Do
we see what is really there? The two areas of the image marked A and B,
and the rectangle connecting them, are all of the same shade: our eyes
automatically "correct" for the shadow of the cylinder.
The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or metaphysical views. Philosophers distinguish internalist accounts, which assume that perceptions of objects, and knowledge or beliefs about them, are aspects of an individual's mind, and externalist accounts, which state that they constitute real aspects of the world external to the individual. The position of naïve realism—the
'everyday' impression of physical objects constituting what is
perceived—is to some extent contradicted by the occurrence of perceptual
illusions and hallucinations and the relativity of perceptual experience as well as certain insights in science. Realist conceptions include phenomenalism and direct and indirect realism. Anti-realist conceptions include idealism and skepticism.
Categories of perception
We may categorize perception as internal or external.
Internal perception (proprioception)
tells us what is going on in our bodies; where our limbs are, whether
we are sitting or standing, whether we are depressed, hungry, tired and
so forth.
External or sensory perception (exteroception),
tells us about the world outside our bodies. Using our senses of sight,
hearing, touch, smell, and taste, we perceive colors, sounds, textures,
etc. of the world at large. There is a growing body of knowledge of the
mechanics of sensory processes in cognitive psychology.
Mixed internal and external perception (e.g., emotion and certain
moods) tells us about what is going on in our bodies and about the
perceived cause of our bodily perceptions.
The philosophy of perception is mainly concerned with exteroception.
Scientific accounts of perception
An
object at some distance from an observer will reflect light in all
directions, some of which will fall upon the corneas of the eyes, where it will be focused upon each retina,
forming an image. The disparity between the electrical output of these
two slightly different images is resolved either at the level of the lateral geniculate nucleus or in a part of the visual cortex
called 'V1'. The resolved data is further processed in the visual
cortex where some areas have specialized functions, for instance area V5
is involved in the modelling of motion and V4 in adding color. The
resulting single image that subjects report as their experience is
called a 'percept'. Studies involving rapidly changing scenes show the
percept derives from numerous processes that involve time delays. Recent fMRI studies
show that dreams, imaginings and perceptions of things such as faces
are accompanied by activity in many of the same areas of brain as are
involved with physical sight. Imagery that originates from the senses
and internally generated imagery may have a shared ontology at higher levels of cortical processing.
Sound is analyzed in term of pressure waves sensed by the cochlea
in the ear. Data from the eyes and ears is combined to form a 'bound'
percept. The problem of how this is produced, known as the binding problem.
Perception is analyzed as a cognitive process in which information processing
is used to transfer information into the mind where it is related to
other information. Some psychologists propose that this processing gives
rise to particular mental states (cognitivism) whilst others envisage a direct path back into the external world in the form of action (radical behaviorism). Behaviorists such as John B. Watson and B.F. Skinner have proposed that perception acts largely as a process between a stimulus and a response but have noted that Gilbert Ryle's "ghost in the machine
of the brain" still seems to exist. "The objection to inner states is
not that they do not exist, but that they are not relevant in a
functional analysis". This view, in which experience is thought to be an incidental by-product of information processing, is known as epiphenomenalism.
Contrary to the behavioralist approach to understanding the elements of cognitive processes, gestalt psychology sought to understand their organization as a whole, studying perception as a process of figure and ground.
Philosophical accounts of perception
Important philosophical problems derive from the epistemology of perception—how we can gain knowledge via perception—such as the question of the nature of qualia. Within the biological study of perception naive realism is unusable. However, outside biology modified forms of naive realism are defended. Thomas Reid, the eighteenth-century founder of the Scottish School of Common Sense,
formulated the idea that sensation was composed of a set of data
transfers but also declared that there is still a direct connection
between perception and the world. This idea, called direct realism, has
again become popular in recent years with the rise of postmodernism.
The succession of data transfers involved in perception suggests that sense data are somehow available to a perceiving subject that is the substrate of the percept. Indirect realism, the view held by John Locke and Nicolas Malebranche, proposes that we can only be aware of mental representations
of objects. However, this may imply an infinite regress (a perceiver
within a perceiver within a perceiver...), though a finite regress is
perfectly possible.
It also assumes that perception is entirely due to data transfer and
information processing, an argument that can be avoided by proposing
that the percept does not depend wholly upon the transfer and
rearrangement of data. This still involves basic ontological issues of
the sort raised by Leibniz, Locke, Hume, Whitehead and others, which remain outstanding particularly in relation to the binding problem,
the question of how different perceptions (e.g. color and contour in
vision) are "bound" to the same object when they are processed by
separate areas of the brain.
Indirect realism (representational views) provides an account of issues such as perceptual contents, qualia, dreams, imaginings, hallucinations, illusions, the resolution of binocular rivalry, the resolution of multistable perception,
the modelling of motion that allows us to watch TV, the sensations that
result from direct brain stimulation, the update of the mental image by
saccades of the eyes and the referral of events backwards in time.
Direct realists must either argue that these experiences do not occur or
else refuse to define them as perceptions.
Idealism holds that reality is limited to mental qualities while
skepticism challenges our ability to know anything outside our minds.
One of the most influential proponents of idealism was George Berkeley who maintained that everything was mind or dependent upon mind. Berkeley's idealism has two main strands, phenomenalism in which physical events are viewed as a special kind of mental event and subjective idealism. David Hume is probably the most influential proponent of skepticism.
A fourth theory of perception in opposition to naive realism, enactivism, attempts to find a middle path between direct realist and indirect realist theories, positing that cognition
arises as a result of the dynamic interplay between an organism's
sensory-motor capabilities and its environment. Instead of seeing
perception as a passive process determined entirely by the features of
an independently existing world, enactivism suggests that organism and
environment are structurally coupled and co-determining. The theory was
first formalized by Francisco Varela, Evan Thompson, and Eleanor Rosch
in "The Embodied Mind".
Spatial representation
An aspect of perception that is common to both realists and anti-realists is the idea of mental or perceptual space. David Hume
concluded that things appear extended because they have attributes of
colour and solidity. A popular modern philosophical view is that the
brain cannot contain images so our sense of space must be due to the
actual space occupied by physical things. However, as René Descartes
noticed, perceptual space has a projective geometry, things within it
appear as if they are viewed from a point. The phenomenon of perspective was closely studied by artists and architects in the Renaissance, who relied mainly on the 11th century polymath, Alhazen (Ibn al-Haytham), who affirmed the visibility of perceptual space in geometric structuring projections. Mathematicians now know of many types of projective geometry such as complex Minkowski space
that might describe the layout of things in perception (see Peters
(2000)) and it has also emerged that parts of the brain contain patterns
of electrical activity that correspond closely to the layout of the
retinal image (this is known as retinotopy). How or whether these become conscious experience is still unknown (see McGinn (1995)).
Humans
are able to have a very good guess on the underlying 3D shape
category/identity/geometry given a silhouette of that shape. Computer vision
researchers have been able to build computational models for perception
that exhibit a similar behavior and are capable of generating and
reconstructing sensible 3D shapes from single or multi-view depth maps
or silhouettes
Perception (from the Latinperceptio) is the organization, identification, and interpretation of sensoryinformation in order to represent and understand the presented information, or the environment.
Perception is not only the passive receipt of these signals, but it's also shaped by the recipient's learning, memory, expectation, and attention.
Perception can be split into two processes:
processing the sensory input, which transforms these
low-level information to higher-level information (e.g., extracts shapes
for object recognition);
processing which is connected with a person's concepts and
expectations (or knowledge), restorative and selective mechanisms (such
as attention) that influence perception.
Perception depends on complex functions of the nervous system, but
subjectively seems mostly effortless because this processing happens
outside conscious awareness.
Since the rise of experimental psychology in the 19th century, psychology's understanding of perception has progressed by combining a variety of techniques. Psychophysics quantitatively describes the relationships between the physical qualities of the sensory input and perception. Sensory neuroscience studies the neural mechanisms underlying perception. Perceptual systems can also be studied computationally, in terms of the information they process. Perceptual issues in philosophy
include the extent to which sensory qualities such as sound, smell or
color exist in objective reality rather than in the mind of the
perceiver.
Although the senses were traditionally viewed as passive receptors, the study of illusions and ambiguous images has demonstrated that the brain's perceptual systems actively and pre-consciously attempt to make sense of their input. There is still active debate about the extent to which perception is an active process of hypothesis testing, analogous to science, or whether realistic sensory information is rich enough to make this process unnecessary.
The perceptual systems of the brain
enable individuals to see the world around them as stable, even though
the sensory information is typically incomplete and rapidly varying.
Human and animal brains are structured in a modular way, with different areas processing different kinds of sensory information. Some of these modules take the form of sensory maps,
mapping some aspect of the world across part of the brain's surface.
These different modules are interconnected and influence each other. For
instance, taste is strongly influenced by smell.
Process and terminology
The process of perception begins with an object in the real world, termed the distal stimulus or distal object.
By means of light, sound or another physical process, the object
stimulates the body's sensory organs. These sensory organs transform the
input energy into neural activity—a process called transduction. This raw pattern of neural activity is called the proximal stimulus. These neural signals are transmitted to the brain and processed. The resulting mental re-creation of the distal stimulus is the percept.
An example would be a shoe. The shoe itself is the distal
stimulus. When light from the shoe enters a person's eye and stimulates
the retina, that stimulation is the proximal stimulus.
The image of the shoe reconstructed by the brain of the person is the
percept. Another example would be a telephone ringing. The ringing of
the telephone is the distal stimulus. The sound stimulating a person's
auditory receptors is the proximal stimulus, and the brain's
interpretation of this as the ringing of a telephone is the percept. The
different kinds of sensation such as warmth, sound, and taste are
called sensory modalities.
Psychologist Jerome Bruner has developed a model of perception. According to him, people go through the following process to form opinions:
when we encounter an unfamiliar target, we are open to different informational cues and want to learn more about the target.
in the second step, we try to collect more information about the
target. Gradually, we encounter some familiar cues which help us
categorize the target.
at this stage, the cues become less open and selective. We try to
search for more cues that confirm the categorization of the target. We
also actively ignore and even distort cues that violate our initial
perceptions. Our perception becomes more selective and we finally paint a
consistent picture of the target.
According to Alan Saks and Gary Johns, there are three components to perception:
the Perceiver, the person who becomes aware about something and
comes to a final understanding. There are 3 factors that can influence
his or her perceptions: experience, motivational state and finally
emotional state. In different motivational or emotional states, the
perceiver will react to or perceive something in different ways. Also in
different situations he or she might employ a "perceptual defence"
where they tend to "see what they want to see".
the Target. This is the person who is being perceived or judged.
"Ambiguity or lack of information about a target leads to a greater need
for interpretation and addition."
the Situation also greatly influences perceptions because different
situations may call for additional information about the target.
Stimuli are not necessarily translated into a percept and rarely does
a single stimulus translate into a percept. An ambiguous stimulus may
be translated into multiple percepts, experienced randomly, one at a
time, in what is called multistable perception.
And the same stimuli, or absence of them, may result in different
percepts depending on subject's culture and previous experiences.
Ambiguous figures demonstrate that a single stimulus can result in more
than one percept; for example the Rubin vase
which can be interpreted either as a vase or as two faces. The percept
can bind sensations from multiple senses into a whole. A picture of a
talking person on a television screen, for example, is bound to the
sound of speech from speakers to form a percept of a talking person. "Percept" is also a term used by Leibniz, Bergson, Deleuze, and Guattari to define perception independent from perceivers.
Types
Vision
In
many ways, vision is the primary human sense. Light is taken in through
each eye and focused in a way which sorts it on the retina according to
direction of origin. A dense surface of photosensitive cells, including
rods, cones, and intrinsically photosensitive retinal ganglion cells
captures information about the intensity, color, and position of
incoming light. Some processing of texture and movement occurs within
the neurons on the retina before the information is sent to the brain.
In total, about 15 differing types of information are then forwarded to
the brain proper via the optic nerve.
Sound
Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image)
Hearing (or audition) is the ability to perceive sound by detecting vibrations. Frequencies capable of being heard by humans are called audio or sonic. The range is typically considered to be between 20 Hz and 20,000 Hz. Frequencies higher than audio are referred to as ultrasonic, while frequencies below audio are referred to as infrasonic. The auditory system includes the outer ears which collect and filter sound waves, the middle ear for transforming the sound pressure (impedance matching), and the inner ear which produces neural signals in response to the sound. By the ascending auditory pathway these are led to the primary auditory cortex within the temporal lobe of the human brain, which is where the auditory information arrives in the cerebral cortex and is further processed there.
Sound does not usually come from a single source: in real
situations, sounds from multiple sources and directions are superimposed
as they arrive at the ears. Hearing involves the computationally
complex task of separating out the sources of interest, often estimating
their distance and direction as well as identifying them.
Touch
Haptic perception is the process of recognizing objects through touch. It involves a combination of somatosensory perception of patterns on the skin surface (e.g., edges, curvature, and texture) and proprioception of hand position and conformation. People can rapidly and accurately identify three-dimensional objects by touch.
This involves exploratory procedures, such as moving the fingers over
the outer surface of the object or holding the entire object in the
hand. Haptic perception relies on the forces experienced during touch.
Gibson defined the haptic system as "The sensibility of the individual to the world adjacent to his body by use of his body".
Gibson and others emphasized the close link between haptic perception
and body movement: haptic perception is active exploration. The concept
of haptic perception is related to the concept of extended physiological proprioception
according to which, when using a tool such as a stick, perceptual
experience is transparently transferred to the end of the tool.
Taste
Taste (or, the more formal term, gustation) is the ability to perceive the flavor of substances including, but not limited to, food. Humans receive tastes through sensory organs called taste buds, or gustatory calyculi, concentrated on the upper surface of the tongue. The human tongue has 100 to 150 taste receptor cells on each of its roughly ten thousand taste buds. There are five primary tastes: sweetness, bitterness, sourness, saltiness, and umami. Other tastes can be mimicked by combining these basic tastes. The recognition and awareness of umami is a relatively recent development in Western cuisine. The basic tastes contribute only partially to the sensation and flavor of food in the mouth — other factors include smell, detected by the olfactory epithelium of the nose; texture, detected through a variety of mechanoreceptors, muscle nerves, etc.; and temperature, detected by thermoreceptors. All basic tastes are classified as either appetitive or aversive, depending upon whether the things they sense are harmful or beneficial.
Smell
Smell
is the process of absorbing molecules through olfactory organs. Humans
absorb these molecules through the nose. These molecules diffuse through
a thick layer of mucus, come into contact with one of thousands of
cilia that are projected from sensory neurons, and are then absorbed
into one of, 347 or so, receptors. It is this process that causes humans to understand the concept of smell from a physical standpoint.
Smell is also a very interactive sense as scientists are have
begun to observe that olfaction comes into contact with the other sense
in unexpected ways.
Smell is also the most primal of the senses. It has been the
discussion of being the sense that drives the most basic of human
survival skills as it being the first indicator of safety or danger,
friend or foe. It can be a catalyst for human behavior on a subconscious
and instinctive level.
Social
Social perception
is the part of perception that allows people to understand the
individuals and groups of their social world, and thus an element of social cognition.
Speech
Though the phrase "I owe you" can be heard as three distinct words, a spectrogram reveals no clear boundaries.
Speech perception is the process by which spoken languages are
heard, interpreted and understood. Research in speech perception seeks
to understand how human listeners recognize speech sounds and use this
information to understand spoken language. The sound of a word can vary
widely according to words around it and the tempo of the speech, as well
as the physical characteristics, accent
and mood of the speaker. Listeners manage to perceive words across this
wide range of different conditions. Another variation is that reverberation
can make a large difference in sound between a word spoken from the far
side of a room and the same word spoken up close. Experiments have
shown that people automatically compensate for this effect when hearing
speech.
The process of perceiving speech begins at the level of the sound within the auditory signal and the process of audition.
The initial auditory signal is compared with visual information —
primarily lip movement — to extract acoustic cues and phonetic
information. It is possible other sensory modalities are integrated at
this stage as well. This speech information can then be used for higher-level language processes, such as word recognition.
Speech perception is not necessarily uni-directional. That is, higher-level language processes connected with morphology, syntax, or semantics may interact with basic speech perception processes to aid in recognition of speech sounds.
It may be the case that it is not necessary and maybe even not possible
for a listener to recognize phonemes before recognizing higher units,
like words for example. In one experiment, Richard M. Warren replaced
one phoneme of a word with a cough-like sound. His subjects restored the
missing speech sound perceptually without any difficulty and what is
more, they were not able to identify accurately which phoneme had been
disturbed.
Faces
Facial perception
refers to cognitive processes specialized for handling human faces,
including perceiving the identity of an individual, and facial
expressions such as emotional cues.
Social touch
The somatosensory cortex encodes incoming sensory information from receptors all over the body. Affective touch
is a type of sensory information that elicits an emotional reaction and
is usually social in nature, such as a physical human touch. This type
of information is actually coded differently than other sensory
information. Intensity of affective touch is still encoded in the
primary somatosensory cortex, but the feeling of pleasantness associated
with affective touch activates the anterior cingulate cortex more than
the primary somatosensory cortex. Functional magnetic resonance imaging
(fMRI) data shows that increased blood oxygen level contrast (BOLD)
signal in the anterior cingulate cortex as well as the prefrontal cortex
is highly correlated with pleasantness scores of an affective touch.
Inhibitory transcranial magnetic stimulation (TMS) of the primary
somatosensory cortex inhibits the perception of affective touch
intensity, but not affective touch pleasantness. Therefore, the S1 is
not directly involved in processing socially affective touch
pleasantness, but still plays a role in discriminating touch location
and intensity.
Other senses
Other
senses enable perception of body balance, acceleration, gravity,
position of body parts, temperature, pain, time, and perception of
internal senses such as suffocation, gag reflex, intestinal distension,
fullness of rectum and urinary bladder, and sensations felt in the
throat and lungs.
Reality
In the case of visual perception, some people can actually see the percept shift in their mind's eye. Others, who are not picture thinkers,
may not necessarily perceive the 'shape-shifting' as their world
changes. The 'esemplastic' nature has been shown by experiment: an ambiguous image has multiple interpretations on the perceptual level.
This confusing ambiguity of perception is exploited in human technologies such as camouflage, and also in biological mimicry, for example by European peacock butterflies, whose wings bear eyespots that birds respond to as though they were the eyes of a dangerous predator.
There is also evidence that the brain in some ways operates on a
slight "delay", to allow nerve impulses from distant parts of the body
to be integrated into simultaneous signals.
Perception is one of the oldest fields in psychology. The oldest quantitative laws in psychology are Weber's law
– which states that the smallest noticeable difference in stimulus
intensity is proportional to the intensity of the reference – and Fechner's law
which quantifies the relationship between the intensity of the physical
stimulus and its perceptual counterpart (for example, testing how much
darker a computer screen can get before the viewer actually notices).
The study of perception gave rise to the Gestalt school of psychology, with its emphasis on holistic approach.
Physiology
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic sensation (touch), taste and olfaction (smell). It has been suggested that the immune system is an overlooked sensory modality. In short, senses are transducers from the physical world to the realm of the mind.
The receptive field
is the specific part of the world to which a receptor organ and
receptor cells respond. For instance, the part of the world an eye can
see, is its receptive field; the light that each rod or cone can see, is its receptive field. Receptive fields have been identified for the visual system, auditory system and somatosensory system,
so far. Research attention is currently focused not only on external
perception processes, but also to "Interoception", considered as the
process of receiving, accessing and appraising internal bodily signals.
Maintaining desired physiological states is critical for an organism’s
well being and survival. Interoception is an iterative process,
requiring the interplay between perception of body states and awareness
of these states to generate proper self-regulation. Afferent sensory
signals continuously interact with higher order cognitive
representations of goals, history, and environment, shaping emotional
experience and motivating regulatory behavior.
Features
Constancy
Perceptual constancy is the ability of perceptual systems to recognize the same object from widely varying sensory inputs.
For example, individual people can be recognized from views, such as
frontal and profile, which form very different shapes on the retina. A
coin looked at face-on makes a circular image on the retina, but when
held at angle it makes an elliptical image.
In normal perception these are recognized as a single three-dimensional
object. Without this correction process, an animal approaching from the
distance would appear to gain in size. One kind of perceptual constancy is color constancy: for example, a white piece of paper can be recognized as such under different colors and intensities of light. Another example is roughness constancy:
when a hand is drawn quickly across a surface, the touch nerves are
stimulated more intensely. The brain compensates for this, so the speed
of contact does not affect the perceived roughness. Other constancies include melody, odor, brightness and words.
This constancy is not always total, but the variation in the
percept is much less than the variation in the physical stimulus.
The perceptual systems of the brain achieve perceptual constancy in a
variety of ways, each specialized for the kind of information being
processed, with phonemic restoration as a notable example from hearing.
Grouping
Law of Closure. The human brain tends to perceive complete shapes even if those forms are incomplete.
The principles of grouping (or Gestalt laws of grouping) are a set of principles in psychology, first proposed by Gestalt psychologists
to explain how humans naturally perceive objects as organized patterns
and objects. Gestalt psychologists argued that these principles exist
because the mind has an innate disposition to perceive patterns in the stimulus based on certain rules. These principles are organized into six categories: proximity, similarity, closure, good continuation, common fate and good form.
The principle of proximity states that, all else being equal, perception tends to group stimuli that are close together as part of the same object, and stimuli that are far apart as two separate objects. The principle of similarity
states that, all else being equal, perception lends itself to seeing
stimuli that physically resemble each other as part of the same object,
and stimuli that are different as part of a different object. This
allows for people to distinguish between adjacent and overlapping
objects based on their visual texture and resemblance. The principle of closure
refers to the mind's tendency to see complete figures or forms even if a
picture is incomplete, partially hidden by other objects, or if part of
the information needed to make a complete picture in our minds is
missing. For example, if part of a shape's border is missing people
still tend to see the shape as completely enclosed by the border and
ignore the gaps. The principle of good continuation makes sense
of stimuli that overlap: when there is an intersection between two or
more objects, people tend to perceive each as a single uninterrupted
object. The principle of common fate groups stimuli together on
the basis of their movement. When visual elements are seen moving in the
same direction at the same rate, perception associates the movement as
part of the same stimulus. This allows people to make out moving objects
even when other details, such as color or outline, are obscured. The
principle of good form refers to the tendency to group together forms of similar shape, pattern, color, etc. Later research has identified additional grouping principles.
Contrast effects
A
common finding across many different kinds of perception is that the
perceived qualities of an object can be affected by the qualities of
context. If one object is extreme on some dimension, then neighboring
objects are perceived as further away from that extreme. "Simultaneous
contrast effect" is the term used when stimuli are presented at the same
time, whereas "successive contrast" applies when stimuli are presented
one after another.
The contrast effect was noted by the 17th Century philosopher John Locke,
who observed that lukewarm water can feel hot or cold, depending on
whether the hand touching it was previously in hot or cold water. In the early 20th Century, Wilhelm Wundt
identified contrast as a fundamental principle of perception, and since
then the effect has been confirmed in many different areas.
These effects shape not only visual qualities like color and
brightness, but other kinds of perception, including how heavy an object
feels. One experiment found that thinking of the name "Hitler" led to subjects rating a person as more hostile.
Whether a piece of music is perceived as good or bad can depend on
whether the music heard before it was pleasant or unpleasant.
For the effect to work, the objects being compared need to be similar
to each other: a television reporter can seem smaller when interviewing a
tall basketball player, but not when standing next to a tall building. In the brain, brightness contrast exerts effects on both neuronal firing rates and neuronal synchrony.
Theories
Perception as direct perception
Cognitive theories of perception assume there is a poverty of stimulus. This (with reference to perception) is the claim that sensations are, by themselves, unable to provide a unique description of the world. Sensations require 'enriching', which is the role of the mental model. A different type of theory is the perceptual ecology approach of James J. Gibson. Gibson rejected the assumption of a poverty of stimulus
by rejecting the notion that perception is based upon sensations –
instead, he investigated what information is actually presented to the
perceptual systems. His theory "assumes the existence of stable,
unbounded, and permanent stimulus-information in the ambient optic array.
And it supposes that the visual system can explore and detect this
information. The theory is information-based, not sensation-based." He and the psychologists who work within this paradigm
detailed how the world could be specified to a mobile, exploring
organism via the lawful projection of information about the world into
energy arrays.
"Specification" would be a 1:1 mapping of some aspect of the world into
a perceptual array; given such a mapping, no enrichment is required and
perception is direct perception.
Perception-in-action
An
ecological understanding of perception derived from Gibson's early work
is that of "perception-in-action", the notion that perception is a
requisite property of animate action; that without perception, action
would be unguided, and without action, perception would serve no
purpose. Animate actions require both perception and motion, and
perception and movement can be described as "two sides of the same coin,
the coin is action". Gibson works from the assumption that singular
entities, which he calls "invariants", already exist in the real world
and that all that the perception process does is to home in upon them. A
view known as constructivism (held by such philosophers as Ernst von Glasersfeld)
regards the continual adjustment of perception and action to the
external input as precisely what constitutes the "entity", which is
therefore far from being invariant.
Glasersfeld considers an "invariant" as a target to be homed in
upon, and a pragmatic necessity to allow an initial measure of
understanding to be established prior to the updating that a statement
aims to achieve. The invariant does not and need not represent an
actuality, and Glasersfeld describes it as extremely unlikely that what
is desired or feared by an organism will never suffer change as time goes on. This social constructionist theory thus allows for a needful evolutionary adjustment.
A mathematical theory of perception-in-action has been devised
and investigated in many forms of controlled movement, and has been
described in many different species of organism using the General Tau Theory. According to this theory, tau information, or time-to-goal information is the fundamental 'percept' in perception.
Evolutionary psychology (EP) and perception
Many
philosophers, such as Jerry Fodor, write that the purpose of perception
is knowledge, but evolutionary psychologists hold that its primary
purpose is to guide action.
For example, they say, depth perception seems to have evolved not to
help us know the distances to other objects but rather to help us move
around in space.
Evolutionary psychologists say that animals from fiddler crabs to
humans use eyesight for collision avoidance, suggesting that vision is
basically for directing action, not providing knowledge.
Building and maintaining sense organs is metabolically expensive,
so these organs evolve only when they improve an organism's fitness.
More than half the brain is devoted to processing sensory information,
and the brain itself consumes roughly one-fourth of one's metabolic
resources, so the senses must provide exceptional benefits to fitness. Perception accurately mirrors the world; animals get useful, accurate information through their senses.
Scientists who study perception and sensation have long understood the human senses as adaptations.
Depth perception consists of processing over half a dozen visual cues,
each of which is based on a regularity of the physical world.
Vision evolved to respond to the narrow range of electromagnetic energy
that is plentiful and that does not pass through objects.
Sound waves provide useful information about the sources of and
distances to objects, with larger animals making and hearing
lower-frequency sounds and smaller animals making and hearing
higher-frequency sounds.
Taste and smell respond to chemicals in the environment that were
significant for fitness in the environment of evolutionary adaptedness. The sense of touch is actually many senses, including pressure, heat, cold, tickle, and pain. Pain, while unpleasant, is adaptive.
An important adaptation for senses is range shifting, by which the
organism becomes temporarily more or less sensitive to sensation. For example, one's eyes automatically adjust to dim or bright ambient light.
Sensory abilities of different organisms often coevolve, as is the case
with the hearing of echo locating bats and that of the moths that have
evolved to respond to the sounds that the bats make.
Evolutionary psychologists claim that perception demonstrates the
principle of modularity, with specialized mechanisms handling
particular perception tasks.
For example, people with damage to a particular part of the brain
suffer from the specific defect of not being able to recognize faces
(prospagnosia). EP suggests that this indicates a so-called face-reading module.
Closed-loop perception
Here
perception is proposed to be a dynamic motor-sensory closed-loop
process in which information flows through the environment and the brain
in continuous loops, converging towards steady-state percepts.
With experience, organisms
can learn to make finer perceptual distinctions, and learn new kinds of
categorization. Wine-tasting, the reading of X-ray images and music
appreciation are applications of this process in the human sphere. Research has focused on the relation of this to other kinds of learning, and whether it takes place in peripheral sensory systems or in the brain's processing of sense information. Empiricalresearch show that specific practices (such as yoga, mindfulness, Tai Chi, meditation,
Daoshi and other mind-body disciplines) can modify human perceptual
modality. Specifically, these practices enable perception skills to
switch from the external (exteroceptive field) towards a higher ability
to focus on internal signals (proprioception). Also, when asked to provide verticality judgments, highly self-transcendent yoga
practitioners were significantly less influenced by a misleading visual
context. Increasing self-transcendence may enable yoga practitioners to
optimize verticality judgment tasks by relying more on internal
(vestibular and proprioceptive) signals coming from their own body,
rather than on exteroceptive, visual cues.
Past actions and events that transpire right before an encounter
or any form of stimulation have a strong degree of influence on how
sensory stimuli are processed and perceived. On a basic level, the
information our senses receive is often ambiguous and incomplete.
However, they are grouped together in order for us to be able to
understand the physical world around us. But it is these various forms
of stimulation, combined with our previous knowledge and experience that
allows us to create our overall perception. For example, when engaging
in conversation, we attempt to understand their message and words by
not only paying attention to what we hear through our ears but also from
the previous shapes we have seen our mouths make. Another example would
be if we had a similar topic come up in another conversation, we would
use our previous knowledge to guess the direction the conversation is
headed in.
Effect of motivation and expectation
A perceptual set, also called perceptual expectancy or just set is a predisposition to perceive things in a certain way. It is an example of how perception can be shaped by "top-down" processes such as drives and expectations. Perceptual sets occur in all the different senses.
They can be long term, such as a special sensitivity to hearing one's
own name in a crowded room, or short term, as in the ease with which
hungry people notice the smell of food.
A simple demonstration of the effect involved very brief presentations
of non-words such as "sael". Subjects who were told to expect words
about animals read it as "seal", but others who were expecting
boat-related words read it as "sail".
Sets can be created by motivation and so can result in people interpreting ambiguous figures so that they see what they want to see. For instance, how someone perceives what unfolds during a sports game can be biased if they strongly support one of the teams.
In one experiment, students were allocated to pleasant or unpleasant
tasks by a computer. They were told that either a number or a letter
would flash on the screen to say whether they were going to taste an
orange juice drink or an unpleasant-tasting health drink. In fact, an
ambiguous figure was flashed on screen, which could either be read as
the letter B or the number 13. When the letters were associated with the
pleasant task, subjects were more likely to perceive a letter B, and
when letters were associated with the unpleasant task they tended to
perceive a number 13.
Perceptual set has been demonstrated in many social contexts.
People who are primed to think of someone as "warm" are more likely to
perceive a variety of positive characteristics in them, than if the word
"warm" is replaced by "cold". When someone has a reputation for being funny, an audience is more likely to find them amusing.
Individual's perceptual sets reflect their own personality traits. For
example, people with an aggressive personality are quicker to correctly
identify aggressive words or situations.
One classic psychological experiment showed slower reaction times and less accurate answers when a deck of playing cards reversed the color of the suit symbol for some cards (e.g. red spades and black hearts).
Philosopher Andy Clark
explains that perception, although it occurs quickly, is not simply a
bottom-up process (where minute details are put together to form larger
wholes). Instead, our brains use what he calls 'predictive coding'.
It starts with very broad constraints and expectations for the state of
the world, and as expectations are met, it makes more detailed
predictions (errors lead to new predictions, or learning
processes). Clark says this research has various implications; not only
can there be no completely "unbiased, unfiltered" perception, but this
means that there is a great deal of feedback between perception and
expectation (perceptual experiences often shape our beliefs, but those
perceptions were based on existing beliefs).
Indeed, predictive coding provides an account where this type of
feedback assists in stabilizing our inference-making process about the
physical world, such as with perceptual constancy examples.
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 and 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 duration 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., post-saccade stimulus) was perceived. This effect
can extend apparent duration 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 among 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 an other'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.
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.
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 mid-line.
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.
