object and they say it is solid and extended, these two descriptors are primary qualities. The second group consists of secondary qualities which are "really nothing but the powers to produce various sensations in us by their primary qualities". Locke argues that the impressions our senses perceive from the objects (i.e. taste, sounds, colors, etc.) are not natural properties of the object itself, but things they induce in us by means of the "size, shape, texture, and motion of their imperceptible parts", or their atoms. The bodies send insensible particles to our senses which let us perceive the object through different faculties; what we perceive is based on the object's composition. With these qualities, people can achieve the object through bringing "co-existing powers and sensible qualities to a common ground for explanation". Locke supposes that one wants to know what "binds these qualities" into an object, and argues that a "substratum" or "substance" has this effect, defining "substance" as follows:

The idea that we have, to which we give the general name substance, being nothing but the supposed, but unknown, support of those qualities we find existing, which we imagine cannot subsist sine re substante, without something to support them, we call that support substantia; which, according to the true import of the word, is, in plain English, standing under or upholding.

— John Locke, An Essay Concerning Human Understanding; book 2, chapter 23; "Of our Complex Ideas of Substances"

This substratum is a construct of the mind in an attempt to bind all the qualities seen together; it is only "a supposition of an unknown support of qualities that are able to cause simple ideas in us". Without making a substratum, people would be at a loss as to how different qualities relate. Locke does, however, mention that this substratum is an unknown, relating it to the story of the world on the turtle's back and how the believers eventually had to concede that the turtle just rested on "something he knew not what". This is how the mind perceives all things and from which it can make ideas about them; it is entirely relative, but it does provide a "regularity and consistency to our ideas". Substance, overall, has two sets of qualities that define it, and how we perceive it. These qualities rush to our minds which must organize them. As a result, it creates a substratum for each object to which it groups related qualities.

Irreducible concepts

Two irreducible concepts encountered in substance theory are the bare particular and inherence.

Bare particular

In substance theory, a bare particular of an object is the element without which the object would not exist, that is, its substance, which exists independently from its properties, even if it is impossible for it to lack properties entirely. It is "bare" because it is considered without its properties and "particular" because it is not abstract. The properties that the substance has are said to inhere in the substance.

Inherence

Another primitive concept in substance theory is the inherence of properties within a substance. For example, in the sentence, "The apple is red" substance theory says that red inheres in the apple. Substance theory takes the meaning of an apple having the property of redness to be understood, and likewise that of a property's inherence in substance, which is similar to, but not identical with, being part of the substance.

The inverse relation is participation. Thus in the example above, just as red inheres in the apple, so the apple participates in red.

Arguments supporting the theory

Two common arguments supporting substance theory are the argument from grammar and the argument from conception.

Argument from grammar

The argument from grammar uses traditional grammar to support substance theory. For example, the sentence "Snow is white" contains a grammatical subject "snow" and the predicate "is white", thereby asserting snow is white. The argument holds that it makes no grammatical sense to speak of "whiteness" disembodied, without asserting that snow or something else is white. Meaningful assertions are formed by virtue of a grammatical subject, of which properties may be predicated, and in substance theory, such assertions are made with regard to a substance.

Bundle theory rejects the argument from grammar on the basis that a grammatical subject does not necessarily refer to a metaphysical subject. Bundle theory, for example, maintains that the grammatical subject of statement refers to its properties. For example, a bundle theorist understands the grammatical subject of the sentence, "Snow is white", to be a bundle of properties such as white. Accordingly, one can make meaningful statements about bodies without referring to substances.

Argument from conception

Another argument for the substance theory is the argument from conception. The argument claims that in order to conceive of an object's properties, like the redness of an apple, one must conceive of the object that has those properties. According to the argument, one cannot conceive of redness, or any other property, distinct from the substance that has that property.

Criticism

The idea of substance was famously critiqued by David Hume, who held that since substance cannot be perceived, it should not be assumed to exist. But the claim that substance cannot be perceived is neither clear nor obvious, and neither is the implication obvious.

Friedrich Nietzsche, and after him Martin Heidegger, Michel Foucault and Gilles Deleuze also rejected the notion of "substance", and in the same movement the concept of subject - seeing both concepts as holdovers from Platonic idealism. For this reason, Althusser's "anti-humanism" and Foucault's statements were criticized, by Jürgen Habermas and others, for misunderstanding that this led to a fatalist conception of social determinism. For Habermas, only a subjective form of liberty could be conceived, to the contrary of Deleuze who talks about "a life", as an impersonal and immanent form of liberty.

For Heidegger, Descartes means by "substance" that by which "we can understand nothing else than an entity which is in such a way that it need no other entity in order to be." Therefore, only God is a substance as Ens perfectissimus (most perfect being). Heidegger showed the inextricable relationship between the concept of substance and of subject, which explains why, instead of talking about "man" or "humankind", he speaks about the Dasein, which is not a simple subject, nor a substance.

Alfred North Whitehead has argued that the concept of substance has only a limited applicability in everyday life and that metaphysics should rely upon the concept of process.

Roman Catholic theologian Karl Rahner, as part of his critique of transubstantiation, rejected substance theory and instead proposed the doctrine of transfinalization, which he felt was more attuned to modern philosophy. However, this doctrine was rejected by Pope Paul VI in his encyclical Mysterium fidei.

Bundle theory

In direct opposition to substance theory is bundle theory, whose most basic premise is that all concrete particulars are merely constructions or 'bundles' of attributes or qualitative properties:

Necessarily, for any concrete entity, ${\displaystyle a}$, if for any entity, ${\displaystyle b}$, ${\displaystyle b}$ is a constituent of ${\displaystyle a}$, then ${\displaystyle b}$ is an attribute.

The bundle theorist's principal objections to substance theory concern the bare particulars of a substance, which substance theory considers independently of the substance's properties. The bundle theorist objects to the notion of a thing with no properties, claiming that such a thing is inconceivable and citing John Locke, who described a substance as "a something, I know not what." To the bundle theorist, as soon as one has any notion of a substance in mind, a property accompanies that notion.

Identity of indiscernibles counterargument

The indiscernibility argument from the substance theorist targets those bundle theorists who are also metaphysical realists. Metaphysical realism uses the identity of universals to compare and identify particulars. Substance theorists say that bundle theory is incompatible with metaphysical realism due to the identity of indiscernibles: particulars may differ from one another only with respect to their attributes or relations.

The substance theorist's indiscernibility argument against the metaphysically realistic bundle theorist states that numerically different concrete particulars are discernible from the self-same concrete particular only by virtue of qualitatively different attributes.

Necessarily, for any complex objects, ${\displaystyle a}$ and ${\displaystyle b}$, if for any entity, ${\displaystyle c}$, ${\displaystyle c}$ is a constituent of ${\displaystyle a}$ if and only if ${\displaystyle c}$ is a constituent of ${\displaystyle b}$, then ${\displaystyle a}$ is numerically identical with ${\displaystyle b}$.

The indiscernibility argument points out that if bundle theory and discernible concrete particulars theory explain the relationship between attributes, then the identity of indiscernibles theory must also be true:

Necessarily, for any concrete objects, ${\displaystyle a}$ and ${\displaystyle b}$, if for any attribute, Φ, Φ is an attribute of ${\displaystyle a}$ if and only if Φ is an attribute of ${\displaystyle b}$, then ${\displaystyle a}$ is numerically identical with ${\displaystyle b}$.

The indiscernibles argument then asserts that the identity of indiscernibles is violated, for example, by identical sheets of paper. All of their qualitative properties are the same (e.g. white, rectangular, 9 x 11 inches...) and thus, the argument claims, bundle theory and metaphysical realism cannot both be correct.

However, bundle theory combined with trope theory (as opposed to metaphysical realism) avoids the indiscernibles argument because each attribute is a trope if can only be held by only one concrete particular.

The argument does not consider whether "position" should be considered an attribute or relation. It is after all through the differing positions that we in practice differentiate between otherwise identical pieces of paper.